Extruded , which is a short polymer chain acrylic cuts better and is a lot better in terms of tolerances thickness wise than cast - it however does not engrave well and , worst of all , is the worst to use for laser processing as the laser induces a huge amount of stress in the material and WILL lead to stress cracking , especially if you use a solvent on or near it...beware of this as the stress cracks can appear instantly or months ahead.
The best way to remove burrs or sharp edges or striations on acrylic is to scrape it with a hard steel flat edge , a scissor blade works well , or a duburring tool for irregular contours
This serves to actually remove a lot of the heat affected zone.
Edge striations (coin effect) is all to do with air assist and remelt ... this can be minimised by using the correct speed and power and air assist pressure and direction.
You need enough speed , power and freq(ppi) to melt the stuff to get the polished effect , but have to reduce the air assist to the point of where it still ejects swarf thru the cut but does not "supercool" the melt which leads to a slightly frosty edge
Ideally the air assist should be directed in a thin stream just after the beam , not co incident with it. You can probably buy an adjustable nozzle at tool supply houses. You will never get a totally striation free edge. There are other issues with straitions in terms of that the perspex or acrylic expands when heated , a lot in fact and the continued expansion and contraction and the micro movement of the pex on the cutting surface (due to machine motions etc) will also contribute. The beam itself "wanders" cos of slight mirror motion and in fact as the beam path gets longer , smaller movements of the mirrors actually translate to much bigger movements. Think of photography , you cannot use low shutter speeds with telephoto lenses , but can with wide angle or normal , as the motion blur in tele's is vastly magnified.
If you do 2 pass cuts into pex , you will never get good results as the melt is never ejected thru the cut on the first pass.
I repeat , honeycomb cutting tables suck with pex as you almost ALWAYS get the tick marks from flashback.
We cut 3-5mm DIRECTLY on the table and thicker on elevated blocks.
PS note to Laser mnfgrs ...I have NEVER seen a decent mirror mounting fixture or one that is easily adjustable. On most , just removing and replacing the mirrors can give a slightly different beam alignment EVERY time.
Another suggestion is to check your beam alignment. This is pretty easy to do.
Cut a square of 5-6mm pex at all corners and the centre of the table ...use a setting that JUST cuts thru at lets say , top left , if any others dont cut thru , you out of alignement. A further test to this is to stand each square on edge , all 4 of their edges , if the square tilts in any direction...you are out of alignment. Obviously use a vernier to see if the acrylic (pex or perspex) itself isnt varying in thickness when you do this
Alignment is fiddly , however pays huge dividends , think about it , any beam divergence off the perpendicular leads to an oval spot and a far smaller spot power density , any time the beam doesnt hit the final focussing optic dead centre , it leads to power density loss as well. Translates to less then ideal engraving and cutting and up to an effective 25% "loss" of power. So you lose 25% in terms of time re cutting , and you have paid for a machine that delivers 75% of the power you thought you were getting.
It's often WELL worth the hr or 2 it takes to align.
PS note to laser mnfgrs -- is there NO way an "autoalign" feature can be included??
Rodney Gold, Toker Bros trophies, Cape Town , South Africa :
Roland 2300 rotary . 3 x ISEL's ..1m x 500mm CnC .
Tekcel 1200x2400 router , 900 x 600 60w Shenui laser , 1200 x 800 80w Reci tube Shenhui Laser
6 x longtai lasers 400x600 60w , 1 x longtai 20w fiber
2x Gravo manual engravers , Roland 540 large format printer/cutter. CLTT setup
1600mm hot and cold laminator , 3x Dopag resin dispensers , sandblasting setup, acid etcher