out by hand in tiny steps to avoid the cuttings jamming it
all up. For brass, use a little cutting oil; ABS plastic doesn’t
need it.
The mirrors are held in their holders by tiny spots of
silicone sealant at the corners. Notice that the mirror
holders for lasers blue1 and red1 are a mirror image to the
holders for mirrors blue2 and red2. This way, the supports
and adjusting screws stay out of the way of the laser
beams. The motor brackets have larger holes in the base
than seems necessary for the mounting screws. This gives
some room to move the glass disks a little to get some
different angles. For some disks, changing the angle a little
can improve the patterns generated. Also, there is room in
the holes for the mounting screws to not touch the edges
of the holes.
The motor brackets need to be acoustically insulated
from the mounting board as shown in Figure 15.
Otherwise, the vibrations of the motor go into the
mounting board which acts like a sound board, and the
noise of the motors is too loud. A 1/4” piece of felt goes
under the bracket; another piece of 1/4” felt on top of the
bracket’s foot; and a small piece of 1/16” aluminum over
that creates a cushion for the motor bracket. The felt pads
dampen the vibrations nicely.
The 3” glass disks come from a stained glass supplier.
I recommend going to a store and try shining a laser
through different pieces of glass while moving the laser
very slowly along the glass. Be sure to shield your eyes
from reflections off the back side of the glass, and just
look at the patterns on the wall or floor coming from the
front of the glass.
The best varieties of glass are very lumpy on one
surface and wavy on the other. Different kinds of glass
produce different kinds of patterns, and it’s nice to have
several kinds among the three pieces. Sometimes one
piece of glass looks the best in the store but isn’t as good
as others when put in very slow motion by a motor.
I picked up 2-3 disks each of four different types of
glass, glued them to the spindles, and tried them out. If a
single dot of laser beam makes it through the glass
without being dispersed into a pattern, then that piece of
glass is not lumpy enough.
The spindles are glued to the smoothest side of the
disks with silicone sealant/glue. If you don’t want to cut
the glass yourself, bring it to a glass store with a bunch of
3” paper circles and ask them if they will do it for you.
They can glue the circles onto the glass to help cut them
out. Compared to making stained glass creations, cutting
circles is a piece of cake.
They’ll use a wet diamond glass grinder to smooth the
sharp edges or you can do it with wet carborundum
sandpaper. There is also lumpy glass available for
bathroom windows and shower doors. Some of it is
tempered, thick, and very difficult to cut. A stained glass
dealer will have many more varieties of very useful glass.
My mounting board and outer cover are made of
1/2” thick plywood. The big window for the lasers is
covered on the inside with 1/8” acrylic, with two 1/2”
holes placed out of the laser paths for ventilation. The
acrylic helps make it quieter.
I lined the inside of the box with thick black blanket
fleece to absorb the light and sound, and make the
motors quieter. Another hole in the wood allows me to
plug in my PIC programmer while the cover is on. There
are also some ventilation holes in the mounting board.
After operating my machine at room temperature for
an hour, the electronics inside feel barely warm enough to
detect with my fingers. There are aluminum guide posts at
three of the corners of the board, so I’m less likely to
bump something out of alignment when placing or
removing the cover. They aren’t necessary if you’re very
careful, but I took the cover on and off a lot of times
during development and it sure was handy.
Programming
The flowchart in Figure 16 outlines the music
program. I programmed it with PICbasic Pro, and a little
bit of assembly language. I like the ease of use of the
PICbasic language, and the low cost of the chips. This
microcontroller is very fast, and can give a PWM display
that is fast enough to not give an appearance of “flicker.” I
48 May/June 2018
■ FIGURE 15. Motor mount, with felt sound-dampening
spacers.
