Can't get consistency with laser

Hi, I’m new to the laser thing and I have a Universal Engraver 15w laser. I can’t seem to get any power out of my laser. The flag was done on white oak with 5000 mm/m, 30 power and around 225 dpi. The Harley logo was done on white oak also but with settings of 2000 mm/m, 95 power and 354 dpi. The JD was done with 3800 mm/m, 80 power and 279 dpi. The bottom of the Harley logo is a little darker because I stopped it and started over. I feel the JD is a little dark do I could have lowered the settings. I’m trying to do an image now with settings of 5300 mm/m, 82.5 power and 229 dpi and it’s not even marking the white oak. Seems strange that using the same wood, a lot more power, roughly the same or slower speeds and higher dpi isn’t doing much. Any thoughts/suggestions?

What flag, harley logo, JD?

You refer to things that you didn’t show us.

Timber is variable - two pieces can behave completely differently. To get consistent results, it may be better to pre-treat your timber with a wash, a coating (like shellac) or with a treatment like bicarbonate of soda, so you’re getting an image based on the laser interacting with the treatment rather than the underlying substrate.

A basic wash is watered down acrylic paint (1:2 paint to water) brushed on, left a few minutes to soak in, then wiped off and left to dry. Bicarb is 30gms/500ml (1oz/pint) - a spray bottle is best. Spray it on, let it dry. Shellac I use at really low concentrations - a cup of flakes in a litre of spirit.

Of those, bicarb gives the darkest result, so you can really turn up the speed and still get a decent image. You may need to seal it after as you can end up with a dusty residue.

Shellac is the quickest/easiest to apply, but will colour light wood (but it also brings out the grain, which may be acceptable, and it seals the wood), bicarb is easy as, but you need to wait for it to dry, and paint takes the longest, plus you need to put it on, wait, then wipe off.

Shoot! I forgot to attach the images. Sorry. Here they are.

I’ll try pretreating.

I tried pretreating with bicarb and it didn’t help, and it darkened the wood. Any other thoughts/suggestions? Are some of my settings possibly wrong?

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