How to Make a Zero Clearance Insert (ZCI) for a Table Saw
When I unveiled my amazing dust collection system a couple of months ago, I remembered Jeff speculating that a zero clearance insert (ZCI) on the table saw may further reduce the amount of dust that escapes, and I squirreled that idea away in the back of my head. Soon after building the custom spice rack for Jocie, Fred and Kim put in a request for me to build another one, and I decided it was time to buy a dado stack. What does all this have in common? I needed some new table saw inserts.
If you look around online, you’ll spend at least $20 on each blank insert. Instead, I chose to build my own inserts, and I started with a zero clearance insert. The key for any insert is to support the workpiece which reduces tear out and splintering. On a ZCI, you have the added benefit that smaller pieces can’t fall through.
Step 1: Remove the OEM Throat Plate
I have a Steel City table saw, and the throat plate is held in place with four powerful magnets.
Step 2: Trace Outline
I traced the outline of my throat plate onto spare 1/2″ plywood I had in the shop. If your throat plate is similar to mine (and I bet it is), the plywood will be just thinner than the original throat plate, and that’s a good thing.
I’m making multiple inserts to accommodate different blades and dado stacks even though I only plan on finishing one today.
I used my table saw and miter saw to cut the inserts roughly to size.
Step 3: Route with Bearing Bit
I was really confused the first time I saw a router bit with a bearing on the end, and I remember trying to take the bearing off. Eventually I learned that these bits are used to follow a template or pattern, and they are really useful for making table saw inserts.
By lining up the bearing with the OEM plate, I cut a perfect match in no time.
Step 4: Position Leveling Screws
I used a rubber mallet to make some indentations where the leveling screws were located.
Step 5: Begin Kerf Cut
Many table saws (mine included) can’t lower the blade far enough to fully seat the ZCI. To start the kerf cut, I replaced the OEM throat plate and clamped my blank overtop. I started the saw and slowly raised the blade.
Step 6: Continue Kerf Cut
After the cut was started, it was easy to set the ZCI in place and continue raising the table saw blade, using a piece of scrap to prevent it from coming out.
Many ZCI’s don’t provide anything in the way of splitter, riving knife or attachment for the blade guard. I decided to extend the kerf cut enough that my riving knife would fit too, and that enables me to use the blade guard as well.
Step 7: Adjust Fit
Originally, I didn’t think this step would be necessary. However, with a zero clearance insert, there’s no extra space, and I didn’t want the insert to move at all. Even on the OEM plate there is a very slight gap so to make my ZCI even more snug, I drove a few roofing nails into the edge. The same results can be achieved more elegantly with a set screw, but I found this to work just as well.
Step 8: Leveling Screws
This is another step that set screws would have come in handy. Again, I opted for my roofing nails to provide contact for the magnets and raise the insert flush with the table. I cut the nails to length with Linemen’s pliers and pre-drilled the holes.
My ZCI was a hair too high on one corner so I sanded that area until it was flush.
Step 9: Drill Pull Hole
Needless to say, it’s almost impossible to remove this insert without a small hole to grab it. The last thing I did was drill a pinky-sized hole off to the side.
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