Thought you guys might be interested to see the power feed I have been working on for my Super 7. It is a sideline project I have been working on for a little while and still needs a fair bit of work but at the moment I finally have something to show for it.
The motor was supplied by bluechip, thanks for him for the kind offer of it. The electronics came from ebay, no pics of them yet as I am trying to think of a good way to house them neatly. For now I am have just been interested in checking everything works ok and I will worry about making it all neat and tidy later on.
This week I finally worked out how I was going to get the power from the motor to the leadscrew, I chose timing belts and pulleys for the job as they would not need the tension of v belts and not slip. The motors max speed is around 700RPM, obviously way to fast for the power feed but to keep maximum torque I wanted to use as fast as possible speed on the motor so I used the smallest possible pulley I could find on the motor and the largest practical size on the leadscrew, that turned out to be a 12 tooth and a 72 tooth. This gives me a step down ratio of 1:6 and means the maximum RPM of the leadscrew would be just over 100RPM. To test if this would be practical I attached my cordless drill to the leadscew, ran it up to around 130RPM and engaged the half nuts, the traversing speed of the carriage looked fine.
Now to attaching the 72 tooth pulley to the leadscrew. While I don't have any issue with modifying parts of the lathe I do prefer to make things reversible if possible or at least keep mods to a minimum. My first idea had been to drill holes around the circumference of the leadscrew handwheel and screw it on, this idea was scrapped because accurately drilling the holes on both parts would have been very difficult and would likely have lead to inbalance. Next idea was to turn the pulley into a new leadscrew handle, this idea was scrapped becuase there was not enough material without extra for the shaft and would involve hand filing slots etc as I don't have a mill so this was also rejected. Then I had a bit of a brainwave, the pulley is a good bit larger than the engraved dial on the leadscrew handle, since I never use this scale for anything, how about sliding the pulley over it. The pulley was chucked up in the lathe and the center roughed out by trepanning, then I carefully bored it out until the handle would almost slide in. the pulley was removed from the lathe and warmed with a blowtorch until it was quite hot and then dropped onto the handle and "persuaded" into place with a hammer. After a quick cool down the pulley had shrunk on nicely and needs no pins or screws to hold it firm. If it ever does get loose I can always add these at a later date however.
Here are some pictures of the setup, the motor is just mounted on a few bits of wood to test everything works ok for the moment, I will be building a tilting table for it soon then the weight of the motor will hold tension on the belt (a spring added it needed) and I can simply lift the motor to relax the belt and slide it off when not needed.
