Construction of A Powered Eight-Rat Treadmill
Keith G. Benedict
Managed to accomplish a number of small tasks this week... unfortunately I didn't get pictures of all of it. The first item to be dealt with was the beveling of the corners on the clevises. I laid out the cut lines using layout dye and a square, then clamped the pieces in the vise and milled the top and both corners off to the lines.
I wanted to finish the side frames, so the next thing to do was to mill the slots for the bearing bolts and roller shaft clearance on the two moveable bearing mounts. These pieces were cut the same way as the fixed bearing mounts. No pictures of this, so look on last week's page if you want to see what I'm referring to. The finished pieces are also shown in the last photogragh on this page, a mockup of the side frame assembly.
The conveyor roller tensioner mechanism is designed to use a coil compression spring as the source of the tensioning force. The tension force is adjustable by means of a screw and nut mechanism. The screw shaft will also act as a guide and will fit within the compression spring. This arrangement can be seen in the last three pictures on this page.
I purchased the springs from MSC Industrial Supply Co. and the 5/8" fine pitch all-thread rod and matching nuts from a local vendor. I needed to make some pieces that would hold the threaded rod and could be fastened to the end of the movable bearing mounts.
The pieces were made from 1-1/2" x 1-1/2" solid square cold-rolled steel stock and were cut to be a little over 2" long. The pieces were clamped in the vise and milled off on either end to be 2" long.
The pieces were then drilled and reamed to 0.500" diameter. The end of a piece of all-thread rod will be turned down to fit into this hole.
The pieces were then turned 90° in the vise and were milled down. This created a piece that resembled an "L" in cross-section.
The pieces were turned over and two holes were drilled and countersinked in one side. These holes are for the socket head cap screws that will anchor the pieces to the moveable bearing mounts.
The photos below show the tensioner assembly. The cover plates that fit over the moveable bearing mounts are not shown. A small piece of angle steel with a hole in it will be welded to the frame and is used to support the end of the all-thread rod used as a tension element/spring guide. The nuts on the rod can be adjusted to compress the spring and increase the amount of tension exerted against the conveyor belt. The moveable bearing mounts will be able to slide slightly to take up the slack in the belt and compensate for any eccentricities in the conveyor rollers.
I'm hoping that I can finish up the side plates and motor mount, and make more headway with the roll-around stand next week.