Longer Ray 5 10W. Holes in 1/8 plywood are consistently smaller than designed. Perfectly round but .03" too small. Holes are supposed to be 1.04". Actual 1.01". Cause?
Unless you’ve done an unusually careful job of eliminating mechanical backlash, half a millimeter is within reason. This checklist points out a bunch of opportunities:
It’s for a Sculpfun, but you’ll recognize most of the parts. Verifying the backlash and its correction using burned-but-not-cut circles or squares will simplify the process; do it on cardboard or paper and make it even cheaper.
Similarly, verify the step/mm calibration by accurately measuring a nominal 100 mm (or 4.0 inch) square. I doubt it will be off by enough to make that much difference on a 1 inch hole, but it’s worth checking.
You’ll eventually find the holes are very slightly elliptical, due to the non-square-ness of the focused spot. There’s no good way around that if you’re really fussy.
Thanks. If it was backlash, I would be surprised that it reproduces exactly across a 6 by four grid and the holes are round. However, thanks for the tip.
Suffice it to say: many people have been. 
If the laser head approaches every hole from the same direction and performs the same motion while cutting, then the same backlash will produce the same results.
However, I made an assumption: no kerf adjustment.
If kerf adjustment is active for that layer, then the geometry will produce exactly the results you describe.
Flip the switch Off and the size error will vanish when the machine does both what you expected and what you asked.
Maybe that’ll be a more pleasant surprise.
As Ed already pointed out, did you take the size of the laser beam into account? The spot can be up to 0.2mm in size. I don’t know the Longer Ray modules, for a Sculpfun 10W, it should be around 0.08mm but most modules are bigger.
Kerf adjustment is off. Each row of holes is approached from the opposite direction. I was a troubleshooter for mechanical, electrical and software on industrial cnc machines of various types for over forty years. I think my expectations for this machine were unrealistic. It performs quite well and is consistent so I’ll just adjust the hole size. Thanks for the assistance. It was helpful and quite prompt.
That counts for a lot!
Fire the laser …
Compared to the price of an industrial machine???
Make friends with the rest of the people in the same boat…
Enjoy what it can do for the price…
That, I am. Having fun. My expectations however, were based on published capability specifications. In some instances, it is interesting to see the specs that aren’t published.
I’m curious. In what ways does the machine performance vary from published specifications? The early diode lasers were known for vastly overstating the power of the lasers but from a mechanical perspective most even basic machines should be capable of precision in the hundredths of millimeters at typical speeds. Rigidity is a potential problem area but less of a concern in laser operation.
My OMTech China Blue 3050, 50W didn’t have a tube in it that would support a 50W output unless I used it like a flash bulb… it would only do 44W, measured with a Mahoney meter.
It was only 880mm in length and a 50W tube is a meter in length… They knew when they built it and put that tube in it, and sold it to me, it wasn’t going to produce 50W…
They also compare some of these small focus dpssl as equal to a 50W co2 laser… I can go on… They are cheap, along with enhance advertising, sell them by the boatloads to the rest of the world.
Most of the people buying these are generally users, not technical types and many have no way to measure and confirm the product is what was advertised…
All you can do is your best diligence in research, pay your money and takes your chances. Just like the rest of us 
At least you’re having fun… that’s all that really matters if you’re not in the commercial end of things.
Good luck
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