Many of the parts of my belt grinder are rounded over with a radius that is concentric with a hole. For example, all of the hinge parts are like this. When I built the grinder, I used my angle grinder to make these parts by hand, but I really wanted to be able to make better-looking rounded corners in the future. So I designed and built a jig that uses the belt grinder to radius corners. The jig consists of a table with an interchangeable pin that the part can rotate on, and a mechanism that lets me advance the workpiece into the belt. Watch the video below to see how I built it and how it works:

Plans

I do not recommend building this. I have stopped using mine. It works ok for parts like those shown in the video, but parts with larger radiuses chatter because they’re not properly supported. I’ve had a few scary incidents that have led me to believe this attachment is not safe, including one incident where a chattering workpiece climbed its way off of the pin (yeah, I don’t understand how that happens either). When using it in horizontal mode, there’s a risk of the part spinning and cutting your hand or pulling your hand into the belt. Since the attachment can’t be adjusted left/right or up/down, it also quickly wears out of the center of the belt.

To get the same functionality without the downsides, try simply using a block of wood with a hole that matches the hole in the workpiece, and pivot the workpiece around a simple cylindrical pin stuck into the block (you can just use the drill bit that you drilled the hole with, although there is some risk of breakage). Put the hole as far back from the edge of the block as your desired radius will allow, so the workpiece is fully supported. Then simply clamp the block to your fixed table, and advance it toward the belt by tapping it with a mallet. It’s not as flashy and cool as the jig in this video, but it works better.

I’m hoping to release plans for an improved version of the radius jig in the future. It will likely be part of the surface grinding attachment, which I hope to unveil by the end of 2024.

If you’d like to build the jig anyway, you can download a free Sketchup model for it below. There are no pdf plans for it, since I’m not willing to sign off on the design.

Sketchup model: Belt grinder radius jig.zip

Note: The .zip file above contains a Sketchup (.skp) file, so you will need to un-zip and extract the .skp file before opening it. You will need the latest version of Sketchup in order to view this model.