Sandpaper disks fall apart quickly. I've laser cut sanding disks from emery cloth that last longer. I tried using my father's old gasket hole punches but the results weren't as clean and accurate as I got with the laser cutter.

Supplies

I've used different grades of emery cloth. This is what I'm using today. This grade is great on smoothing the edges of plywood

Step 1: Size of Sanding Disk

The outside diameter is between 22 and 25mm. The hole in the centre is 2.4mm. Rotary tools operate at very high RPM. The larger the diameter, the faster the edge speed and there's a greater risk of the disk falling apart.

Step 2: Load Up the Laser Cutter

I am fortunate to have a public makerspace in my city. This is attached to the library and is part of the broader educational program. It's free to use. One only needs to pay for materials. There are 3d printers, an electronics lab, small woodwork shop, CNC router, sewing machines and a lovely big central table were people gather and talk as they work on their projects. Lightburn is a common program used to control the settings on a variety of laser cutters. The onboard camera (sorry not a good clear photo) helps line up the cut on the material.

Step 3: Glue Sanding Disks Together

Time to glue the emery cloth cutouts to make a double sided disk. Clamp it so it doesn't curl

Step 4: Attach to Mandrel and Here Are Some Results

Step 5: Safety Stuff

Rotary tools operate at very high speeds. They are not toys and all safety precautions should be taken. Read the instructions supplied with your rotary tool. Wear appropriate safety equipment.