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DPI tests
Ed Krome Dec 2022
Since the lasers at Rolling Acres (60W) and Brownwood (30W) seem to vary from day to day, one can never make definitive instructions on etching parameters that will always work. So, one generally has to do scrap testing (with the intended substrate) to find the combination that suits you best.
One thing that doesn’t seem to have much data is the effect of DPI (dots per inch) on text in raster mode. So I ran a series of tests with the available range (150-1200) of DPI, while keeping the power and speed constant. And used different series at different power levels. I did this at both RA and Brownwood. Tests were done on 2 different substrates; Baltic Birch plywood and MDF. What I was looking for was both text definition (and how dark) and burning haze around the letters. I used standard top-down etching. I also tried multiple passes to see what would happen. So this really was a test of the effect of DPI only, since sequences were done at each dpi.
The results on BB showed a rather even increase in etch depth and darkness from 150 DPI (faint but visible) to 1200 DPI (quite a bit darker and deeper). Two passes was, as expected, even darker/deeper. There wasn’t much difference between RA and BW when the same tests were done at the same power and speed settings. I suspect that the RA machine’s performance is quite a bit below what would be expected. I did not clean the mirrors, but these results were consistent with what I have seen before.
A really big difference was seen when using MDF. At 150 DPI, the text is almost invisible and still a bit faint at 600 DPI, but quite dark/deep at 1200 DPI. The amount of haze is, as expected, related to power and speed. Two passes at 1200 DPI, 100 power and 75 speed resulted in less burn haze while almost as dark as a single pass at 50 speed (same power and dpi).
Your results may vary! Try it.
On BB plywood at Rolling Acres 60W All 100 power, left group 50 speed, right group 75 speed DPI as noted
On BB plywood at Brownwood 30W laser
On MDF at Brownwood All 100 power, top group 50 speed, lower group 75 speed. DPI as noted