Mortice and Tenon

[Fred Page]

I'm cutting mortices and tenons at that time of the year when humidity is high in my generally unheated workshop. It is easy to see that there will be some dimensional change in the tenons when drier conditions prevail but what about the mortices? Do they contract similarly? Will these winter-made joints lose their strength in drier summer days?
Fred.

 

[johnelliott]

Seeing as this one has had 30 views and no replies, I think I will jump in and say that I have never heard of seasonal variations causing a problem with M&T joints. I am of the opinion that it is safe to assume that the timbers involved will expand and contract at the same rate, and that in anycase the overall dimensions are low enough that such movement will not loosen the joint. This is just as well when one considers the differnce in grain directions
Even with a small amount of heat one can sometimes find that the relative humidity can be lower in the winter, due to the moisture in the air condensing out in the form of frost and snow
John

 

[Bean]

Fred I dont know if your design will stand them but my personal preference with M&T joints is to peg them with a dowel. But to do this you have to be sure that you do not want to take it apart again.

Bean

 

[Midnight]

there's always the option of wedging em... esp if they're destined to be dismantled..

 

[Philly]

Hi Fred
As far as I can recall, you will have no problem with the width of the tenons as the movement of the timber should be similar. But you could have a problem with the depth of the tenon if it is excessively long (i.e. 6 inches or more) If the tenon is as long as that (and as it is a cross-grain situation) the solution is to use double tenons instead of one long one-thatwill relieve the pressure and give a stronger, stable joint.
hope this is of help,
Philly

 

[woodburner]

My (unheated) workshop may have higher humidity than the (heated) house, however I think that the real issue is the absolute moisture content of the air. Things made in the workshop grow when I take them inside, higher temp leads to a higher moisture content at a lower relative humidity, which is why my drawers no longer slide.

Pedantic?

 

[Fred Page]

Fred I dont know if your design will stand them but my personal preference with M&T joints is to peg them with a dowel.

Bean

Bean,
This is what I intend to do. My initial fear came over me because the piece I'm working on (in my humid and unheated workshop!) is to be delivered to the South of France. For a while I had the nightmare vision of all the M & Ts becoming loose.
Don't ask how I got this particular commission.
Thanks.
Fred.
Kington