Upsize A Pulley Workshop Projects

Pulleys are expensive these days. Especially large pulleys, so it’s handy when you can make one to the size that you need. In this article I go through how I turned a 7″ pulley into a 12″ pulley.

There are a few challenges to overcome when making a pulley: Making it round enough and balanced enough is relatively easy. Cutting the groove for the belt in the edge can easily be done either on a lathe or on the table saw, as I did in this instance. The biggest problem is how to reliably mount it on the shaft that it will be driving. It can be done, but it’s more difficult to do with wood than metal.
So instead of making a complete pulley, I decided to resize one that I already had that fits on the shaft. It’s a 7″ pulley for a 3/4″ shaft:

the metal pulley is measured

I cut a piece of 3/4″ Baltic birch plywood to make the outside of the pulley with and used my compact compass to draw the 7″ diameter circle. I then cut that out with my jigsaw and smoothed the cut on my spindle sander:

drawing the circle to cut out
the jigsaw cut

The pulley fit snuggly inside the cutout. To fasten it solidly to the ring, I cut a piece of v-belt just long enough to fit into the groove of the pulley and glued that in with polyurethane construction adhesive. This fills up the groove in the metal pulley:

fitting the metal pulley
gluing in a piece of belt

I then glued that into the plywood ring and left it to dry overnight. The next day, I set up a quick and dirty circle jig by using a 13mm socket that fit fairly well in the shaft hole in the pulley:

the metal pulley glued in
a quick and dirty circle jig

I screwed through the socket into a scrap of melamine and clamped that in place on my band saw to cut the circle. I then made that perfect using the same jig on the disk sander:

cutting the circle on the band saw
rounding the pulley on the disk sander

To cut the v-groove in the edge, I tilted the saw blade to match the belt. This turned out to be 15 degrees:

setting the saw blade angle

The scrap of melamine is used again as a guide to run the pulley on edge above the blade. The blade is raised by a small amount after each pass until the belt fits:

cutting the v-groove
truing the belt fit

Ready to go:

the v-groove up close
the completed pulley

I did have some concerns that the glue may let go at some point (not likely, but anything can happen), so I added some panhead screws on both sides as insurance:

pulley with screws added

These lip over the edge of the metal pulley and are evenly spaced so they don’t upset the balance of the pulley.