Cutting foam sheets... with a needle!

2jujube7

Well-known member
How are you setting the z height when cutting foam board? When I start the motor and get the speed right with the tach, the z likes to slide down. With only a 7mm max Z travel for cuts it doesn't take much to be too low or too high. I need some kind of gauge and then maybe a command in Repeater Host to hold the Z in the right spot.
I just start the motor and move it down to the surface of the foamboard (this would have to be 1 mm away for you), then set Estlcam to go down 5mm. Foamboard is 4.7mm deep, so anything around there should work.
 

Kennyd

New member
I just start the motor and move it down to the surface of the foamboard (this would have to be 1 mm away for you), then set Estlcam to go down 5mm. Foamboard is 4.7mm deep, so anything around there should work.
That is basically whatI have been doing as well. Every now and then, the running motor will vibrate the z axis down a bit before I can start Estlcam. I have been doing some research and I think I found a solution. I have the mini-rambo board and if I use a copper plate and a clip to the needle attached to the mechanical Z stop then use an offset of the copper board to get z zero, it should work.
I can put something like this in the beginning of all my gcode

G0 F25 ; Go slow when homing z so needle doesn't break
G28 Z ; Home Z axis
G92 Zx.x ; x.x is the thickness of the copper plate
P 10 ; Wait 10 seconds so I can remove the plate before starting print.
; Plan code starts here
 

dkj4linux

Elite member
@Kennyd,

I'm not sure what your Z axis looks like but it's a big problem IMO if it doesn't hold its position when the cutter is running. I don't see that ever being a reliable setup if that's not dealt with first.

Regards setting Z=0, I simply start the needle cutter and then lower Z until I hear the needle just start "tickling" the surface of the foamboard... there a distinct change in sound when it makes contact. This video shows the basic steps for setting up a needle-cutting job and setting Z=0 is at about the 1:55 minute mark. Note the distinct sound difference when the needle makes contact with the foamboard (turn down the sound a bit)...


-- David
 
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Kennyd

New member
@Kennyd,

I'm not sure what your Z axis looks like but it's a big problem IMO if it doesn't hold its position when the cutter is running. I don't see that ever being a reliable setup if that's not dealt with first.

Regards setting Z=0, I simply start the needle cutter and then lower Z until I hear the needle just start "tickling" the surface of the foamboard... there a distinct change in sound when it makes contact. This video shows the basic steps for setting up a needle-cutting job and setting Z=0 is at about the 1:55 minute mark. Note the distinct sound difference when the needle makes contact with the foamboard (turn down the sound a bit)...


-- David
Thanks. I think the problem is because Estlcam hasn't started yet the steppers are still free running. I am using the needle cutter with the cam and the stepper motor rotating a threaded rod. Everything is working great except the initial setting of Z0 which takes a lot of care to get right.

Cable management is the next step. Just need to print the parts.
 

RHill051

New member
Hey guys, just a couple of questions. I've been running my needle cutter for a while now but I still have an issue with the needle coming off every 7-10 sheets. I think the issue is with a buildup of hard black material on the shaft of the needle that will eventually catch in the MIG welder tip and cause the needle to pop off the bearing. I finally put some cotton ball above the mig tip to add some oil but I'm wondering if anyone else has had or heard of this issue. I read someone who mentioned a "crude" needle cutter that worked flawlessly for over 100 sheets and that is what I want lol I'm just wondering what I should change to make this a little better/more reliable.
https://photos.app.goo.gl/pcE4hQ4qc8MfRX6fA
 

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dkj4linux

Elite member
Hey guys, just a couple of questions. I've been running my needle cutter for a while now but I still have an issue with the needle coming off every 7-10 sheets. I think the issue is with a buildup of hard black material on the shaft of the needle that will eventually catch in the MIG welder tip and cause the needle to pop off the bearing. I finally put some cotton ball above the mig tip to add some oil but I'm wondering if anyone else has had or heard of this issue. I read someone who mentioned a "crude" needle cutter that worked flawlessly for over 100 sheets and that is what I want lol I'm just wondering what I should change to make this a little better/more reliable.
In my experience, too high cutter rpms can cause excessive Mig-tip heating and localized melting of the foam around the needle, resulting in foam clinging to the needle, fuzzying the top and bottom paper, being pulled up into and clogging the needle guide, and the appearance of little black, glass-like "gnat droppings" bouncing around on the foam while cutting and embedded in the cut edges.

142958_2eb7798153c3424e63b8edc5b0adf33f (1).jpg


142960_39a769c00fb2313eaaca4dcd85b87868.jpg


142962_1a6d780684fab2a5d113df14e7384b19.jpg


--David
 

RHill051

New member
In my experience, too high cutter rpms can cause excessive Mig-tip heating and localized melting of the foam around the needle, resulting in foam clinging to the needle, fuzzying the top and bottom paper, being pulled up into and clogging the needle guide, and the appearance of little black, glass-like "gnat droppings" bouncing around on the foam while cutting and embedded in the cut edges.

View attachment 192108

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--David
hmm ok, I think I'm cutting at 10,000 rpm (M42 P0 S70 is the command I use to start the cutter at the same speed every time) with a feed rate of 8mm/sec. I've never seen the black bits you show in the edges of the cuts or the small black bits bouncing around on the foam just a bulge around the shaft of the needle. It seems to be a lot more isolated than what you've shown. I could slow the cutter down a bit and see if that helps and I added some oil to the tip for an extra bit of insurance so we'll see how it looks :). When it does work I get super clean cuts and the cuts just fall out of the sheet but I'm also cutting a little deep I think. I appreciate the super quick response btw it's really appreciated.
 

dkj4linux

Elite member
hmm ok, I think I'm cutting at 10,000 rpm (M42 P0 S70 is the command I use to start the cutter at the same speed every time) with a feed rate of 8mm/sec. I've never seen the black bits you show in the edges of the cuts or the small black bits bouncing around on the foam just a bulge around the shaft of the needle. It seems to be a lot more isolated than what you've shown. I could slow the cutter down a bit and see if that helps and I added some oil to the tip for an extra bit of insurance so we'll see how it looks :). When it does work I get super clean cuts and the cuts just fall out of the sheet but I'm also cutting a little deep I think. I appreciate the super quick response btw it's really appreciated.
Do you have a tach and really know what rpms you are turning? I use this one. I found early on that 10-15 perforations per millimeter of travel seemed to give decent cuts for DTFB (paper on)... so came up with a "rule of 10"-type ballpark estimate for feed and speed; i.e. 600 mm/min and 6000 rpm or similar. That works out to 10 perfs/mm and I could stretch it to 600 and 9000 for 15 perfs/mm. Above that, I would start seeing the black specs and needle coating with my cutters at the time. It appears that for 10000/480 you are running in the 20+ perfs/mm range.

I think what is happening is that the increased cutter rpms result in increased Mig-tip friction heating that transfers to the steel needle... which results in highly localized melting of the foam (hard black specs/"gnat droppings" and shiny/glassy-looking foam edge in my photos), which clings to the needle, and eventually leads to failure of some sort; i.e. flying/broken needle, clog/seized needle guide, etc.

If your cutter otherwise runs comfortably at the speeds you've been using, I'd suggest increasing your feed rate to lower the amount of time the needle spends in an area... say, 900-1000 mm/min (15-17 mm/s) for 10-11 perfs/mm. The parts won't generally fall out on their own but should still easily pop out of the sheet. I found concentrating on 10-15 perfs/mm made it easier to find a feed/speed "sweet spot" that still resulted in decent cuts. You might also try slowing the cutter rpms and/or remove the Mig-tip heat with some form of active/passive cooling. Also recognize the needle cutter is an inherently "sloppy" mechanism by necessity and will probably last longer the less it's "stressed"... i.e. absolute fewest rpms necessary for decent cuts in acceptable time frame. Just sayin'... ;)

Good luck! -- David
 

RHill051

New member
Do you have a tach and really know what RPMs you are turning? I use this one. I found early on that 10-15 perforations per millimeter of travel seemed to give decent cuts for DTFB (paper on)... so came up with a "rule of 10"-type ballpark estimate for feed and speed; i.e. 600 mm/min and 6000 rpm or similar. That works out to 10 perfs/mm and I could stretch it to 600 and 9000 for 15 perfs/mm. Above that, I would start seeing the black specs and needle coating with my cutters at the time. It appears that for 10000/480 you are running in the 20+ perfs/mm range.

I think what is happening is that the increased cutter RPMs result in increased Mig-tip friction heating that transfers to the steel needle... which results in highly localized melting of the foam (hard black specs/"gnat droppings" and shiny/glassy-looking foam edge in my photos), which clings to the needle, and eventually leads to failure of some sort; i.e. flying/broken needle, clog/seized needle guide, etc.

If your cutter otherwise runs comfortably at the speeds you've been using, I'd suggest increasing your feed rate to lower the amount of time the needle spends in an area... say, 900-1000 mm/min (15-17 mm/s) for 10-11 perfs/mm. The parts won't generally fall out on their own but should still easily pop out of the sheet. I found concentrating on 10-15 perfs/mm made it easier to find a feed/speed "sweet spot" that still resulted in decent cuts. You might also try slowing the cutter RPMs and/or remove the Mig-tip heat with some form of active/passive cooling. Also recognize the needle cutter is an inherently "sloppy" mechanism by necessity and will probably last longer the less it's "stressed"... i.e. absolute fewest RPMs necessary for decent cuts in acceptable time frame. Just sayin'... ;)

Good luck! -- David
Yeah, I was thinking I was running 10,000 but I just checked with the tach I bought with your recommendation last year and it said I've been using 9350 RPM's under no load. I can try lowering the RPS's and seeing where that goes. Your explanation is outstanding! It gives me quite a few different ideas to consider. I haven't tried speeding it up, I also like the idea of potentially adding some sort of localized cooling to keep the needle guide from heating up. I'll have to look for some ideas as to how I might add some compressed air or a fan to cool the tip.
 

dkj4linux

Elite member
Yeah, I was thinking I was running 10,000 but I just checked with the tach I bought with your recommendation last year and it said I've been using 9350 RPM's under no load. I can try lowering the RPS's and seeing where that goes. Your explanation is outstanding! It gives me quite a few different ideas to consider. I haven't tried speeding it up, I also like the idea of potentially adding some sort of localized cooling to keep the needle guide from heating up. I'll have to look for some ideas as to how I might add some compressed air or a fan to cool the tip.
Daunting, I know, but this thread is full of good information... including most of what I've shared here. There is a search function that can be constrained to search just this thread... I use it all the time to retrieve and share information I remember is __in there somewhere__ but have temporarily lost track of.
 

Bristolian

New member
Yeah, I was thinking I was running 10,000 but I just checked with the tach I bought with your recommendation last year and it said I've been using 9350 RPM's under no load. I can try lowering the RPS's and seeing where that goes. Your explanation is outstanding! It gives me quite a few different ideas to consider. I haven't tried speeding it up, I also like the idea of potentially adding some sort of localized cooling to keep the needle guide from heating up. I'll have to look for some ideas as to how I might add some compressed air or a fan to cool the tip.
I'm using a 0.54mm needle running in a 0.6mm nozzle, so very accurate and fine cuts, but a lot of friction heating. So, more for a bit of tinkering than anything else, I tried water cooling. It actually works very well, the tip is almost stone cold after half an hour's cutting, when it used to sizzle! I wound 3mm copper tube around the 5mm brass rod nozzle, all soldered together, connected by 1.2mm PVC tubing to a small aquarium water pump. This is switched by the Arduino motor controller so it comes on with the motor.
 

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Wildthing

Legendary member
Daunting, I know, but this thread is full of good information... including most of what I've shared here. There is a search function that can be constrained to search just this thread... I use it all the time to retrieve and share information I remember is __in there somewhere__ but have temporarily lost track of.
Yoda :)
 

RHill051

New member
There is a search function that can be constrained to search just this thread... I use it all the time to retrieve and share information I remember is __in there somewhere__ but have temporarily lost track of.
I have done my best to leverage the search function but sometimes I'm just not sure how to best word my search to get the results I'm looking for or what I did get didn't seem like it was all that could be out there. I definitely don't want to offend anyone by seeming lazy or inconsiderate of your time. your responses are very much so appreciated.

I tried water cooling. It actually works very well
I think I'm going to have to give this a shot!! It sounds too cool not to try lol
 

bperc

Member
Britt, I think 1/2" MDF would probably be fine... I just used what I had on hand. I haven't posted an exact set of STLs for spacers/bushings and bearing guides on this project because I find it simpler to measure, CAD, and print exactly what I need... as opposed to spending a lot of time trying to find something I may have already done and that may, or may not, fit. Hopefully it will be the same for you. Though I prefer Onshape for more serious CAD work, I find TinkerCad can be extremely useful for designing simple parts such as spacers and bushings, which is all I needed to add to what Mark provides with his Foam Ripper "thing" on TV. -- David
David,
I finished the Foam Ripper. I have done some test cuts, squares, triangles and circles. The square and triangles come out great. The circle is a little out of round and has a slight flat spot on the right side. I read on the v1engineering forum that some people have had the same thing with the LowRider. They found that the X axis belt had too much play in it. I checked mine and found it had some play too. I tightened it up and it's better, but still not a circle. Do you have any suggestions for me on what else to check? I know you have built many many CNC machines and have a lot more experience than I do.
Thanks,
Britt
 

dkj4linux

Elite member
David,
I finished the Foam Ripper. I have done some test cuts, squares, triangles and circles. The square and triangles come out great. The circle is a little out of round and has a slight flat spot on the right side. I read on the v1engineering forum that some people have had the same thing with the LowRider. They found that the X axis belt had too much play in it. I checked mine and found it had some play too. I tightened it up and it's better, but still not a circle. Do you have any suggestions for me on what else to check? I know you have built many many CNC machines and have a lot more experience than I do.
Thanks,
Britt
Sorry for the late reply, Britt. Currently no electricity with the winter storm in N Texas... two days of 5-8" of snow on the ground and near-0F temps at night. This has resulted in so-called "rolling black-outs" that have resulted in 12+ hour outages. Thankfully my old farm house has propane tank for heating and cookstove...

No better suggestions than what you've already got wrt belts, etc. Grub screws always need to be checked. Series or parallel connection of dual motor axis? If parallel, one motor can skip steps while the other doesn't and could result in wonky shapes.

I can't think of anything more at the moment. Hopefully I'll have stable electricity within a couple of days. Stay warm! -- David
 

Michael9865

Elite member
Sorry for the late reply, Britt. Currently no electricity with the winter storm in N Texas... two days of 5-8" of snow on the ground and near-0F temps at night. This has resulted in so-called "rolling black-outs" that have resulted in 12+ hour outages. Thankfully my old farm house has propane tank for heating and cookstove...

No better suggestions than what you've already got wrt belts, etc. Grub screws always need to be checked. Series or parallel connection of dual motor axis? If parallel, one motor can skip steps while the other doesn't and could result in wonky shapes.

I can't think of anything more at the moment. Hopefully I'll have stable electricity within a couple of days. Stay warm! -- David

Praying that they get the electricity situation rectified soon. Stay safe and warm In the meantime.
 

bperc

Member
Sorry for the late reply, Britt. Currently no electricity with the winter storm in N Texas... two days of 5-8" of snow on the ground and near-0F temps at night. This has resulted in so-called "rolling black-outs" that have resulted in 12+ hour outages. Thankfully my old farm house has propane tank for heating and cookstove...

No better suggestions than what you've already got wrt belts, etc. Grub screws always need to be checked. Series or parallel connection of dual motor axis? If parallel, one motor can skip steps while the other doesn't and could result in wonky shapes.

I can't think of anything more at the moment. Hopefully I'll have stable electricity within a couple of days. Stay warm! -- David

Thanks David,
Wow, this storm has been a rough one for you. I sure hope it lets up soon and your power gets back to normal.
The Y axis steppers are in series. I have rechecked the grub screws too. I will let you know when I get it sorted out. My Y axis belts are a little loose so I am 3D printing some brackets to better secure them.
You should be able to see the left and right side are slightly flat in my photos.
Take care and stay warm!
Britt
 

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bperc

Member
Hey guys, just a couple of questions. I've been running my needle cutter for a while now but I still have an issue with the needle coming off every 7-10 sheets. I think the issue is with a buildup of hard black material on the shaft of the needle that will eventually catch in the MIG welder tip and cause the needle to pop off the bearing. I finally put some cotton ball above the mig tip to add some oil but I'm wondering if anyone else has had or heard of this issue. I read someone who mentioned a "crude" needle cutter that worked flawlessly for over 100 sheets and that is what I want lol I'm just wondering what I should change to make this a little better/more reliable.
https://photos.app.goo.gl/pcE4hQ4qc8MfRX6fA

I have a setup just like yours. Initially I had trouble with the needle coming off too. What solved my problem was to change to .025" wire that fully retracts into the MIG tip on the up stroke, use cotton with oil, and slow down the RPMs to around 6200. After making those changes I have not had a needle come off.