Cutting acrylic

I need to cut 3" and 3-1/2" circles in 3/8" acrylic. I'll use the 3/16" cutting bit. Should I cut full depth, or make multiple passes?

I would say do multi pass.

is this cast acrylic or extruded? Like with lithopanes they say to use only cast because the extruded will ball up (melt) on the bit and may break your bit. I'd be very careful and stand watching it if you're not sure what you have. Just my 2¢ worth.

It's cast. Curious if anyone has done a cutout like this.

i have cut 3/16" on a single pass with an 1/8" bit with no problems. Thinking a one pass should work with the big bit. Do you have a spare piece to try and cut just to be sure.

I have machined quite a lot of thick cast acrylic. I would not even think about a single pass. Use a new bit. (I use two flute short bits.)

I would use a carrier board and 1/4 inch strips of double stick tape to hold the loose circle. I would make a vector path or circle and assign the 1/4 inch bull nose bit. But actually use the 3/16 cutting bit.

My thinking is that this would lock the feed rate into 1st or it's slowest gear giving you a smoother cut. Not use Cut Path and Tabs. Because remember the machine is going to think you are cutting wood and will likely shift into the faster cutting rate destroying something...

LHR... What are your thoughts...?

Thanks all for the input. I have not had good luck with double-sided tape, but will consider it. I am doing this for a friend who sent me two 12" square sheets, so yes I can screw one or two up but would rather not. I will probably take 1/8" passes.

I cut two of these rings today using tabs and 1/8" passes. One of the reasons for using tabs is it allowed me to load the blanks into my drill press to sand and polish the outside edges. The machine did not strain near as much as when cutting oak. No issues with melting or any other problems.

Attachment 86935 Attachment 86936

I may have to try making an acrylic clock.

That would be interesting!

Like I stated earlier, I have cut at 3/16" with one pass with a 1/8" bit. I have done this many times for making edge lit projects. A trick that I picked up on was that you can flame polish cast acrylic. Propane will not give enough heat with out extra help, but Mapp gas burns hotter and does have the heat to get the job done. Sand, then polish, then to get that clear edge we want to see again, heat brings it out for you quick and easy.

I actually tried my propane torch on one of the inner circle scrap pieces. It polished the edge nicely, but also left a 1/16" bump on the surfaces top and bottom, so mixed results.

Propane not being hot enough causes you to keep heat on long then you want. MAPP being hotter allows for a faster pass, so you don't that to heat the piece as much.

On Sawmill Creek are a few threads on Flame Polishing. Even 2 that I know of where they did group purchases of Flame Polishers from China. I got in on the first batch. Never used it yet.

Is there any way to tell if it is cast or extruded acrylic before it goes into the CW? Cutting with my band saw first maybe to see if it balls up? I am having a really difficult time in my area to get cast acrylic. The vendors/glass companies all say it is cast but it all gums up when I use the CW. I tried to etch some letters with a depth of 0.04 and a 60v bit, with no luck.

I did some looking around to see if I could find a answer for you. This is what I found. Extruded has higher tolerances and if thickness checked should be with in .05, where cast can be as far off as .2. Another method I came across was to burn a little piece/strip. Extruded burns silently and drips molten flaming balls , cast burns with a crackly flame and wont drip burning pieces. I hope this helps you out a bit. Cut edges can also be a tell tale they say, cast being more grannie looking, extruded should be smoother and clearer after cutting.

Thank you for the reply, I did find that when I cut it on my band saw that the edges were quite coarse. I will try these tests as I go along, and let you know. Thanks again.

Sawmill Creek has a forum that I visited often but not lately. Lots on working with Acrylic. I even got in on a group purchase of some flame polishers from China... They did a 2nd buy....

I will check out the site, thank you Al.