Cutting foam sheets... with a needle!

[jhitesma]

I had a minor inspiration. Buy a sheet of foam insulation and some MDF, glue them together, cut the channels by hand down to the MDF and then frame it. Need to size it all so that your peeled DTFB waste board lays flush with your frame. It needs to be bolted down though to keep it flat or the MDF can warp.

One thing to watch for with MDF...it's porus. Probably more so than you'd expect. So if you cut all the way through to the MDF you'll probably have to seal the MDF in some way.

CNCNUTZ ran into this with his vacuum table a few weeks ago and does some demos showing just how porus the MDF turned out to be:

One thing I hadn't thought of that he does is he uses large holes against his work - but with very small holes connecting them to the plenum. He explains the benefits of this better than I can right now - it's something I'm considering experimenting with if I rebuild my vac table.

 

[ironkane]

White glue thinned with water is the suggestions that I hear. But you want a certain amount of air flow to get maximum suckage.
My waste board? She have very small holes. Air moves faster when constricted.


Anyways, here's my current needle cutter mounted and waiting on my new drag chain and final tweaking

Did a quick freehand cut with the help of my wife

 

[dkj4linux]

White glue thinned with water is the suggestions that I hear. But you want a certain amount of air flow to get maximum suckage.
My waste board? She have very small holes. Air moves faster when constricted.


Anyways, here's my current needle cutter mounted and waiting on my new drag chain and final tweaking

That's a really clean looking needle cutter and machine, Steve. Well done!

 

[Michael9865]

I have now successfully completed the longest run on my updated MPCNC, almost 54 minutes. This is a ManiacRC Mighty Mini B-25 Beta designed by Sankaran Ramanarayanan, next is to begin the building process. Very happy with the needle cutter and the new middle assembly.

Sheet 1


Sheet 2

 

[ironkane]

I have now successfully completed the longest run on my updated MPCNC, almost 54 minutes. This is a ManiacRC Mighty Mini B-25 Beta designed by Sankaran Ramanarayanan, next is to begin the building process. Very happy with the needle cutter and the new middle assembly.

Sheet 1
View attachment 106866

Sheet 2
View attachment 106867

Link to the plans?

 

[Michael9865]

Link to the plans?

I wish I could, but these are not my plans. I am helping to do the Beta build. I believe that the design is getting close. I am testing an adjusted airfoil. I will share the info as soon as I am allowed.

 

[jhitesma]

Ran the snot out of my needle cutter this weekend. I've been experimenting with fiberglass and composites lately and a local guy hooked me up with some really nice epoxy so I could see what a difference high quality epoxy makes over the hobby grade stuff I've been using. Well, long story short I'm now sold. The stuff he gave me is not only FAA (and German FAA) rated for fabricating manned aircraft and WAY easier/nicer to work with...it's also half the price of the "cheap" epoxy from the hobby store. Only catch is you have to buy at least a gallon of resin and quart of hardener (and more realistically 2 quarts of hardener because the fast is too fast and the slow is too slow so you have to blend them to get a better cure rate) plus there's a hazardous material shipping fee...so it ends up being $150-$200 to buy it...but the per oz price is about half what epoxy in the little 4.5oz bottles goes for at the LHS or online.

Anyway, he hooked me up with a nice big bottle of the resin and enough blended hardener to go with it. And then mentioned that his grandkids were interested in building the Alpha/Bravo/Charlie jets from FT if I could cut them on my MPCNC. And another local guy did me a favor and I offered to repay him will a FT Dart and FT Arrow. So I had some cutting to do this weekend.

Got off to a rocky start Friday evening. Pulled out my vac table and found it had warped again. Didn't really want to wait for it to flatten out under weights so decided to cut myself the Long-EZ jpot1 has been working on in the Mad Scratch Builders section. I've been kind of gung ho about composites lately because a good friend of mine recently bought a used Velocity XL which is a composite aircraft very similar to the Cozy MarkIV which is in turn based on the Long-EZ only modified for 4 passengers. So I figured cutting jpot1's experimental build would be a good warm up for the weekend.

I've been experimenting with cncjs on a pine64 (kind of like a RaspPi only cheaper) instead of using the LCD lately - so after I created my gcode in estlcam I loaded it up in there and gave it a go.

Unfortunately after just a few operations I saw and heard the machine do something odd. It was almost like it skipped a few steps...except it didn't skip - it actually moved backwards then continued. The end result was the same as skipped steps with it getting out of position...but I swear it didn't skip it actually moved backwards. 95% of the sheet came out ok...but due to that issue one of the B folds on the fuselage was too wide and the other too narrow. So the long-EZ came out a bit crooked and there was no way to install the motor pod because one of the mounting slots was partly covered. Oh well...it's still a halfway decent chuck glider and gave me a feel for how the plane will go together.

With that done I called it a night.

Saturday I ran up and bought 15 sheets of foam...then dug in on the cut fest.

I cut the Alpha using the LCD/SD like I usually do. But the Bravo and Charlie I cut using cncjs. They all came out great except for two minor issues. One sheet of the Bravo I didn't quite position correctly and a tiny bit of one wing fell off the edge of the foam...oops. It will be ok...just isn't perfect. And on one sheet of the Charlie cncJS did the same thing again suddenly backtracked loosing position. Thankfully it did it at time that didn't really affect anything. Just left one score cut a few mm short and the rest of the parts on the sheet nested a few mm closer together.

So that was 9 sheets of foam back to back with only 2 very minor issues. I did notice my cuts are getting a little less clean...guess it's time to finally sharpen this needle...it did seem to be getting a little dull.

But first I have the Dart and Arrow for the other guy.

I cut both of them with cncJS and only had one issue. On the last sheet of the Arrow cutting out the motor pod part it only cut 1 of the 4 sides. It cut that side 4 times though. No clue what caused that. The preview on CNCjs looked correct and the CAM looks correct. So not sure if it was a cncjs issue or a marlin issue. No big deal because he's going to use a 3D printed motor pod on this build anyway but still kind of crazy and hard to explain. I guess cncjs is still not 100% with marlin...or at least not with the 2 year old version of Marlin I'm still running. I really need to upgrade to the latest beta of Marlin since there are some really nice upgrades for CNC use I want to try.

But 15 sheets of foam in one weekend is a new personal best...and I could tell the needle was getting duller as the cut quality on the 15th sheet was not as nice as on the 1st. But...doing all those planes gave me the itch to build and the Alpha jet looked kind of fun.....

So I just fired it up to cut an alpha for myself. 1st sheet went great. 2nd sheet went great for the first half....then...suddenly the machine seemed rather quiet. I looked over and sure enough I couldn't see a needle on it anymore. Oops.

Shut it down...and sure enough the needle is gone. The bit around the bearing was still there but the rest was nowhere to be found - it broke off right where it bent around the bearing. I wonder if it would have lasted longer if I had sharpened it so the forces on it were a bit easier.

Still...it lasted almost a year (I made that needle in July of Last year and have totally lost track of how many sheets of foam I've cut with it. I've made almost 20 planes for myself (explorer, arrow, dart, mini-dr1, x29, mirage chuck glider, a couple beta gliders from Sponz, tinywhoovs, the vactable, simple scout, 2 mini scouts, xb-70 chuck glider, 3 sparrows, ft cub with floats, baby bugatti), even more for friends (almost every plane I cut for myself I also cut one or two for friends), my ink organizers, my solar projectors, a few dinosaur skeletons, a few cardboard projects, and a couple of other random DTFB projects....that needle had a good life

I should be bending up a new one right now to finish cutting my Alpha....but...I think I may give moebeasts needle holder a try instead. So going to fire up the 3D printer and crank one of those out and give the MPCNC a rest for the rest of the evening

 

[dkj4linux]

Ran the snot out of my needle cutter this weekend. I've been experimenting with fiberglass and composites lately and a local guy hooked me up with some really nice epoxy so I could see what a difference high quality epoxy makes over the hobby grade stuff I've been using. Well, long story short I'm now sold. The stuff he gave me is not only FAA (and German FAA) rated for fabricating manned aircraft and WAY easier/nicer to work with...it's also half the price of the "cheap" epoxy from the hobby store. Only catch is you have to buy at least a gallon of resin and quart of hardener (and more realistically 2 quarts of hardener because the fast is too fast and the slow is too slow so you have to blend them to get a better cure rate) plus there's a hazardous material shipping fee...so it ends up being $150-$200 to buy it...but the per oz price is about half what epoxy in the little 4.5oz bottles goes for at the LHS or online.

Anyway, he hooked me up with a nice big bottle of the resin and enough blended hardener to go with it. And then mentioned that his grandkids were interested in building the Alpha/Bravo/Charlie jets from FT if I could cut them on my MPCNC. And another local guy did me a favor and I offered to repay him will a FT Dart and FT Arrow. So I had some cutting to do this weekend.

Got off to a rocky start Friday evening. Pulled out my vac table and found it had warped again. Didn't really want to wait for it to flatten out under weights so decided to cut myself the Long-EZ jpot1 has been working on in the Mad Scratch Builders section. I've been kind of gung ho about composites lately because a good friend of mine recently bought a used Velocity XL which is a composite aircraft very similar to the Cozy MarkIV which is in turn based on the Long-EZ only modified for 4 passengers. So I figured cutting jpot1's experimental build would be a good warm up for the weekend.

I've been experimenting with cncjs on a pine64 (kind of like a RaspPi only cheaper) instead of using the LCD lately - so after I created my gcode in estlcam I loaded it up in there and gave it a go.

Unfortunately after just a few operations I saw and heard the machine do something odd. It was almost like it skipped a few steps...except it didn't skip - it actually moved backwards then continued. The end result was the same as skipped steps with it getting out of position...but I swear it didn't skip it actually moved backwards. 95% of the sheet came out ok...but due to that issue one of the B folds on the fuselage was too wide and the other too narrow. So the long-EZ came out a bit crooked and there was no way to install the motor pod because one of the mounting slots was partly covered. Oh well...it's still a halfway decent chuck glider and gave me a feel for how the plane will go together.

View attachment 107263

With that done I called it a night.

Saturday I ran up and bought 15 sheets of foam...then dug in on the cut fest.

I cut the Alpha using the LCD/SD like I usually do. But the Bravo and Charlie I cut using cncjs. They all came out great except for two minor issues. One sheet of the Bravo I didn't quite position correctly and a tiny bit of one wing fell off the edge of the foam...oops. It will be ok...just isn't perfect. And on one sheet of the Charlie cncJS did the same thing again suddenly backtracked loosing position. Thankfully it did it at time that didn't really affect anything. Just left one score cut a few mm short and the rest of the parts on the sheet nested a few mm closer together.

So that was 9 sheets of foam back to back with only 2 very minor issues. I did notice my cuts are getting a little less clean...guess it's time to finally sharpen this needle...it did seem to be getting a little dull.

But first I have the Dart and Arrow for the other guy.

I cut both of them with cncJS and only had one issue. On the last sheet of the Arrow cutting out the motor pod part it only cut 1 of the 4 sides. It cut that side 4 times though. No clue what caused that. The preview on CNCjs looked correct and the CAM looks correct. So not sure if it was a cncjs issue or a marlin issue. No big deal because he's going to use a 3D printed motor pod on this build anyway but still kind of crazy and hard to explain. I guess cncjs is still not 100% with marlin...or at least not with the 2 year old version of Marlin I'm still running. I really need to upgrade to the latest beta of Marlin since there are some really nice upgrades for CNC use I want to try.

But 15 sheets of foam in one weekend is a new personal best...and I could tell the needle was getting duller as the cut quality on the 15th sheet was not as nice as on the 1st. But...doing all those planes gave me the itch to build and the Alpha jet looked kind of fun.....

So I just fired it up to cut an alpha for myself. 1st sheet went great. 2nd sheet went great for the first half....then...suddenly the machine seemed rather quiet. I looked over and sure enough I couldn't see a needle on it anymore. Oops.

Shut it down...and sure enough the needle is gone. The bit around the bearing was still there but the rest was nowhere to be found - it broke off right where it bent around the bearing. I wonder if it would have lasted longer if I had sharpened it so the forces on it were a bit easier.

Still...it lasted almost a year (I made that needle in July of Last year and have totally lost track of how many sheets of foam I've cut with it. I've made almost 20 planes for myself (explorer, arrow, dart, mini-dr1, x29, mirage chuck glider, a couple beta gliders from Sponz, tinywhoovs, the vactable, simple scout, 2 mini scouts, xb-70 chuck glider, 3 sparrows, ft cub with floats, baby bugatti), even more for friends (almost every plane I cut for myself I also cut one or two for friends), my ink organizers, my solar projectors, a few dinosaur skeletons, a few cardboard projects, and a couple of other random DTFB projects....that needle had a good life

I should be bending up a new one right now to finish cutting my Alpha....but...I think I may give moebeasts needle holder a try instead. So going to fire up the 3D printer and crank one of those out and give the MPCNC a rest for the rest of the evening

Wow! You've mentioned that bent, dull needle several times in the past and I was always puzzled why you didn't do something about it. Had you done it you probably would have gotten another 30 minutes out of it... at least!

Seriously, I'm thrilled your needle cutter setup has served you so well. I'm aware that several of you more avid plane builders have been using needle cutters to cut planes -- EdinCT's B-17 build comes to mind -- and it's gratifying to know that in at least a few cases it's proving itself to be a truly useful tool. Not quite mainstream yet... but it's a start.

 

[TEAJR66]

That needle definitely had a good run.

I've only cut just over 50 sheets with my current needle. I hope it keeps going for 50 more.

 

[TEAJR66]

Anyone bringing an MPCNC to FF in Ohio?

 

[bperc]

Hello,
I have built a MPCNC with a needle cutter. It has cut out many planes. In fact, so many I recently had to replace the 2212 motor because the bearings were worn out. I have it in my classroom at school. I am having trouble with the MIG tip building up foam dust inside and then melting and causing a lot of drag. The only way I've found to free it back up is to periodically spray a little WD-40 in it. What are you guys doing to alleviate the build up of foam dust in the MIG tip?
Thanks for all your great tips in this thread.

 

[dkj4linux]

Hello,
I have built a MPCNC with a needle cutter. It has cut out many planes. In fact, so many I recently had to replace the 2212 motor because the bearings were worn out. I have it in my classroom at school. I am having trouble with the MIG tip building up foam dust inside and then melting and causing a lot of drag. The only way I've found to free it back up is to periodically spray a little WD-40 in it. What are you guys doing to alleviate the build up of foam dust in the MIG tip?
Thanks for all your great tips in this thread.

Thanks and welcome! That's a great looking machine and needle cutter... very straight-forward/simple; i.e. KISS!

Since you've been able to cut many planes, your maintenance routine is probably as good as anybody's and might actually be classified as "normal". I've never heard of using WD40 specifically to free/loosen a clogged MIG tip guide but it's nice to know that works. Prevention is probably the right answer but I'm not sure how that is accomplished with heavier use... blowing it out with compressed air every sheet or two? Also, unsure of its effect in this case, you may want to try incorporating a little cotton-wad oiler/stabilizer stuffed into the opening/throat, around the needle and above the MIG tip. A few drops of light machine oil, applied periodically, provides a little lubrication and helps control friction heating in the guide. It'll also help quieten(?)/stabilize the needle in the guide and give slightly cleaner cuts.

Again, welcome! Being in a classroom, are the students involved in any way with the CNC operation and/or planes you are producing? Please tell us more about yourself and what you are doing with the MPCNC and needle cutter. We would love to hear more.

-- David

 

[DKchris]

Has anybody ever experimented with placing a magnet in the flywheel opposite the needle attachment point, and then having another magnet on the base mounted just under the flywheel, with the intention of having the needle always stop at the top position?

If it works, it might eliminate the need for having a 3rd axis to lift the needle. Won't work for both through- and score-cuts in one go, but still might be useable for making extremely simple cnc solutions?

(I did try searching this thread, but didn't find anything)

 

[dkj4linux]

Has anybody ever experimented with placing a magnet in the flywheel opposite the needle attachment point, and then having another magnet on the base mounted just under the flywheel, with the intention of having the needle always stop at the top position?

If it works, it might eliminate the need for having a 3rd axis to lift the needle. Won't work for both through- and score-cuts in one go, but still might be useable for making extremely simple cnc solutions?

(I did try searching this thread, but didn't find anything)

The inspiration for my needle cutter came from a very talented engineer/artist, Tom ("atomicwire") McGuire, whose foam cutting machine does exactly what you are describing... stopping the needle at the top of its stroke to allow movement to a new cut area. Rather than magnets, however, he used a DC motor and solenoid-operated wire loop... momentarily reversing the motor and activating the solenoid to catch a stud protruding from the edge of the flywheel to stop it at TDC. With no Z-lift requirement, his foam cutting machine is a simpler, lighter machine that works quite well...

All I did was take the concept and adapt it to a conventional 3-axis CNC machine... where having a true Z-axis allows for a simpler, free-running needle cutter mechanism and variable depth cuts. -- David

 

[bperc]

Thanks and welcome! That's a great looking machine and needle cutter... very straight-forward/simple; i.e. KISS!

Since you've been able to cut many planes, your maintenance routine is probably as good as anybody's and might actually be classified as "normal". I've never heard of using WD40 specifically to free/loosen a clogged MIG tip guide but it's nice to know that works. Prevention is probably the right answer but I'm not sure how that is accomplished with heavier use... blowing it out with compressed air every sheet or two? Also, unsure of its effect in this case, you may want to try incorporating a little cotton-wad oiler/stabilizer stuffed into the opening/throat, around the needle and above the MIG tip. A few drops of light machine oil, applied periodically, provides a little lubrication and helps control friction heating in the guide. It'll also help quieten(?)/stabilize the needle in the guide and give slightly cleaner cuts.

Again, welcome! Being in a classroom, are the students involved in any way with the CNC operation and/or planes you are producing? Please tell us more about yourself and what you are doing with the MPCNC and needle cutter. We would love to hear more.

-- David

Thank you David. I have used the cotton-wad and oil. I was hoping that someone had found a solution to prevent foam dust build up. A few weeks ago I took the needle cutter apart and found a very large fused cylinder of melted foam between the cotton and MIG tip.

I teach at a junior high school. I have cut out several planes that students have built. They have built around 50 Sparrow gliders, 4 Tiny Trainer gliders, 3 Tiny Trainers with motors, an Alpha and Charlie with motors. 40 of the Sparrows were built by junior high students in the MESA program on a Saturday at Fresno State. I have cut out several planes for friends and family to build also. It's a great machine and definitely speeds up the building process. Before building the MPCNC I was printing out plans and cutting them out manually. I really enjoy having the CNC to cut them out now. All told, I have cut out 22 different models of planes so far.

-Britt

 

[jhitesma]

Thank you David. I have used the cotton-wad and oil. I was hoping that someone had found a solution to prevent foam dust build up. A few weeks ago I took the needle cutter apart and found a very large fused cylinder of melted foam between the cotton and MIG tip.

Hmmm, maybe try pushing the cotton in deeper? I've run cotton with oil on mine since before my latest design revision and have yet to experience that. What kind of speed are you running at - I don't really get things warm enough to result in any kind of melting of the foam with my latest cutter.

 

[jhitesma]

Hey @mobeast - or anyone else using his needle retainer.

What are you guys doing to keep the needle retainer from rubbing on the flywheel? The hole in the back of the retainer is too small for the washer I used to have between my bearing and flywheel...and even if it wasn't the "seat" is thicker than the washer. I figure I could add a tiny little bit of copper tubing that fits over the M3 screw...but curious what everyone else is doing before I get too fancy

 

[dkj4linux]

Thanks, Jason. I also think feeds and speeds is the next issue to address...

Britt, I've only noticed melting of the foam when running too fast rpms and/or too slow feedrate... and that was before I used any sort of pre-guide. Is your cutterspeed/feedrate ratio in the 10-15 range, for DTFB? Above 15 perforations per mm I noticed localized heating of the needle (from the friction heating in the guide) would start melting the foam, which then coated the needle, and then be drawn up into the guide... again, before we ever had near straight-line motion of the needle in the guide.

I notice that you're using a single-row, 2-bearing preguide... and I know Jason's setup is dual-row, 4-bearing design. I think it's possible that you still have excessive friction heating in the guide itself since the needle is rubbing against a bearing and the top of your guide at the 3 and 9 o'clock positions. With the dual-row, 4-bearing setup the needle always rubs an upper bearing and the opposite side lower bearing... and effectively constrains the motion of the needle to straight-line motion *before* it enters the guide proper; i.e. less friction heating in the guide. Maybe you'll want to consider going to the 4-bearing setup... AFAICT it appears to be the most popular and successful preguide setup so far.

I think it is wonderful how you've got the kids so involved in building all those planes... how fun and instructive. The kids will be thankful, when they look back on their education, for teachers such as you.

-- David

 

[dkj4linux]

Hey @mobeast - or anyone else using his needle retainer.

What are you guys doing to keep the needle retainer from rubbing on the flywheel? The hole in the back of the retainer is too small for the washer I used to have between my bearing and flywheel...and even if it wasn't the "seat" is thicker than the washer. I figure I could add a tiny little bit of copper tubing that fits over the M3 screw...but curious what everyone else is doing before I get too fancy

Jason, here's my needle cutter on the Phlatprinter-inspired machine I built. I essentially replaced the small washer between bearing and flywheel with a 3mm nut. Gives sufficient clearance for retainer and also counter-balance hardware...

 

[jhitesma]

Hmm, your needle retainer looks different than moebeast's - his has a lip that the bearing rides against so the retainer can't slip off the bearing. The opening in that lip is too small to clear a nut or a washer is the issue I'm having.

I considered just cutting the lip out...but I do like the idea of it being there so the retainer can't come off.

I wonder if I still have a damaged bearing...I could take the inner race from that and use it as a spacer.....