Cutting foam sheets... with a needle!

[TheSFReader]

I'm trying to print moebeast's plenum wkith no luck so far.. Will try again, slower, but as is it's already 10 hours... Any tips ?

 

[IsmaelPR77]

Absolutely super needle cutter and plane! I'd love to see more pics/detail with regards to your cutter... any plans to share it? -- David

Hi David. I'll try to get more details up. I initially started with @jhitesma's needle design but eventually designed my own to fit my esc and romorrow sensor. I also added about 20mm of needle length to limit needle flex and brought the guide bearings closer by about .25mm. I cut at 35mm/s with 2 passes to make cleaner cuts each at about 3mm per pass depth.

 

[IsmaelPR77]

Oh, yes, and what that sensor is ? Is it used to control speed on the motor ? Do you use any kind of feedback control ?

That's a rpm sensor so I can easily see the rpms on my lcd attached to the sensor.

 

[Verris]

So it's been a while since I participated in flying, building or cutting anything. I've moved from sunny Ottawa, Canada to beautiful New Jersey. Most of my planes were destroyed by the moving company and / or while in storage.

I took this chance to rebuild my mpcnc from scratch with all the latest parts, stainless steel tubing and fancy upgrades like the dual endstops. I also redesigned my cutter to be faster to print and lighter, along with working with the new stock tool mount. After sharpening my trusty needle to be too short and not having much luck getting a new one as nicely made and able to stay on the crank shaft, I decided to try a flywheel. I printed one up for a 10mm bearing I had that I dremeled a groove into, made a slot I could feed a bolt and nut into so I can simply slide it in and out to adjust the balance, and off I went. It cuts much nicer and way faster.

I also realized that while rebuilding, my spoil board had a bow to it in the middle. While a long term solution would be a vacuum hold down, short term me found a box of assorted springs in a drawer and printed a foot. I just tried it out on some test movements and it seems to work really well. The only problem I see with it is to attach the spring to the top, I just printed a 9mm->6.2mm ring and slipped it over the mig tip. This will not hold up well to heat.

Here's an album of the new and improved cutter.

Link

 

[Michael9865]

I like the round foot. It should work near the edges of the DTF.

 

[IsmaelPR77]

So it's been a while since I participated in flying, building or cutting anything. I've moved from sunny Ottawa, Canada to beautiful New Jersey. Most of my planes were destroyed by the moving company and / or while in storage.

I took this chance to rebuild my mpcnc from scratch with all the latest parts, stainless steel tubing and fancy upgrades like the dual endstops. I also redesigned my cutter to be faster to print and lighter, along with working with the new stock tool mount. After sharpening my trusty needle to be too short and not having much luck getting a new one as nicely made and able to stay on the crank shaft, I decided to try a flywheel. I printed one up for a 10mm bearing I had that I dremeled a groove into, made a slot I could feed a bolt and nut into so I can simply slide it in and out to adjust the balance, and off I went. It cuts much nicer and way faster.

I also realized that while rebuilding, my spoil board had a bow to it in the middle. While a long term solution would be a vacuum hold down, short term me found a box of assorted springs in a drawer and printed a foot. I just tried it out on some test movements and it seems to work really well. The only problem I see with it is to attach the spring to the top, I just printed a 9mm->6.2mm ring and slipped it over the mig tip. This will not hold up well to heat.

Here's an album of the new and improved cutter.

Link

Very nice. The foot idea is what I had tried to work on but wasn't that successful. Can you shareo more info on it? I would love to try it. Does the foot come in contact with that board even for score cuts?

 

[Headbang]

Older design with a spring crank, no bearings and mig tip. I got through about 60 sheets of cutting before breaking my first needle. Funny part is, no idea where it went! Was running unattended when it broke or threw it.

 

[Headbang]

Ok, so I just assembled and tested my new prusa mk3. My current cutter is old school design, frame made with ply. It is great, lots of cutting done with good quality of cuts. Now I want to go faster, at least higher rpm. i was looking at Jason's design with guide bearings and fly wheel. I was considering a few things, brushed motor to run off the rambo board its self. Built in rpm display (thinking magnet and sensor from a gas engine) or possibly if I go brushless pulling rpm from the esc.
Question is to those who have been there and done that. If you were to build it again, what is on your list of must have's? Or what is on the list of "wish I had done that differently, it's annoying the crap out of me"?

Thanks for any input!

 

[IsmaelPR77]

Ok, so I just assembled and tested my new prusa mk3. My current cutter is old school design, frame made with ply. It is great, lots of cutting done with good quality of cuts. Now I want to go faster, at least higher rpm. i was looking at Jason's design with guide bearings and fly wheel. I was considering a few things, brushed motor to run off the rambo board its self. Built in rpm display (thinking magnet and sensor from a gas engine) or possibly if I go brushless pulling rpm from the esc.
Question is to those who have been there and done that. If you were to build it again, what is on your list of must have's? Or what is on the list of "wish I had done that differently, it's annoying the crap out of me"?

Thanks for any input!

This is my setup, brushed motor not running off Rambo board with rpm LCD display using an rmp sensor I bought on Amazon.

 

[dkj4linux]

Older design with a spring crank, no bearings and mig tip. I got through about 60 sheets of cutting before breaking my first needle. Funny part is, no idea where it went! Was running unattended when it broke or threw it.

That's amazing... 60 sheets or so, with the crankpin version. I never got more than 2-3 sheets before the crankpin itself wore through...

I really love Ismael's variation of Jason's design with the bearing guide and flywheel. I really think either or those would be a fantastic upgrade and a great project for your new Prusa Mk3. Congrats on the new printer... you'll love it!

Please keep us posted on your progress. -- David

 

[jhitesma]

I'm kind of torn on RPM monitoring. I was pretty obsessed about it for a bit - but I've come to feel that while it's important when getting a setup dialed in once I got things working reliably my tach has sat unused.

I feel having a way to measure it is more important than a way to maintain it exactly - but I still want to experiment with more of a closed loop setup which I still think is best handled by the ESC. The ESC already knows the RPM internally and governed modes are available so why re-invent the wheel and add more things that can go wrong.

That said, if you're not controlling the RPM through your gcode then a built in RPM sensor makes a lot more sense. Once I found a setting that works for me and dialed it into my gcode with the controller controlling my ESC/Motor I was able to put my tach away and not think about RPM anymore. When I was still using a servo controller to manually set the speed manually checking the RPM each time I started up the cutter was critical to good results.

Aside from RPM monitoring/control experience and experiments have left me with the following conclusions:

• Height helps. I'm not sure what the upper limit is but I've yet to get worse results by making things taller above the guides. I'd try going taller but my cutter works great and I'm too lazy and impatient to try taller just for the sake of trying it
• Guides are critical and there's no single solution. By this I mean you need both "macro" guides and "micro" guides. The mig tip is the micro guide that does the fine control but it's not enough by itself and really needs a macro pre-guide. Bearings seem to let you get away with a shorter overall setup - but plate style guides can be just as effective if there's enough height for them. The better the guide setup is the less heat you'll have and that will lead to longer lasting needles and cleaner cuts.
• The less the needle protrudes the better - but don't lose sleep over it. Guides above the point the needle sticks out seems to make a bigger difference than how much it sticks out. I do seem to get better cooling and cleaner cuts with the needle retracting fully up into the guide on the upstroke (though I accept that others have seen the opposite with their setups for reasons I have no theory to explain.)
• Flywheel beats crank. The crank appears simpler and easier...but in my experience is a lot more finicky and difficult to get working and even more difficult to make reliable. I still think a grooved bearing would be best for the flywheel. I haven't had luck with printed needle holders and getting the coil on the needle to stay on the bearing without a groove is tricky, my super glue method works for me but feels like a hack and I've had no luck with cutting a groove into a bearing myself only managing to burn out bearings before putting a noticeable groove in them.
• Either way smoothness/balance makes a big difference. A bit of time spent adjusting counterweights to get things as smooth as possible will pay for itself big time in increased reliability and longevity.
• It's not part of the cutter itself but workholding matters more than I originally assumed. My only complaint about my vacuum table is the noise of the vacuum, I really wish I could come up with a silent solution that worked as well.

Also - I'm not convinced that even more guides is necessarily beneficial but I also don't think they'd detract. I like Verris's setup with bearings on all four sides, the only reason I didn't try that myself is I didn't have that many bearings on hand and haven't had any issues with needle deflection front to back since I took time to shim everything to make sure the needle rides in the center of the guide bearings.


If I was to try and redesign my cutter (which I've considered doing just for the fun of doing it) the things I'd change are:

• Try to find a way to accomodate a wider range of motors or at least focus on a cheap readily available and common motor. This is my biggest regret about my current design by far due to the difficulty in finding the motor I used and the importance of the motor dimensions to the design working reliably.
• Plan on lights on the bottom from the start - I really wish I had 1 or 2 more LED's on there as I really love the way they make it easy to see how well things are working. Adding them was an afterthought and they barely fit - on a new design I'd definitely plan on them.
• Accommodating the ESC as part of the mount like @ishmaelpr77 did. I thought I had left enough room for this when I designed mine and was disappointed to find the ESC I used didn't actually fit.
• Rethinking the overall design so it's easier to mount to a wider variety of machines/mounts. Maybe a two piece design where the mount is separate though I hate to add the additional complexity and potential point of failure.

Don't take any of this as "gospel", it's just my observations of my own setup and experiments - and it's been almost half a year since I fired mine up due to a lack of time to work in my shop since becoming a single father. Just figured I'd share what I've learned for anyone who's looking to continue to try to improve things!

 

[Headbang]

Jason. I am using your vacuum hold down. But I did not like the sound of a shop vac either. So I stole the house vacuum. A shark. Is much quieter! And works great.

Thank you for such detailed insight! I will post as the new one comes together.

 

[jhitesma]

Jason. I am using your vacuum hold down. But I did not like the sound of a shop vac either. So I stole the house vacuum. A shark. Is much quieter! And works great.

I actually have an old house vac that I tried as well, but it's no quieter than the little $25 1 gallon shop vac I use

There are vacuum motors designed just for this kind of use that are supposed to be pretty quiet...but they start at about $130 and while I do want it quieter I can't justify spending that much to get it quieter especially without knowing how much (if any) quieter it actually is! (had to dig a bit to find the link: https://www.centralvacuummotor.com/shopbot.htm)

 

[Headbang]

I actually have an old house vac that I tried as well, but it's no quieter than the little $25 1 gallon shop vac I use

There are vacuum motors designed just for this kind of use that are supposed to be pretty quiet...but they start at about $130 and while I do want it quieter I can't justify spending that much to get it quieter especially without knowing how much (if any) quieter it actually is! (had to dig a bit to find the link: https://www.centralvacuummotor.com/shopbot.htm)

If the "slow" time of year decides to finally slow down, i have a few ideas i have mathed out that have promise. After a few tests I found how little one needs to hold a sheet of foam down. Of course you need more then bare minimum to account for leaks from cuts. Sound is a function of size and rpm which make such great suction. Increase the fan size and slow it down, and you get some suction, but nothing like a vacuum or edf. Add more fans to account for losses, you start to trade space for sound. In theory a quiet solution gets big.
So much to test, so little time.

 

[dkj4linux]

I got to thinking (uh-oh!) and decided to try a cheap router speed control that I had on hand... to control the speed of the small shop-vac that I used with my last vacuum hold-down tests. Turn your volume down...

I haven't actually tried this with the vacuum pad yet but, as you can hear, there is a significant difference in the volume level from least to full power. Whether the lowest power setting is enough to hold down a sheet of DTFB -- that remains to be seen -- but being continuously variable there should be a point at which there is adequate hold-down and least noise... at least for this particular shop-vac.

Just a thought... -- David

 

[jhitesma]

Interesting idea David. I'd also potentially be concerned about cooling at lower speeds.

And my little $25 stanley vac is barely enough even at full power It holes the foam noticeably weaker than my big vac, and the far corner I have to watch to make sure it doesn't start to lift sometimes. Of course this is against my MDF table which could be leaking a lot of air as well, sealing that may potentially help quite a bit since my vac also sucks against that to hold itself in position....

 

[dkj4linux]

I guess I'm hoping that the cooling requirements will be in proportion to the motor rpm's. If these shop vacs can run/suck at full power for the time it takes to cut a sheet of DTFB without burning up -- which I gather some folks are doing routinely -- then I'm thinking/hoping that they should be able to do it at lower power levels as well... and be less noisy doing it?

 

[jhitesma]

I've run mine for close to two hours straight cutting a stack of planes back to back. The only break it got was less than a minute between sheets while I swapped sheets of foam and reset the machine. I've actually done that 2-3 times with it. So far the little cheapie vac has done great with that. I do hope your experiment works out. I was just thinking about putting a small hole in my wall and mounting the vac outside to cut down on the noise - but I assume that's not a viable option for most people.

 

[dkj4linux]

For less than $20 you could give it a try yourself... might be a handy device to have around anyway. I'm not real energetic these days so I can't swear I'll ever get around to actually doing anything with it myself...

https://www.ebay.com/itm/Newest-AC-...h=item3fb686fe29:g:27oAAOSwhspcNEpI:rk:3:pf:0

 

[jhitesma]

I have one, I use it on the dewalt in the MPCNC when I need a spindle. Just never thought to try it with the vac.

Unfortunately I haven't been able to get out to my shop for months. And when I do get out there I'll need a full weekend of cleaning before I can do anything at this point