I tried to make a 7.54mm round hole to accommodate a clock movement and I measured the shaft, it was 7.54mm so I made a circle and I input 7.65mm so it would be a good fit. When I burned it on a scrape piece of wood the diameter was like 1/2". can anyone tell me what Im doing wrong?
Does your machine otherwise burn dimensionally correct shapes? If not, then I’ll assume this is a generalized problem.
- Design a rectangle as large as can be accommodated in your laser. Use framing to make sure it fits within the bounds since your calibration seems sufficiently off that you’re in danger of overrunning the boundaries.
- Burn the rectangle
- Measure width and length of burn
- With the laser connected to go Edit->Machine Settings->Calibrate Axis and enter values for nominal size (as designed) vs actual measured size. Repeat for both axes
Once complete, run a test for another rectangle. Bigger is better. Measure. If the dimensions are still off then repeat the calibration with the values of this test.
Rinse and repeat until you have acceptable results.
If your machine otherwise burns to dimension, then it may be a design issue. Upload the .lbrn file here for review.
Because you care about the exact OD, after you finish the axis calibration you must measure the cut width in whatever material you’re using and either offset the hole diameter or apply kerf compensation to the layer.
A convenient kerf measurement tool:
However, a laser-cut hole does not make a particularly good bearing, as the side walls are not smooth and the hole is not cylindrical. You may want to cut the hole slightly undersize and ream it for a good fit.
A little thing I have observed in the last days while experimenter with a 20watt diode laser, the elongated laser beam of the diode is very clearly seen in smaller circles. At first I thought the steppes were not akurate, but a 200x200 square holds the precis dimensions.
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