Hi all,
Yorahome 6550 15w diode laser. Trying to do photo on birch plywood. Used Imag R to do pic and get png , uploaded to lightburn set to speed 3000 in/min and power 15% burn is about 15% done in 1 hour but what I see on the plywood looks nothing like the pic. Speed of 3000 in/min is 50 feet/min which doesn’t seem possible even because laser is physically moving across the 4 inch pic in 62 seconds and burn is very dark so I obviously don’t have speed and power settings correct !!! Please help me figure out what to do. THANK YOU IN ADVANCE 
I don’t quite understand this. Are you saying you have set in the software to cut at 3000in/min (quite fast for a diode laser) and the hardware is taking 62seconds to travel 4 inches (3.87 in/min)?
I have an Ortur LM2 with the 15 watt (input) diode. My setting for engraving on Red Alder is 2600mm/min (Note metric units here (Almost 30 times slower than your setting) @ 60% power. This should get you in the ballpark for your Birch, maybe need just a bit less power.
3000 inches per minute would be 50 inches/sec, or 1270 mm/sec, which is faster than most CO2 lasers will move. Your Yorahome machine is using an 8 bit controller and a diode laser, neither of which will do much of anything at those speeds. 
An 8 bit GRBL controller can process about 250 GCode instructions per second. If you take an image and dither it at 254 DPI (the default), that could create up to 254 unique instructions per inch of travel, which means you’d be limited to roughly 1 inch per second based on the computation speed of the controller at that DPI.
Dithering varies in density - some parts will have longer runs of black or white, so your actual speed will be somewhat faster, but your expectations are out of whack by a fair bit. The 3000 number you used is more commonly used in mm/minute, not inches/minute, which translates to about 118 inches/min, or 50 mm/sec. If you just took the “3000” number from someone else and didn’t notice the units, that would explain the disconnect.
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Discovered machines $32 was 0 not 1 laser not on just redid burn took 32 minutes at 1500 mm per minute and 75 percent power dpi was only 78 so not great but at least it looks like a pic. Redoing it now with dpi at 309 and burn looks pretty dark so maybe a dpi of 200 or so? At least I’m seeing a picture
254 DPI is the default because it’s a good starting point, and it makes relatively small GCode (0.1mm is a nice round number). 1500mm/min might need you to lower the power value a little, but yes, you’re on the right track.
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