Alternative Tracker Bar
Construction
I have a mini-milling machine, which I used for the drilling of the top bar.
This made it easy to keep the holes in line and to adjust the spacing. I
positioned the drill bit by eye at each hole, so I could have achieved about
the same result with the drill press with little additional effort. The photo
below shows the pattern and bars with drilling partially completed.
Even before reading the item Alternative Construction of Tracker Bar by Walt
Lysack on this web site, I had decided on a 3-bar construction, using milled
openings, rather than making them with a scroll saw. I made patterns for
each of the three pieces, using copy-and-paste of pattern elements to assure
that the alignment would be identical. When I moved to the shop, I drilled
and slotted the top and middle bars at the same time. I then drilled the
tube hole pattern in the middle bar, then used it as a pattern when drilling
the base. I used two small nails as locating pins to assure that all three
pieces would align for assembly.
My first attempt was made with wood, but, as I feared, the only varieties
I could find locally split out between holes in the drilling process. I looked
specifically for maple, but would have had to cut down a tree and season
the timber to do that. I could have used the first set of parts with extensive
use of wood filler and files, but I chose to try again.
I resorted to aluminium bar for the top and center sections on my second
attempt. Since the stock on hand was 1/8 and 1/2 inch thick, I made a 9/16
inch thick wooden base bar in order to achieve the height specified in the
plans. I also chose to make the base wider, after checking clearances in
the pressure box, of course.
The thicker base block helps in fitting the air tubes securely. In order
to make it easier to insert the tubes, I made a "tube pusher" by turning
a 3/16 inch diameter stub on a 3/8 inch rod. This was chucked in the drill
press, and then used to "press fit" the tubes into the wood. This is far
less likely to go wrong than pounding them in with a hammer. The photo shows
this little gizzmo.
I'm a "machine owner," not a real machinist, (I tend to feed too heavily
and not to adjust for play until too late) so my results fell short of my
dreams, but with some filing, I achieved acceptable results with the first
attempt with metal. I assembled the complete bar with epoxy in two
stages. First I glued the top to the center section, leaving the base open
to facilitate final cleaning and touch-up with needle files. Then I added
the base block, keeping it base-down to ensure that any excess epoxy was
at the bottom where it could be removed by running drills through the tube-holes.
I am pleased with the result. The photo shows the finished result.
Wallace Venable |
