Zero Clearance Table Saw Inserts

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Buy 'em, or make your own? June 28, 2005

Do any of you make your own zero clearance table saw inserts out of MDF? If so, what is the best way, and can you see a big difference in cut quality over factory-provided inserts?

Forum Responses
(Cabinetmaking Forum)
From contributor J:
I buy the blanks from the box stores, like Home Depot or Lowes. I made one for blades and dadoes. Yes, the difference is major if you're working with veneered plywood.

From contributor F:
They make a difference. Your blade still needs to correct for what you are cutting and it still needs to be sharp. Also, you need to keep your material pressed down in the area of the throat plate as you cut, because the purpose of zero clearance is to support the material on both sides of the saw kerf so it doesn't splinter.

I don't think a cabinetmaker should have to buy throat plates any more than he or she should have to buy a push stick. Making these types of things is just part of being a cabinetmaker.

I do make them from MDF because it is inexpensive and I can plane it to thickness in my planer without dulling the knives (like with particleboard or plywood). I use a saw factory throat plate to make a rough pattern, which I then refine so it fits fairly tight. I save that first one for a flush trimming pattern.

For most saws, you can find a width dimension that fits well and then rip a bunch of MDF strips to that size. Then crosscut them a little longer than net size and use the master pattern to trace the shape on the ends (usually round).

I like to bandsaw first, leaving a little MDF on the waste side of the line before I flush trim them while they are screwed to the master pattern. MDF comes in a lot of thicknesses and I use one that can be planed so it is exactly flush with the saw table top - that is important. If you don't have a planer, you can make them thinner than the depth of your insert hole and then use screws underneath as levelers. The saw kerf in them gets larger over time, so I only use a fresh one when I am cutting something that needs a perfect cut on the bottom. For general sawing I use one of my worn out ones. I have ones for dadoing and also common angles like 45 degrees and 22.5 degrees. I made them of hardwood for years, until I discovered MDF. It's just easier to shape and costs less. The hardwood ones did hold a tight slot longer, though, and they are stiffer. If I am doing a routine that requires a super stiff throat plate, I glue a 1.5" cleat to the underside of the MDF throat plate. I flip mine end for end and side for side as they wear out. That gives me 4 fresh kerfs per plate. Make them fairly tight and they will stay "zero" longer.

From contributor A:
As far as I know, MDF is about as abrasive a material as we all use. It dulls carbide real fast... so I can't imagine what it's doing to your HSS planer knives.

From contributor B:
When mine are real used, I put tape over the slot on the face side and apply Bondo to the back. When hard, remove the tape, sand a little, and it's all new again. It's easier than remaking all the time. I use a pin router to copy the original by screwing it to a piece of MDF.

From contributor F:
Contributor A, maybe your suppliers are selling you particleboard and telling you it's MDF. MDF is easier on tools than solid wood. I ran a CNC router at one time and used a single flute carbide straight bit. When you cut parts from 30 or so sheets of material per day it becomes really clear which ones dull tooling the fastest.

In this order:
2-particle board
3-solid wood

If you know how to sharpen a chisel, take a sharp one to a piece of MDF. Now try a piece of oak.

From contributor R:
I've made mine out of MDF with a piece of laminate glued on top. If you make up 6 or so at a time, you'd be surprised how little time is spent on each one. After the glue dries for the laminate, I rough cut to size. Double face tape your existing plate to the MDF one and use it as a guide for your router with a guided bushing cutter. Set up your router table to get a slot under the plate for your saw blade to go into. Drill the end and side to accommodate a 6-32 flat head screw. No need to tap - the screw will cut its own threads. Do the same from the top for your leveling screws. You also have to countersink all of these holes, as the screw will need this clearance. I then use my saber saw to cut a slot for the splitter.