Cutting foam sheets... with a needle!

[jhitesma]

Any tips on getting the cotton wad to stay put? I think that will help with cooling as well.

Not sure what to suggest with the mig tip. What worked for me on the inflation needle was putting it in the top of the inflation needle not just into the 3D printed support. I did add a second one to the top support just for good measure and haven't had either come out since I did that. Though I did have the upper one start to gunk up and harden then start throwing little bits of blackened crud the other day. No harm...but think it's time for fresh cotton

Since the mig tip doesn't have that little pocket I'm not sure what to suggest for it. Maybe redesign the 3D printed part so it flares out at the bottom so it can help hold the cotton ball in....since you have the bearings you probably don't have much slop on the needle as it enters the mount there so maybe you could put something like a bit of old credit card over the top with just a small slit or hole for the needle to pass through?

 

[dkj4linux]

Hi David,
in my so called "prototyp" the bearings are on a differend position as show in your picture

As you can see in my older pic, the bearings are nearer to the crank and are taking most of the bending force...
http://forum.flitetest.com/attachment.php?attachmentid=80429&d=1484594107&thumb=1
...the small wooden (and greased) blocks are working as an additional guides to straighten the movement...they also act as an oiler/greaser.
Only an idea--> may be, in your deisgn there is not enough force on the bearings to bring them to a rotation...try to mount the rails nearer to the metal guide and bring the bearings nearer to the crank (or try without)

Yeah, I remembered them being positioned differently. I just wanted to see their effect and actually installed them too tight (gap between bearings) in my little cutter... and simply by touching one bearing with my finger I was able to load the motor down. They rolled continuously.

But since the cutter was also "growling" at me at the time, I thought I may have a bad bearing, So I took one guide bearing completely off and things quieted completely. And since I had some little side-rails installed by that time I just ran with them for a while... and it ran beautifully in comparison.

So finally I decided to do away with the bearings altogether and go with side-rails only. I fashioned a couple of longer side-rails and installed them and I think this is the configuration I want to go with for now. I runs beautifully and I can smoothly increase the speed all the way to full throttle without any stress... 8500 rpm or so.





This one nearly matches your newer KISS cutter anyway... so I'm really thinking this one should be relatively trouble-free and long-lasting. I'll lube it up with some grease after playing with it some more... but I'm feeling pretty good about the potential of this configuration -- David

 

[dkj4linux]

Not sure what to suggest with the mig tip. What worked for me on the inflation needle was putting it in the top of the inflation needle not just into the 3D printed support. I did add a second one to the top support just for good measure and haven't had either come out since I did that. Though I did have the upper one start to gunk up and harden then start throwing little bits of blackened crud the other day. No harm...but think it's time for fresh cotton

Since the mig tip doesn't have that little pocket I'm not sure what to suggest for it. Maybe redesign the 3D printed part so it flares out at the bottom so it can help hold the cotton ball in....since you have the bearings you probably don't have much slop on the needle as it enters the mount there so maybe you could put something like a bit of old credit card over the top with just a small slit or hole for the needle to pass through?

When I came up with the cotton-wad oiler I was indeed using an inflation needle -- with that handy little "reservoir" in the top -- and I never had trouble keeping the wad in place... once it had been saturated with oil and packed with a toothpick tip a couple more times. My thinking is that the oiler was primarily for light lubrication where the original cutter's flexing needle entered the guide and rubbed so vigorously... not so much cooling, though of course any reduction of friction would also reduce the heat produced.

I'm thinking now -- with all our attempts at getting near/almost straight-line motion of the needle in the guide -- the oiler shouldn't even be necessary... unless, of course, you still want a little light lube in the guide. But there's no where near the same friction produced at the top of the guide when the flex in the needle has already been dealt with, with side-rails or bearings... and, in my experience so far, running these newer cutters freely in the open air produces very little/no heat at all, even with the welding tip guide. There will still be the friction (and heat) due to side-forces produced when actually cutting foam -- the needle will trail slightly in the guide bore and rub the wall opposite the direction of travel -- but I think that should be controllable with sane (reasonable) feeds and speeds.

That's my $0.02.

-- David

 

[Basscor]

David,

Sorry, typo and context. The tach is only reading 'HI' regardless of rpm, nothing to do with the RPM control. I tried it on my drill, which maxes out at 3600 rpm, with the same result. That is why i mentioned that I ordered a new one.

I will say that the bearing block has helped a lot with the mig tip heating up. I have another config where I want to try putting in another set of bearings closer to the mig tip.

 

[x33]

good idea

So my solution is to narrow the needle only at the part which actually penetrates the foam.

just wondering how long this sharp tip will stay in shape My needle is 0,5mm and have had a very sharp "pencil-tip"...after cutting a lot of Depron, the tip is now some kind of "semi-blunt" ( like a cone without a sharp tip) - but without loosing any performance!

 

[GremlinRC]

just wondering how long this sharp tip will stay in shape My needle is 0,5mm and have had a very sharp "pencil-tip"...after cutting a lot of Depron, the tip is now some kind of "semi-blunt" ( like a cone without a sharp tip) - but without loosing any performance!

I wonder too! Maybe I made it a bit too sharp and narrow. I did some cuts tonight and It seemed to stand up ok but maybe not for too long. I will also make another needle narrowing from 1.2mm to maybe 0.8mm. I may try to make some sort of a 'jig' to do this so I can be more precise, then I will sharpen the tip just like if was a normal 0.8mm needle.

Cheers
Dave.

 

[dkj4linux]

I wonder too! Maybe I made it a bit too sharp and narrow. I did some cuts tonight and It seemed to stand up ok but maybe not for too long. I will also make another needle narrowing from 1.2mm to maybe 0.8mm. I may try to make some sort of a 'jig' to do this so I can be more precise, then I will sharpen the tip just like if was a normal 0.8mm needle.

Cheers
Dave.

I wondered how you thinned that needle so precisely by hand... I doubt any of us could have come close to doing as well. I struggle to just put a rough conical point on the needle at times... and was impressed by the long tapered needle point. I wonder also if that wasn't the reason the paper was so cleanly cut on the star and roundel? -- David

 

[WarHawk8080]

Hello

Was referred here dkj4linux
My response on his MPCNC 2826 Brushless RC Motor Foam Cutter page

My feeble attempt at designing a crosshead bearing design for this needle cutter
Reciprocating motion is now limited to a loop in the needle twisted above the bearing, the bearing has a 3mm hole for a small 3m screw to bind the needle into the bearing, all lateral movement for the most part should be eliminated and now motion should be limited to an inline reciprocating motion...similar to the design of really old and large diesel/steam ship engines

Not sure how well plastic will hold up with mega high rpm's but I hope you see where I'm going with this

https://www.tinkercad.com/things/e66cWBsdG51-needle-crosshead <- sorry I had it private...now public
http://www.dieselduck.info/machine/01 prime movers/diesel_engine/modified.ani.sulzer.gif

If you see the design flaw in regular piston type the side load due to the connector rod being tied directly to the piston (this is why over a long time the piston itself wallows out the cylinder wall, with the crosshead bearing, all the side load forces are removed
https://upload.wikimedia.org/wikipedia/commons/d/dc/4StrokeEngine_Ortho_3D_Small.gif

I really hope you guys see where I am going with this

Question...how much throw is needed? Isn't this thing equivalent to a "tattoo gun" why not use electromechanical coils, and a heck a simple flexible plastic armature bar, or even an electronic solenoid actuator?

I am still in the process of building my MPCNC (almost have all the part printed and waiting for tax return to order all the electronics) but definitely want to start cutting foam board (for planes and the cool 3D skeleton model thingys)

The closest I have seen to what I described above was the dual bearing setup, and using the flex of the wire as the crosshead bearing.

Seems like someone already thought of that
http://www.thingiverse.com/thing:776358

Also there is this thing
http://www.thingiverse.com/thing:1481782

Not to mention the ready made tools available
https://www.amazon.com/Round-Liner-Tattoo-Needles-Pack/dp/B001DC5IU6

 

[x33]

....
Question...how much throw is needed? Isn't this thing equivalent to a "tattoo gun" why not use electromechanical coils, and a heck a simple flexible plastic armature bar, or even an electronic solenoid actuator?
....

My 2 reasons for using a motor/flywheel/crankpin-version

1 -- For cutting 6mm Depron you will need a 7 to 8mm displacement...would be a hard job for a solenoid.

2 -- optimal adjustment of motor revs (needle speed) in conjunction with the toolpath speed will not be easy for a solenoid system. The best working speed for the solenoid is a resonance point. The resonance frequeniy is given by the parameters of the whole system (weights + movements) and therefor fixed.

To realize an electronic sytem with speed control, you can think on a speaker(subwoover) coil+magnet with a needle instead of the mebrane and a power-amp with frequency generator for driving...will be a big effort and a heavier contruction.
You will need a lot of amp-power to drive the needle-coil-combination for cutting 5mm foamboard (or 6mm Depron) with ~100Hz (aka 6000upm)

Joachim

P.S.

important to be mentionend! Because of the rotating masses, the flywheel in the motor/crank-system can eliminate nearly any vibrations of the movements -> you only have to build it heavy enough and do some good balancing.
The motor has not to be very powerfull - the flywheel is supporting the motor during the cutting stroke

 

[dkj4linux]

Hello

Was referred here dkj4linux
My response on his MPCNC 2826 Brushless RC Motor Foam Cutter page


Question...how much throw is needed? Isn't this thing equivalent to a "tattoo gun" why not use electromechanical coils, and a heck a simple flexible plastic armature bar, or even an electronic solenoid actuator?

I am still in the process of building my MPCNC (almost have all the part printed and waiting for tax return to order all the electronics) but definitely want to start cutting foam board (for planes and the cool 3D skeleton model thingys)

The closest I have seen to what I described above was the dual bearing setup, and using the flex of the wire as the crosshead bearing.

Seems like someone already thought of that
http://www.thingiverse.com/thing:776358

Also there is this thing
http://www.thingiverse.com/thing:1481782

Not to mention the ready made tools available
https://www.amazon.com/Round-Liner-Tattoo-Needles-Pack/dp/B001DC5IU6

Welcome, Warhawk! I see you found us okay. One thing you will note here... this is a place not only to talk about stuff, but do it... or at least make the attempt. Most of us like to work with our hands, and our tools, to make stuff... and everybody seems to get a real big kick out of trying to "do the impossible, with next-to-nothing, in no time flat"

First, I apologize for the length of the thread... but it will be worth your time to work your way through it; i.e. there's lots of good information throughout. This started as an introduction to cutting foam with a reciprocating needle cutter I developed 6-7 years ago (not my original idea... but adapting to conventional 3-axis CNC was), to cut fanfold insulation foam for RC aircraft. And since it's primary use is with a CNC machine... those are fair game, too. And other tools are potentially of use as well... drag-knives, lasers, dremels, etc... so they are not off-limits either. Everybody seems to be extremely happy with the "spirit" of the thread and its content and the information sharing is tops... and there are some really talented -- and extremely helpful -- folks here.

The KISS philosophy the original cutter is based on has been tested over and over again... and continues to hang around. The last 25 pages or so, we've looked at a number of ways to straighten the path of movement of needle-in-guide and it has resulted in major improvement to the original cutter... with only simple modifications. Cutters with more moving parts have been devised -- and demonstrated -- but largely they suffer when it comes to simplicity, durability and performance.

But it's all fun to play with. And I hope you like to get your hands dirty. Based on the ideas/questions you have, I'd suggest reading through the last 25 pages or so to get an idea of where we've been and what we've looked at... and then join in the discussion. Everybody is friendly and helpful and seems to be having a ball.

Welcome to the party!

-- David

 

[GremlinRC]

Welcome, Warhawk!

+1

As David said were a laid back sort of bunch so just jump right in.

I too like the principle of using an electro magnetic approach like a relay or a solenoid. However as has been mentioned you really need about 7mm travel to be able to cut through ~5mm foam. The greater travel increases greatly the stresses and fatigue on the components and thus requires a fairly complex mechanical arrangement. What we've found through our experiments, is that trying to model this complexity leads to multiple failure points and an aggregation of tolerances ends up with something that usually doesn't stand up to the rigours demanded or introduces uncontrollable vibrations. We went back to basics to a degree implementing the KISS principle to try and reduce or elimate points of failure whilst at the same time trying to improve performance.

I'd certainly look forward to your input.

Cheers
Dave.

 

[x33]

The result of ~90min cutting...

The bigger fuselage parts are from depron (3mm)... the other parts are cutted out of 3mm EPP.

The EPP is the soft/lightweighted version and can only be cut with a much slower toolpath speed compared to the Depron.
The EPP-foam-bubbles are all of different sizes and the structure is very inconsistent with some dense spot and big, soft, "hollow" bubbles here and there
When choosing the right speed, the needle is cutting this stuff very precissly...much more better than a small milling tool can (which is nearly imossible )

 

[GremlinRC]

Joachim, Maybe its just me but I can't view your attachment.
Cheers
Dave.

 

[x33]

reloaded

 

[Verris]

Now with all the parts printed, the ramps cover and lcd case done, the new universal mount done and currently printing some of the z drill guides



I've started making the needle cutter attachment.



I decided to go with the original, modified height version Jhitesma had and was lucky to find perfect sized clothespins at the dollar store. Strangely enough, it worked quite well on my first attempt at assembling everything. I've got a good travel distance at 7.63mm, I just need to try again to grind off the end of the guide to get rid of the lip, then shorten the needle a bit to make up for the removal.




Now just need to start building everything this weekend.

 

[dkj4linux]

just wondering how long this sharp tip will stay in shape My needle is 0,5mm and have had a very sharp "pencil-tip"...after cutting a lot of Depron, the tip is now some kind of "semi-blunt" ( like a cone without a sharp tip) - but without loosing any performance!

I'm sure it's the conical *symmetry* rather than the sharp point that's most important. My wife used to sew a lot and, when modern synthetic fabrics came on the scene, she bought *ball-point* needles for her machine. They pushed the fabric strands apart rather than biting/piercing them.

--- David

 

[dkj4linux]

Outstanding work, Verris! You'll want to put a wooden plate on the bottom, however, to thread the needle guide into... those plastic threads will soften and deform as heat builds up with the original cutter design.

For a 3d-printed version, I'm thinking of adding a support block beneath the motor and near the guide entry to allow adding longer "Joachim-style" wooden side-rails... as in my latest wooden cutter a few posts back. And similar to the one Basscor made for adding bearings... but taller. But I'd think you still want the wooden plate for the needle guide. -- David

 

[GremlinRC]

David I found that PTFE/Teflon sheet makes great side rail supports. I'm at work right now so a photo will follow later but basically, like your cutter, I built up with a wooden block to just 1mm under the needle, then added some 2mm PTFE strip instead of wooden strip. The main benefit is the PTFE doesn't need messy grease for lubrication. Another small piece of PTFE horizontally on top of these two side rails makes sure the needle cant bend outward under any circumstances and helps constrain it in case of failures.

Dave.

 

[jhitesma]

I'm actually thinking about making another modified version of the design that's a bit taller still and includes some mounting posts for wooden blocks. Just still debating how I want to do it.

And yes, I agree with David that you'll want to add a wooden block under the base of the cutter for the inflation needle to mount in - the needle gets hot enough in use that it can soften the PLA and come out - mounting it to wood eliminates that.

 

[x33]

The main benefit is the PTFE doesn't need messy grease for lubrication......
Dave.

you don't like black dots?
PTFE will be a good stuff...may be Delrin will work also??
.....................................
For mounting the needle guide -> this special nut will do a good job?!