Making a Motor Pulley Adapter

A local customer recently purchased the K1019 lathe kit and found a nice old 1/4 hp AC motor on craigslist (and for only $25 $15!). The catch?  Well, the shaft was 5/8" and that makes it 1/8" larger than the 1/2" pulley bore.

.625 inch motor shaft and 0.500 inch pulley

So there were two options:  1) Bore out the pulley to 5/8" or  2)  Make an adapter to step down from 5/8" to a 1/2" shaft.  Boring out the pulley would sacrifice the lowest belt setting (since the smallest groove is at less than 5/8" diameter) so we decided to make an adapter instead.

We started out with 1.5" diameter aluminum bar stock and cut off a 2" piece.  Here is the stock mounted in the four jaw and cleaned up with a facing cut and a few turning cuts:

stock mounted in 4 jaw chuck

Next step was to turn down down a shaft to fit the 1/2" pulley.  I turned it to 0.502" with the cutting tool and then used sand paper to ease it down to around 0.501" while testing the pulley fit between sandings.  Here is the shaft after turning:

stock turned from 1.5 in to 0.5 in

And here is the pulley fitting snugly... almost an interference fit:

pulley on shaft


Now the part is flipped and loaded into the 3 jaw chuck for drilling and boring a hole to fit the motor shaft.  First I made a few turning and facing cuts to clean up the outer diameter.  I used a center drill to start the hole and then stepped up in 1/32" or so twist drill bit sizes to get to a 3/8" hole.  Next I used the 1/2" end mill to open the hole to 1/2" before boring to final diameter. 

At this point the hole is large enough to widen precisely with the boring bar.  I bored the hole out to .624" (.001" less than the motor shaft).  The pulley could be slipped onto the motor shaft after warming evenly with a butane torch.  Here is the setup with standard Taig boring bar:
boring operation


That was it for the lathe work.  I could have used the lathe milling attachment to perform the next operations, but it was easier to just use the mill to quickly add flats to both round surfaces and then drill and tap a 3/8-32 hole for a set screw on the motor side.

Finally finished!  You can see the small flat for the pulley set screw and hole with set screw for the motor shaft flat:

completed adapter  adapter and pulley installed on motor