Zero-clearance inserts reduce tearout and improve safety on a tablesaw
After setting up his new sliding table saw, Marius Hornberger is making some zero clearance inserts.
- He begins by removing the existing insert and measuring the depth of the opening—8mm
- Next, he considers materials to use. Softwood, hardwood, or laminated birch plywood, of which has has a couple of different thicknesses (9mm and 15mm). The extra depth is OK because he will make cutouts for the internal parts.
- He cuts strips to the correct width.
- And cuts the shape of the original insert: double-sided tape holds the insert to the laminated plywood, and a flush-cut router bit follows the shape.
- He aligns the template to the new insert to locate the hole positions ...
- ... and drills (and counter-sinks) them on a drill press.
- He marks the cutouts that will be needed on the underside to make clearance for the internal parts.
- Then he hogs out the extra material with multiple passes on a router table.
At this point the new insert fits nicely, but is a little below the surface (as planned).
Next he installs leveling screws (8 per insert), located next to the set screws by drilling the holes, slightly countersunk (to remove burrs), tapping the holes, and installing the set screws.
Now he installs the insert and notices that the set screws are offset from the mounting screws, which can cause an uneven tilt. He moves one of the set screws so that the two set screws and the mounting screw are in a straight line, which seems to work well.
- Using a straightedge, he flushes the insert to the table.
- He removes the riving knife and plunge cuts the blade through the insert.
- Next, he reinforces the slot section (which has a skinny, weak side) with a strip of hardwood.
[insert ‘professional glue-spreading tool joke here]
Recutting the slot and finishing up
He recuts the slot, beginning with a small blade, and moving to a larger blade. To cut a slot for the riving knife, he marks and insert and cuts it on a bandsaw. At the end, Marius decides that next time he will use the thicker (15 mm) stock.
Why make a zero clearance insert? (9:32)
- To prevent offcuts from being sucked down into the throat plate during cutting (6:32)
- much improved cut quality on crosscuts and thin-veneer plywood. The tight tolerance between the blade and the insert prevent tearout substantially.,
— Marius Hornberger works in a little basement shop on woodworking, making homemade machines, wood-turning, making jigs, and more. His YouTube channel is full of good stuff.