Might be ok on a gremlin sized...but I'd rather use delrin (stiffer) even then.
I don't have any bits small enough to drill the motor holes on a gremlin with the CNC though
Even my smallest bit is too big for those tiny screws!
jhitesma's Danaus style thing?
- Thread starter jhitesma
- Start date
Might be ok on a gremlin sized...but I'd rather use delrin (stiffer) even then.
I don't have any bits small enough to drill the motor holes on a gremlin with the CNC though
Even my smallest bit is too big for those tiny screws!
Haven't had time to do the CAD on the new PVC frame idea....been too busy building an X-29 and Simple Scout as well as repairing the halloween animatronics I built and doing another video contest entry....
But...I did do a little destructive testing on the two pieces I solvent welded tonight now that they've had 48 hours to cure. The results were very encouraging. It took considerably more effort than I expected to separate them - and for the most part they separated near the joint but not on the joint. It actually took me three tries to get them to separate and the break was clean enough it could be welded back together again. There was one small spot where the break was along the joint instead of near it - but that looks like it was due to me not getting any solvent on that part - doh.
So feeling fairly encouraged. Tomorrow night I'll be tied up with Halloween...but wednesday I'll try and fire up onshape and see if I can't design something that will take advantage of this idea. It won't be a protected Danus style frame - at least not at first. Just a simple 230 acro frame to start.
But...I did do a little destructive testing on the two pieces I solvent welded tonight now that they've had 48 hours to cure. The results were very encouraging. It took considerably more effort than I expected to separate them - and for the most part they separated near the joint but not on the joint. It actually took me three tries to get them to separate and the break was clean enough it could be welded back together again. There was one small spot where the break was along the joint instead of near it - but that looks like it was due to me not getting any solvent on that part - doh.
So feeling fairly encouraged. Tomorrow night I'll be tied up with Halloween...but wednesday I'll try and fire up onshape and see if I can't design something that will take advantage of this idea. It won't be a protected Danus style frame - at least not at first. Just a simple 230 acro frame to start.
So a couple of things have conspired to get me thinking about this project again.
One of my friends who's a full scale pilot recently bought a Velocity XL which is a composite kit plane, and he's been learning how to repair and maintain it himself. He took a week long class from the manufacturer, then another class from EAA on composite construction. He liked the EAA class so much he wants to send me to it - which I'm totally up for an hope happens. But it's got me thinking about composites again and how I've wanted to experiment with some of my own ideas.
And someone on the v1engineering.com forums where I posted about this since I used my MPCNC to cut the parts recently asked me a few questions about it which brought it back to mind.
So with composites on the mind I did a bit of reading and found @HilldaFlyer's excellent article on covering DTFB: https://www.flitetest.com/articles/super-strong-waterproof-foam-core I also remembered his DTFB tiny-whoop: https://www.flitetest.com/articles/foam-whoop So figured I may as well give this a bit of a try.
However, I don't have much on hand as far as FG cloth - just some small bits of heavy cloth from my friends full scale plane....and some really nasty super thick fiberglass matt strips from a friends boat project. Neither big enough or suitable for trying to cover DTFB.
But I also saw that Hilldaflyer found red rosin paper worked almost as well as FG cloth in his experiments so Figured I'd hit Home Depot.
I came up empty on rosin paper but I did get some of the bondo FG cloth. I wouldn't recommend it but it was available locally and I'm more interested in stiffness than light weight right now so figured it would be fun to experiment with. I also picked up the bondo fiberglass resin because all I have is some west systems G/Flex and some Devcon 2 hour...neither of which I had a whole lot of.
So...I got home cut an ~13" square piece of DTFB and peeled the paper off of it. Then cut out two pieces of the bondo cloth slightly larger than the piece of DTFB. Layed down some plastic wrap to protect my work surface and mixed up 1oz of the Bondo resin....poured it out and used a hotel room key to squeegee it in. 1oz seemed to be just barely enough which had me feeling pretty good about this.
Then I flipped it over and repeated on the other side. Here I started to get nervous...thought I smelled foam melting and 1oz seemed to be WAY too much resin...so scraped off all the excess then put another layer of plastic wrap over it - covered it in a flat board...put some weights on it and went out for a few hours.
It's 95f out today and this was outside....Bondo claims 2 hours for this epoxy to set at 75f. Well...2 hours later I've got a soupy mess with no foam. It appears the Bondo resin dissolved the DTFB
Oh well. Guess I should break down and order some good resin and a few yards of proper cloth....Still not sure if it will be stiff enough....but I need some FG for a few other projects anyway so may as well get some supplies I figure....more to come....
One of my friends who's a full scale pilot recently bought a Velocity XL which is a composite kit plane, and he's been learning how to repair and maintain it himself. He took a week long class from the manufacturer, then another class from EAA on composite construction. He liked the EAA class so much he wants to send me to it - which I'm totally up for an hope happens. But it's got me thinking about composites again and how I've wanted to experiment with some of my own ideas.
And someone on the v1engineering.com forums where I posted about this since I used my MPCNC to cut the parts recently asked me a few questions about it which brought it back to mind.
So with composites on the mind I did a bit of reading and found @HilldaFlyer's excellent article on covering DTFB: https://www.flitetest.com/articles/super-strong-waterproof-foam-core I also remembered his DTFB tiny-whoop: https://www.flitetest.com/articles/foam-whoop So figured I may as well give this a bit of a try.
However, I don't have much on hand as far as FG cloth - just some small bits of heavy cloth from my friends full scale plane....and some really nasty super thick fiberglass matt strips from a friends boat project. Neither big enough or suitable for trying to cover DTFB.
But I also saw that Hilldaflyer found red rosin paper worked almost as well as FG cloth in his experiments so Figured I'd hit Home Depot.
I came up empty on rosin paper but I did get some of the bondo FG cloth. I wouldn't recommend it but it was available locally and I'm more interested in stiffness than light weight right now so figured it would be fun to experiment with. I also picked up the bondo fiberglass resin because all I have is some west systems G/Flex and some Devcon 2 hour...neither of which I had a whole lot of.
So...I got home cut an ~13" square piece of DTFB and peeled the paper off of it. Then cut out two pieces of the bondo cloth slightly larger than the piece of DTFB. Layed down some plastic wrap to protect my work surface and mixed up 1oz of the Bondo resin....poured it out and used a hotel room key to squeegee it in. 1oz seemed to be just barely enough which had me feeling pretty good about this.
Then I flipped it over and repeated on the other side. Here I started to get nervous...thought I smelled foam melting and 1oz seemed to be WAY too much resin...so scraped off all the excess then put another layer of plastic wrap over it - covered it in a flat board...put some weights on it and went out for a few hours.
It's 95f out today and this was outside....Bondo claims 2 hours for this epoxy to set at 75f. Well...2 hours later I've got a soupy mess with no foam. It appears the Bondo resin dissolved the DTFB
Oh well. Guess I should break down and order some good resin and a few yards of proper cloth....Still not sure if it will be stiff enough....but I need some FG for a few other projects anyway so may as well get some supplies I figure....more to come....
I was just about to go to sleep and it hit me.
I know why the foam melted.
The Bondo "fiberglass resin" isn't epoxy. It's a polyurethane resin. Which...eats foam.
When I was mixing it I thought it was odd that it used a little tube of very liquid hardener and only called for 10 drops of it for 1 oz of resin. I'd never seen epoxy like that before. Duh...it's not epoxy and I just didn't think of it.
Seems obvious in retrospect though. Polyester resin uses MEK as a hardener - which is a liquid and a very powerful solvent.
I have some good FG cloth on order though...now I just need to make a decision on some actual epoxy....I know a few good choices but they aren't cheap...and the cheap choices aren't optimal...sigh....
I know why the foam melted.
The Bondo "fiberglass resin" isn't epoxy. It's a polyurethane resin. Which...eats foam.
When I was mixing it I thought it was odd that it used a little tube of very liquid hardener and only called for 10 drops of it for 1 oz of resin. I'd never seen epoxy like that before. Duh...it's not epoxy and I just didn't think of it.
Seems obvious in retrospect though. Polyester resin uses MEK as a hardener - which is a liquid and a very powerful solvent.
I have some good FG cloth on order though...now I just need to make a decision on some actual epoxy....I know a few good choices but they aren't cheap...and the cheap choices aren't optimal...sigh....
Thank you so much for posting this! I just got a quart of fiberglass resin I was about to use on a foam body plane and it's got the same little tiny tube of hardner with it. I'll test on a separate piece for sure now! You've just saved my airframe!
And here I almost waited until morning to post
Glad I got back out of bed to share when it hit me Check the label - if it says it's polyurethane - it's probably not going to be foam safe. Epoxy resin is safe, polyester resin...not so much:
Waste of fiberglass and resin
Maybe I'll try some smaller sample pieces before trying another 13"x13" blank....But...bigger pieces are easier to evaluate stiffness on....
Check out the article I linked from hilldaflyer. He links to some good resin options. willsonman's thread about FG and foam also includes links so some good resin options: http://forum.flitetest.com/index.php?threads/fiberglass-foam-a-tutorial-and-discussion.23228/
He got me started down this path.... him and Hildaflyer
I've been using the Thayercraft fiberglass and the Famowood Glaze coat that Josh recommends so far, but I found some fiberglass resin that sold cheaper by volume to do the big wing and body panels. And I foolishly didn't look into getting other recommendations on the product before putting the "Buy It Now" button.
Oh well... it's just a quart and if I don't use it for planes, maybe you might want to use it to fiberglass over your dashboard in the fall
I've been using the Thayercraft fiberglass and the Famowood Glaze coat that Josh recommends so far, but I found some fiberglass resin that sold cheaper by volume to do the big wing and body panels. And I foolishly didn't look into getting other recommendations on the product before putting the "Buy It Now" button.
Oh well... it's just a quart and if I don't use it for planes, maybe you might want to use it to fiberglass over your dashboard in the fall
I'm tempted to try the Famowood - just...that slow cure worries me. I'm impatient Though here in the summer with our heat it may cure a bit quicker....
Right now I'm leaning towards either the Resin Research Kwik Kick or US Composites thin with the medium speed hardener. But no budget for either for a few weeks. So I may just hit hobby lobby or my LHS for some of the BSI...but I don't think they had the 30 minute last time I was there...and my experiences with BSI epoxy have been rather mixed.
I was able to do a successful test with the 6oz Bondo cloth and west systems Gflex yesterday:
It went much smoother than with the foam eating polyester resin It seemed to use much less resin - in fact I'm pretty sure I had too much on there despite my best attempts to squeegee most of it off. Most of the surface is smooth and you can't feel the weave. And we had a sudden dip in temperature so my nice 90 degree easy curing temps left me for low 70's mid 60's. The bottle suggested that the gflex has a pot life of 75 minutes and cures in 3 hours at 75F. When I started it was 80f...but after an hour it was down to 73f. And after 3 hours it was still gooey and not set. Which started to get me worried that I may not have measured or mixed well.
But...I noticed that the west systems website says 7-10 hours to cure...so...ok maybe it just needs more time. But then their video on how to use the gflex shows them hitting it with a heat gun and says it can be fully cured in under an hour with proper conditions. So...that's some pretty conflicting info right from the manufacturer
I decided to give it over night.
This morning it was set...I wouldn't call it tacky anymore but it doesn't quite feel full 100% cured either...but it did get down to under 60 last night so that may have slowed it.
I will say that this gflex is indeed flexy. The stuff that was left in my pot I was able to peel out...not chip out...despite not being tacky it was still bendable - not easily but still bendable. And my test piece I can rap with my knuckles and it sounds solid....but it's kind of flexy. Along the direction of the weave it's fairly stiff - but diagonally it can twist very easily. I suspect a second layer set at 45 degrees would do a lot to stiffen it up...but with 6oz cloth that's going to make for heavier final product than I was hoping for.
The potential is there though. With some better stiffer epoxy and 2-3 layers of thinner cloth (which should be here Friday) this has a lot of potential. Already despite the flex it still exhibits I'd say it's stiffer than the PVC sheet I tried cutting the frame out of. A little more expensive by my back of the envelope calculations...but it still looks like I could potentially cut 2 or 3 frames for <$10 in materials. Just...I have to buy about $100 in materials due to minimum quantities
Though here in the summer with our heat it may cure a bit quicker....Right now I'm leaning towards either the Resin Research Kwik Kick or US Composites thin with the medium speed hardener. But no budget for either for a few weeks. So I may just hit hobby lobby or my LHS for some of the BSI...but I don't think they had the 30 minute last time I was there...and my experiences with BSI epoxy have been rather mixed.
I was able to do a successful test with the 6oz Bondo cloth and west systems Gflex yesterday:
It went much smoother than with the foam eating polyester resin
It seemed to use much less resin - in fact I'm pretty sure I had too much on there despite my best attempts to squeegee most of it off. Most of the surface is smooth and you can't feel the weave. And we had a sudden dip in temperature so my nice 90 degree easy curing temps left me for low 70's mid 60's. The bottle suggested that the gflex has a pot life of 75 minutes and cures in 3 hours at 75F. When I started it was 80f...but after an hour it was down to 73f. And after 3 hours it was still gooey and not set. Which started to get me worried that I may not have measured or mixed well.But...I noticed that the west systems website says 7-10 hours to cure...so...ok maybe it just needs more time. But then their video on how to use the gflex shows them hitting it with a heat gun and says it can be fully cured in under an hour with proper conditions. So...that's some pretty conflicting info right from the manufacturer
I decided to give it over night.
This morning it was set...I wouldn't call it tacky anymore but it doesn't quite feel full 100% cured either...but it did get down to under 60 last night so that may have slowed it.
I will say that this gflex is indeed flexy. The stuff that was left in my pot I was able to peel out...not chip out...despite not being tacky it was still bendable - not easily but still bendable. And my test piece I can rap with my knuckles and it sounds solid....but it's kind of flexy. Along the direction of the weave it's fairly stiff - but diagonally it can twist very easily. I suspect a second layer set at 45 degrees would do a lot to stiffen it up...but with 6oz cloth that's going to make for heavier final product than I was hoping for.
The potential is there though. With some better stiffer epoxy and 2-3 layers of thinner cloth (which should be here Friday) this has a lot of potential. Already despite the flex it still exhibits I'd say it's stiffer than the PVC sheet I tried cutting the frame out of. A little more expensive by my back of the envelope calculations...but it still looks like I could potentially cut 2 or 3 frames for <$10 in materials. Just...I have to buy about $100 in materials due to minimum quantities
Yeah...I don't think that will be happening
I mentioned my little project in a local RC discussion chat on FB and one of the guys on there offered me some 3/4oz cloth and resin from his supply - so that should help me make progress a little quicker.
I put the little sample piece outside this morning hoping it would be warm to help it cure better - I had it sitting on a table with a little piece of wood on one edge to keep it from flying away. Looks like the resin doesn't like UV very much as this is how it looked when I got home for lunch:
The white edge is where it was protected from the sun.
And it's overcast today and only 72f out. So no help from heat...I should have left it in my truck instead - nice and warm in there
I suspect summer sun would not play nice with it.
People don't believe me when I tell them just how intense the UV is here. A few examples - when I moved here our newspaper was afternoon delivery, even so when I'd go out and get it at 5PM the top half would be yellowed..and our driveway was shaded. If I leave a plastic shopping bag outside in the summer, within 3 days it will be broken down enough to disintegrate if I try to pick it up.
In related news I really need to get some solar panels.....
Figured I may as well try a second layer since I've got a few more days until I get the lighter cloth and come up with some better resin.
So...cut two more pieces of cloth - this time making them so the weave goes at 45 degrees to the original layers.
Mixed up some epoxy - still using the gflex but this time weighed it out instead of going by volume, I mixed up 8g total and it was more than enough to wet up both sides.
Since the original layer had had 24 hours to cure at this point I took some 80 grid sandpaper to it and roughed up the surface until there was no shine left and the weave of the first layer was exposed.
Then same basic procedure. Put the cloth down, poured a bit of epoxy over it, and used a gift card to spread it out and squeegee as much as possible off. Flip it over and do the same thing.
Then put it between two sheets of plastic wrap, some nice flat boards and a cast iron grill on top for weight. This time after 3 hours it was less tacky even though it was a bit cooler out. I guess I was more accurate measuring by weight instead of volume, and I was careful to give it more time mixing as well. Even so I gave it overnight.
This morning it's looking really good. VERY stiff and no longer able to twist. Though it is getting noticeably heavier with this 6oz cloth. Very curious to see how many layers of 0.74oz cloth it takes to get as stiff as I'd like..though again I suspect less flexible epoxy will help as well.
But what I've got now is definitely stiffer than the PVC sheet or Lexan sheet...and probably stiffer than the plywood. I'd be very tempted to try doing a full sheet this way and cutting the frame to see how it does.
The one big concern I have is hardpoints. Specifically where my screws go through to connect the layers. While this is stiff and tough it's also a little squishy. I suspect that even with washers trying to bolt layers together won't work well because it will squish and deform. The PVC and PLY did this a little as well...but they were both considerably tougher to squish than this. I know on composite aircraft they usually embed a bit of plywood where they want a hard point, or sometimes just mix up flox and epoxy to create a hard spot. And I could do either. But...that would require more machining steps or careful planning to make sure I prep the right areas before cutting. I'm kind of thinking that instead of drilling 3mm holes like I have in the past I'll drill 5mm holes then fill them with flox/epoxy - then go back and hand drill the holes back out using one of the previous frame pieces as a template. That seems easier than trying to get the work back into the CNC accurately to do a second machining pass.
The other thing I want to try is the technique my friend showed me that he learned at the EAA class (which it sounds like I'll be attending in October or January) They used polyester dress liner fabric as "peel ply" along with cotton batting to absorb extra epoxy. The trick is that epoxy won't stick to polyester. So after you wet up the FG cloth you put a layer of polyester fabric over the top of it then a layer of cotton batting over that - then put it between boards or vac bag it. The excess epoxy will get squished through the weave of the polyester and absorbed into the cotton batting - the end result is not a smooth surface since you have little dimples from where the epoxy went through the weave. But that's a good thing because it leaves a surface suitable for laminating additional layers on.
So I'll probably pick up a roll of batting and a few yards of polyester (Supposedly you can get 100% poly dress liner for about $1 a yard) and give that a try. Should make for a lighter final product without excess epoxy.
So...cut two more pieces of cloth - this time making them so the weave goes at 45 degrees to the original layers.
Mixed up some epoxy - still using the gflex but this time weighed it out instead of going by volume, I mixed up 8g total and it was more than enough to wet up both sides.
Since the original layer had had 24 hours to cure at this point I took some 80 grid sandpaper to it and roughed up the surface until there was no shine left and the weave of the first layer was exposed.
Then same basic procedure. Put the cloth down, poured a bit of epoxy over it, and used a gift card to spread it out and squeegee as much as possible off. Flip it over and do the same thing.
Then put it between two sheets of plastic wrap, some nice flat boards and a cast iron grill on top for weight. This time after 3 hours it was less tacky even though it was a bit cooler out. I guess I was more accurate measuring by weight instead of volume, and I was careful to give it more time mixing as well. Even so I gave it overnight.
This morning it's looking really good. VERY stiff and no longer able to twist. Though it is getting noticeably heavier with this 6oz cloth. Very curious to see how many layers of 0.74oz cloth it takes to get as stiff as I'd like..though again I suspect less flexible epoxy will help as well.
But what I've got now is definitely stiffer than the PVC sheet or Lexan sheet...and probably stiffer than the plywood. I'd be very tempted to try doing a full sheet this way and cutting the frame to see how it does.
The one big concern I have is hardpoints. Specifically where my screws go through to connect the layers. While this is stiff and tough it's also a little squishy. I suspect that even with washers trying to bolt layers together won't work well because it will squish and deform. The PVC and PLY did this a little as well...but they were both considerably tougher to squish than this. I know on composite aircraft they usually embed a bit of plywood where they want a hard point, or sometimes just mix up flox and epoxy to create a hard spot. And I could do either. But...that would require more machining steps or careful planning to make sure I prep the right areas before cutting. I'm kind of thinking that instead of drilling 3mm holes like I have in the past I'll drill 5mm holes then fill them with flox/epoxy - then go back and hand drill the holes back out using one of the previous frame pieces as a template. That seems easier than trying to get the work back into the CNC accurately to do a second machining pass.
The other thing I want to try is the technique my friend showed me that he learned at the EAA class (which it sounds like I'll be attending in October or January) They used polyester dress liner fabric as "peel ply" along with cotton batting to absorb extra epoxy. The trick is that epoxy won't stick to polyester. So after you wet up the FG cloth you put a layer of polyester fabric over the top of it then a layer of cotton batting over that - then put it between boards or vac bag it. The excess epoxy will get squished through the weave of the polyester and absorbed into the cotton batting - the end result is not a smooth surface since you have little dimples from where the epoxy went through the weave. But that's a good thing because it leaves a surface suitable for laminating additional layers on.
So I'll probably pick up a roll of batting and a few yards of polyester (Supposedly you can get 100% poly dress liner for about $1 a yard) and give that a try. Should make for a lighter final product without excess epoxy.
Well the local RC guy hooked me up with some nice resin! Meet up with him over lunch yesterday and he gave me about 10-12oz of MGS 335 resin and enough hardener to go with it. This is serious stuff that's approved for construction of manned composite aircraft: http://www.aircraftspruce.com/catalog/cmpages/mgsresin.php I'll have to cut him a couple of FT planes on my MPCNC as thanks
Not going to waste it on this heavy 6oz cloth...will wait for my good cloth order which should be here tomorrow. I'm not sure if he gave me fast or slow hardener either...if it's slow then I'm looking at 6 hours pot life and a few days for full cure so going to take some patience. This resin is also best used with a post cure at elevated temps. Thankfully it's about to be summer so I have easy access to high temps with no equipment here in the desert
He has a lot of experience with glass (he has a lot of composite pylon racers he's built and competes with) and seemed rather impressed with the little sample piece I did. Was lighter than he expected and surprisingly strong.
Speaking of strength...decided to do some destructive testing last night. I challenged my daughter to try and bend it - she wasn't able to. Though after she said "I may not be trying hard enough because I like it and don't really WANT to break it." My wife wasn't so sentimental. But she still had to put more effort in than she expected to get it to bend. As expected the side in elongation showed no damage but the side in compression collapsed. It did not snap or break though:
You can also see I tested adding a bolt to it. And if you look carefully you can see it is dimpling the surface like I was afraid it would. And that's just finger tight into a plastic standoff.
I didn't do a great job "drilling" the hole either. I just turned on the router on my CNC and jabbed the piece against it - so my hole was a little oblong:
You can also see the damage from the bend there - Honestly that could be repairable in use....the foam core is compromised, but most of the strength comes from the skin.
Here's another view of the dimpling...it's hard to show in a photo. The light I was using is ring shaped which kind of creates reflections that look like the dimpling but aren't:
So yeah, looks like I will have to drill larger holes and fill with epoxy/flox to create hard points.
Reading the EAA composite workshop manual suggests also carving out some of the foam around the exposed edges and filling it with flox as well - so I may do that to finish the edges...we'll see. Still have to laminate up some larger sheets and cut the frame out of them to see if they'll be usable before I worry about that!
Not going to waste it on this heavy 6oz cloth...will wait for my good cloth order which should be here tomorrow. I'm not sure if he gave me fast or slow hardener either...if it's slow then I'm looking at 6 hours pot life and a few days for full cure so going to take some patience. This resin is also best used with a post cure at elevated temps. Thankfully it's about to be summer so I have easy access to high temps with no equipment here in the desert
He has a lot of experience with glass (he has a lot of composite pylon racers he's built and competes with) and seemed rather impressed with the little sample piece I did. Was lighter than he expected and surprisingly strong.
Speaking of strength...decided to do some destructive testing last night. I challenged my daughter to try and bend it - she wasn't able to. Though after she said "I may not be trying hard enough because I like it and don't really WANT to break it."
My wife wasn't so sentimental. But she still had to put more effort in than she expected to get it to bend. As expected the side in elongation showed no damage but the side in compression collapsed. It did not snap or break though:
You can also see I tested adding a bolt to it. And if you look carefully you can see it is dimpling the surface like I was afraid it would. And that's just finger tight into a plastic standoff.
I didn't do a great job "drilling" the hole either. I just turned on the router on my CNC and jabbed the piece against it - so my hole was a little oblong:
You can also see the damage from the bend there - Honestly that could be repairable in use....the foam core is compromised, but most of the strength comes from the skin.
Here's another view of the dimpling...it's hard to show in a photo. The light I was using is ring shaped which kind of creates reflections that look like the dimpling but aren't:
So yeah, looks like I will have to drill larger holes and fill with epoxy/flox to create hard points.
Reading the EAA composite workshop manual suggests also carving out some of the foam around the exposed edges and filling it with flox as well - so I may do that to finish the edges...we'll see. Still have to laminate up some larger sheets and cut the frame out of them to see if they'll be usable before I worry about that!
I don't have time for a full update right now...but...have to share.
Got my cloth order from Thayercraft yesterday and this light cloth is amazing! Did an initial layup on some 14" square pieces of DTFB with the 1.43oz cloth last night. Wasn't sure how long the epoxy would take to cure but after about 1-1.5 hours it was gelling and starting to cure so I figured there was a chance it would be cured by today (the slow hardener takes 6 hours to gell and 2-3 days to cure the fast takes 15 minutes to gell - so this must be a mix of the two I was given)
The foam was 34g to start, and 21g once I peeled off the paper. After the first layer of FG it's now at 55g which is pretty close to what I was expecting. The cloth weighed 7g each and I tried to use about 7g of resin on each side so I was hoping to pick up about 14g of weight per side...instead I picked up 17g of weight per side...but also learned a few things I can do better.
The polyester peel ply worked great! So much nicer of a surface finish and the poly was pretty much fully saturated with epoxy so it definitely removed excess. The paper towels I used as backer behind it barely absorbed any epoxy so I must not have had much more than needed on there to start.
Here's the first side I peeled. This was the second side I glued up and I did this one a little better. Specifically to took more time to make sure the peel ply was smoothed out over the surface. The finish is gorgeous, you can still seem the ripples in the foam while the 6oz cloth I tested initially pretty much obliterated them.
The other side...the first that I did...did not come out quite as nice. I neglected to smooth the peel ply here and just hoped the weight of being between two boards would do it for me. Nope, need to smooth it manually. Good to know for the future.
That side isn't quite as nice but still beats my initial attempts. The areas where the peel ply was bubbled up are a little smoother - so it seems extra epoxy was left behind there. I suspect that's part of how I picked up the extra weight:
The 1.43oz cloth added more strength than I expected. Like my initial tests it's fairly stiff across the grain but still susceptible to twisting. So I'll do the next layer at 45 degrees like in my initial test. But I won't have time to do that until Sunday evening
It's definitely not as strong as the 6oz cloth -- but the finish is much nicer and this MGS epoxy is way nicer to work with than the west systems gflex was. One layer made this stiff enough it would be great for a plane. But for what I'm going to do I definitely need more. Not sure if 2 layers will be enough - I suspect I'll do 3 or maybe even 4 depending on how it goes. So stay tuned for more updates!
Got my cloth order from Thayercraft yesterday and this light cloth is amazing! Did an initial layup on some 14" square pieces of DTFB with the 1.43oz cloth last night. Wasn't sure how long the epoxy would take to cure but after about 1-1.5 hours it was gelling and starting to cure so I figured there was a chance it would be cured by today (the slow hardener takes 6 hours to gell and 2-3 days to cure the fast takes 15 minutes to gell - so this must be a mix of the two I was given)
The foam was 34g to start, and 21g once I peeled off the paper. After the first layer of FG it's now at 55g which is pretty close to what I was expecting. The cloth weighed 7g each and I tried to use about 7g of resin on each side so I was hoping to pick up about 14g of weight per side...instead I picked up 17g of weight per side...but also learned a few things I can do better.
The polyester peel ply worked great! So much nicer of a surface finish and the poly was pretty much fully saturated with epoxy so it definitely removed excess. The paper towels I used as backer behind it barely absorbed any epoxy so I must not have had much more than needed on there to start.
Here's the first side I peeled. This was the second side I glued up and I did this one a little better. Specifically to took more time to make sure the peel ply was smoothed out over the surface. The finish is gorgeous, you can still seem the ripples in the foam while the 6oz cloth I tested initially pretty much obliterated them.
The other side...the first that I did...did not come out quite as nice. I neglected to smooth the peel ply here and just hoped the weight of being between two boards would do it for me. Nope, need to smooth it manually. Good to know for the future.
That side isn't quite as nice but still beats my initial attempts. The areas where the peel ply was bubbled up are a little smoother - so it seems extra epoxy was left behind there. I suspect that's part of how I picked up the extra weight:
The 1.43oz cloth added more strength than I expected. Like my initial tests it's fairly stiff across the grain but still susceptible to twisting. So I'll do the next layer at 45 degrees like in my initial test. But I won't have time to do that until Sunday evening
It's definitely not as strong as the 6oz cloth -- but the finish is much nicer and this MGS epoxy is way nicer to work with than the west systems gflex was. One layer made this stiff enough it would be great for a plane. But for what I'm going to do I definitely need more. Not sure if 2 layers will be enough - I suspect I'll do 3 or maybe even 4 depending on how it goes. So stay tuned for more updates!
Well, I did a second layer of the 1.43oz cloth last night at 45 degrees. Few observations.
I really need a bigger work area. Very hard to keep the cloth nice with the limited space I have to roll it out. Cutting the 45 degree pieces results in a lot more "waste" than I'd like with the odd triangular pieces left over. I'm sure I'll use them eventually on something so they're not really "waste" but it's hard to make good use of the cloth. With the grain of the cloth rotated like this it's a LOT harder to get it to lay flat and not have any wrinkles. I made the mistake of cutting these pieces a little smaller (only about 1" overhang instead of closer to 2") since there seemed to be a lot of waste from that on the first layer...but it was very hard to get the cloth to actually cover my workpiece because of how it stretches and tries to bunch up with the grain going this way.
The peel ply technique is amazing. Feels wasteful using that much polyester cloth that just gets tossed because it's soaked in resin...but wow does it leave a great surface finish and keep the excess resin down.
Once again I used 14g of resin on each side - on the first side I used most of the 14g, but on the second side I wound up with quite a bit left over. Odd how that keeps happening. My technique does seem to be improving overall for wetting out the cloth though and it's getting easier and I'm having less waste with lighter layups.
And like my test with the heavy 6oz cloth adding that second layer at 45 degrees made a HUGE difference in stiffness and strength. I'm still not sure this is strong enough for what I want so I'm going to do a 3rd and possibly a 4th layer still...but the difference from one layer to two layers was almost as big as going from bare foam to one layer.
I am picking up weight quicker than I had hoped. I still haven't trimmed off the excess so this will come down a bit but I'm at 71g already for a 14"x14" sheet.
The weight history so far:
34g - Stock DTFB
21g - Paper removed
55g - One layer of 1.43oz FG (34g additional, 14g of glass, 20g of resin)
71g - Two layers of 1.43oz FG (16g additional, 14g of glass, 2oz of resin?)
So I picked up a lot less weight with this second layer...I'm guessing it's because I'm getting better at using less resin...but I find it hard to believe I only used 2oz of resin since I added so much more to start. I know the FG cloth weighed 14g each time (7g per side) because I was able to weigh it and confirm. And it didn't seem like that much more resin was left in my pot or squeezed into the peel ply this second layer.
But we'll see what happens with the 3rd layer.
I'm not sure how this compares for weight to the other raw materials I've used for this frame before yet. Partly because I don't know what the final weight will be...but also because I didn't weight raw materials just cut frames. But I do know that the one ply wood frame piece I weighed was close to 70g so I'd say there's a VERY good chance that even if I do 4 or 5 layers of FG this will wind up being lighter than the original plywood version.
I really need a bigger work area. Very hard to keep the cloth nice with the limited space I have to roll it out. Cutting the 45 degree pieces results in a lot more "waste" than I'd like with the odd triangular pieces left over. I'm sure I'll use them eventually on something so they're not really "waste" but it's hard to make good use of the cloth. With the grain of the cloth rotated like this it's a LOT harder to get it to lay flat and not have any wrinkles. I made the mistake of cutting these pieces a little smaller (only about 1" overhang instead of closer to 2") since there seemed to be a lot of waste from that on the first layer...but it was very hard to get the cloth to actually cover my workpiece because of how it stretches and tries to bunch up with the grain going this way.
The peel ply technique is amazing. Feels wasteful using that much polyester cloth that just gets tossed because it's soaked in resin...but wow does it leave a great surface finish and keep the excess resin down.
Once again I used 14g of resin on each side - on the first side I used most of the 14g, but on the second side I wound up with quite a bit left over. Odd how that keeps happening. My technique does seem to be improving overall for wetting out the cloth though and it's getting easier and I'm having less waste with lighter layups.
And like my test with the heavy 6oz cloth adding that second layer at 45 degrees made a HUGE difference in stiffness and strength. I'm still not sure this is strong enough for what I want so I'm going to do a 3rd and possibly a 4th layer still...but the difference from one layer to two layers was almost as big as going from bare foam to one layer.
I am picking up weight quicker than I had hoped. I still haven't trimmed off the excess so this will come down a bit but I'm at 71g already for a 14"x14" sheet.
The weight history so far:
34g - Stock DTFB
21g - Paper removed
55g - One layer of 1.43oz FG (34g additional, 14g of glass, 20g of resin)
71g - Two layers of 1.43oz FG (16g additional, 14g of glass, 2oz of resin?)
So I picked up a lot less weight with this second layer...I'm guessing it's because I'm getting better at using less resin...but I find it hard to believe I only used 2oz of resin since I added so much more to start. I know the FG cloth weighed 14g each time (7g per side) because I was able to weigh it and confirm. And it didn't seem like that much more resin was left in my pot or squeezed into the peel ply this second layer.
But we'll see what happens with the 3rd layer.
I'm not sure how this compares for weight to the other raw materials I've used for this frame before yet. Partly because I don't know what the final weight will be...but also because I didn't weight raw materials just cut frames. But I do know that the one ply wood frame piece I weighed was close to 70g so I'd say there's a VERY good chance that even if I do 4 or 5 layers of FG this will wind up being lighter than the original plywood version.
So 3rd layer....
I remembered to weigh the polyester peel ply before using it this time - and again after. Looks like it soaked up 2g of resin on one side and 3g on the other.
Final weight is now at 102g so I picked up another 31g, 14g from glass 17 from epoxy. Which still has me scratching my head. Because I mixed up 32g of epoxy and used most of it...5g of that was absorbed into the peel ply so what happened to the other 10g? It doesn't seem like that much was left in the pot...though I suppose I can try weighing it to see - but I didn't weigh it before but I have more of the little plastic cups so I can weigh another to get a tare weight.
And this thing is getting crazy stiff. I'm going to do one more layer...I'm going through epoxy faster than I'd hoped...so 4 layers is probably going to be my limit. The one thing I'm a little concerned about is that while it's stiff it still seems more squishy than the heavier cloth and gflex resin...so I'm almost certainly going to have to do some hard points - but have had a few new ideas on that too.
I remembered to weigh the polyester peel ply before using it this time - and again after. Looks like it soaked up 2g of resin on one side and 3g on the other.
Final weight is now at 102g so I picked up another 31g, 14g from glass 17 from epoxy. Which still has me scratching my head. Because I mixed up 32g of epoxy and used most of it...5g of that was absorbed into the peel ply so what happened to the other 10g? It doesn't seem like that much was left in the pot...though I suppose I can try weighing it to see - but I didn't weigh it before but I have more of the little plastic cups so I can weigh another to get a tare weight.
And this thing is getting crazy stiff. I'm going to do one more layer...I'm going through epoxy faster than I'd hoped...so 4 layers is probably going to be my limit. The one thing I'm a little concerned about is that while it's stiff it still seems more squishy than the heavier cloth and gflex resin...so I'm almost certainly going to have to do some hard points - but have had a few new ideas on that too.
Another offset layer last night. Went a little better than the first one but it's still really tricky working with the cloth when it's cut like this.
Weight update:
34g - Stock DTFB
21g - Paper removed
55g - One layer of 1.43oz FG (34g additional, 14g of glass, 20g of resin)
71g - Two layers of 1.43oz FG (16g additional, 14g of glass, 2g of resin?)
102g - Three layers of 1.43oz FG (31g additional, 14g of glass, 17g of resin)
140g - Four layers of 1.43oz FG (38g additional, 14g of glass, 24g of resin)
I didn't weigh the peel ply after it came off yet...but it didn't seem to soak up quite as much resin this time.
Part of me would like to do one more layer...but doing this on a 14" piece I'm going through cloth and resin faster than I'd like. I've already determined I don't have enough resin to do two sheets of this material which is a bummer because I really need two sheets to cut the frame. I may try doing the second sheet in a heavier more budget friendly way with the 6oz bondo cloth and BSI epoxy. I'd like to try that with the peel ply and see how it comes out - it's a lot more budget friendly and two layers of cloth is probably plenty strong.
The cloth I'm using now is 0.0021" thick...so four layers of that puts me at .0084 thick and double that since I'm doing both sides and I've only added 0.0168" (~0.5mm!) of thickness (not accounting for any thickness added by the resin.) I'll measure the finished piece to see exactly how much thickness it picked up. I suspect it's still considerably less thickness and weight than just one layer of the 6oz cloth. But the stiffness I've achieved at this point is remarkable. I'm still just a little concerned that it's too squishy - but like I've said I've got some ideas on how to deal with that.
Tonight I'm going to trim off the excess on this board and if I'm feeling gusty maybe even toss it on the CNC and cut out a frame. There's still some finishing to do but I plan on cutting it first so I don't have to finish parts that will be cut away.
Weight update:
34g - Stock DTFB
21g - Paper removed
55g - One layer of 1.43oz FG (34g additional, 14g of glass, 20g of resin)
71g - Two layers of 1.43oz FG (16g additional, 14g of glass, 2g of resin?)
102g - Three layers of 1.43oz FG (31g additional, 14g of glass, 17g of resin)
140g - Four layers of 1.43oz FG (38g additional, 14g of glass, 24g of resin)
I didn't weigh the peel ply after it came off yet...but it didn't seem to soak up quite as much resin this time.
Part of me would like to do one more layer...but doing this on a 14" piece I'm going through cloth and resin faster than I'd like. I've already determined I don't have enough resin to do two sheets of this material which is a bummer because I really need two sheets to cut the frame. I may try doing the second sheet in a heavier more budget friendly way with the 6oz bondo cloth and BSI epoxy. I'd like to try that with the peel ply and see how it comes out - it's a lot more budget friendly and two layers of cloth is probably plenty strong.
The cloth I'm using now is 0.0021" thick...so four layers of that puts me at .0084 thick and double that since I'm doing both sides and I've only added 0.0168" (~0.5mm!) of thickness (not accounting for any thickness added by the resin.) I'll measure the finished piece to see exactly how much thickness it picked up. I suspect it's still considerably less thickness and weight than just one layer of the 6oz cloth. But the stiffness I've achieved at this point is remarkable. I'm still just a little concerned that it's too squishy - but like I've said I've got some ideas on how to deal with that.
Tonight I'm going to trim off the excess on this board and if I'm feeling gusty maybe even toss it on the CNC and cut out a frame. There's still some finishing to do but I plan on cutting it first so I don't have to finish parts that will be cut away.
Didn't realize I haven't updated this since Wednesday.
After 4 layers on each side I did stop. I trimmed off the excess and the panel weight came down to 120g. So I added about 100g of glass and epoxy. The final board is VERY stiff and I think probably viable...though I'd still rather have a few more layers on it for more strength....but I can't justify going through that much more epoxy and cloth.
I may do just one more layer...if the friend who got me going on composites come by this weekend and wants to see how nice the MGS resin is to work with.
However today I decided to do another test. I wanted to see what kind of results I could do with locally available products only. So I got 2 packs of the 6oz bondo cloth from walmart (only $4.50 each there!) and a pack of BSI 30 minute epoxy from Hobby Lobby ($10) since it was all they had. The 15 minute BSI "Finishing Resin" would be better for this kind of work but HL didn't have it and I didn't have time to try my LHS (who last time I checked only had ZPoxy finishing resin which is $20.)
So $20 total outlay. This initially feels like a cheaper option...but if you work out the price per ounce for the resin it's actually over twice as expensive as the MGS resin. It's just that the BSI comes in handy 4.5oz bottles while the MGS you have to buy 1 gallon of resin and 1qt of hardener (or better yet 1qt of fast and 1qt of slow you can can mix them to get an optimal cure time.)
30 minute epoxy is a bit trickier to work with than the slower curing BSI...especially because that's 30 minutes when mixed in a thin layer...in a small plastic cup you have considerably less time. In fact my first layup with it the epoxy went off and turned into a puck before I was done giving off enough heat in the process to melt through the cup I mixed it in...oops. The 15 minute finishing epoxy from BSI supposedly is formulated to work better mixed in larger quantities like this...but 15 minutes pot time is still pretty tricky to work with.
Anyway, I cut two sheets of peel ply and 2 sheets of the 6oz cloth. The cloth came in at 30g each...a bit more than 4x heavier than the 1.45oz cloth I've been working with. Which is what I expected since 1.45 X 4 = 5.8. So each layer of this heavier cloth is like 4 layers of the light cloth I've been using.
I mixed up 30g of epoxy (15g each hardener and resin since BSI is a 1:1 ratio) and started wetting out my cloth. This epoxy is considerably thicker and trickier to work with. But the larger quantity was a bit nicer to work with since I could pour it over a larger area easier. 30g turned out to be more than I needed though and I was left with almost a 1/4" thick layer in the bottom of the cup. While I was applying the peel ply and paper towels and getting the core flipped that went off and melted through the cup as I already mentioned.
I repeated on the other side using just 24g of resin which worked better.
After about an hour I checked on it and sure enough the epoxy was no longer sticky. I peeled off the peel ply and it was looking pretty good. Not as much epoxy absorbed into the ply as I anticipated but it was still a nice surface with no puddles. The workpiece was fairly strong but still able to twist like my first test.
So I cut out two more pieces at 45 degrees. Due to the size of the 8sqft packs from bondo I was only able to get enough cloth for one layer out of each pack - I have a lot of leftover but it's in thinner strips I can't use for this.
I repeated the layups with 24g of resin on each side again.
I then let this sit all afternoon while I was out. When I got back I peeled the ply and then trimmed the edges down. The final piece is very strong and resists twisting much like my test did after two layers.
I weighed it and it comes n at 192g! Wow...70g heavier than my first panel with the lighter cloth. It feels about the same strength - maybe a little stronger...after all there's twice as much cloth on it. This definitely doesn't need a 3rd layer of 6oz cloth...but I am tempted to do a layer of the 1.45 just to give it a nicer surface finish with the finer weave. Instead I'll probably use some kind of surface coat on both to smooth them out.
So...next step will be to cut my frame out of this stuff and then try finishing it to see if it's usable and which I prefer. In an idea world lots of layers of light cloth is definitely the way to go...but the locally available option is cheaper and quicker (especially if I had used the MGS resin instead of the more than twice as expensive and not as nice to work with BSI.) But it's neat to see how the two end products compare!
After 4 layers on each side I did stop. I trimmed off the excess and the panel weight came down to 120g. So I added about 100g of glass and epoxy. The final board is VERY stiff and I think probably viable...though I'd still rather have a few more layers on it for more strength....but I can't justify going through that much more epoxy and cloth.
I may do just one more layer...if the friend who got me going on composites come by this weekend and wants to see how nice the MGS resin is to work with.
However today I decided to do another test. I wanted to see what kind of results I could do with locally available products only. So I got 2 packs of the 6oz bondo cloth from walmart (only $4.50 each there!) and a pack of BSI 30 minute epoxy from Hobby Lobby ($10) since it was all they had. The 15 minute BSI "Finishing Resin" would be better for this kind of work but HL didn't have it and I didn't have time to try my LHS (who last time I checked only had ZPoxy finishing resin which is $20.)
So $20 total outlay. This initially feels like a cheaper option...but if you work out the price per ounce for the resin it's actually over twice as expensive as the MGS resin. It's just that the BSI comes in handy 4.5oz bottles while the MGS you have to buy 1 gallon of resin and 1qt of hardener (or better yet 1qt of fast and 1qt of slow you can can mix them to get an optimal cure time.)
30 minute epoxy is a bit trickier to work with than the slower curing BSI...especially because that's 30 minutes when mixed in a thin layer...in a small plastic cup you have considerably less time. In fact my first layup with it the epoxy went off and turned into a puck before I was done giving off enough heat in the process to melt through the cup I mixed it in...oops. The 15 minute finishing epoxy from BSI supposedly is formulated to work better mixed in larger quantities like this...but 15 minutes pot time is still pretty tricky to work with.
Anyway, I cut two sheets of peel ply and 2 sheets of the 6oz cloth. The cloth came in at 30g each...a bit more than 4x heavier than the 1.45oz cloth I've been working with. Which is what I expected since 1.45 X 4 = 5.8. So each layer of this heavier cloth is like 4 layers of the light cloth I've been using.
I mixed up 30g of epoxy (15g each hardener and resin since BSI is a 1:1 ratio) and started wetting out my cloth. This epoxy is considerably thicker and trickier to work with. But the larger quantity was a bit nicer to work with since I could pour it over a larger area easier. 30g turned out to be more than I needed though and I was left with almost a 1/4" thick layer in the bottom of the cup. While I was applying the peel ply and paper towels and getting the core flipped that went off and melted through the cup as I already mentioned.
I repeated on the other side using just 24g of resin which worked better.
After about an hour I checked on it and sure enough the epoxy was no longer sticky. I peeled off the peel ply and it was looking pretty good. Not as much epoxy absorbed into the ply as I anticipated but it was still a nice surface with no puddles. The workpiece was fairly strong but still able to twist like my first test.
So I cut out two more pieces at 45 degrees. Due to the size of the 8sqft packs from bondo I was only able to get enough cloth for one layer out of each pack - I have a lot of leftover but it's in thinner strips I can't use for this.
I repeated the layups with 24g of resin on each side again.
I then let this sit all afternoon while I was out. When I got back I peeled the ply and then trimmed the edges down. The final piece is very strong and resists twisting much like my test did after two layers.
I weighed it and it comes n at 192g! Wow...70g heavier than my first panel with the lighter cloth. It feels about the same strength - maybe a little stronger...after all there's twice as much cloth on it. This definitely doesn't need a 3rd layer of 6oz cloth...but I am tempted to do a layer of the 1.45 just to give it a nicer surface finish with the finer weave. Instead I'll probably use some kind of surface coat on both to smooth them out.
So...next step will be to cut my frame out of this stuff and then try finishing it to see if it's usable and which I prefer. In an idea world lots of layers of light cloth is definitely the way to go...but the locally available option is cheaper and quicker (especially if I had used the MGS resin instead of the more than twice as expensive and not as nice to work with BSI.) But it's neat to see how the two end products compare!
Well, after spending all day in his hanger performing surgery on the fuel tanks in the wings of his velocity (He's apparently adding sight gauges) my friend stopped by today to check out the panels I've been making.
He was quite impressed with the work I've done. He's now worried that the EAA class he wants to send me to isn't advanced enough
However he's really unimpressed with DTFB and is disgusted that I'm "wasting my talents" with FG on such a crummy core material. I'm not as worried...at least not for this particular application. Yeah, it's not going to compare to higher quality stiffer foam - but for a low cost alternative to sheets of G10 or CF for this frame I still think it has potential.
Now that he's seen the sheets I'll be firing up the CNC later this week and giving a go at cutting them. I do want to pick up a better respirator first though since cutting FG isn't much better than cutting CF...it's not quite as bad but still not great and the simple filter mask I use while cutting wood isn't enough protection. Ideally I'd cut it under water but I can't really do that on my current setup. And it's not something I'll be doing regularly so I'm not super worried...but it's a good excuse for some better safety gear and the wife is always ok with me spending money on safety
I also picked up some WBPU and baby powder to see if it will work for a finishing coat. Not sure if the WBPU will stick to epoxy or not though so will have to experiment on a small test piece first.
He was quite impressed with the work I've done. He's now worried that the EAA class he wants to send me to isn't advanced enough
However he's really unimpressed with DTFB and is disgusted that I'm "wasting my talents" with FG on such a crummy core material. I'm not as worried...at least not for this particular application. Yeah, it's not going to compare to higher quality stiffer foam - but for a low cost alternative to sheets of G10 or CF for this frame I still think it has potential.
Now that he's seen the sheets I'll be firing up the CNC later this week and giving a go at cutting them. I do want to pick up a better respirator first though since cutting FG isn't much better than cutting CF...it's not quite as bad but still not great and the simple filter mask I use while cutting wood isn't enough protection. Ideally I'd cut it under water but I can't really do that on my current setup. And it's not something I'll be doing regularly so I'm not super worried...but it's a good excuse for some better safety gear and the wife is always ok with me spending money on safety
I also picked up some WBPU and baby powder to see if it will work for a finishing coat. Not sure if the WBPU will stick to epoxy or not though so will have to experiment on a small test piece first.
