I have a Commarker B4 20W fiber laser. When I etch the upper portion of the work area it seems to run at a lower power than the lower portion of the work area.(I hope I explained the right.) Has anyone ever run across this before?
Hi Dave
I can’t help you with that issue except to say that a screenshot of your settings and a picture of the results your actually getting would be of assistance to those who can inform you better.
A focus issue due to a not-quite-aligned platform or laser head would cause the power to fade away like that.
I recall a previous discussion along those lines, but can’t come up with enough keywords to retrieve it from the other problems. 
It’s nice to know what lens you’re using? Fiber is very sensitive to focus.
If the head isn’t square with the table, you can go out of the focal range relatively easy depending on your lens length.
I think this is what @ednisley saying, but both responses are correct..
None of the settings for my laser have been altered over the last three years.
Here is a pic of the issue I was having.
(Sorry for the lousy pic. It was the best I could come up with.)
As you can see, the upper letters etched in less than the lower ones.
Just to update on this. I had two more sets of these stainless steel book marks. When I etched them they all turned out fine. My guess is it had something to do with the material. Maybe?
How do you focus this? It has the typical look of on it’s edge focusing. Top is light, but as it goes down it’s actually like the beam is getting larger (unfocused)?
What lens are you using?
110mm lens.
The shorter the lens the shorter it’s depth of focus (dof), meaning focus is even more critical.
Using this on-line calculator for spot size, the size will vary, but I got these values from memory from my manual, so they aren’t double checked against it.
Dof is 931 microns or less than 1mm to stay in focus. A mm is 1/25th of an inch, you have less than that range in focus.
I’d start by ensuring ensuring the head is perpendicular to the table.
Does this make sense?