What size mortise do you use?

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Forum topic by Hewy posted 02-28-2011 12:13 AM 1662 views 0 times favorited 2 replies Add to Favorites Watch
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23 posts in 1724 days

02-28-2011 12:13 AM

Topic tags/keywords: mortise size

I just got a hollow chisel mortising machine. What I would would like to know is what width mortise
to use in 3/4” oak. If you use the rule of 1/3 the stock width you would use a 1/4” wide
mortise. This just seems on the small side to me. Would 5/16” be a better choice? Please
let me know what you are using.


2 replies so far

View richgreer's profile


4541 posts in 2111 days

#1 posted 02-28-2011 02:49 AM

I personally think the 1/3rd rule is about right. Too big of a mortise can be just as weak as too small of a mortise.

I use 1/4” mortises on 3/4 stock.

-- Rich, Cedar Rapids, IA - I'm a woodworker. I don't create beauty, I reveal it.

View TheDane's profile


4473 posts in 2700 days

#2 posted 02-28-2011 03:08 AM

It depends. In most projects, I use the 1/3rd rule just as Rich does … especially if the mortise and tenon are both made of 3/4” thick stock.

The exception might be if the project calls for through mortise and tenons (a lot of A&C / Mission furniture uses through M&T). I think 1/4” through tenons look odd, so I will generally go to 3/8” if the tenon will just have a rounded-over end, 1/2” if the tenon will be chamfered.


-- Gerry -- "I don't plan to ever really grow up ... I'm just going to learn how to act in public!"

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