Recent posts of line shaft clutches have captured my attention and I guess I won't be able to ignore the urge to make one so here is my tentative plan. The basic concept here is the same as the other ones that have been shown, in that a sliding actuator forces a shoe into contact with the inner surface of a drum. The outer surface of the drum can be driven by a round. flat. or vee belt or it could be a gear.
I would like to make it as small as possible so the shaft diameter is 1/4" and the inner surface of the drum is 1". The OD can be anything larger than 1.25 inch. To make it a little bit different, I have designed it as a double clutch which could be set up as a forward/reverse system or one that selects 1 of 2 inputs or outputs. At this point, I have not designed any input or output or control mechanism, just the two clutches.
I will probably make it out of cast iron but may use some mild steel. The 1/4" shaft is steel. The only items that are fixed to the shaft are the two clutch bodies (green) which are attached with set screws and the two collars (yellow). The two drums (blue, only one shown) are free to turn on the shaft. Each clutch body has two semi-circular shoes (dark gray). Between the two clutch bodies is a sliding actuator (light gray). There are two lugs extending from the face that slide in slots in the clutch bodies, and with a sloped face on the surface of the lug, forces the clutch shoes outward to contact the drum. The distance between the two clutch bodies is set up so that only one set of shoes is raise at any time and there is a point between where neither set is activated.
I don't think that it is possible to accurately make the clutch shoes and the slope of the lugs so that contact will be even without some adjustment so each shoe has a small hex drive set screw (4-40tpi) that will be the actual contact point between the lugs and the shoes to allow adjustment for engagement and wear.
I have been giving this a lot of thought since a little back pain has kept me out of the shop for most of the past week. Take a look, please, and lt me know if you see any gotchas or goofs. I hope to get back in the shop this week to play with this.
Jerry