are so responsive to the music that changing the motor
speed and direction is not really needed.
Although it may work without speed control to some
extent, I found that being able to set the motor to the best
speed is important. Different types of glass will look better
at one speed than at others, so it was useful to be able to
set the speed for each glass wheel.
The speed that is important is really the number of
inches per minute that the glass is going by the laser. This
is a function of the speed of the motor, but also the
distance from the center of the disk (radius) that the laser
beam hits. This may be found by the formula:
(Glass Speed) = radius 2 (PWM) (motor speed)
Here, PWM is the fractional “on” time of the PWM
duty cycle. My motors are 1 RPM, so for my Motor 3:
(Glass Speed) = 1.125” 2 3. 14 (200/255) 1 = 5. 5
inches/minute
I’m using glass speeds of 2. 9, 1.8, and 5. 5 inches per
minute for motors 1, 2, and 3, respectively. Adjusting the
speed of the glass is very helpful to get the best out of
each piece of glass. Adjusting the motor speed is the
easiest way of doing this, since you just need to change
one number in the code. Adjusting the position of the
motors/disks will work to some extent.
To make the design for the front panel, I drew it first
with my computer using TurboCAD for Windows. I
printed it on photo paper, and then laminated it with 3 mil
plastic. I used Grafix double tack archival film to stick the
design to the aluminum panel. The Grafix film was also
useful to make laser warning labels to stick on the outside
of the box. This was inspired by a great Instructables
article, called “Make Your Own Front Panels.”
My front panel design is available with the downloads
for this article. The circuit board is mounted on 3/16”
spacers off the mounting board, and then the shaft of the
hex switch lines up with the hole in the front panel.
Mechanical Things
I printed brackets for the motors, spindles for the glass
disks, the laser brackets, and the laser mirror brackets with
a 3D printer using ABS plastic. The laser and mirror
holders can be seen up close in Figure 14.
If I didn’t have the printer, I would have made them
out of 0.050 inch thick sheet brass, which is easy to cut,
file, bend, drill, tap threads, and solder, and could be
made to do the same thing.
I created the plastic parts with Autodesk Fusion 360,
which is an excellent free program. The references for files
for designing and making these parts can be found in the
Resources sidebar. The .stl files that you can put directly
into slicer software (such as Cura) are also available with
the article downloads.
Each laser and mirror is adjusted with three 6-32 Allen
cap screws, and springs hold the tension on the pieces.
The lasers and mirrors can then be adjusted in two
directions. I recommend a ball-end Allen wrench, which
can engage the socket on the cap screws from a wide
angle of directions and helps you get in there to make any
adjustments.
Where the adjustment screws go through the
moveable laser holders and mirror holders, it’s possible for
the plastic to bind on a screw thread where the spring will
not overcome this. I put a #26 (0.147”) drill into those
holes. While spinning the drill, I moved the electric drill’s
body in a circular manner to widen the holes at the outer
edges. When adjusting these to aim mirrors or lasers, the
adjustments will be most reliable if done while tightening
the screws.
If the screw is tightened past the best point, it is
backed up and done again until the best point is reached
while tightening. This will keep the moving part from
catching on a thread and then loosening later when the
whole thing is jarred. My first adjusters used springs that
were a little thin, and jarring the machine could knock the
lasers out of alignment. The lasers are each held in their
holders by two 6-32 Allen setscrews. The glass disk
mounting spindles are held to the motor shaft by 6-32
setscrews. There are holes in the brackets and spindles
that need to be drilled out and threaded for the 6-32
screws. I use a #36 drill (0.106”), and a “gun tap.”
A gun tap is for through-holes, has two flutes, and
pushes the cuttings out the far end of the hole. You can
chuck it in your electric drill, and motor the tap into and
back out of the hole in short order. Other taps will load
up with the cuttings and must be slowly cranked in and
May/June 2018 47
■ FIGURE 14. Close-up of laser and mirror mountings.
