Question: I’ve just purchased and set up a hollow-chisel mortiser. However, when I turn the machine on, it makes a screeching noise and then when I cut a mortise, the chips clog the chisel and burn. What am I doing wrong?
-- Arthur Laney , Pittsburgh , PA

Answer:

By the sound of it, your auger bit must have little or no room to turn within the hollow chisel. The bit is fatter at its tip and needs to stick out from the end of the chisel a little. To set this clearance properly, I use the “dime trick”: Simply install the chisel with a dime between the chisel and mortiser and tighten it in place. Then, using a scrap as a pad, push the bit up until it is seated against the chisel and tighten it. Finally, loosen the chisel and push it up as far as it goes—the space where the dime used to be will create the necessary clearance. While you’re at it, put a square against the fence to ensure that the chisel is properly aligned.

Chisel Solution

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Set it, raise it, and square it. First, set the hollow chisel at the correct clearance using a dime.


Chisel Solution

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Then raise the auger bit up firmly into the chisel and tighten it.


Chisel Solution

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Finally, reset the chisel by raising it fully and simultaneously squaring it to the mortiser fence.


From Fine Woodworking #219 April 7, 2011