Cutting foam sheets... with a needle!

[dkj4linux]

An quick update on my living situation...

I'm now getting settled in to my new home/hideout. Got new internet... quite the upgrade (for less $$, even) from 10Mbps to 250Mbps (fiber)! I've not got any machines set up yet... still trying to find stuff and get it out where I can find it again. Built a quick, crude "entertainment center" to house a couple of prized possessions (TV and Prusa printer) within eyeshot... and several other machines are rather unceremoniously pushed/piled into one corner yet.

Also enjoying having my grand-daughter, and her friend, just drop in unexpectedly, on a whim... they like to pile into my cheapie massage chair and crank it up to watch TV. And I'm getting educated to a few new shows...

Getting there... slowly.

-- David

 

[Springer]

Very cool, David! Love the high tech entertainment table, with SPF labels still on it!😄 I expect having grandkids around will add a whole new dimension to your life! Maybe even allow you to start them on a STEM career.

Back to needles, I agree with you and headbang on the vibration issue. When I originally set mine up I did basically what you both said. Spent lots of time tweaking the balance screw to minimize vibes. It seemed low and stable the whole time I had it on before swapping the laser in. Went south half way through the first cutting after refitting. At this point, I think the 3 point mount should stabilize motor and I double nutted the needler frame to z axis for lock nut function. (Will pick up some 3mm cap screws for grub screw replacement too.) Today, I will go through the rebalancing tedium. It occurred to me that a sound analyzer ap on phone might be useful. I remember it got really tough to tell if each change was better or worse as I got vibration down. Have to look for one on play store. All the fun of DIY!

 

[Kratho]

What feed rates are you guys using now?

Current RPM’s are 14,800 under load

I ran a bunch of tests with 5mm/sec increases from 30mm/sec up to 130mm/sec

From 30mm/sec to 70mm/sec the foam shrank slightly I would conclude from friction heat. 80mm/sec seems to be the sweet spot with all the speeds above that cutting great but just not as easy to pop out of the board after cutting.

 

[Kratho]

An quick update on my living situation...

I'm now getting settled in to my new home/hideout. Got new internet... quite the upgrade (for less $$, even) from 10Mbps to 250Mbps (fiber)! I've not got any machines set up yet... still trying to find stuff and get it out where I can find it again. Built a quick, crude "entertainment center" to house a couple of prized possessions (TV and Prusa printer) within eyeshot... and several other machines are rather unceremoniously pushed/piled into one corner yet.

View attachment 145180

View attachment 145181

Also enjoying having my grand-daughter, and her friend, just drop in unexpectedly, on a whim... they like to pile into my cheapie massage chair and crank it up to watch TV. And I'm getting educated to a few new shows...

View attachment 145182

Getting there... slowly.

-- David

Congratulations!!!

 

[Springer]

Well, I spent a relatively pleasant afternoon tinkering. The 3 screw mounting of the 2812 motor seems to have solved the grub screw loosening, so far. I tried using a sound analyzer ap to measure noise as a function of balance. The one I used is Sound Analyzer free. I ran the cutter to about10,000 rpm and measured loudness by freezing the screen and noting the highest frequency and level. I then unscrewed the adjusting screw out some and retained it. Unscrewing it out about 1/4 turn provided a lightly lower sound level. I did this several times and got lower noise, but then eventually it started rising so I quit. Not absolutely sure it worked as I'd hoped, but feels smoother now. I broke the needle (melted foam on it) relatively quickly, replaced it and thought I had it, but it broke again. Decided to make more robust loop and that seems to be working. I cut one of the yaks we were cutting yesterday. I was running at 9200rpm, and 600mm/minute. The needle seems to bend opposite direction a small amount while cutting. Does this mean I should slow down? I don't remember this side thrust before.

 

[Keno]

This is getting interesting. Speed is a issue and when you arrive at a speed vs all the all other issues then it will produces a product that you have set you goal upon. You mentioned that you may need additional bearing place to reduce "upper end needle vibration". I note this as it is an issue to be dealt with. I really liked your needle lubrication method. My present issue of "needle tracking wonder". This issue could be related to other problems in my MPCNC build. Still working on these issues. Anyway, it keeps the mind active. Keep up the great work as I am looking for your end product.

PS: David, things are looking pretty good for you, enjoy the grand Kids and your new digs.
Ken

 

[dkj4linux]

All,

For DTFB, I've found from experience that 10-15 perforations/mm gives clean cuts and parts that should pop out of the sheet easily. So, at 14800 rpm on the cutter,10 perfs/mm would require a feed rate of 1480 mm/min (24.7 mm/sec)... 15 perf/mm, 986.7 mm/min (16.4 mm/sec). Though I doubt optimal, IIRC other folks have cut other foams successfully with similar rates.

Early on, I tried increasing the cutter rpms and feed rates and found that localized heating of the foam became a problem... with molten foam eventually coating the needle and being pulled up into the needle guide. Catastrophic failure of some sort follows...

I've always suspected the needle guide is heating up faster and to higher temps with the increasing rpms and transferring it to the needle. Dwelling in one spot too long leads to the localized heating and molten foam migration... gotta keep moving to have any chance at all. But then, you run the risk of not putting down enough perfs/mm to cleanly cut out your parts. I think that is what Kratho saw in his last post...

If this IS what is going on... I suspect ACTIVE COOLING should take care of it. Adding a small fan, directly at the guide (similar to a part cooling fan on a 3d printer) should help?

Thoughts?

-- David

 

[dkj4linux]

Thanks, guys, for all the well-wishes as I settle in to my new hideout. It's fun sitting here, writing this, and watching deer graze in my front yard... they are all over the place! These were in my daughter's yard next door a few weeks ago...

-- David

 

[Headbang]

All,

For DTFB, I've found from experience that 10-15 perforations/mm gives clean cuts and parts that should pop out of the sheet easily. So, at 14800 rpm on the cutter,10 perfs/mm would require a feed rate of 1480 mm/min (24.7 mm/sec)... 15 perf/mm, 986.7 mm/min (16.4 mm/sec). Though I doubt optimal, IIRC other folks have cut other foams successfully with similar rates.

Early on, I tried increasing the cutter rpms and feed rates and found that localized heating of the foam became a problem... with molten foam eventually coating the needle and being pulled up into the needle guide. Catastrophic failure of some sort follows...

I've always suspected the needle guide is heating up faster and to higher temps with the increasing rpms and transferring it to the needle. Dwelling in one spot too long leads to the localized heating and molten foam migration... gotta keep moving to have any chance at all. But then, you run the risk of not putting down enough perfs/mm to cleanly cut out your parts. I think that is what Kratho saw in his last post...

If this IS what is going on... I suspect ACTIVE COOLING should take care of it. Adding a small fan, directly at the guide (similar to a part cooling fan on a 3d printer) should help?

Thoughts?

-- David

I run at 12-15rpm per mm. I had heat issues until I wrapped the mig tip in wire. New design with the 486 heat sink is cool no matter what I do. No fan.

 

[Springer]

David, 8 pointers! Perhaps one will mysteriously fall dead in your yard. Venison sausage for winter!

 

[Springer]

On feeds, If I run at around 9200 rpm and feed at 600 mm/min, That's about 15 strokes/mm. The cut is clean but I notice the wire looks like it is angled aft of path direction when moving. What is y'alls typical wire max extension from the guide at full down stroke? I'm beginning to think my needle may be too long.

Another acectdotal comment, I ground a longer taper in one needle yesterday, and got plastic buildup on it that jammed in the guide and bent/broke the needle. I went back to the 45° grind I originally got from David, no problems so far. I wonder if we need to polish the ground tip?

 

[Headbang]

On feeds, If I run at around 9200 rpm and feed at 600 mm/min, That's about 15 strokes/mm. The cut is clean but I notice the wire looks like it is angled aft of path direction when moving. What is y'alls typical wire max extension from the guide at full down stroke? I'm beginning to think my needle may be too long.

Another acectdotal comment, I ground a longer taper in one needle yesterday, and got plastic buildup on it that jammed in the guide and bent/broke the needle. I went back to the 45° grind I originally got from David, no problems so far. I wonder if we need to polish the ground tip?

There is always a little flex while cutting. I have done most of my cuts with a 10-12mm stroke. Latest stuff is with an 8mm stroke. Cuts are better with a shorter stroke.

 

[dkj4linux]

Depending on the degree of needle-in-guide "slop", the needle will always trail "aft of the path direction" some amount when moving... but it should always "catch up" with a change of direction. I try to keep the needle guide pretty close to the work piece surface... within 2-3mm or so. That's, of course, easier done the "flatter" the workpiece is held... maybe good reason for a vac pad or somesuch. If you allow 3mm clearance, 5mm material thickness, and a couple of mm into the waste piece below... I find 10mm or so needle extension below the guide should be a decent needle length.

 

[Springer]

Hmm, that would explain my drag. My current needle extends 18 mm from guide! Suppose I should trim that a bit. Although as you mentioned, it seems to "catch up" at the end of a run. I set my zero at just above the bottom of the MPF sheet. That way it leaves a tiny skin of foam that keeps all parts together on the sheet. Probably helps with vacuum too. But, that means the guide is ~12mm above surface. Should add that the sketchup plugin i use to generate g-code (wafer) inserts a "G01 Z0.0" before each cut set of moves, so leaving zero at bottom of foam means no editing of Z axis. I have been using the daylights out of wafer for both foam (needler) and vinyl/packing tape letters and logos (using the 2.5 watt laser David turned me onto - thanks guy!). So far it has handled everything I throw at it, as long as all parts are full closed loops. For CF slots, I use a loop .5mm wide. Haven't tried partial depth for fold lines, but they would have to be part of loops too.

 

[Springer]

You guys probably already know this, but with latest needle, i did 2 wraps of wire and left the top end long enough to get cut beyond the retaining nuts. I noticed lots of wear when i left the cut end in the loop. Also had two break on loop next to the cut end-fatigue/scoring? The longer top end seems robust.

 

[TEAJR66]

I've had great luck with a 10mm stroke. No tac but rpm is guestemated at 9600rpm. Feed rates of 25.4mm/sec. Cut through at 5.5mm, score cuts at 2.5mm and etching at .1mm.

 

[Headbang]

I am still playing, as time has gone on there have been some very small warps develop in my vacuum bed, I was noticing the other day that I have a solid 1mm and maybe even up to 2mm in some spots variance. This makes an 8mm stroke just barely adequate. 10mm will definatly allow for a greater margin of error. I did not really notice the warping with a 10mm stroke.

 

[Edwardchew]

At last revealing this publicly, people went crazy. haha. Thank you David for inspiring this!
https://www.facebook.com/photo.php?...z_TqLRXPZkrxOCDGLFgUiqKAaLcdpPKbbXSMwvMZ9fL_M

 

[dkj4linux]

Hey, Edward! Good to see you!

Unfortunately I'm not able get that link to work for me... says "the page isn't available". Could be me as I'm not a Facebook kinda guy...

Are you going to start a thread on FT as well?

Again, welcome to the party!

-- David

 

[Edwardchew]

Hey, Edward! Good to see you!

Unfortunately I'm not able get that link to work for me... says "the page isn't available". Could be me as I'm not a Facebook kinda guy...

Are you going to start a thread on FT as well?

Again, welcome to the party!

-- David

Hi David. Good to see you too!

Sorry ya that's the FB link. Hmm do you prefer that i continue sharing updates here or open a new thread?

I've also opened a FB group already for early access to 5 BETA tester then will open the group for more people once i got the build instructions ready.