Polycarbonate woes

I'm trying to do edgelit designs in plexi but I can't seem to stop the stuff from melting.

I've had the best luck with 2-flute 0.048 ball nose cutters, but only for a short while. Inevitably after a time the plastic starts to melt and load up on the cutter and either I have to stop the job, chip the plastic off and restart, or snap the cutter trying.

I like the little 2-flute roundovers because they leave a nice clean cut in the plastic. I've tried engraving cutters but they look like crap (and similarly load up); and a few rototool (Dremel) cutters but they load up even faster.

I have tried very slow feed and very slow speed, very high speed and feed but eventually the cutter always loads up

Is this a problem with the wrong cutter? I feel like there's a magical 0-flute 048 ballnose cutter with an 030 cutting depth (so sort of a triangle tip) out there but I have yet to find it.

Or is this a problem with my feeds and speeds? I definitely don't have any problems cutting outlines in the plastic using larger (1875) 0-flute cutters so the root of my problem is the minuscule size of the cutter I need to use to get the detail I want. But since I've tried really fast and really slow I can't imagine there's something in between that would work.

I am thinking about setting up an air system and blowing cold air across the piece as I cut. That would take a lot of work but I'm willing to do it if it solves the problem.

Anyway, suggestions are greatly appreciated,

Thank you,

"Plexi", is short for Plexiglass, a brand name for acrylic sheet. Polycarbonate is a different material entirely; the most common brand is Lexan. Which one are you trying to cut? From the description of how it's working for you, I'd suspect you're cutting acrylic, because polycarbonate has much less tendency to load up on the cutter. But either way, yes, an air chiller can help. The one I use is a Vortec chiller, which works off an air compressor. https://www.vortec.com/en-us/cold-air-guns Here's a similar one made by Exair: https://www.grainger.com/product/4LCK2

Yes, you're absolutely right, I meant plexiglass, not Lexan. If I stuck to the brand names I'd be fine :-)

Weirdly I can't seem to edit the original post.

I'll give the chiller a try.

Thank you,

Clear water as coolant.

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Originally Posted by dmetzler

Weirdly I can't seem to edit the original post.

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Quote:

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Originally Posted by dmetzler

Weirdly I can't seem to edit the original post.

---

Moderator note: There is a 60 minute window from the initial post to edit that message. Its unfortunate that this is necessary, but otherwise spammers would make the forum very unpleasant. Their technique is to post an innocuous message, then later go back and edit the message to insert spam links. This pattern is very difficult to detect/block with the current vBulletin forum software. So the one hour edit limit cuts the spam down to a mostly manageable level.

Hi,
I use acrylic, largely because its cheap.

It cuts well but its heat sensitivity means you get Built-Up-Edge (BUE) very easily. I use flood coolant, and that is the night and day difference, I cannot
machine acrylic without coolant. Used to use air but it did does not work consistently enough to be called successful. When I tried flood coolant it was just so much
better that I realized the I have found 'the magic bullet'

I use tools from 10mm down to 0.5mm.

I try to spin them so the surface speed is 200m/min.

10mm Speed = 200 / (.010 x pi)=6366rpm
3mm Speed= 200 / (0.003 x pi) =21220rpm
1.5mm Speed=200 / (0.0015 x pi) = 42400rpm, I set my spindle to 34000rpm, its effective max speed.

I allow 1% of tool diameter advancee per tooth per revolution. As an example:

3mm four flute tool, at 21220 rpm Feed rate = (0.01 x 3) x 21220 x 4 = 2546mm/min

For a slotting or plunging tool path I'd go slower, but with a stepover and good chip clearance with well directed coolant I'd go faster.

Craig

Hi,
this is an example, it is a simple speedo that I restored for a customer, or rather had to make a new dial. The dial is 2mm thick acrylic, painted opaque black of the reverse side and then the numbers are engraved
with a 0.5mm two flute endmill (34krpm, 400mm/min) with DOC of 0.5mm, under coolant.

The numbers are well defined and no BUE was experienced.

Craig

Hi,
the only thing worse than acrylic for heat sensitivity is ABS. You only need look sideways at it and it forms a bib lump on the end of the tool, and almost impossible to get off.
Its 'use coolant' or 'don't bother'.

Craig

Thank you all for your help. I am working on a chiller that uses Peltiers but as you can imagine that's a bit of a rabbit hole.

In the meantime I actually found single flute (0 flute?) 1/16 cutters

https://www.amazon.com/dp/B0BHW3NWJL...sin_title&th=1

using max spindle speed and aggressive cutting speed I am able to get through the material without drama.

Hi,
I use coolant, on just about all jobs, and just about all of them benefit from it.

A while back I bought a new spindle (3.5kW(S1),3.4Nm(S1), 10krpm (rated), 40krpm(max),400V, HSK32E tool interface) and suddenly I'm producing a lot
more chips than before, and that has stretched my coolant filter/tank etc.

Just pulled the trigger on getting a new tank made. It will have a three phase pump with two impellors, one high volume (80l/min hopefully) low pressure for flood cooling,
and the other low volume (20l/min) higher pressure that will go through a fine secondary filter before going into stainless gear pumps for high pressure cooling jets.

Craig