Perhaps a bit old-fashioned these days, overhead drives were once very common and used to power all manner of lathe accessories from milling heads to spot drills and grinding wheels. My opinion is that there is still a place for the overhead, the system offering a very flexible way of powering a range of attachments. It saves each of these having to have it's own motor, and the single motor itself can be located out of the way rather than sitting on the cross-slide. The drive is also pleasantly quiet compared to some of the screaming high-speed motors I have! All the necessary parts were obtained from scrap machinery, the drive motor was a 1425 rpm 1/4 horse, though a 3000 rpm motor geared down for milling might have been better (grinding requires high speed with the small grind wheels usually employed).
Peering into the odds 'n ends bin one day turned up a pair of self-aligning plummer blocks, the bearings were mounted in substantial castings and had a 1" bores. These seemed suited to supporting the main shaft for the overhead drive, though I didn't want a 1" diameter shaft so sleaves were turned up with a 5/8" bore for a more sensible size. My lathe is bench mounted with not too much room behind for drive frame, and I also tend to keep a lot of lathe accessories on the wall and there were shelves where a vetical drive frame needed to go. A cabinate mounted lathe would be much easier to work with. Anyway, the main supports were made from 3" x 4" planed timber screwed and glued together, and attached directly to the wall at the back of the lathe - no uprights were needed. The bearing blocks were bolted to the arms with the end of the 5/8" mild steel shaft extending some 4" through the right hand support. Onto this protruding end was mounted the drive pulley, the motor being mounted beneath the bench out of the way. The motor to main pulley drive was taken care of using a length of 'bond-a-belt' 0.275" diameter purchased from Hemmingway. This was the first time I'd tried using this stuff but I found it quite easy to get a sound joint. The advice given was to take the exact length and subtract 6% for tensioning, I found this quite tight and used something more like 3-4%. Two matching 2-step pulleys were turned up from alluminium bar with diameters of 2.8" and 2", one for the motor and one for the shaft, this enabled the primary drive to offer two speeds to the primary drive shaft (approx 1000 and 2000 rpm).
A scrap multi-step pulley was bored out to 5/8" and mounted such that it could be moved to best position along the 18" length of the primary drive shaft, this provided further ratios giving a speed range from about 300 to 5000 rpm depending upon which accessory was used. At some point I may make a long key for the drive shaft and let the multi-step pulley 'float', but at the moment it is just held in one position with a setscrew, the flex in belt allows 2-3 inches working range. The picture shows the jockey pulley arrangement and weighted tensioning device which takes up any slack, the drive again being supplied by a length of bond-a-belt. The jockey pulleys have a round groove and were mounted on ball bearings to avoid power loss.
There is little more to be said that cannot be gathered from examination of the photographs, I would hardly expect my own solution to be copied exactly but the idea and overall construction should be quite obvious. All I can say is that I have found the drive convenient in use, it's quick to set up, and it provides a handy power source for any other accessories I may find necessary in the future. If you can find the room I can recommend it - those old-machinists had some good ideas!
(c) Chris Heapy 1996.
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