onto the work surface. The intersection of the two laser
lines will accurately show where the center point of the
machine tool will land.
For this to work, one must pay very close attention to
the laser alignments to the spindle axis, and laser
perpendicularity to the X-Y stage.
Since lasers are cheap and simple laser mounts are
straightforward to design and fabricate, a fixed-mount dual
laser design can be very inexpensive and easy to
implement. This became the first method I chose to
Don’t waste your time (as I did!) trying to use super
cheap laser pointers. I bought some inexpensive laser
modules, but found them to be dim and poorly focused.
They end up projecting a
huge (> 2 mm) dim spot
that while good for
teasing your cat, is not
useful for this project.
Instead, I selected a
more expensive focusable
model I found on eBay
from asab.design priced
(at the time) at three for
$12. These modules are
high quality, spec’d to
output 5 mw of optical
power, yet can still be run
from a simple 3-5 VDC
power source. They came
in a three-module set: one
outputting a dot; one a
line; and one a cross.
The line and cross
units featured an extra
lens element (refer back
to Figure 1) to transform
the output from dot to
line/cross. As seen in
These laser modules are internally threaded and feature
an outer ring that is rotated to bring the beam into focus. I
found that these lasers could be well-focused as close as
2. 5 inches or so from the face of the laser. Furthermore,
their ‘depth of field’ (the distance where they remain
reasonably well-focused) seems to be fairly large (several
inches). This means that the laser focus can be a set-and-forget one-time adjustment.
I did notice, however, that the output “wobbled” as the
lens focus adjustment was turned or touched. This seems to
be the result of excessive play in the focus threads. I found
that by adding a wrap of Teflon™plumber’s tape around
the focus adjustment threads served to tighten things up.
Making a Fixed Mount
To get started, I connected a line-style
laser to a battery pack that held a pair of
AAA batteries ( 3 VDC). This got me going
quickly so I could begin to experiment. By
holding the laser up to the side and the
front surface of the spindle housing, I
Figure 3. Focusable 5 mw laser module.
64 SERVO 05/06.2018