choosing the right sized chisel for a mortise

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Forum topic by cgm_md posted 03-09-2014 05:52 PM 798 views 0 times favorited 7 replies Add to Favorites Watch
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60 posts in 1266 days

03-09-2014 05:52 PM

Okay, this may seem like a silly question, but I am working on my first piece of furniture that utilizes mortise and tenon joinery. Let’s say you are making 1” square mortises and started by drilling out the material to the proper depth. In order to clean up the remaining material, would you use a 1” chisel or a smaller chisel, such as 3/4”?

I am sure there are differing opinions on this, but I just wanted to get a taste of people’s preferences. Thanks!

7 replies so far

View madts's profile


1661 posts in 1757 days

#1 posted 03-09-2014 06:21 PM

I would use a 1/2” or a 3/4” Just make sure that they are sharp sharp.

-- Thor and Odin are still the greatest of Gods.

View djwong's profile


167 posts in 2637 days

#2 posted 03-09-2014 06:26 PM

I would use either a 1 inch chisel, or a much smaller chisel (1/2 or 3/8). A 1 inch chisel will give you equal “bite” on the cutting edge, so there is less chance of the chisel unexpectedly turning. A 3/4 inch chisel would embed one side of the cutting edge more than the other, so the side with less contact could slip. Using a smaller chisel, you would work each corner in the mortise individually.

-- David W. Cupertino, CA

View DocBailey's profile


584 posts in 1777 days

#3 posted 03-09-2014 06:26 PM

Ideally, you would use a 1” square mortising chisel.

Historically, the work-flow goes like this:

Assume that a 1” wide mortise is appropriate for the application. The marking gauge would be set to the width of the chisel.
The same gauge is then used to strike the thickness of the tenon on the end of the piece to be joined.

View Loren's profile


8156 posts in 3065 days

#4 posted 03-09-2014 07:50 PM

Well, you just want to take the corners out, so assuming the
drill is 1” I’d use a 1/2” wide chisel at most in order to work
on one corner at a time without the stock on the neighboring
corner interfering. Depending on how clean the sides of
the mortise need to be, you’d either chop out most of the
waste then sneak up on the lines making paring cuts, or
if it’s a quicky just chop away.

View LeTurbo's profile


217 posts in 1002 days

#5 posted 03-09-2014 08:42 PM

Make your mortise the size of the chisel. This procedure of drilling out first is a new “invention” and completely unnecessary. Once you’ve marked the length, put the flat side of your chisel just short of that mark, with the bevelled side facing into the waste. One shot with the mallet, then move the chisel back slightly. Two whacks with the mallet. Move chisel back. Three whacks with the mallet. Before you know it, you’re done. A quick clean up of the sides and you’re finished.

View cgm_md's profile


60 posts in 1266 days

#6 posted 03-10-2014 03:21 PM

This is about the range of opinions I was expecting. Thanks for the info!

View Rick M.'s profile

Rick M.

7668 posts in 1797 days

#7 posted 03-10-2014 04:50 PM

LeTurbo is correct. Size the mortises to your chisels, 1” chisel = 1” mortise.


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