There are many commercially available sanding blocks for different purposes out there. Simple blocks of rubber, fancy injected molded plastic with cam action holding points, premade sections of foam that have sanding grit applied. Sometimes though you need a simple flat sanding block with no give to flatten or level out a surface. You can use this to wet sand a project with wet/dry sandpaper, or use it almost like a rabbet/shoulder plane to clean up tenons/shoulders/inside corners, or to simply break an edge on a sharp outside corner consistently..
This short instructable makes use of a woodworking shops tools so it isn't for everyone. I used a table saw and powered miter saw to cut my block to length and width, and the use of a router and slot cutting bit to create a 1/16" slot along the short edge of the piece of plywood. If you are handy with manual tools you can create something similar. The thin kerf allows the sand paper to hold itself to itself and provides a solid surface to hold, move, and apply even pressure to sand a section.
So let's get started.
Step 1: Cut to Length and Width a 3/4" Piece of Plywood
I had some walnut ply scrap ( fancy sanding block ) lying around the shop to make this one.
"Before we use any power tools, let's take a moment to talk about shop safety. Be sure to read, understand, and follow all the safety rules that come with your power tools. Knowing how to use your power tools properly will greatly reduce the risk of personal injury. And remember this: there is no more important safety rule than to wear these — safety glasses."
Might want to add hearing and dust mask to that list as wood fibers are known carcinogens. Also not the use of a push stick while using the table saw.
On a table saw rip a section to 3 1/4" and then bring to the miter saw to cut to 11" length.
If you only have a miter saw, you can cut a 3 1/4" section off of a wide board and then cut to 11"
If you only have a hand saw, mark carefully and try to give yourself nice 90" angles.
Step 2: Install Router Bit and Setup Depth
Take the slot cutter set and pick out the 1/16" cutter and install into your router. Adjust the depth so the cutter lines up to the middle of the 3/4" edge of plywood, this isn't critical so don't split hairs getting it right, just ball park it.
You'll want to securely clamp the plywood in a vice or clamp it to a sturdy table while you route the slot out of one side. You'll end up with a 1/2" groove along the length on the short grained section of wood as shown.
Step 3: Sand Paper Origami
Now you'll lay the piece of sandpaper into the slot as shown. Make a slight crease to mark where the crease will lay. remove the sand paper and really give it a good fold over like when you used to make paper airplanes. put it back in the groove and repeat for each corner working your way around the block. crease, fold, crease, fold. Now it is important to keep tension on the sand paper so you get accurate tight creases as you go around, this helps keep the sandpaper from moving about and bunching up while using it.
When you get all the way around to the slot, run your fingernail in the groove over the paper to mark the crease. Once that final crease is in place it can be difficult to reinsert the block, to ease that , hold the section of sandpaper that goes into the slot and rest the block in at an angle and start feeding the rest of the block in.
That's it! now you have a handheld block that you can fit with various grits of sandpaper, the process is easy, so if you wanted to, you could fashion a block for each grit you use to have on hand. Other variations of this process can make smaller blocks to fit a 1/2 sheet for smaller spaces, you could cut a 45* miter on one edge so you can get into tight spaces and work right up to a corner, or if you know you have a specific angle to match, make a mating bevel on the long side of the plywood.
Sometimes it's the simple things in a shop that help make the process of creating a joy.