Single-bore mortises

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Blog entry by galooticus posted 09-04-2017 12:15 AM 838 reads 0 times favorited 1 comment Add to Favorites Watch

As I’m preparing to cut various joints for a project, I’ll go through my copy of The Woodworker from Lost Art Press to refresh myself on how to do the joint in question. In this case, mortise and tenons. One included article, a reader submission, suggests a more efficient way to cut a mortise, instead of boring out as much as possible and cleaning the remainder up with chisels. I tried it out, and thought I’d share my experience since I haven’t seen this approach noted anywhere else.

Instead, bore a single hole:

Then start chopping a V around that hole, just as you would when you chop the whole mortise instead of boring:

The single bore gives an easy escape path for waste and the chisel and allows for steeper/deeper cuts initially. I’m finding that chopping speed is greatly increased, and the relief makes it easier on the chisel when wedging out the waste. The mortise I’m doing here is 1 1/2” deep. Here’s how deep I was able to go on the first pass:

If you’re careful to bore to the right final depth (stick some masking tape on your auger), you can use the bored hole to gauge your chopping depth. So above, I’m not quite to the bottom yet; one more V pass will get me there no problem.

In summary, I like this technique and will continue using it. It’s most appropriate when you have a mortise chisel that’s an exact match to the mortise width. For wider mortises especially, I’ll bore as much as possible and clean up with mostly bench chisels.

Finally, not so related to the above technique, here’s how I check the mortise sides for square. First I get pretty close by eye, being a bit shy on purpose. Then I take my combo square and adjust the ruler’s projection to the desired mortise depth. Put the ruler extension down into the mortise, sliding it all over to check for depth. Then run it up into the corners:

There’s a bit of a gap; not quite there yet. A quick paring action with the mortise chisel gets me there:

There we go.

-- Andy in CA

1 comment so far

View Dave Polaschek's profile

Dave Polaschek

5845 posts in 1431 days

#1 posted 09-04-2017 01:16 AM

Thanks for the tip! I’ve got The Woodworker, but haven’t had time to get through it. Looks like I should find time soon.

-- Dave - Santa Fe

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