FIGURE 4
mounting holes should be included
in the pattern so that they can be
added to the part after it is routed.
Extra countersunk holes were
added so that the pattern could be
securely fixed in place. The patterns
for two of my parts can be seen in
Figure 2.
The routing bit (Figure 3) has a
1/2” diameter ball bearing just
above the cutting blade. This
bearing will contact and follow the
pattern and as the blade is also 1/2”
in diameter, the part will be a copy
of the pattern.
WARNING: Router cutters
are very sharp and must only be
handled using thick leather gloves
or you will get severe cuts (learn
from my mistakes!). Safety glasses
must also be worn.
The router bit has a 1” long
cutting depth, so it is necessary
to build a jig that will allow the
blade to cut the thin 0.2” UHMW
(Ultra High Molecular Weight)
without always having to cut 0.8”
of supporting material each
time. I made the jig (Figure 4) by
gluing four 24” squares of 1/2”
FIGURE 5
plywood together. The squares
were cut to size for free by the
local DIY store and secured
together using Liquid Nails®
adhesive. To make sure they were
pressed together firmly while the
glue set, I parked one of the
wheels of my car in the center of
the square!
I then screwed the patterns
onto the jig and (with the router
depth set so the bearing would
run on the pattern) then routed
out a clear channel around the
pattern and removed all the
material within the openings. The
router I used was a cheap 1-3/4
HP model from Harbor Freight. It
does the job, but the collet used
to secure the cutting bit was poor
quality and took some packing
with thin paper to get it to grip
the cutter adequately. I would
buy a better quality machine next
time.
The UHMW comes in quite
large sheets so in order to make the
parts easier to handle, I outlined
some oversize blanks (Figure 5)
and cut them out with a jigsaw.
FIGURE 6
These were then sandwiched
between the pattern and the jig,
and then secured in place with
woodscrews (Figure 6). I set the
router bit height again so that the
bearing would contact the edge of
the pattern; the perimeter of the
parts were then routed (Figure 7).
The router makes quick work of
this, but be sure to maintain a firm
grip on it and keep it level
throughout the cuts.
The interior openings are
done in the same way, but first
you drill through the center of the
area with the end of the router bit.
This completes the router work
and the remaining small holes
can be added using appropriately-sized drill bits and the pattern as
a guide.
With a little practice and care,
high quality parts can be produced
very quickly. I made three complete
sets of parts is about an hour
(Figure 8).
FIGURE 7
FIGURE 8
My next
beetleweight design
requires two sides
which are near identical.
Using the above
method, all that I need
to do is create one
pattern and then I can
produce both sides and
as many spares as I
want from that pattern,
reducing both the time
and cost of building and
repairing my bot. SV
30 SERVO 03.2010
