Zero Clearance Inserts - Canadian Woodworking Magazine

A zero clearance insert is easy to make and goes a long way in reducing tearout.

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Zero Clearance Inserts



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SUPPLY CHECKLIST:
  • 1/2" Baltic birch
  • 3/8" dowels
  • double sided tape
  • four #4 flathead screws
The throat insert that comes as standard equipment on a table saw is meant to provide sufficient clearance around the blade as it moves through its full range of motion. While this is convenient, it does little to support stock close to the side of the blade, which often results in chip-out (particularly on sheet goods) and can also result in thin pieces of waste material jamming between the throat insert and the saw blade.

A Zero Clearance Insert (ZCI) is a replacement for the throat insert that came with your table saw. While you can buy a ZCI, as you’ll see, they are very easy to make. Once you install the ZCI on your table saw you’ll cut the opening for the saw blade so that it’s the exact width of the saw blade kerf. It’s a good idea to make a 'master' ZCI that you then use to make a new insert any time the need arises. But don’t throw your original throat insert out – you’ll still need to use it whenever you cut beveled angles with your table saw.

Make the Master ZCI


  1. Begin with a piece of ¼" or ½" (which ever is closest to the thickness of your insert) Baltic birch ply or a similar rigid ply that is a couple of inches longer than the length of the throat opening on your table saw.
  2. Using a ruler or calipers, measure the width of the throat opening, set the table saw rip fence to this measurement, and cut the ply blank. Be sure that both edges are parallel and straight.
  3. Remove the throat insert from the table saw.
  4. Put a couple of strips of double-sided tape on the insert, and place the blank over the insert, ensuring that the sides are flush.
  5. Trim the excess at the corners of the blank with your band saw, staying about ⅛" away from the insert. Install a flush trim bit in a table-mounted router and rout the blank to size.
  6. Before separating the insert and the blank, mark the four holes for the levelling screws on the blank.
  7. Separate the insert and the blank and test that the blank fits snugly in the table saw throat – you may have to fine tune with a bit of sandpaper for the perfect fit.
  8. Using a drill press drill ⅛" holes on the marks for the levelling screws, and drill two ⅜" holes 1 ¼" from the left edge of the insert.
  9. You now have a master ZCI that you can use to make working ZCIs.
Make Working ZCIs

  1. You’ll need several ZCIs: one for standard ⅛" thick blades, one for thin kerf blades, and one for dado blades.
  2. Cut a blank for a new insert just slightly larger than the master. Place dowel centers in the two dowel holes and press the master onto the blank.
  3. Drill out the holes, insert dowels into the master and place the blank on the master.
  4. Remove the excess material at the ends with a band saw and then use a flush trim bit in a router table to create an exact copy of the master. Before separating the two pieces use an awl to mark the locations for the levelling screws; this will be the bottom side of the ZCI.
  5. Now separate the two pieces.
  6. Install #4 flat head wood screws as levelling feet on the bottom side of the ZCI, and then level the top of the insert to the top of the saw table.
  7. Add a screw to the rear of the insert to catch on the recess under the table; this is to keep the ZCI in the opening when the saw is turned on.
  8. Lower your table saw blade all the way down, and put the ZCI in place (if the blade is too high for the ZCI to seat properly, install a smaller diameter blade on your saw).
  9. Move the rip fence so that it covers as much of the insert as it can without the risk of being damaged by the saw blade. Ensure that the blade is set to 90º and gently raise the blade through the insert.
  10. When using the ZCI for cuts with the blade at 90º it is advisable to add a splitter as well. The one we like is the Micro Jig splitter. Now you’re ready to make a ZCI for your thin kerf and dado blades.
SOURCES:
Micro Jig Splitter and Dowel Centers
leevalley.com