Wedged Through Mortise and Tenon Joint-Size of the Kerf to Accept the Wedge?

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Forum topic by gerrym526 posted 12-08-2009 12:28 AM 3520 views 0 times favorited 4 replies Add to Favorites Watch
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266 posts in 3231 days

12-08-2009 12:28 AM

Just finishing up a pair of the James Krenov style “Smart Sawhorses” in the Dec 09 isssue of FWW. I’ll put pics up in the project area after they’re finished.
Looking for advice from you advanced jocks-specifically, how wide do you typically cut the kerfs in the through tenons to accept the wedges. Or, from another perspective, how thick should the leading edge of the wedge be?
I’ve used this joint in other projects (see my blanket chest pics) but always have had the problem of the wedges cracking at the tips when they’re pounded into the through tenons. Causes lots of extra work in repairing the joint with little pieces of wood-a real pain!
On the sawhorses, I cut the kerfs in the tenons on my bandsaw, so think their width was probably no more than 1/16th. This caused me to use wedges with a very thin front edgel-with the usually results.
Can you guys help?

-- Gerry

4 replies so far

View SNSpencer's profile


133 posts in 2536 days

#1 posted 12-08-2009 01:39 AM

OK, I have done this with a few pieces myself and have not run into the same problems as you have. Maybe you are trying to pound them in a bit too hard? For the wedged tennons that I have done I cut the slots about 1/8” wide and used a wedge with a tip at about half that. Of course make sure that the slot id plenty deep enough so your wedge does not “bottom out”. I also made sure to keep a very small angle on my wedges so that they would enter the slot at least 1/4” before actually filling the slot. That way I am sure that there is enough glue surface to keep them in there. Then I “tap” not “pound” them in making sure to stop before things go awry. Also, I would cut my wedge material long enough so that the end that gets hit with the mallet is as wide as possible. Sometimes the wedge gets pretty long with the small angle. Also, with a wedge that is 4” or so you can use your fist to hold the wedge steady while tapping to keep it from being knocked sideways and getting snapped off.

-- Jef Spencer - Refined Pallet -

View gerrym526's profile


266 posts in 3231 days

#2 posted 12-08-2009 07:24 PM

Thanks for the response. You may have solved my problem. I’ll cut the kerf wider in the next joint, and make the wedges longer, with a wider surface for hitting with the hammer.
To your point, I might have gotten a little too ambitious with my “pounding” as opposed to tapping the wedge in.

-- Gerry

View Kent Shepherd's profile

Kent Shepherd

2715 posts in 2709 days

#3 posted 12-10-2009 12:54 AM

You might also use a block against the wedge to tap in, instead of hitting directly with the hammer.
If you use a regular steel hammer, you might try a wooden mallet.

Good luck,


View jaydub's profile


63 posts in 2538 days

#4 posted 12-10-2009 06:24 PM

Hey Gerry,
You might be doing this already anyway – but if you flare/angle the end of the mortise where the wedges go, it allows for more movement of the tenon, thus allowing for a wider, strudier wedge.

- jw

-- happiness is a sharp plane iron

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