The table saw inserts that come with most table saws are less than ideal. The blade opening is too wide, providing no support under the wood near the cut. This of course invites tearout and splintering, especially when crosscutting.
Another common problem is those small cut-offs can find their way into that wide opening in the throat plate and may be thrown back at you if they get caught by the blade's teeth. Or they could wedge themselves between the blade and opening.
An easy way to avoid these issues is with a zero clearance insert. These inserts have a slot only as wide as the blade, so there is no gap between the blade and the insert. This arrangement provides support directly under the workpiece where the blade exits, eliminating tearout. And with such a narrow slot, cut-offs can't get between the blade and zero clearance table saw insert.
Store bought table saw inserts are expensive, but you can make your own for just pennies. Here's how I make mine.
Just about any hard, flat and machinable material can be used to make a zero clearance table saw insert. I've used plywood, mdf, hardwood, plastics and laminate flooring to name a few.
Making the inserts out of cut-offs and scraps makes them practically free. A quick search through the scrap pile will usually reward me with enough material to make many inserts.
For this article, I found a couple of rough sawn 2 x 6 birch cut-offs and resawed them with the table saw into 5/8" slabs. These were planed flat to 3/8", which is how thick my stock insert is. This will give me enough to make four table saw inserts.
The easiest way to make table saw inserts is to use the stock throat plate as a template, and then use the router table to copy the shape.
Marking the location of the leveling screw holes with a transfer punch through the stock throat plate.
Leaving a bit of material on two sides of the insert material, I traced a line around the template (throat plate). It's easier to do each step to all four pieces of birch before moving on to the next step. This saves a lot of time.
After removing the leveling screws from the stock insert, I centerpunched the birch through the four leveling screw holes using a transfer punch. I also marked the location of the tapered screw that holds the throat plate to the saw table.
After drilling the four small holes to 3/32" and the other hole to 7/32", I trimmed the excess material from the birch with a miter gauge set at 45 degrees, leaving a small amount of material for the router bit to remove. A band saw works better as it can cut closer on the curves. The 7/32" hole was then countersunk for the screw that holds the front of the insert down to the table.
The template is secured with four short screws.
To attach the template to the birch workpiece, I used short screws through the leveling holes and into the holes that were drilled earlier.
Make sure the screws don't protrude though the bottom or they could make a mess of your router table.
You can also use double sided tape to stick the template down to the wood, but the screws are quicker and hold well.
Note: If your throat plate is a loose fit in the table, now is the time to add a few wraps of masking tape around the plate. Use as many wraps as you think will take out the slop, you can always remove some and recut.
Now that the template is secure, I can finish shaping the workpiece on the router table. I'll use a 1/2" diameter flush trim router bit with the bearing on the bottom end of the bit.
The flush trim router bit is set to cut just above the top of the workpiece.
With this type of router bit, the bearing is actually on the top when the router is mounted under the table.
The height is set so that the top of the carbide is about 1/32" above the top of the wood. The bearing will follow the shape of the template and the cutting edge of the bit will follow that shape precisely.
The work is then fed into the router bit against the bit's rotation, keeping a tight grip on the setup at all times. Always keep your fingers on the opposite side of the router bit.
The tang on the end of the insert is cut to match the original throat plate.
The stock throat plate has a tang on the rear that fits into a slot cut in the table's opening.
I wanted to keep this feature because it helps keep the rear of the insert from lifting out of the opening.
I removed the excess material with a combination blade and miter gauge. The blank table saw inserts were then given a light sanding to clean them up and round over the edges.
Leveling screws are added to the bottom of the insert and the insert is leveled with the table. The dado blade is set to cut a 3/4" slot.
Short screws were inserted into the bottom of the insert in the four holes that were drilled earlier and the zero clearance insert blank was leveled with the saw's table by moving these screws in or out as needed.
After the dado blade was lowered well below the bottom of the dado insert, the insert blank was set in place and the tapered hold down screw was threaded in to lock the insert into place.
The dado blade is raised into the insert blank until it's comes through a bit more than 5/8".
I moved the rip fence over the insert blank making sure it was well clear of the dado blade.
As added insurance against the plate lifting, I inserted a couple of tapered shims used to hang doors and windows under the fence before locking the fence down.
Once everything looked good, I turned on the saw and raised the dado into the insert until it was through the top by just over 5/8" or so. I seldom cut dados or grooves deeper than that.
Cutting up through the top of the dado insert was pretty easy considering the width of the dado and the fact that I'm actually cutting with both the front and rear of the blade at the same time.
I use two 7 1/4" circular saw blades to cut a starter slot in the insert blank because a 10" blade won't retract low enough to clear the insert.
Making a slot for a 10" blade follows pretty much the same procedures as the dado, except for one little problem. The 10" blade won't retract below the insert blank. This is common with most table saws.
To get around this small problem, I use two 7 1/4" circular saw blades to create a starter slot in the insert.
I mount the blades on the arbor, making sure the teeth clear each other, and then cut a slot about half way through the insert. You don't want to go completely through, only enough to clear the larger blade.
Even with this starter slot cut, I still had to remove a sliver of material from the left side of the slot in the bottom of the insert with a chisel. This is because the teeth on the circular saw blades aren't quite as wide as the teeth on the 10" blade.
Raising a 10" combination blade up through the zero clearance table saw insert blank.
With the insert blank leveled and secured as before, I checked to make sure the blade turned freely by hand before turning the table saw on.
Now it was just a matter of raising the blade up through the insert blank like I did with the dado.
Out of the four blanks that were cut, I made two dado inserts (3/4" and 1/2" wide), one for a 10" combination blade and one for an 80 tooth crosscutting blade.
I usually try to keep a few blanks on hand, ready to go, just in case I need one for a special job such as cutting bevels in plywood. Making them for bevel cuts follows the same procedures as square cuts, except you bring the blade up through the zero clearance insert at whatever angle you need.
Once you start using these shop made zero clearance table saw inserts, and see the improvement in cut quality, your stock insert plate will probably end up on a shelf gathering dust.