Mortise and Tenon Question

[jteneyck]

Tenons will rack less the deeper they are 

The intersection of the two does not mean they should meet but more depth is your friend when dealing with large legs and smaller aprons. The key is to reduce racking.

Not disagreeing only trying to understand.  I've always thought that the depth of a glued mortise and tenon should be at least 3 times the thickness of the tenon.  So, for a 1/2" thick tenon you'd want the mortise to be at least 1-1/2" deep.  Glue is what holds the tenon in the mortise and there comes a point whee increased depth/length offers no added benefit to breaking strength or racking.  If the joint is unglued, sure, deeper/longer will have less racking up to a point but for a glued joint I don't see the benefit.  What am I missing?

John

[JGrout]

Not disagreeing only trying to understand.  I've always thought that the depth of a glued mortise and tenon should be at least 3 times the thickness of the tenon.  So, for a 1/2" thick tenon you'd want the mortise to be at least 1-1/2" deep.  Glue is what holds the tenon in the mortise and there comes a point whee  increased depth/length offers no added benefit to breaking strength or racking.  If the joint is unglued, sure, deeper/longer will have less racking up to a point but for a glued joint I don't see the benefit.  What am I missing?

John

What am I missing?   The racking of a shorter apron tenon especially one as big as the OP wants. 

I have built tables similar to the one here and the one thing that made for a sturdy connection to the leg was the use of a longer tenon. 

Can you get by with less? sure. 

Should you?  not from my view. 

Joe

[jteneyck]

What am I missing?   The racking of a shorter apron tenon especially one as big as the OP wants. 

I have built tables similar to the one here and the one thing that made for a sturdy connection to the leg was the use of a longer tenon. 

Can you get by with less? sure. 

Should you?  not from my view. 

Joe

I understand how a longer tenon has less racking during dry fitting, to a point, but in a glued joint I don't see any benefit with regards to racking of a tenon longer than the minimum requirement. Once the glue is dry it can't move, short or long.  I guess we'll agree to look at this one differently. 

John

[Admiral]

I understand how a longer tenon has less racking during dry fitting, to a point, but in a glued joint I don't see any benefit with regards to racking of a tenon longer than the minimum requirement. Once the glue is dry it can't move, short or long.  I guess we'll agree to look at this one differently. 

John

I think its a matter of scale.  I get your rule of thumb, but when I design, I make the tenon's as long (i.e., deep) as I can given the design constraints of how deep I can mortise, and while it may be a bit of over-engineering, it doesn't hurt.  I've even maxed out, where I put a 45 deg. bevel on the ends of the tenons where they met at a corner. With a large table where the rails/aprons really do take all the stress, I do think it matters.  Not so much on an end table, enclosed cabinet table where there are multiple rails for drawers, etc.

[Steve N]

You don't mention how long each skirt will span.

That being said, the size of your columns make your skirt size seem suspiciously thin.
Assuming you are spanning over 4' or so, I would go to 6/4 material and use a 3/4" tenon about 3" deep.
Either drawbore it if glued, or use  bedbolts if disassemby is needed.
This is likely overkill, but so are 6" columns.

I think this would be my flavor too. I also agree that 6" columns are huge, unless it's a 20+ foot table very wide,. and then you get to, is that size actually going to service people sitting at it, or will they all wish the table was a portion of it's size, when trying to reach for the taters, n dressing. Bedbolts, never would have gone there
Of course break down tables aren't my thing.