Cutting acrylic panels for MP3DP

Mostly Printed 3D Printer - MP3DP Advice
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Did you figure this out already?

Been trying to make some straight line cuts with 90 deg V-bit (NOT trochoidal) in Polycarbonate.

  • DOC = 2mm, XY Feedrate = 20mm/s results in LR3 doing major bunny hopping (chatter?), bearing wheels lift up, my struts are Ply, so not huge amount of weight on the gantry.

  • DOC = 2mm, XY Feedrate = 5mm/s results in too much heat building up, globs of plastic form around the bit and scratch the crap out of the surrounding area. Don’t do this unless distressed/disturbed look is your thing.

  • DOC = 0.5mm XY Feedrate = 15mm/s results in fine dust with minor bunny hopping.

Discovered and fix Core being too loose, adjusted only couple months ago. Sharpie marked line on bolt and nuts to help detect whether they’re loosen over time, and/or something else is contributing to Core bearings loosen from the 3/4" EMT.

Have a weighted vest with sand pouches, wondering whether to load up the gantry with sand-bags/something see if that helps?

Back up option is to live with wider lines and use Trochoidal so deeper DOC can be used to create chips.

For V Bit, should toolpath software ideally enable specifying material removal rate per pass, instead of same DOC for each pass, seems like deeper passes need to go slower, but earlier shallower cuts shouldn’t be hampered with slower feedrates that work for deeper cuts. This is a non-issue if Trochoidal cutting I guess.

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No I never did figure it out. I tried to make everything large enough to mill with a 1/16th bit. If you figure it out I would love to know what you come up with lol

Edit: @DougJoseph had a recent YouTube video on it. That might help some

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Cheers Jonathan, will check out Doug’s video…

Edit: Any suggestions for cheap, easy to source, heavy material that can be incrementally thrown onto/into the Gantry (at the ends, not center), and/or YZ Plates?

Hoping weight can be added in balanced way that doesn’t do more harm than good. For example strap on a bunch of 1/2" x 1’ Rebar in various spots. Each Rebar would add 0.67lb for $3, so that’d be ~$4.50 per lb. Poured concrete would be cheaper, but am not sure how much additional weight should be thrown on to help enable faster feed rates for 1/4" v-bit, or down cut bits. With a 1/4"+ bit in the Makita, currently feels like machine’s light weight is the limiting factor, not the Stepper current-torque limits. Guessing that adding weight is an easy upgrade, rather than some captured YZ plate mod?

Willing to try out a few things before just going with Trochoidal cuts…

Edit #2 : Giving up on v-bit carving for now, figured out better option for my situation.

Was trying v-bit carving, then using metal spray paint on the carved channel to try redirecting light, results were dismal, not usable imo. I don’t have silver paint on hand either. For me, trying to feed light into an interior area and redirect that light internally just isn’t as good as simply doing edge lit panels. Initial plan was to put 5mm lights into 2020 channels facing forwards, then somehow direct light 90 degrees into the panel. Giving up on that…

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New plan is to put lights into 2020 channels facing towards edges of an interior panel that’ll be part of a double panel front door. Panels and spacers held together via solvent welds.

Edit #3 : Picked up some scrap offcut blocks of steel from my local www.metalsupermarkets.com for $0.50 per lb. Strapping to gantry and YZ plates, seeing if that helps make faster v-cuts.

Edit #4: Adding 10lbs of steel to the gantry, 5lb either side does help make deeper cuts. However, it also helps Z steps to be skipped if/when bit runs past end of the stock and suddenly drops. Steppers are unable to handle the momentum and skip, when this happens a few times you ultimately end up with the bit lodged into the stock, unable to move, then we end up with the bit getting hot, dulling and potentially a thermal runaway situation. Maybe the bit I’m using isn’t good for this task, Spetool 90 Degree Carbide V Bits with Tiain Coated 4 Flutes, too many flutes maybe… @Jonathjon what v-bit have you been trying?

Am trying out my next dumbbell idea…

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Tried a few…

https://www.amazon.com/gp/product/B000ALY4E2/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

I’ve been trying to find some with a flat tip but have been unsuccessful. Have seen @vicious1 talk about how the tip of a v bit doesn’t really spin it just gets drug along. And I think that is creating a lot of heat/resistance and why we cant move fast enough to get a good clean cut. So far I’ve only been able to find 90° bits with a flat tip but I really need something narrower that than for some tighter areas. If anyone knows of anything please share a link!!!

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:slight_smile:

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Im guessing something like this…

But after looking at that. If I could cut it with that then I could just use a 1/16" (1.5875mm) endmill and skip the v carve all together. So that’s not going to help any. Needs to be a smaller tip than that. Unless there is a way to do 90% of the carve with that bit and only go in and touch up the real tight spots with the pointy one. But at this point in time that kind of cam is above my pay grade LOL

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I put that bits info into estlcam just to see what would happen…

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According to the preview it will work. Makes me want to order one just to see what will happen. I have several scrap pieces left I could try it out on. And try ipa on the polycarbonate at the same time to see what happens there.

Edit… Bit will be here Saturday. Hopefully ill have time to give it a try and report back LOL

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Cool. Just ordered some 2 flute v-bits and rounded bits as well, arrive Fri/Sat, will share results…

Am able to get decent results with 1/8" single flute downcut carbide. However, am wanting to learn and figure out how to do polycarbonate projects with v-bit, and/or other engraving bits.

Hoping a seasoned machinist reading this topic that’s been kicking back giggling and eating popcorn will chime in with some wisdom :slight_smile: ?

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I just try to make it the right depth so most of it has a flat bottom, start with a flat endmill, that will pocket it out, then use the vbit to get the corners and edges.

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That sounds easier than my Bowflex adapter for YZ plates…

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That’s what I did for the serial tag. Problem is so much of it was so small that even a 1/16" endmill couldn’t pocket enough of it. And I was only going 2mm deep. I guess I could go shallower but wanted it deep enough to catch a good bit of the edge lighting. With the tag so small I might be better off to just do the drag bit on it. Then I know it will clean up nice. But I’m in the same boat as @azab2c now. I want to figure out how to make it work LOL

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Hoping this’ll stop LR3 popping wheelies during v bit cuts… It might stop the LR3 altogether though…

Edit: Extra 20lbs on left YZ plate stopped the wheelies. But v bit just doesn’t want to cut to full depth. Core and gantry are starting to flex now when bit is not able to cut into Polycarbonate.
Trying other settings and other v bits, with and without trochoidal. Am expecting to ultimately end up following Ryan’s advice to use single flute flat end bit first.

Figured this Bowflex mod would be fun and quick to try out. Maybe useful even for fast experimenting with diff weights for diff cuts.

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23-08-11 Edit: As mad as this looks, I swear it helped. However, correct fix for this situation was to use a different bit. There could be some value in supplementing the YZ weight for other situations though… So, if/when I have time and interest, am planning to test various feedrates with and without LR3 loaded up with additional weight on YZ Plates, but not the X gantry. Until then, ping me if you want the bowflex-mount.dxf if you’re curious enough to have a go and experiment.

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I was thinking about this all day yesterday. Since the tip is basically getting dragged, and the V bit take a very large bite with each depth change, I think moving fast taking shallow passes is the ticket.

A 40% (3mm diam=1.2mm step over) step over on a regular bit is a normal/large step over. So what is the equivalent step down on a Vbit? I would say less than 1.2mm (not doing trig before I finish my coffee). I would do 0.5-1mm at 30-40mm/s as a starting point. Plastic is super picky about its feed rate though.

The hard part is the first pass is basically just dragging the tip through, so maybe the trick is full depth and getting the RPM and feedrate perfect? So easy in wood, so hard in everything else. I did get it in Aluminum and wrote down my setting in here somewhere.

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You wouldn’t happen to have the file for that hose end handy would you? looks like the same 2.5" dust collection hose I use. So far everything I have found has worked but not like I wanted it. That looks different than anything I’ve tried.

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Always check his crazy(awesome) amounts of detailed documentation…

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I wonder if one of those offset tip bits would work better for acrylic. The tip of the regular V bit doesn’t cut anything. The offset ones has the very tip off to one side, so it effectively has a flat bottom. But the whole thing is at least cutting something.

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Do you have a link to an example? Not sure I’ve ever seen one like that before. I ordered one with a “blunt” tip that will be here tomorrow. Curious to see how that’s going to work.

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I always forget about his github :man_facepalming: Thank you!!

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Somewhere there is an OpenScad file for this… :smiley:

I‘ve got you:

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Thanks @Michael_Melancon and @Tokoloshe !

Yeah, initially shared vac hose adaptor am using (based on a parametric SCAD script) in my LR3 Build post.

Just uploaded current version to printables incase people aren’t stumbling across my semi structured v1e mods/notes repo on github.

Latest files (this Vac Hose and the Bowflex nonsense for example) will always be on GitHub here. Am only occasionally uploading to Printables. Am always backing up my v1e notes/mods to github, effort I put into structuring content will be proportional to interest from folks.

Time to try some more BowFlex assisted Acrylic cuts…

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