Incremental cutting of thick acrylic? Multiple cuts

[Gene Uselman]

Post by fred ungewitter » Sun Feb 05, 2017 5:51 pm

Having only recently put my replacement laser tube into use and discovering that the ammeter isn't working properly, I'm hesitant to go beyond 50 percent power on my research and projects. The DooHICkey tells me I'm getting 59 watts at 50 percent. I hope I'm not over-driving it, but I'm also hopeful that a 60w puri tube is a 60w tube.
I've been able to cut 3mm acrylic at 30 percent power, 10 mm / second. It cuts cleanly, perhaps with a wider kerf than needed, but that's not an issue at the moment.
I have an unrelated project involving 11mm / 7/16" thick acrylic. I really want the precision capability of the laser to provide me with a cleanly cut circle. Using my bandsaw to hack away at this plastic is a last resort sort of thing. If I create a program to cut the circle at the required dimension and make repeated passes, what could be expected?
If I raise the table a mm or two after each pass, will I have a greater chance of success? The circle edge does not have to be cylindrical. If I increase the diameter of the circle a tenth or so each time, will I have a better shot?
I don't have an edge jig on my table (yet), but have read of the method involving changing the origin, say from upper left to lower left and re-positioning the workpiece accordingly, flipping the piece upside down. I don't know that I can get the necessary precision to accomplish that, however.

by Pete Cyr » Sun Feb 05, 2017 6:33 pm
Why can't you do 2 or 3 passes @ 30%


Sébastien Laforet

if i remember correctly in one video of russ (the one when he cuts a plexiglas knife holder), he says that he tried with 2 passes, and did not get a clean edge, and by using only one pass at very low speed it was ok. this was 10mm thick plexi.

if you do 2 passes, the first one will not cut through, and the air assistance will not evacuate all the fumes, the cut may not be very clean.

GDU
I think I have had success with cutting halfway a half mm or so outside of the desired cut and then cutting at full power alongside the first cut [IE- where I actually want the cut]. I rarely do not have enough power to cut in one pass however.