Cut First, or Etch First?

Cut_or_etch

Yesterday, I tried an experiment.

In the process of lasering the board, there are two operations,
cutting and etching. Cutting uses vector input and blasts the laser
all the way through the wood. Etching uses raster input and cuts at
various depths into the wood, with the head passing back and forth
across the entire piece.

Usually, I do the cutting first and then the etching. I decided to
try the other way around because the raised outlines of the pips were
slightly imperfect circles. The raised outline is formed between the
cut perimeter and the dark etched “band” of the pip. My theory is that
after the cut, the pips drop onto the cutting surface, and shift by a
tiny amount, either during the drop, or from subsequent vibrations.

Doing the etching first seems to have made the circles more perfect
(the band is etched first, and then the circle is cut, so no shifting
is possible). There was an added bonus of less stain on the wood
(though other factors could have been at play there), but there was a
downside as well. The photo above shows detail from two different
wheat tiles. The left was cut a couple weeks ago using the cut-first
method, and the right was cut yesterday using etch-first. As you can
see the projections from the wheat kernels have been “chewed up”. It
only happens to 2 of the 6 spikelets on the tile (as for why, I’ll
leave that for you to puzzle out – maybe it will be the subject of
another blog post).

I suspect this result is due to the warp of the board (usually boards
have a warp of a couple mm difference between the edge and the
middle). When I focus the laser, I focus it only on one section of
the board, usually near the edge. When it is etching tiles near the
middle, it is ever-so-slightly out of focus. This doesn’t happen with
the cut-first method because all the pieces have dropped and are on
the same level. Usually a small mis-focus wouldn’t be noticeable, but
my design is very tight and broadening the beam even by 0.1mm chews
the edges of my wheat.

I may have to get more sophisticated in the ordering of my cutting and
etching, splitting them up and interleaving them. Another option,
though expensive, would be to cut the tiles separately from the frame.

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