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Cutting foam sheets... with a needle!

In general some kind of guide does seem to be helpful. I like the bearings and use them. David (dkj4linux) has had good luck with oiled wooden guides of various styles.

The guides help the needle bend along a longer area spreading the forces instead of concentrating them in one area. This can potentially help prevent breakage (though I'm not sure anyone has seen breakage down low on the needle where it bends going into the tip.) but mostly it seems to help the needle run cooler since there's less friction from the needle rubbing against the sides of the tip. So while the guides themselves do add some additional friction they appear to overall lower friction by letting the needle deflect over more of its length.
I believe Jason's explanation of what is going with the pre-guides here is entirely correct. Further, I believe the Mig welding tip, which is our "main guide", with its relatively large thermal mass and its proximity to the needle point and the material being cut, is likely going to be the culprit with most heat-related foam-cutting issues.

In my thinking and experience -- without pre-guides of some sort -- the flexing needle enters the Mig-welding tip, bends as it can within the bore, and then exits the tip... all with considerable friction and the resultant buildup of heat. If it gets hot enough -- and it will, if something isn't done to control it -- some heat is transferred to the business end of the needle and the foam it contacts, and the localized heating will eventually result in melted foam coating the needle, and eventually being drawn up into the tip. Only bad things result... and the cutter and cut quality suffer.

The pre-guides are simply an attempt to move the flexing needle's points of constraint out of the Mig-tip (the main guide) to a point ABOVE it. In constraining the needle's motion to as near straight-line, up-and-down as possible BEFORE it enters the main guide... we hopefully reduce the friction, and generation of heat, to manageable levels.

So, effective pre-guides have at least two points of constraint... an entry at the top and an exit at the bottom. The bearings on Jason's cutter are arranged such that the two upper-most bearings serve as entry constraint and the lower-most bearings, the exit constraint. On my oil-saturated wooden pre-guides, I have upper and lower wooden "plates" (or stacks of plates) with a very small aperture (hole), separated by the thickness of the plastic cutter body platform... and providing the points of constraint. In addition, I most often fill the area between the upper and lower guides with packed cotton, which is saturated with light machine oil, and helps lubricate and stabilize any erratic motion of the needle.

Alternatively, you could simply do away with the pre-guides and direct a flow of air at the Mig-welding tip, sufficient to keep it cool... similar to the part-cooling fan on a 3d printer. Fins are sometimes added to the tip as well... to increase the surface area. Another possibility is to use a main guide that doesn't have the thermal mass the Mig-tip does. The sports-ball inflation needles used on early cutter seemed to stay cooler far better... but it isn't as robust and long-lasting. Another thought I've kicked around -- but not yet tried -- is using the wooden stack idea to build a non-metallic main guide. And, there is at least one person I know of that has used a teflon/nylon/? tip to surprisingly good effect... but I suspect it -- and possibly the wooden-stack -- won't be as robust and long lasting as the Mig-tip.

So, which is better? Since this is all seat-of-the-pants engineering... you decide. Thankfully, the cutter is such a simple and inexpensive mechanism, trial and error methods to sneak up on something that works for you is not out of the question; i.e. YMMV.

Have fun. That is, after all, what DIY is all about... isn't it? ;)

-- David
 

Keno

Active member
Thanks all for expressing your opinion and thoughts.

I have had to reprint some of the parts I received and this has slowed my build. Not complaining as the purchase of a 3D printer has been one of my best buy's. Now I have move on to 3D drafting, the learning curve continually reforms itself over and over. Thanks again.
 
Hello all and hello David,

The concept of a needle cutter intrigued me for a long time. I have a working machine and I wanted to share my experiences.

I haven't followed the recent postings and I can't even claim to have read the majority of the older stuff. Still, I've found what I have read to be incredibly interesting. Also, kudos to David on how supporting and positive you are with everyone and every idea. A discouraging word is not just seldom heard. it's not heard at all. My compliments to you.

Here's the video:


Miles
 
Hello all and hello David,

The concept of a needle cutter intrigued me for a long time. I have a working machine and I wanted to share my experiences.

I haven't followed the recent postings and I can't even claim to have read the majority of the older stuff. Still, I've found what I have read to be incredibly interesting. Also, kudos to David on how supporting and positive you are with everyone and every idea. A discouraging word is not just seldom heard. it's not heard at all. My compliments to you.

Here's the video:


Miles
Thank you, Miles, for your kind words... and for sharing your work. Welcome!

And congratulations on getting your machine running so well. I must admit I was taken aback by the twisted needle you're using... what kind of wire are you using? I notice it comes in a spool... the 0.025" (0.635mm) music-/piano-wire I use comes as straight pieces of varying lengths. This piano-wire, in 36" lengths, is similar to what I use and provides for many needles... and is far easier to work with.

A possibility -- though I've not tried it with piano-wire -- I've "twist-straightened" spooled, solid, 0.025" Mig-wire to make needles, early on, that worked quite well. Take a length of wire to be straightened -- 24" to 36" will do -- and form a small eye in one end. Take a short length of wire coat hanger and make a small hook that can be chucked up into a power hand drill... like a cup hook. Tightly clamp the end of the wire to be straightened -- without the eye -- in a small vice and place it on the floor. Stand on it and then hook the eye in the wire to be straightened with the coat hanger hook and pull up on it until taut. Turn on the drill and twist the wire... either direction, while maintaining the tension... for 10, 15, 20 seconds or more... or until the wire breaks. The wire will work-harden to some degree and be perfectly straight. I've made many needles that way... and since you're twisting your wire to some degree, it will probably "twist-straighten" as well?

Please keep us posted on your progress. And, thanks again!

-- David
 

jhitesma

Some guy in the desert
Mentor
I haven't followed the recent postings and I can't even claim to have read the majority of the older stuff. Still, I've found what I have read to be incredibly interesting. Also, kudos to David on how supporting and positive you are with everyone and every idea. A discouraging word is not just seldom heard. it's not heard at all. My compliments to you.
Miles
Great work Miles and some interesting solutions to the issues you ran into. I've been meaning to try a 2204 sized motor like you used for many of the same reasons...plus I have a number of spares on hand. But my current cutter has been so reliable it's hard to get motivated to change it :D Still, I know the motor I designed mine around is now hard to find so it's no longer a great choice even if I still have a couple of them kicking around in my parts box. (and since they were the size used on early 550 quads and DJI's I figured there were more of them out there than there apparently actually are.)

Sounds like David has some great tips for your needle issues. That music wire definitely looks different than what we get here as "music wire" which is not nearly as flexible and sold in 3' rods rather than rolls. So that's probably why you're having so much difficulty with your needle.

Mechanically the machine looks great! Hope you continue to have success and work out your final issues!
 
Howdy all,

Interesting thoughts on the wire I'm using. I got it here.

The wire I have is pretty stiff, certainly stiffer than regular wire or the picture hanging stuff from the hardware store. I guess I need to find a local hobby/model shop to get the straight stuff. I'll also try David's suggestion though I don't have a whole lot left from this crop of wire.

Thanks for the feedback

I'm generally please with the machine. My main gripe is I'd like it to run a little faster. There, I'm mostly limited by the resistance of the belt being squeezed in the bearing. The needle wheel could run faster than it is now. It's interesting how I can set the speed of it by the sound. If it sounds ragged, I need to up the speed. I've also thought of using a laser, but I'm hesitant to do that since my kids are still little. This cutter is a great alternative.

Miles
 
When last I left off, FoamRipper had gotten a new laser. To continue, here are my latest adventures in air-assist…

Still a fan of “pawpawpaw85″‘s air-assist shroud I’ve used several times, I’ve discovered one I think I like a bit more… “danwar”‘s “Laser Air Assist Shroud” (https://www.thingiverse.com/thing:2626593). I’ve replaced the radial fan, however, with a small printed adapter that allows connection of some vinyl tubing (3/8″ ID x 1/2″ OD) from the big box store. At the other end, I’ve connected a fairly nice, relatively quiet, air pump… powered by an inexpensive router speed control, for adjusting the flow of air from nozzle.

A crude test over the range of the speed control, showing the air flow from MIN to MAX…


Here’s the air pump, router speed control, and vinyl tubing connected through another printed adapter…

20190624_093431.jpg

Shroud with printed adapter and vinyl tubing…

20190624_093308.jpg

20190624_093227.jpg

Mounted on the FoamRipper’s laser housing…

20190624_215225.jpg

Top-view…

20190624_215347.jpg

and “shades of gray” test run.

20190624_212530.jpg

Later.

— David
 

Chuppster

Well-known member
I believe Jason's explanation of what is going with the pre-guides here is entirely correct. Further, I believe the Mig welding tip, which is our "main guide", with its relatively large thermal mass and its proximity to the needle point and the material being cut, is likely going to be the culprit with most heat-related foam-cutting issues.

In my thinking and experience -- without pre-guides of some sort -- the flexing needle enters the Mig-welding tip, bends as it can within the bore, and then exits the tip... all with considerable friction and the resultant buildup of heat. If it gets hot enough -- and it will, if something isn't done to control it -- some heat is transferred to the business end of the needle and the foam it contacts, and the localized heating will eventually result in melted foam coating the needle, and eventually being drawn up into the tip. Only bad things result... and the cutter and cut quality suffer.

The pre-guides are simply an attempt to move the flexing needle's points of constraint out of the Mig-tip (the main guide) to a point ABOVE it. In constraining the needle's motion to as near straight-line, up-and-down as possible BEFORE it enters the main guide... we hopefully reduce the friction, and generation of heat, to manageable levels.

So, effective pre-guides have at least two points of constraint... an entry at the top and an exit at the bottom. The bearings on Jason's cutter are arranged such that the two upper-most bearings serve as entry constraint and the lower-most bearings, the exit constraint. On my oil-saturated wooden pre-guides, I have upper and lower wooden "plates" (or stacks of plates) with a very small aperture (hole), separated by the thickness of the plastic cutter body platform... and providing the points of constraint. In addition, I most often fill the area between the upper and lower guides with packed cotton, which is saturated with light machine oil, and helps lubricate and stabilize any erratic motion of the needle.

Alternatively, you could simply do away with the pre-guides and direct a flow of air at the Mig-welding tip, sufficient to keep it cool... similar to the part-cooling fan on a 3d printer. Fins are sometimes added to the tip as well... to increase the surface area. Another possibility is to use a main guide that doesn't have the thermal mass the Mig-tip does. The sports-ball inflation needles used on early cutter seemed to stay cooler far better... but it isn't as robust and long-lasting. Another thought I've kicked around -- but not yet tried -- is using the wooden stack idea to build a non-metallic main guide. And, there is at least one person I know of that has used a teflon/nylon/? tip to surprisingly good effect... but I suspect it -- and possibly the wooden-stack -- won't be as robust and long lasting as the Mig-tip.

So, which is better? Since this is all seat-of-the-pants engineering... you decide. Thankfully, the cutter is such a simple and inexpensive mechanism, trial and error methods to sneak up on something that works for you is not out of the question; i.e. YMMV.

Have fun. That is, after all, what DIY is all about... isn't it? ;)

-- David
Thanks for the run-down, it's very helpful! I went ahead and ordered bearings. I'm planning to use either a 2212 or an old "blue wonder" type motor I have laying around, whatever I can get to line up with the pre-existing design.

As I think ahead to using a spindle, has anyone tried extending the shaft on a BLDC motor, adding good bearings to mount the shaft, stuck a drill collet on the end of the shaft, and used it as a quiet alternative to a spindle? I'm strongly debating doing that.
 

jhitesma

Some guy in the desert
Mentor
As I think ahead to using a spindle, has anyone tried extending the shaft on a BLDC motor, adding good bearings to mount the shaft, stuck a drill collet on the end of the shaft, and used it as a quiet alternative to a spindle? I'm strongly debating doing that.
It can be done...but it's hard to do well. I've seen a few people who machined up adapters to do it but without access to a machine shop and skills it's usually cheaper to just buy a purpose built spindle (or just use a router.)
 

jhitesma

Some guy in the desert
Mentor
I'm generally please with the machine. My main gripe is I'd like it to run a little faster. There, I'm mostly limited by the resistance of the belt being squeezed in the bearing. The needle wheel could run faster than it is now. It's interesting how I can set the speed of it by the sound. If it sounds ragged, I need to up the speed. I've also thought of using a laser, but I'm hesitant to do that since my kids are still little. This cutter is a great alternative.
I noticed you seemed to be running very slow, that 4x sped up video still looked a little slower than I run mine at. But since that seems to be a limitation of your mechanical setup I'm not sure what to suggest. I currently run mine at 15mm/s - I can push it faster but quality starts to drop off and increasing the speed on the needle doesn't help bring the quality back up much and the"scary" factor goes up quick. So 15mm/s is what I've settled on as my happy speed for cutting with the needle. If I ever get the time to rebuild my machine and fix some of the mechanical quirks I may look into getting things moving faster again...but for now I'm pretty good with these settings.
 

Chuppster

Well-known member
Wow, this MPCNC thing is pretty sweet! I'm impressed at how quickly it builds and how well it works. I've got a little bit of "snagging" in my X-axis because it's so long, but I hope it'll "wear in".

2019-06-30 08.18.32.jpg

Here's some pics. I'm going at 15mm/s. Not sure what my spindle speed is (tach isn't working), but I would guess it's in the ballpark of 7-8k rpm. Any tips on getting a cleaner cut, especially on the exit?

2019-06-30 08.31.09.jpg

2019-06-30 08.30.55.jpg
 
Fantastic, Chuppster! What great progress... and so fast! It's only been a couple of weeks since you first dropped in, hasn't it?

We really need some more information to fine tune things but what you have so far really looks good. A few detailed photos of the needle cutter, info on the motor/ESC/power setup, needle length, etc. would help immensely.

Yep! MPCNC is an impressive piece of engineering... and we all owe Ryan a debt of gratitude for sharing it with us. I'd love to see you strap a pen on it and do some pretty serious plotting... the crown and Jamie's test pattern generator would go a long way in helping tune up your axes. And there's hardly anything more satisfying than seeing this machine you've built in your garage print some accurate rulers! :eek::)

Great work! I really wanna see more... :D

-- David
 

Chuppster

Well-known member
Here's a picture of the needle setup. At full stroke, the needle sticks out of the mig tip 10mm. I believe it's .025" music wire. I didn't sharpen it, is that important?

2019-06-30 11.41.20.jpg

I'll see about a pen attachment.
 
Getting ready for FliteFest. Still can't bring myself to go back to the needle cutter after trying these .8mm bits on the spindle. Cutting at 40mm/sec and getting super crisp edges. The vacuum table is working amazingly, I get perfect suction down to even 30% power. I did have to move it from my basement to the guest room after some flooding and the following crew adding a french drain last week, but aside from my wife's complaints, no problems!

1561910098678.png
1561910112225.png 1561910123300.png
 

TEAJR66

Flite is good
Mentor
Here's a picture of the needle setup. At full stroke, the needle sticks out of the mig tip 10mm. I believe it's .025" music wire. I didn't sharpen it, is that important?

View attachment 134884

I'll see about a pen attachment.
I have a pen holder that will hold a Sharpie marker, number 2 pencil or a ball point pen in the same place you found that needle cutter. The pen holder put the writing tip in the same position as your needle.

https://www.thingiverse.com/thing:3148651

20190630_115321.jpg

20190630_115404.jpg
 
Last edited:
.. I didn't sharpen it, is that important?
...
Regarding the needle's point... think BULLETS and exit wounds. Armor-piercing vs. hollow-point... piercing vs. punching...

Blunt bullets enter, do lots of damage, and then exit ... leaving lots of debris/damage in their wake and a large exit wound.

Pointed bullets enter, do lesser damage, and then exit... leaving minimal debris and a smaller exit wound.

A short conical point on the needle (like a wooden pencil point) pierces the foam, cuts equally well in all directions, and leaves little/no debris in its wake. The bottom-side, though probably not as clean as the top-side, should also show relatively clean cuts and little/no debris/damage.

Blunt points, on the other hand, punch their way through the foam, the cuts will not be as clean, and the bottom-side will show considerably more damage/debris.

If barbed or chisel-pointed, as snipped with side-cutters, the needle will also favor cutting in certain directions more than others... you'll hear the motor load up more in some directions as the cutting forces increase.
 

TEAJR66

Flite is good
Mentor
Nothing new or ground breaking. Just enjoying the new vacuum table.
20190630_115418.jpg

Got the waste board cut .
20190630_115536.jpg


Then the board to get cut goes on.

20190630_115558.jpg


Then the vacuum gets turned on and everything gets sucked flat.

20190630_115626.jpg

The wood blocks are a mechanical stop that keeps everything square.

20190630_115438.jpg

20190630_115449.jpg

Here it is cutting away.

 

Chuppster

Well-known member
Nothing new or ground breaking. Just enjoying the new vacuum table.
View attachment 134897

Got the waste board cut .
View attachment 134903


Then the board to get cut goes on.

View attachment 134904


Then the vacuum gets turned on and everything gets sucked flat.

View attachment 134900

The wood blocks are a mechanical stop that keeps everything square.

View attachment 134901

View attachment 134902

Here it is cutting away.

These are good ideas, I may adopt your wood block implementation!
 

Chuppster

Well-known member
Regarding the needle's point... think BULLETS and exit wounds. Armor-piercing vs. hollow-point... piercing vs. punching...

Blunt bullets enter, do lots of damage, and then exit ... leaving lots of debris/damage in their wake and a large exit wound.

Pointed bullets enter, do lesser damage, and then exit... leaving minimal debris and a smaller exit wound.

A short conical point on the needle (like a wooden pencil point) pierces the foam, cuts equally well in all directions, and leaves little/no debris in its wake. The bottom-side, though probably not as clean as the top-side, should also show relatively clean cuts and little/no debris/damage.

Blunt points, on the other hand, punch their way through the foam, the cuts will not be as clean, and the bottom-side will show considerably more damage/debris.

If barbed or chisel-pointed, as snipped with side-cutters, the needle will also favor cutting in certain directions more than others... you'll hear the motor load up more in some directions as the cutting forces increase.

Alright, after putting a point on the needle it cuts much better. I also loosened every bolt on the machine and it rides a lot smoother. I'm happy with my results, about 6 sheets in and no sign of stopping soon! This is brilliant, thank you for sharing it friends!
 
Howdy all,

Interesting thoughts on the wire I'm using. I got it here.

The wire I have is pretty stiff, certainly stiffer than regular wire or the picture hanging stuff from the hardware store. I guess I need to find a local hobby/model shop to get the straight stuff. I'll also try David's suggestion though I don't have a whole lot left from this crop of wire.
...

Miles
Miles,

I found the following photos that show twist-straightening a piece of 0.025" Mig-wire fresh off the spool. You'll need a strong vice, a power drill, a big enough hook to chuck up in the drill, and a piece of wire to be straightened.

20170130_171529.jpg

Standing on the vice, I then pull upward until the wire is taut... and then power on the drill motor while keeping the tension. In this case I think I probably just kept going until the wire broke... and it's standing straight up on its own; i.e. I'm not holding it up at all...

20170130_171702.jpg

Removed from the vice, the wire is perfectly straight...

20170130_171804.jpg

and ready to be formed into a needle. I made many needles this way early-on, before I started using piano-wire...

20170130_171844.jpg

This has straightened all the kinds of wire I've ever tried... solid copper electrical wire, baling wire, Mig-wire, galvanized wire, etc. I'm not sure about piano-wire (I've only used the straight stuff) but I'll bet it will. It will work-harden and probably not have quite the tensile strength it once had but it works nicely if you just need a straight, stiff, piece of wire... :eek::)

-- David