The machine is built of pine, maple and plywood. It has a footprint of about 18 X 30. Pine is used for the box frame. Ply is used for the structural parts. Where extra strength or machineability is needed maple was used. It uses a lot of ball bearings because I could get them so cheaply at American Science and Surplus.
It uses a surplus 1/2 h.p. 600 RPM motor from A.S.&S. ( American Science & Surplus). I have more power than I need. The first stage of speed reduction is sprocket and chain left over from my first under powered attempt at the machine. The rest of the reduction is 3/8 belt drive with pulleys from A.S.&S. and Berry Bearing. I was lucky that one belt was just the right length. The other belt required a tensioner made up of a roller on an arm and a bungee cord to provide the pressure. The cooling fan is a 6 axial flow muffin fan. I have plenty of cooling, although the motor runs warmer when polishing than grinding. My final reduction gives me about 31 RPM and 8 strokes per minute.
The overarm is made of 3/4 ply with 3/4 maple added for strength and as a bearing surface for the drive pin. It is hinged to the arm drive plate with 2 10 hinges. These hinges have plastic bushings and have almost no play. A stop was fabricated and installed under one of the overarm hinges to prevent any possibility of the drive pin hitting the mirror. The drive pin is made of a 1/2 bolt and a 7/8 or so steel ball. It is adjustable vertically. The overarm hinges are attached to a 3/4 ply drive plate that uses maple for reinforcement and as an arm to attach the drive hinge. It also has upper and lower maple bearing blocks attached for the assembly to pivot on. A piece of steel shaft is used as an axle. I used wood boring bits to make holes for the bearings. They give a reasonably flat bottomed hole to absorb thrust loads.
The table is several layers of ply to a total thickness of 1 1/2. It has an aluminum bushing installed at the center and 2 maple blocks that engage the drive arm. The top has a pizza pan as a drip pan, and 3 cleats to retain the work and drip pan. The table rides on 3 urethane wheels (A.S.&S.) set on shafts in maple blocks. The mirror, tile tool and pitch tool all rest on 1 ply disks with aluminum bushings in the center. Each can be used in either top or bottom position. The mirror has a 1/4 dense foam rubber pad between it and the ply disk, and is attached with duct tape.
At present I cannot change RPM or stroke rate with out major rework. I can adjust the stroke length from 0 to 12 inches and adjust the stroke centering. The arm drive is a modified pulley that acts as a crank, a pushrod with spherical rod ends, an adjustable belcrank, a turnbuckle, and a hinge attached to the arm drive plate. The adjustable belcrank rides in bronze bushings. The adjustment bolt has its end machined down for a close fit in the hole. A square nut has 2 tabs brazed to it. A carriage bolt had its head ground to a square and then was drilled to fit the nut assembly. I wedge a couple of washers under it and that takes out all play. The carriage bolt screws into one end of the turnbuckle. The other end attaches to a hinge bolted to the arm drive plate. The belcrank adjusts the total throw and the turnbuckle adjust centering.
My design did require the use of a lathe, but careful selection of shafts,
bearings and pulleys might eliminate the need. I also used a welding torch
for brazing. Braising is rather a no-brainer compared to welding. You do
it like soldering, but at a much higher temperature. Most wood joints were
made with carpenter's glue and screws. When viewed from the table end,
looking across toward the arm assembly the table rotates counter clockwise,
and the arm is set to swing to the left. Both motors are grounded. As the
works of this machine are exposed considerable care must be exercised
to prevent injury. You need to be very careful if there are children around.
My E-Mail address is klilja@atl.mediaone.net
My machine underway and me watching it work
Last modified 10/20/99
