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post #1 of 9 (permalink) Old 04-05-2009, 09:37 AM Thread Starter
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Default Mortise Width?

How important is the mortise width?

For a 3/4” stock the Trend MT jig manual says that the width of the mortise should be 1/4”

The woodworking for routers book I have says that it should be 3/8”

Not that it’s so important but if you are going to learn might as well get it right

Nicolas
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post #2 of 9 (permalink) Old 04-05-2009, 09:54 AM
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Hi Nicolas

To me the bigger the better,, I will some times use a 1/2" one in 3/4" thick stock..

The sheer of a 1/2" teton is way up on the scale it's just a butt joint on steroids

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Originally Posted by kolias View Post
How important is the mortise width?

For a 3/4” stock the Trend MT jig manual says that the width of the mortise should be 1/4”

The woodworking for routers book I have says that it should be 3/8”

Not that it’s so important but if you are going to learn might as well get it right

Nicolas


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post #3 of 9 (permalink) Old 04-05-2009, 10:08 AM
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Although 1/3 of the width is a reasonable rule of thumb for heavier stock, I think it's sort of dinky for 3/4" thick material. I'd go with 3/8".

The joint test that Fine Woodworking ran recently also showed a significant increase in joint strength for the 3/8" tenon over 1/4".

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post #4 of 9 (permalink) Old 04-05-2009, 10:18 AM Thread Starter
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So there is no standard, good to know

I will go with 3/8" mortise for this stock

Thanks
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post #5 of 9 (permalink) Old 04-05-2009, 10:31 AM
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The 1/3 rule of thumb or guideline is probably as close to a "standard" as one gets with woodworking. But, I think it's best to consider the nature of the stress a particular joint is likely to encounter, and then design accordingly.

The testing that FWW did was in a machine that exerted force parallel to the face of the boards. That may not be representative of some joints in actual use, however. If, for example, the joint were subject to more of a twisting force, the lateral wall strength of the mortise might be more important.

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post #6 of 9 (permalink) Old 04-05-2009, 10:59 AM
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Bob and Rick recommend half the material thickness.

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post #7 of 9 (permalink) Old 04-05-2009, 12:53 PM
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I have always used 3/8" on 3/4" wood. I have not had any problems.
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post #8 of 9 (permalink) Old 04-05-2009, 01:03 PM
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Ummm... actually, you need to consider what it's going to support. Weight makes a difference too. Just so long as you don't go over 1/2 the material thickness, you'll be fine.

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post #9 of 9 (permalink) Old 04-06-2009, 08:27 AM
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Nick
I've always used the 1/3 rule and I don't recall ever having a mortise and tenon joint fail. Having said that it only stands to reason 3/8 would be stronger.
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