Thanks much for the input, Ben! I apologize for the delay in replying. We've been on vacation, meaning I was AFL (Away From Laser) for two weeks.
The machine is capable of PPI and uses the DSP controller from LightObject. I was already cutting at 100/200 PPI and still getting those same results, so I tried a different type of wood, and I think I identified my problem- the birch. Apparently birch has a much higher oil content than other woods and is more prone to this type of scorching. When I tried the exact same settings for two other woods, the edges were gorgeous.
Some photo examples:
1/8" Birch Plywood from Revell on the left, leaves carbon deposits on my fingers from the burned wood. 1/8" Craft Plywood from Midwest on the right, nice dark brown edges with no carbon. I don't mind the darker burned edge (I actually like it), but I absolutely can't have little bits of soot flaking off. Both were cut with Speed = 6, Power = 17, PPI = 200, in two passes.
DSC_2492.jpg by
scrappyJedi, on Flickr
The 1/8" stuff was just to play with while I waited for my order of 1/16" material to arrive. 1/16" is what I absolutely have to work with for my application, and here were my results (both cut at Speed = 6, Power = 15, PPI = 100, though I've since stepped that up to 200 to smooth out the edges, single pass).
DSC_2496.jpg by
scrappyJedi, on Flickr
The left side is 1/16" Birch Plywood from National Balsa- lots of carbon and soot. The right is a 1/16" Basswood sheet from Midwest and is my favorite cut of the whole bunch. Smooth cutting, no carbon, nice walnut brown edge. This may be the type of wood I have to go with, though I do wish it were a plywood for a little more added stability. I'd go with the craft plywood from Midwest if it came in a 1/16" thickness, but 1/8" is as thin as that stuff gets.
I'll be cutting small decorative wood pieces for a couple of craft companies (examples with the 1/16" basswood below), which is why I can't have the pieces leaving black marks on anything and everything they touch.
DSC_2483.jpg by
scrappyJedi, on Flickr
DSC_2484.jpg by
scrappyJedi, on Flickr