All my machines are 30w, this was done on the Triumph. Your 20 will do it, just takes a bit longer.
IIRC I did some test lines at 0 power and about 60 freq to test, I just did one or two centerlines, hoping to engrave a mark from the highest to lowest points. Once I lowered the focus to where it DID fully mark, I ran with it. If it wouldn't have worked, the idea was the marks that did show up could be sanded and polished out easily. Fortunately it worked okay!
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