Not that long ago I went to great lengths to make zero clearance inserts for my table saw. I had fancy (expensive) phenolic resin plywood, set screws with brass threaded inserts, and anything else you could want. While working on my baby bookcase, I noticed the old store bought insert was getting wallowed out and needed replacing. “No worries” I thought, I made my own inserts. After messing around with the level of it, I realized there was a problem. It wasn’t flat.
It had a pretty strong cup in the center. I don’t know if it started like this or gradually shifted since I first made them, but I can’t use it with that much of a gap (red arrow shows flashlight shining through). I needed something, so I nailed down a flat piece of 3/4″ plywood to the back where the motor wouldn’t hit it. That reduced the cup, but it still wasn’t perfect.
That was a band-aide let me get past the worst part of the problem and on to other projects. I needed a better solution though. The plywood inserts I made weren’t flat, and they wore out quickly. They plywood is just not going to stand up to any blade wobble. Gaps create tear out. I thought about buying more of the professional inserts. They are very well made (100% phenolic), but also kind of expensive.
Instead I thought about taking some of the 1/4″ material I bought for making miter saw inserts, and adapting that. After trying fancy plywood, 3d prints and pure phenolic, the phenolic wins hands down. My miter saw insert is still going strong 6 months later after lots of use. The printed ones were shot after a month or two.
Speaking of 3D printing, I printed a template to go onto the professional insert and guide my router to make a pocket just deep enough for the 1/4″ sheets. It sticks on and lets me use a router bit and bushing to make an exact cutout.
With a recess pocket milled out, (I forgot the picture) I was able to use another printed template to cut out the insert. It uses a template cutting bit that follows the printed part with a bearing and cuts away the extra phenolic below.
The holes in the brown printed plastic let me use a transfer punch to set the spacing for a few countersunk holes for 4-40 screws to bolt my insert to the store bought plate.
I again used a transfer punch to transfer the holes from the white insert into the larger store bought throat plate. Transferring holes like that means it will always fit and line up.
The only thing left to do was try it out. I sat the plate on top with everything adjusted in, moved the fence over to keep it from skipping out, and slowly raised the blade. I just so happened to buy a brand new blade at this time, so witness the birth of a new blade! A 20 dollar sheet of the white phenolic material can make a few dozen inserts, so I should be set for life with this system assuming the larger insert never gets seriously damaged.