Laser Cutter: Scan vs. Cut Alignment

Laser-cutting alignment pin holes in the most recent smashed-glass coaster raised the question of whether it’s feasible to engrave a deep recess around a hole with Good Enough accuracy for things like recessed screw heads.

The test image:

Scan vs cut offset
Scan vs cut offset

The top two rows create engraved recesses and cut holes from 1.0 to 1.5 mm and the next two rows run from 1.5 to 2.0 mm. The bottom row has 1.0 mm holes centered in engraved pits from 0.5 mm to 3.0 mm; obviously, the first hole will subsume its pit.

The first pass looked promising, although the edges of the engraved pits seemed ragged:

Scan vs cut alignment - first test
Scan vs cut alignment – first test

Perhaps the replacement power supply has different timing than the original one?

I’m still surprised that the core of a laser-cut hole falls right out of the sheet, right down to a sliver from a 1 mm hole:

Cut hole cores
Cut hole cores

Recalibrating the scan offset got the errors down to 0.1 mm in either direction:

Scan offset - 300 200 mm-s 0.15mm offset
Scan offset – 300 200 mm-s 0.15mm offset

The lines in the middle column are spaced 0.15 mm apart at scan speeds of 300 mm/s (top) and 200 mm/s (bottom).

Another test pattern puts an engraved rectangle inside a dot-mode cut line with 1 mm spacing on all sides:

Scan vs cut alignment - 300 mm-s 0.15mm
Scan vs cut alignment – 300 mm-s 0.15mm

That’s wonderfully accurate!

A few more test pieces later:

Scan vs cut alignment - test pieces
Scan vs cut alignment – test pieces

Returning to the pits-and-holes test, with one engraving pass:

Scan vs cut alignment - holes x1 engrave
Scan vs cut alignment – holes x1 engrave

That’s lined up to be looking directly down the 3 mm pit in the lower right, which looks fine.

Two engraving passes makes the pits deeper (nearly through the 2.5 mm arylic) and somewhat messier, but still nicely aligned with the holes:

Scan vs cut alignment - holes x2 engrave
Scan vs cut alignment – holes x2 engrave

Engraving the recess before cutting the hole seems to produce a better result, perhaps because both the engraving and the cutting encounter uniform surfaces.

All in all, this worked out better than I expected.

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