to the spindle center line is also
required. At first, this would seem
simple as the laser module itself
has a tubular case and everything
sort of looks like it will be
However, the centering and
perpendicularity of the laser diode
within its case may not be well
controlled. Thus, the challenge
begins. While this issue seems
solvable, some imagination and
tinkering will be needed to achieve
successful alignment. For myself, I
opted not to “reinvent this wheel.”
Another centering idea I found
was well demonstrated in a You Tube video called “Making
Prototypes” by Dan Gelbart. Part 15 of his series
showed (among other things) how milling machine workpiece center finding can be achieved using a rotating laser
device. This is different from the spindle laser method
previously described in that here, the laser is mounted at a
slight angle from vertical and offset from the axis of the
spindle. Also, with this approach, the spindle is turning
while using this laser centering device!
The rotating spindle laser center finder is depicted in
Figure 2. As shown, this rotating laser device actually
traces a circle onto the surface of the workpiece. By
changing the height of the Z axis, the diameter of the laser
circle grows larger or smaller. At exactly one Z axis height,
the laser beam converges to a single point marking the
exact center of the machine tool bit.
In his video, Dan showed how easy it is to use a device
like this to center the machine on any fixed spot or circular
work piece feature. He also showed how this approach can
be used to easily find the precise center of any rectilinear
feature of the work piece. These are very handy attributes
that are only possible with this rotating laser scheme.
Nigel Taylor is another individual who has reduced this
to practice and produced a video of his accomplishments
This scheme seemed way cool to me and gave me the
itch to give it a try.
Rotating Center Finder Device
Since I couldn’t find any “fabrication-ready” part
documentation, I proceeded to lay out and model my own
version using my SOLIDWORKS CAD program. Since I used
SOLIDWORKS professionally, I was able to leverage this tool
to develop this device.
For other designers, there are many low cost/zero cost
2D and 3D software packages you might consider.
However, this project is simple enough that a calculator and
the back of an envelope can suffice.
Figure 3 shows the device geometry. The formulas that
define the sides and angles within a right triangle are used
to define relationships and calculate the key values.
To provide mechanical clearance between the laser
body and the spindle body, the laser offset radius, “X,”
needs to be at least the mill Spindle _Radius +
Laser_Body_Radius. Since the diameter of my spindle is
38 mm (~1.5 in), its radius is about . 75 inches. The
diameter of the laser body is about . 5 in, making its
radius about . 25 in. Therefore, I set X to be 1.0 in.
By Edward W. Andrews
SERVO 07/08.2018 37
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Figure 1. Spindle
mounted laser scheme.
Figure 2. Basic
geometry of a