Negative cut into acrylic

[coryatjohn]

I made this instrument panel faceplate for the vacuum hold down system using 0.08" acrylic plexiglass (from Lowes) by painting the back of the panel (Krylon Fusion), cutting it from the back and then filling in the letters with white paint (acrylic). Size is 6"x12"

I used a 90 degree V-Bit (Orange Tools) at 14,000 RPM's, 2 IPS to cut the letters 0.03" deep.

They came out pretty good but letter edges weren't very sharp. It's hard to tell from this picture there is a slight jagged edge to straight lines. I'm guessing that I went too deep with the letters as the "USNaviguide" part came out nearly perfect. Those letters are smaller and didn't go as deep.

What bit, speed, depth, or whatever should I have done to improve the final product?

http://www.usnaviguide.com/shopbot/Vacuum-Faceplate.jpg

[bleeth]

John:

Your piece of Acrylic was likely extruded rather than cast and it is harder to get a clean cut on. By Orange I guess you mean CMT carbide tipped. For a CNC you are better off with an all carbide tool like Centurian, Whiteside, Onsrud, etc. or at least a solid carbide insert bit like Amana, although I know that CMT is decent router bits. I would cut this at around 10-12k and 1.5 ips. Sometimes on v-cutting plastic you get a better finish by running a second pass a fraction deeper.

BTW, You can buy prelayered panel material in many color combos from Johnson Plastics. No back-painting and you can just engrave the face.

[br928]

If you go to Johnson plastic you can get precolored acrylic for reverse engraving too. If you want your letters on the back and a smooth front.

But what you did looks good for not having to special order it.

[coryatjohn]

Dave, Stan,

Thanks for the advice.

I used a 1/8" two flute upcut carbide bit for the cut-outs. That went pretty smoothly and left clean holes. There's a bit of white paint splashed over from the back to the side that looks like a bad cut but it just needed some cleanup. The cut-outs didn't cut through the protective plastic layer so everything held together nicely. I used a vacuum hold down with clamps for that belt and suspenders effect.

[Bob Eustace]

John - do a lot of trophies - always use cast as Dave reccomends - never go deeper than 0.02 and 1.5 at 13K. Love your painting work-around! Another nice material to use for this sort of work is Alucobond. Think you call it sign board over there. Its two thin bits of aluminium prefinished with a usyally black substate in betwwen. Shopbots love this stuff.