Build a Torque Tester
By R. Kennedy
All photos are on separate page with descriptions of each photo. Each has a link below. I've got a return link to bring you back to this page.
The base is made from a piece of angle iron 1 1/2 x 1/8 x 48 long. I then drilled a set of holes every inch, (picture #3) (1) 1/4 reamed and (1) clearance for a 1/4 allen head bolt. I drilled 18 sets of holes. I then welded the angle iron to a piece of 1square tubing, this will give the whole unit enough rigidity to keep the arm that carries the scale from sagging under its own weight. I then attached a piece of 1 1/2 x 1/8 x 12 at a right angle to the base. This will support the scale. I bolted mine together but you could probably weld the arm to the base easier. However make sure that you maintain the 90* square to the base plus the flatness with the base surface.
I took a piece of 3/4 x 1 1/2 x 3 3/4 aluminum bar and drilled and tapped (1) 1/4-20 hole and reamed (1) .250 hole in the bottom. Before proceeding with this operation make the "V piece first as the "V height is very important with the placement of the .750 bore. I then drilled and bored a .750 hole through the 3/4 section. I then drill & tapped a 1/4-20 hole through to the centerline of the bore. I then took some .750 RD x 3/4 long aluminum bar stock (2) per shaft tip size, and drilled a hole through them. I then cut them in half there-by making (4) half round sections. When I cut them in half I made sure that I cut them so that one half was thicker that the other. I then took the two thickness pieces and milled them flat so that they were .365 thick. ( .750 / 2 = .375 - clamping pressure = .365) This concludes the tip end clamp.
Picture #5 shows the torque arm assembly. Picture #6 shows the torque arm clamp assembly. The assembly is made from (2) piece of aluminum bar stock, (1) piece, main body, 3/4 x 2 x 3 3/4 & (1) piece, clamp, 3/4 x 2 x 1. First I milled a step into the main body, 2 x 3 3/4 piece 1 deep x 2 long. I then drilled and tapped (2) 1/4-20 holes on the step face. I then took the 1 x 2, clamp, and drilled a counterbored (2) clearance holes for a 1/4 allen headed bolt on the same centerline and spacing as the main body. I then clamped the two pieces together and located the exact parting line between the two pieces and the exact center between the two bolt holes and drilled and bored a .625 hole through them. I used a Jig Bore reamer for both this operation and the tip clamp bore. A Jig Bore Reamer is best to use but any reamer will do, I just like them because they cut a perfect hole right to size. I would not however try using them in a drill press. I then took the main body and milled a pocket 1/8 deep x 1.00 wide x 1 1/4 long. This will house the scale arm. I drilled and tapped a 1/4-20 hole on center of both the width and length. This will hold the scale arm in place. I then took the two pieces and milled .015 off both of their faces to give it better clamping force and to better hold smaller sized shafts. I then made a "V to rest the butt end of the shaft. I made it from a piece of 3/4 x 1 1/2 x 2 3/4 aluminum stock. I milled a "V in the top of the bar and drilled and tapped (2) holes in the bottom so that I could attach it to the base. I then located the exact centerline of a .600 butt in the "V and transferred that measurement to the tip clamp for its center line of the .750 bore.
Scale Arm
I made the torque arm from a piece of 1/8 x 1 x 12 aluminum bar. I milled a step in the one end to act as a sight. I drilled a 3/16 hole at 12 from centerline of the butt clamp bore. I then drilled a clearance hole the hold the arm in place.
I took a piece of 1/4 x 3 1/2 x 6 1/2 aluminum plate and painted it black. I then transferred the centerline reading from the "V to the plate, this formed my base line. I then took the plate and squaring the base line on my drafting table measured from the center of the plate out 12 and marked a point on the table. From that point I, using my drafting machine, scribed lines starting a 2* and marked every .5* up to 5.5*, I could of gone further but I don,t get much call for many shafts above that.
Picture #8 shows all the butt clamp/torque arm assembly parts disassembled.