So I just put a new 4" lens on my laser and am trying to get my cut parameters correct. To try and calculate the new beam kerf setting I figured I could cut out a 50x50mm square and use micrometers to determine both the cut our side and the hole size it left. I could then subtract the two values and get the beam size.
I made sure that the kerf settings in LightBurn were disable and ran the cut. The square that was cut out was 49.75x49.62mm. The square hole that was left though was 50.08x49.99mm. This tells me my laser is cutting undersized holes. Not by a lot, but slightly.
When I grab the machine’s settings in LightBurn it is showing the X Step Length as 12.741729. The Y Step Length is 12.716880. The fact that these are close but different values implies that Monport did actually calibrate this at their factory, but the calibration is off. Most likely from differences in temp from my workshop and the factory.
I think I know how to get this closer, but I would like someone to check my work and this seemed like a great spot to find someone to help. From what I can tell the beam diameter is about 0.3mm. As such I would like the hole to be cut to be 50.15mm.
50.15 / 50 = 1.003
12.741729 * 1.003 = 12.779954
12.716880 * 1.003 = 12.755031
If I set my steps per mm to that value and rerun the test I SHOULD be closer to the correct value.
Lacking a pointer, you could measure the distance between two pulsed holes in paper or some such. The key concept is that the distance does not depend on actually cutting a shape; you can estimate the center of a dot or hole very accurately.
Once you have that for each axis, never change it. It is a property of the machine axis, not the lens or cut or power or anything else.
Then use a kerf measurement tool to find the cut width in whatever material you’re using. Apply half that value as the kerf adjustment in the Cut Editor or Offset tool.
That should get you as close to perfect as you need to be.
I have a red-dot pointer but the new 4" lens tube gets in the way with its current mounting position. I am going to 3D print a new mount for the red-dot laser so it can clear the tube. The beam it makes is also really wide. Good for estimating where the cut will start. Not great for pin pointing a spot on a scale. Ill go with the hole method.
If you can cut holes to closely fit a couple dowels of equal diameter, you can very accurately measure centers by measuring from surface of one dowel to the other, then adding or subtracting one dowel diameter. I do this at work when I have to measure centers on a part that won’t fit my other gages.
