Workbench — Tenon sizes

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    I am (very slowly) making progress on my Paul Sellers workbench. Yesterday I went to lay out the mortises in the legs, but I found out that the cheap combination gauge that I bought for $6 at Harbor Freight doesn’t have a long enough brass beam to let me set a 1/2″ mortise in the middle of a 3-1/2″ piece of wood. The fence just can’t move back far enough, it’s blocked by the knob for the movable pin.

    I could try to find a better gauge (though looking online they all seem very similarly sized), but I thought that another fix would be to just make my tenons a bit thicker. It seems like the legs, at just under 3-1/2 inches wide could accommodate mortise holes of an inch wide or thicker, though I really don’t know enough yet to say for sure. From what I’ve been able to read, tenon thickness and length ratios matter as well as the ratios of the width of the wood being mortised to the width of the mortise hole.

    Can anyone advise me on what the best plan of action would be? I could try laying out the mortises with some less efficient or less precise technique, make the tenons thicker, or just wait until I can get the “proper” tool for the job.

    Thanks in advance.


    I see you say it’s a combination gauge, so there’s always the option of using the one pin to set out one side of the mortise, re-set, then lay out the other. Not quite as efficient as doing it with the two points but certainly more efficient than waiting for the ideal gauge to arrive.

    If you’re chopping you’ll cost yourself a lot of time using larger mortises, especially if they’re not the exact size of a chisel you have. Even if you do have the right sized chisel, a larger chisel will not drive as deep with each blow, so that option at least would be a false economy.

    I would still get a new gauge, but wouldn’t rush to do it. It’s unlikely you’re going to encounter mortises outside the extreme of your current gauge much once you’ve finished your bench.

    Southampton, UK

    mike forbes

    I wouldn’t worry about it too much. If you make the tenons oversized and then clean them up to fit them snug you’ll be fine. I used a router plane and block plane to clean my tenons up. My bench can be seen here as well in the projects category as well as here

    Use the right size chisel will be the main thing to keep them uniform more so than your lines on the side. I used a 1/2 inch chisel and that really defined my layout. You can always layout with a square and a knife line and I think you would be fine.

    If they are off center a bit things will still work. They might twist a bit with the legs together due to a not so perfect mortise. Things will work out anyways, its just a bench and no one that I know will be taking a machinist square to it. The end goal for me was not perfection on my bench, it was to learn as much as possible on 130 bucks worth of lumber and as quickly as possible since I actually wanted to make projects.



    I believe the bench tenons calls for 1/2 inch? Or is it 3/4? Either way it’s best to use the chisel you are going to use to set the pins on the mortice gauge. In your case becuase the gauge won’t reach I would use a comb square to set the location of the mortise registering from the registration face. Place the chisel against the edge of the square and give it a tap to locate the ends and sides, do the same for the other end of the mortice, now just connect the lines and you should have a fairly accurate location for your chisel placement. Make sure you measure and set the mortice locations in exactly the same position on each leg using the same setting on the square. If you have a single pin marking guage you can use that as well, you will just have to ensure you mark each leg the same way each time.


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