original:
I engrave leather all the time.
I think I have a 100w machine 
My settings are different for engraving on different leather… this was engraved after using the ImagR app to modify the image (if you don’t know it, let me know)
And this image was modified with photoshop and illustrator I think. (not sure anymore)
The settings I use on the first one:
300-350 mm/s power max: 11% and min: 0%
The second image I used:
300-350 mm/s power 15%
Turn the speed up! 
And only 1 pass is what I used.
(oh and I do use compressor air… sooth can be wiped off easily with a dry cloth)