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Table Saw Inserts with Splitters

 

That insert around your table saw's blade isn't there to just plug a hole. It can play a critical role when it comes to the quality of the cuts you make. If there's a wide gap next to the blade, the fibers on the underside of the wood will be unsupported and crosscuts will result in nasty chipping. And if your saw isn't equipped with a riving knife, you are in serious danger of kick-back should the workpiece turn during the cut or otherwise pinch on the back of the saw blade. In fact, most table saw accidents occur, not from sticking your hand into the blade, but from a workpiece catching on the back teeth and pulling your hand in. We can kill both these birds with one stone by making an insert that supports the fibers around the blade, and includes a splitter to prevent kickback.

 

The most common way to make a new insert for your saw is to attach your existing insert to a piece of wood and use a template router bit to trim it to the exact shape and size. But I find that many of the inserts that come with saws fit too loosely, or like mine, they have protuberances that make the router process difficult. So, we're going to custom cut ours to fit the throat hole in our saw.

Watch the video...

...or read about it.

3/4" was too thick for my saw, so I measure from the surface of the saw top to the tabs in the throat that support the insert. I am going to make my inserts a little thinner than this measurement to leave room for shims later, so precision isn't vital, you just don't want the insert to be too thick.

 

A planer is the best tool to reduce the thickness of the blanks, or a band saw, but since this is a table saw tutorial, I used that. If you don't do much table saw re-sawing, you are likely to end up with a slight crown in the center of the freshly sawn side. You can see the peak running down the center where the two cuts meet. Sand or plane that as flat as you can, and make that the underside of the insert. That'll solve the problem.

 

If the wide gap or poor fit of your current insert makes re-sawing difficult, consider ripping part way into a thin piece of MDF or plywood to create a temporary, flat surface. Whatever you do, be very careful if your saw doesn't have a riving knife. In fact, I would say you should not re-saw on the table saw if you don't have a splitter or a riving knife. It's too dangerous. Use a band saw or a planer instead, or try to find stock that's already the correct thickness.

Now we have to round off the ends to fit the throat of our saw. This is easier than it looks. Find the center of your workpiece. I'm using a special center-finding ruler. These are handy tools that don't cost much. Once I find the center, I carry that line down the workpiece a few inches. Then I set a compass point on that line, and the other point at the edge of the insert. Now, with pivot point on the line, and the point of the compass at the end of the insert, I strike my curve. Unless you have a strange shaped insert, this should work just fine for you too.

 

Cut and sand to that line carefully, remember, you want a good fit inside the throat. Be careful when you test the fit, though. It can be hard to get the insert back out if you put in all the way in at this stage.

Many saws require a few recesses to be cut in the underside of the insert for things like the arbor that may keep the insert from lying flat. Rough in their locations with a pencil. Remember, you're drawing on the underside of the insert, which means the locations are reversed when you flip it over. One way to quickly mark some of those locations is to tap the insert with a mallet to make some indentations in the underside, just be sure you don't get it stuck in there.

 

I used a forstner bit to cut the recesses, and I added a finger hole, so I don't have to worry about getting it stuck in the throat anymore. Just make sure the hole isn't aligned with the kerf the blade will cut later.

The most common way to make a new insert for your saw is to attach your existing insert to a piece of wood and use a template router bit to trim it to the exact shape and size. But I find that many of the inserts that come with saws fit too loosely, or like mine, they have protuberances that make the router process difficult. So, we're going to custom cut ours to fit the throat hole in our saw.

 

I start with some good plywood. This is the 3/4", 5-ply birch veneered stuff you get off the rack at a home center. I prefer this to hardwood because it won't split at the thinner points once we cut all the recesses and slots cut.

 

I measure the length of the throat opening, then cut a couple blanks to length. I check the fit by slipping the board into the opening on edge. Then I carefully trim them to width. I want a good fit, so the blanks will stay in place during use.

Before we cut that kerf, we need to set the fence so it's exactly even with the edge of the throat opening. I used a straightedge to make sure. This is critical to the next step. Once the fence is set, put your old insert back in, and install the blade you want to use every time you use this insert. If you use blades that have different thicknesses, like thin kerf and full kerf, you'll need separate inserts. So, match he blade to the insert for this next step. Now with the blade fully raised, rip into the insert, stopping when the end closest to you reaches the end of the throat opening. Turn off the saw and let the blade come to a stop before removing the new insert.

 

All of the blades I use are 1/8" thick, so I don't need separate inserts for each blade. But I did make two of them. One is for regular cutting, when the blade is about an inch above the table, the other for deep cuts when the blade is fully raised. I marked where the back of the blade fell in both these instances, because that's where my splitter will go. You'll see what I mean shortly.

Finding splitter material can be tricky. It must be exactly as thick as your saw blade. To test the material's thickness, it should slide inside the kerf all the way to the stopped end of the cut. Don’t just test it at the beginning of the cut because the kerf may spread open there and a piece that's too thick may seem like a good fit. Hardwood is the best material for a splitter. I cut mine on the band saw. It'll be too thin to run through a planer unless you attach it to a sled of some sort. You could also use the table saw to cut some narrow strips to the proper thickness, and edge-glue them within the insert’s kerf.

 

The height of the splitter depends on what you plan on using it for. I made mine about 3/4" tall for my regular insert, and twice that tall for the insert I plan to use for deep cuts. The most important thing is that the grain runs upward from the surface of the insert, otherwise it will break off.

 

As you glue the splitters in place, make sure you get plenty of glue in the slot. And if you're piecing the splitter together, get some glue of the edges of the pieces. Be careful that the seams align just as if it were a single piece. I didn't really see a need to continue piecing it all the way to the end of the insert, so I finished filling the slot with a filler strip. The grain direction doesn't matter on that. (For the other splitter, I decided to go the full length of the slot because my piece of hardwood was wide enough. Really, an inch and a half would have been plenty wide.)

After the glue is dry use a file or rasp to round off the corners on the splitter’s leading edge. You don't need a sharp edge, you just want it to slip into the kerf of your freshly cut workpieces easily.

 

We made the inserts intentionally a little thinner than needed so we could shim them even with the saws surface. Except we aren't using shims, we're going to use glue.

 

First, attach some strips of wood to the top side of the insert with double-sided tape. Make sure the tape runs the full length of the strips, not just the width of the insert. Now put a little paste wax on each of the tabs in the throat of your saw. Finally, wipe a thin film around the surface of the saw to keep that double-sided tape from sticking. Now work quickly. Put a glob of hot-melt glue on each tab. Be sure to get them all. Then set the insert in place, using the strips to keep it flush with the surface of the saw. Give the glue time to harden, then remove the insert. The hot glue should have hardened to fill the gaps, creating custom shims. Good idea, eh?

 

The first time you raise your saw blade it may cut into the splitter a bit. That's why I made two inserts. This way I keep one close to the rear of my saw blade for both regular and thick cuts.

A splitter is one of the most important safety accessories your saw can have. You should never use a saw without one, and now you don't have to.  Be sure to check out the latest issue of Stumpy Nubs Woodworking Journal. It's always full of great tips, tricks and tutorials designed to make you a better woodworker. You can read and subscribe for free at stumpynubs.com. Happy splitting!

 

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