The other day, I needed to make several plastic pulleys for my heliostat project. These pulleys were made by first cutting a circle out of plastic with a hole saw. The plastic circle is then attached to a power drill and spun while a threaded rod is used to cut a groove in the side of it.
Previously, I have done this just by holding the threaded rod against the spinning plastic with my bare hands; however, it is hard to keep the groove centered when doing it like this. To make it easier to cut the groove, I designed a simple jig in Sketchup and then cut it out with my CNC.
If you want to make your own, here is the CamBam file. PulleyMaker.zip
Also, the Sketchup model is below so you can see how it’s put together.
Notice that I’ve made some changes to the design. This is why the CamBam file and the Sketchup model look slightly different from the pictures.
You may want to double check the CamBam file before you generate the G-code because I never actually cut this one out with my CNC.
Pulley Jig Pictures
Here are some pictures which should help you figure out how this device works. Some of the parts look a little mangled. My jigsaw broke earlier, and I had to cut the tabs off with a circular saw. No matter though, the jig works fine regardless.
In the picture below, you can see a couple of the design changes that I mentioned. Notice that there is a hole at the bottom right corner for a bad idea that didn’t work. Also, you can see at the bottom left corner one of the skateboard bearings that ended up being unneeded after that aforementioned bad idea was discarded. It is left out of the design that I made available for download.
Here is an overhead shot of the pulley making jig. You can only see one end of it, but the threaded rod that cuts the groove is only about 1′ long. This rod is pressed down against the plastic circle by hand with one end braced against the pivot point to cut the groove.
Here is a close up of the pivot point. The nuts are used to keep the threaded rod centered with the plastic circle. They can also be adjusted easily for plastic circles of different thicknesses.
Here is a picture of the hole saw that I used to cut the plastic circles. This one is 3″ in diameter, but you can use other sizes as well.
The grooves in these pulleys are 1/4″ deep, but you can choose whatever depth you want. I used digital calipers to measure the depth periodically as I cut the grooves and stopped when they reached 1/4″.
What I’m using for a bearing is just a simple bolt in the center of the pulley. If you need something better though, you could easily just use a 7/8″ hole saw on both sides to make a hole for a couple of skateboard bearings.