Cutting foam sheets... with a needle!

[dkj4linux]

Alright! All this silliness aside, on to some more serious subject matter…
https://us2.dh-cdn.net/uploads/db5587/original/3X/a/3/a35dd36cd1575a484d1f9839ef07ffacf61f7b22.jpeg

https://us2.dh-cdn.net/uploads/db5587/original/3X/4/7/47fc171c0c821f5513702fff91be28e1eb203994.jpeg

Things are looking up…

– David

 

[dkj4linux]

Okay! Just a little more absurdity…
https://us2.dh-cdn.net/uploads/db5587/original/3X/3/e/3e16b09268262d169beadf3ecfa44f8856657726.jpeg

And, with no frolicking lady-friends in sight, it’s just my good buddy, Mac, and me…
https://us2.dh-cdn.net/uploads/db5587/original/3X/1/5/157bdb144804a3bc5d8647ba70246bae56330872.jpeg

– David

 

[dkj4linux]

I saw these and couldn’t resist…
https://us2.dh-cdn.net/uploads/db5587/original/3X/e/e/ee6dcc5dc42d331365b40716290cd91ea0b9f364.jpeg

Holy hand grenade…
https://us2.dh-cdn.net/uploads/db5587/original/3X/f/c/fc3788d69554465ea5f3a565d1fdf766657ea516.jpeg

Killer rabbit…
https://us2.dh-cdn.net/uploads/db5587/original/3X/f/e/fe850fdf6f4858322e6ff483db2b8b0fd6cd363e.jpeg

A grouping for the fun-loving among us…
https://us2.dh-cdn.net/uploads/db5587/original/3X/6/7/67a5fe31169728ad04aabf379c31236d0c5ee747.jpeg

– David

 

[graza]

Hi David, @dkj4linux

I've been away from this for a bit and tonight have been catching up with the thread. David, your tiles are amazing - it's amazing how well the different shades of grey are represented in the final result. I imagine it's some sort of sintering process that's involved?

Thanks for your amazingly detailed response to my earlier post. I've started down a particular path, using some IKEA aluminium curtain rails that have been replaced. They're not especially strong but a needle cutter probably doesn't need to be? As you said:

lots of opportunity to alter/explore and use whatever materials you may have on hand

A bunch of stuff has been ordered on Aliexpress and is supposedly on its way from who knows where. The stepper motors I ordered were meant to be from their Spanish warehouse, but according to the tracking info originated in a German warehouse and were successfully delivered to the customer in France! (I'm in Ireland. ) Ah, the joys of using cheap Chinese websites.

Hi Frank, @effdubya

Perhaps I would have been better going through eBay, but I find trying to get stuff delivered by eBay sellers to the West of Ireland expensive or not possible.

I have decided to fit it with a variation of the needle cutter using one designed by zero_o on thingiverse

I used a design by @CapnBry who's also posted it here back in April. https://www.thingiverse.com/thing:4298224

Anyway, so far still having fun.

Graham

 

[dkj4linux]

Thank you, Graham, for the kind words. I really don't know what "magic" is going on with the tile engraving... something in the paint, in contact with the ceramic, and bombarded with a laser. Whatever it is... it's a fantastic result.

Two or three months ago, I had ordered some laser equipment from AliExpress and, similarly, my order was "delivered" to someone up north, in Maryland... and I'm down south, in Texas. To their credit, I communicated with the seller through the AliExpress site, told them my order never came to me... and they resent the order, which then came to me surprisingly quickly. I'd recommend signing in, look up your order, and click on the "contact seller" link... hopefully someone will respond. The person I "talked" to kept referring to me as "dear" and was very responsive, almost as if I was her(?) BFF... but, in the end, she was very effective in getting my order to me. I've since ordered from AliExpress again...

Good to hear from you... and keep having fun.

-- David

 

[RHill051]

I'm hoping to get a little advice, I finished assembling my needle cutter by adapting this one to the new MPCNC Primo mount. All is working great so far except if I adjust the RPMS up too high the needle just pops off the bearing. My guess is I'm setting the needle speed too high but I don't have a tool to get a read for the actual RPMs so I'm just setting it at 1/2 throttle using a servo tester. (Powering ESC off of 12v DC power supply that is also powering my ARCHIM board, I've got a 3.3v step down that I hooked in line with the power to supply power to the servo tester. Lastly this is the motor I'm using.) Is there a trick for making the needle and getting it to stay on the cutter? Maybe my flywheel isn't balanced enough? I don't know what a balanced flywheel would sound like but I do have a counter weight on it so maybe it just needs more weight? I'm super excited to get cutting so any advice would be greatly appreciated.

 

[dkj4linux]

Too high rpms will generally result in flying needles. You really need to get an optical tach... this is the one I use. I'll guarantee that if you are setting in 1/2 throttle on the servo tester, you are running far too fast. I usually try to set in 6000-8000 rpm and run at 600-800 mm/min feedrate. You'll probably pass through the appropriate range with no more than 1/4 - 1/3 throttle on the servo tester. Get the tach and be sure. There's no way anyone can know whether your flywheel in balanced well enough but if you're running at an good rate it should not sound or feel "angry"... it should run and cut fairly comfortably and stress-free.

Welcome to the party.

-- David

 

[RHill051]

Too high rpms will generally result in flying needles. You really need to get an optical tach... this is the one I use. I'll guarantee that if you are setting in 1/2 throttle on the servo tester, you are running far too fast. I usually try to set in 6000-8000 rpm and run at 600-800 mm/min feedrate. You'll probably pass through the appropriate range with no more than 1/4 - 1/3 throttle on the servo tester. Get the tach and be sure. There's no way anyone can know whether your flywheel in balanced well enough but if you're running at an good rate it should not sound or feel "angry"... it should run and cut fairly comfortably and stress-free.

Welcome to the party.

-- David

Just ordered it, have to wait till Thursday for it go get here!! (so spoiled with prime shipping that having to wait a few extra days can be painful lol) was chatting with jhitesma and he said he uses a dab of CA to secure the needle to the bearing. I might give that a try to see if I can get the thing to stay on for more than a minute and I'll also slow down the motor speeds. I've been trying to get 15mm/sec to work but that ends up being 900mm/min so I'll back it down for now to make sure I can get some consistent cuts before trying to speed things up.

 

[dkj4linux]

Just ordered it, have to wait till Thursday for it go get here!! (so spoiled with prime shipping that having to wait a few extra days can be painful lol) was chatting with jhitesma and he said he uses a dab of CA to secure the needle to the bearing. I might give that a try to see if I can get the thing to stay on for more than a minute and I'll also slow down the motor speeds. I've been trying to get 15mm/sec to work but that ends up being 900mm/min so I'll back it down for now to make sure I can get some consistent cuts before trying to speed things up.

Sounds like a good plan. And Jason is the guy to talk to about that needle cutter design. You might ask him about his adventures with high rpms and flying needles as well...

 

[Springer]

+1 on David's tach, he talked me into getting one, now I use it every time I run my cutter. One thing about mine, it seems to eat batteries when 8nvstorage, do I remove it when I finish working tach and 9v batt live in the nice zippered bag that come with tach. I also target around 8000-9000 rpm, and set default feed at 800mm/min. This is for 6mm MPF (no paper). Somewhere on the thread, I recall a post on balancing the head. If you have the machine screw and two nuts like in David's head, you can turn the screw in or out a half turn at a time and check for lowest noise level when running. Not perfect, but I was able to significantly reduce vibration and noise by adjusting the screw.

Alfo, for what it is worth, I run the brushless (cf2812) esc from the 12v part of the laser port on my eleksmaker main board. Have a servo tester as a speed reohstat. With that setup, I set the tester at about 20% for 8500 rpm.

 

[TEAJR66]

Pay attention to the alignment of the needle to the bearing. Top dead center and bottom dead center, the needle should be straight, front to rear, side to side.

A little medium or thick CA around the bearing and needle, hit with some accelerator. Or, finger nail polish, can help keep the needle on. Keep the glue out of the bearing.

 

[RHill051]

I had a pretty successful cut yesterday demoing the machine for my grandpa but when it was on the last line the need popped off the bearing I suspect because the foam had pulled up from my table in the corner causing the cutting depth to increase significantly... I need a better way to hold the foam down... I've seen the vacuum board on the MPCNC site and was thinking of doing that but if there are other suggestions I'm all ears. Also, I'm using a scrap piece of dollar tree foam underneath and the top sheet was fusing with the bottom due to what I'm assuming is heat from the needle rubbing inside the tig welder tip. I've seen mention of putting some cotton or something in the cavity above the welding tip with some sort of lubricant. What are you guys using? I've bot some sewing machine oil I could use with some cotton ball in there to help reduce the heat build-up.

 

[RHill051]

Well, I just put a little bit of cotton ball above the welder tip and added some sewing oil we'll see how it goes now. can't find my super glue so I'll hope for the best on the needle staying on the bearing... I might be able to find some of my wife's nail polish though

 

[Michael9865]

Well, I just put a little bit of cotton ball above the welder tip and added some sewing oil we'll see how it goes now. can't find my super glue so I'll hope for the best on the needle staying on the bearing... I might be able to find some of my wife's nail polish though

Just remember if you use your wife’s nail polish to put it back and also be sure that it is dry before turning the cutter on. If it isn’t completely dry you may have some “overspray“ to clean up. 😃 😉

 

[RHill051]

Just remember if you use your wife’s nail polish to put it back and also be sure that it is dry before turning the cutter on. If it isn’t completely dry you may have some “overspray“ to clean up. 😃 😉

So far so good no wet nail polish to clean up and the wife is non the wiser I did notice that I'm getting some grey spots on my white foam board which I'm guessing is from the cotton and sewing oil. I set my cutting depth to 7.5mm and was running at 8mm/second but without knowing the speed I think I had it too slow since I had to come back and cut the back of the board to get everything out. What's the consensus on cutting depth? Will 7.5 be sufficient when I get the motor RPS dialed in? or do others do something a little deeper? I tried 8mm the other day but since the foamboard kept lifting around the edges I'm sure I was actually cutting much deeper. In the end all the pieces came out without any effort so maybe Its better to cut a little deeper? I know all these questions have been asked many times before in this thread but its grown so large I'm not sure what page to look at for the answers and unless there is a hidden thread search function I'm missing I can't easily find the info I'm looking for. Thanks again for your eager willingness to help me get up and running with as few hiccups as possible

 

[Keno]

Interesting! I have been through this and it is a learning curve. Today I received the 3/8X24"X44" piece if of plate glass to replace my cutting bed. This provided me with very flat bed with only a 1mm overall variation. We are talking about a MPCNC machine made with 3/4" conduit tubing. Ok, we keep spending money but It give me the accuracy that I am looking for. I found that it better to forget the cotton/oil and lube you needle with some synthetic grease lubricate it will fair great. My experience from all the above post that most needle cutter are, "over engineered". I have reviewed most designer and have taken the best of their ideas and construct mine with the KISS theory. (Keep it Simple Stupid") I take no credit for my cutter as it is simplification of those who put great thought into their designs. All have a great day and fly safe and as a Safety Office my last words are (Keep it out there and not over us).

 

[jhitesma]

The foam melting into the spoil foam is another sign that your RPM's are probably still too high. It is from heat but when the RPM's are good there shouldn't be that much heat even without the cotton ball and oil (I still use the cotton ball and oil just in case though.)

Remember a lot of ESC's are linear. So just doing the math to try and calculate the RPM's based on motor kv and voltage doesn't work out...I learned that the hard way until I got my tach. I had calculated that about half throttle should put me where I wanted to be...but it turned out due to the non-linear curve of the ESC I actually needed barely 1/4 throttle and was running more than twice the RPM's I thought I was - which resulted in tons of tossed needles and foam melting into the spoil foam.

For awhile I did use my tach each time to make sure my speed was good. Then I finally switched to using a servo output on my RAMPS to control the cutter ESC and added some g-code to the start/finish of my projects to consistently set the motor at the same setting.

If you don't want to wait for the tach you may try an audio tach on your phone...not sure how accurate it would be but may be better than nothing.

 

[jhitesma]

Oh, and the grey spots...yeah...too much oil. It doesn't take much and is easy to add more than needed. It should dry up fairly quickly though and then the spots will go away. When I have that happen usually it stops spotting after just a few minutes. Once I added the guide bearings to my cutter I found the oil didn't really give any benefit but I still do it out of habit. But if you need the oil to keep the temps under control it's probably a sign that you're still running too high of an RPM if you're using a proven cutter design. (If it's not a proven design then it may be too short or benefit from some form of guiding to help the needle have less friction in the welding tip.) Or you may have too high of a feed rate...but that seems to be the least common situation. I can run a high enough feed rate I see the needle deflecting but still don't get heat built up as long as the RPM's are within the safe range.

I don't even use 7.5mm cutting depth. I use 6mm for a full cut and 2.5mm for score lines and .75mm for marking cuts or paper peel lines where I just want to go through the top paper and not the foam.

The vacuum table does help a lot with keeping foam flat and consistent due to the way foam sheets just aren't very flat to begin with. I couldn't get away with the 0.75mm marking cuts until I switched to the vacuum table - they were always either deeper than I wanted or missed the paper entirely. I used to just put the foam down "crown down" so the high part was facing down in the center...and then some pins on the outside corners to flatten it out. And on particularly bad pieces of foam sometimes pins along the edges if it was still curling up with the corners pinned down. I used a sheet of 1/2" pink insulation foam as the spoil board so it would be larger than the foam and I'd have room to pin things down well.

 

[RHill051]

Awesome insight into my current situation. Any chance you have pictures of your vacuum table setup? I'd like to try to make one as well. I suspect my temp issues were the result of me being ignorant and just bending my current needle back to "strait" after it popped off the bearing and was pulled around the foam before I could kill the cnc. I've switched to a new needle which seems to have made a really big difference. I'm inclined to think my motor speed isn't fast enough since my cuts at 7.5mm depth and 8mm/second resulted in a dotted line on the backside of the foamboard. Didn't take much to just run the Exacto knife over it to separate everything but I know it could be better so just going to be patient one more day till the optical tack gets here. I also have plans to set up my cnc to use the control board to manage the ESC at some point. I guess my question for you is regarding the modifications to the firmware, will that need to be reflashed if I were to switch the cnc over to cutting wood at some other point?

Edit: I wonder if my cutting depth is affected by the way I sharpen my needles? I've been putting a pretty deep taper on them, it probably goes up the needle a good mm or so. This is what the back of my foam board looks like

 

[RHill051]

Yet another update on my journey, I've been too impatient to wait for the optical tachometer so I just tried to do some slower testing but twice now I've had the need sheer off where it wraps around the bearing. I managed to get a really clean bend with no sharp edges so I'm surprised to see it breaking there but suspect its the result of still being too fast on the motor RPM's... I'll know more on that front tomorrow. I'd like to see if anyone else can shed some light on the break given the included pictures. I looked a little closer and saw that the screw holding the bearing on the flywheel appears to be angled out from the center ever so slightly not sure if it's gotten hot and caused the PLA to get soft or what but I'll be printing one or two extra flywheels now that I'm realizing its got issues.