Cutting Acrylic Mirror - preparing for paint

Hi everyone.

So, I have several different instances where I am cutting out acrylic mirror shapes, and also, need to "etch" shapes or words into the acrylic coating in order to paint the acrylic. Example attached.

On that project, I cut a pocket in the coated side of the mirror about .040 deep using a 1/4" O-Flute bit. It came out great!

These new projects are much smaller, so a 1/4" bit is too large. So, I'm using a 1/8" O-flute and having mixed results. Generally, when pocketing, I have it offset 80% of the bit diameter per pass (so, .1" in this case). The worst results come when choosing "offset". The generated toolpaths end up having some - I guess you would call it - abrupt direction changes, and that leaves small divots in the back of the mirror that show up through the paint.

When I have manually offset the toolpaths, making sure there were no direction changes or Z-up and Z-down moves during the pocketing, results have been better.

My question is whether there is a better bit to do the material removal on the back of the acrylic mirror to leave a more uniform surface? Also, do y'all think that "raster" is a better method for toolpathing for this purpose? I'd prefer to not have to create manual toolpaths if I can avoid it (time consuming).

Thanks everyone!

What is your hold down method? Sounds like your material is moving up and down.

I have a vacuum system, so it's definitely not that. I even leave of dust collection so that it's not fighting the vacuum. I also recently skimmed the spoilboard.

It seems to happen when leaving the software to generate the toolpath, and then it sometimes has the z-axis go up, move, go down, and the clear a small portion.

Quote:

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Originally Posted by BoilermakerAndy

...These new projects are much smaller, so a 1/4" bit is too large. So, I'm using a 1/8" O-flute and having mixed results. Generally, when pocketing, I have it offset 80% of the bit diameter per pass (so, .1" in this case)...

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First, set your tool to 40% in the tool database and unless you are cutting something really dense, like aluminum or brass - just leave it there. It is going to be the fastest/most aggressive setting for pocketing without leaving little triangular islands in the corners.

Second, if you haven't already, go here: http://www.plasticrouting.com/BitSea...?Page=Material and enter in your material (or closest to what you have) and see what they recommend. I do know that Onsrud makes an O-flute specifically for getting a cleaner bottom finish. You're more than likely going to get a better finish using a multi-fluted O-flute vs a single O - spiral or straight. Don't underestimate the advantages of making friends with your local tooling dealer. You'll get better tools at better prices than schmucky retail - plus in many cases the professional answers you need.

Lastly...Use raster for anything that people are going to see. The offset strategy seems to draw the eye to it - rather than your overall design. It has a regular look to it and is much easier to either camouflage or clean up.

I've lurked on this forum for some time, and have marveled at you responses, Brady Watson. It is humbling that you responded to my post. Thank you VERY much.

I do know my local Onsrud supplier, and I will reach out. This is a big help......thanks again..

Andy

Andy
Glad to help. No need to be humble for me... I'm just a regular guy.

Quote:

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Originally Posted by Brady Watson

Andy
Glad to help. No need to be humble for me... I'm just a regular guy.

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With super human cnc powers... ;)

If you need help Andy... just say "come here Watson, I need you"

and he comes right over...