Mike B
Established Member
Hi
I am planning on joining some oak rails (140 x 30mm) to some oak posts (55 x 60mm) to form a kind of bed frame arrangement, using mortise and tenon joints. I have been trying to do some research but as usual most of the descriptions appear to be a “what I did” and do not contain the “whys” or dimensioning decisions behind the designs. They do however raise wood movement concerns when using rails of this size.
From what I can gather there are 2 approaches for joints of this size :
1) a double tenon with a haunch in between, glue applied to only the tenons
2) a larger single tenon with a haunch either side, glue applied to tenon only
I am tending toward the first method as it appears to be stronger but am having to guess as to the best dimensions – I was thinking along the lines of 40mm wide tenons, 15mm clear at the top, and a 40mm central haunch. For tenon thickness I was thinking of either 16 or even 18mm
even though it breaks the “thirds rule” as there will be plenty of mortise wall either side. For tenon length, I was thinking of 25mm with 10mm for the haunch.
Should I allow for wood movement and if so how?? I could make the mortise slightly wider than the tenon but this seems daft if the tenon is glued…
Also, if the joint is to be held together by a central bolt instead of glued so it can be disassembled should I adjust any of the sizes?? E.g. make the tenon length shorter??
As I said these are my best “guesstimates” based on what looks right to my eyes but any advice on a more scientific approach to deciding tenon lengths, widths etc for max strength would be most welcome, as would any recommendations of a good text that describes the “whys” as well as “how to”??
Thanks
Mike
I am planning on joining some oak rails (140 x 30mm) to some oak posts (55 x 60mm) to form a kind of bed frame arrangement, using mortise and tenon joints. I have been trying to do some research but as usual most of the descriptions appear to be a “what I did” and do not contain the “whys” or dimensioning decisions behind the designs. They do however raise wood movement concerns when using rails of this size.
From what I can gather there are 2 approaches for joints of this size :
1) a double tenon with a haunch in between, glue applied to only the tenons
2) a larger single tenon with a haunch either side, glue applied to tenon only
I am tending toward the first method as it appears to be stronger but am having to guess as to the best dimensions – I was thinking along the lines of 40mm wide tenons, 15mm clear at the top, and a 40mm central haunch. For tenon thickness I was thinking of either 16 or even 18mm
even though it breaks the “thirds rule” as there will be plenty of mortise wall either side. For tenon length, I was thinking of 25mm with 10mm for the haunch.
Should I allow for wood movement and if so how?? I could make the mortise slightly wider than the tenon but this seems daft if the tenon is glued…
Also, if the joint is to be held together by a central bolt instead of glued so it can be disassembled should I adjust any of the sizes?? E.g. make the tenon length shorter??
As I said these are my best “guesstimates” based on what looks right to my eyes but any advice on a more scientific approach to deciding tenon lengths, widths etc for max strength would be most welcome, as would any recommendations of a good text that describes the “whys” as well as “how to”??
Thanks
Mike