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HankMcSpank
07-14-2009, 09:25 AM
I have an annoying 'problem-ette'.

I need to make a part that uses 2mm black acrylic - therein lies the problem, nobody appears to sell it. I can buy 2mm clear acrylic just about anywhere, but nobody sells 2mm black!

So I'm now pondering my options towards coming up with a 'workaround'....

I can't use clear acrylic, so that option is out.

Therefore I was wondering about milling one side of the acrylic to reduce the thickness from 3mm to 2mm (for those still using base 8, 16 & 32 systems, that's a reduction in thickness of about 0.03937"!).

It's a small part size ....only about 60mm long x 18mm wide (2.5" x 0.75")

So my questions are...

1. Is trimming 1mm off a 3mm thick bit of acrylic doable?

By this I mean what finish can expect to achieve? (the actual side I mill won't be seen, but still needs to be reasonably flat as it'll be glued against another part that is completely flat)...

2 What type of endmill/cutter would be best? (presumably the wider the better - less passes needed)



Many thanks.

LeeWay
07-14-2009, 09:39 AM
Personally I think you will cause warpage in it. You are taking off a third (metric third, as well a sae third). ;)

You can get some very good coatings to apply for the bottom or inside. As long as it doesn't see any wear, should look great.

Another idea is to possibly try polycarbonate. May not come in black though. I know it comes in different smoked colors. PET G may be another option. Both it and poly are stronger than acrylic and perhaps a few pence more for PET G and a shilling more for poly. I am talking small sheets. 50 CM x 50 CM. With such a small part, it wouldn't increase your part cost much.

Geof
07-14-2009, 09:46 AM
....(for those still using base 8, 16 & 32 systems, that's a reduction in thickness of about 0.03937"!)...

You must have a good machine if it can get down to 0.00007" precision. :)

You can face it okay but if it is cast acrylic you may run into stress cracking problems when you do the gluing.

Use a small flycutter with a wonderfully sharp HSS tool with no top rake. Cut the strips a few millimeters too wide, clamp them along the edges and run the cutter down between the clamps doing your full width, full depth. Something like 2000 rpm should be fine so long as the flycutter is not badly out of balance with a feed of around 0.002" per rev (you can do the conversion :) ) Soapy water sprayed on as a coolant might help with the finish.

The finish will be opaque and the flatness depends entirely on how good your machine is aligned.

HankMcSpank
07-14-2009, 09:56 AM
Thanks guys....just to fill you in, this is for a guitar pickup type device (though it isn't actually a pickup). You'll see here the top part I'm referring to that's 3mm (& too thick).....

http://yfrog.com/0w63684098j

BTW: That's just a quick rough cut & I've since found a rounding bit which rounds the top edge & therefore makes it look a little slimmer in profile, but I really need to get that thickness down a bit.

Steve Seebold
07-14-2009, 09:59 AM
It can be done, but I would start with larger pieces, maybe 3 X 4 inches. Hold them down with a vacuum chuck or double back tape and you should be good to go.

LeeWay
07-14-2009, 11:14 AM
You can get some very good coatings to apply for the bottom or inside. As long as it doesn't see any wear, should look great.




This statement was in case you wanted to use clear and color the back. I have done this many times. Even painted pictures, designs and lettering on back.
I have used both acrylic paints and "Testor's" paint meant for plastic models with great results.
Would save the machining.

judleroy
07-14-2009, 09:54 PM
You can get black acrylic in 1/16th or .06 sheet. That might work for what your doing with it.

HankMcSpank
07-29-2009, 07:40 PM
Thanks chaps...in the end I milled thicker acrylic down...albeit I had a change of thought wrt the number of parts used in my device, so the bit being milled down, did not need to be milled down across its entire surface. To get a flavour of what I'm on about, here's 3mm milled to have a 1mm perimeter (ignore the fact it snapped ...that was me being careless with it!)....

http://img43.imageshack.us/img43/3666/bobbin.jpg

And to give you an idea of the end result (therefore two of the above joined on the "milled" side)...

http://img169.imageshack.us/img169/9101/30107683.jpg

which is a lot 'finer' looking than my first attempt (& what prompted me to pose the question!)...

http://img119.imageshack.us/i/16001950.jpg/

thanks once again for all your comments