Single or Double Mortice and Tenons

[John15]

After an unplanned delay on my 6' x 3' oak gates I've finally made a serious start, and immediately I have a query on the mortice and tenon joints.

The stiles are 100 x 48mm and the rails are 100 x 27mm. I'm planning the mortices to be 90 x 13mm and 50mm deep.

My question is should I form a single mortice 90 x 13 or a double one, say two at 35mm leaving a 20mm section in between? My book (Collins Complete Woodworker's Manual) says for a double joint a short stub should be formed for additional strength.

Any advice very much appreciated.

John

 

[Zeddedhed]

My (limited ) understanding of M&T joints is that the tenon should be approx a third of the thickness of the timber. Therefore 90 x 9.
After that I can of no further use...

 

[PAC1]

If the stile extends beyond the rail I would just use one tenon as per your original idea

 

[John15]

Thanks for pointing out my mistake Zeddedhed - you are correct, the width of the mortice should be 9mm not 13. But that apart, my query still stands. Should it be a single or a double m and t for a joint length of 90mm?

Thanks PAC1

John

 

[Racers]

Single through tenon with wedges and/or dowels and glue.

Pete

 

[Mike.S]

When I was faced with a similar query I found this guidance by Chris Schwarz (plus comment below the article) very useful.

 

[John15]

Thanks Pete for the single tenon preference. I intend to do blind tenons and will dowel them.

Thanks Mike for the Chris Schwarz link. I followed it OK until around the 9th paragraph when I completely lost him - I'll try again later but from the bit of logic I did grasp a single tenon is OK as PAC and Pete have said.

John

 

[Phil Pascoe]

I would say either through and wedged or as deep as possible (and pegged? shouldn't really be necessary with good adhesive). The best thing about not going through is there is no exposed end grain, but of course you can't then easily wedge them (fox wedging being a little extreme, maybe, for a gate ).

 

[blackrodd]

This should help on the gate joints
Possibly Worth a thousand words. Regards Rodders
http://www.gatesandfencesuk.co.uk/contact-2-w.asp

 

[Biliphuster]

Thanks for pointing out my mistake Zeddedhed - you are correct, the width of the mortice should be 9mm not 13. But that apart, my query still stands. Should it be a single or a double m and t for a joint length of 90mm?

Thanks PAC1

John

I go by the rule that the mortice should be 1/3 the thickness of the receiving stock (the stile), so 48/3 would give you 16. I had always assumed the he purpose of the rule is to avoid hollowing out the receiving stock too much, you may as well try to make your tenon as thick as possible, whilst leaving some shoulders for twisting resistance.

 

[RossJarvis]

After an unplanned delay on my 6' x 3' oak gates I've finally made a serious start, and immediately I have a query on the mortice and tenon joints.

The stiles are 100 x 48mm and the rails are 100 x 27mm. I'm planning the mortices to be 90 x 13mm and 50mm deep.

My question is should I form a single mortice 90 x 13 or a double one, say two at 35mm leaving a 20mm section in between? My book (Collins Complete Woodworker's Manual) says for a double joint a short stub should be formed for additional strength.

Any advice very much appreciated.

John

I may be wrong, but I thought double tenons were used on household doors to help keep everything flat on thinner materials, particularly at the bottom, and doubled due to something to do with wedge spacing. I would have thought a gate of your size would be more robust and be okay with a medium wide tenon. I think a lot of oak joinery can cope with tenons less than 1/3 thickness.

 

[Benchwayze]

John'

It's down to gluing area I would have thought. The more massive the frame, the more glue area you need; hence a double tenon. There also comes a point when a third of the width becomes a thick, clumsy and ugly tenon. So maybe aesthetics come into play as well? Just my two-pennorth.

John

 

[deema]

The gates will need to be through tenoned and either wedged or preferably draw pinned. The general rule for the length of tenons is that they should be no longer the 4 to 6 times the thickness. The two tenons are connected together by a stub tenon which should also be used at the corners of the gate. The stub tenon should be no more than a third of the size of the main tenon or 1" which ever is the smallest. I typically make mine c3/4" for gates / doors.

 

[Benchwayze]

Maybe I was thinking of the wrong kind of double-tenon.
I envisaged a 'twin-tenon'; side by side.
Thus:

https://www.youtube.com/watch?v=fuI-8x81fwA

As opposed to :

https://www.youtube.com/watch?v=xWm9hi4ojVY
Sorry!

 

[Phil Pascoe]

This has cropped up before - twin tenons to me are side by side. I'm not actually sure what the other type should be called (or indeed that I'm right )

 

[Sgian Dubh]

This has cropped up before - twin tenons to me are side by side. I'm not actually sure what the other type should be called (or indeed that I'm right )

I've always known them as forked tenons if used on wide members, and double, twin, triple, etc tenons when used on thick members, but also in other situations, such as one example below.

Typically, what I know as a forked tenon is used in situations such as the middle (lock) rail of an architectural door, and a double or twin (stub) tenon used for things like horizontal front and rear drawer dividers into a carcass side, or for joining two thick members.

And to add even more complexity, you might occasionally come across a double forked tenon. Following my explanations above, I suspect you'll realise these tend to be used on thick members that are also wide! Slainte.

 

[Phil Pascoe]

I'd not heard "forked tenons" - but it makes perfect sense.

 

[Zeddedhed]

you might occasionally come across a double forked tenon. Following my explanations above, I suspect you'll realise these tend to be used on thick members that are also wide! Slainte.

My wife has a double forked tongue.
She uses it on.....I'll get my coat.

 

[John15]

I've settled on a single tenon 14mm wide, and this morning I ordered a Narex chisel from Workshop Heaven which should be with me tomorrow 1st class post. I've not chopped out a mortice this wide before - any suggestions on making it as easy and accurate as possible?

John

 

[mseries]

- any suggestions on making it as easy and accurate as possible?

John

My first preference would be using my router but when I made my gates the mortices were too deep for my longest cutter so I did it by hand. I removed most of the material using my brace and bit then cleaned up with my chisels. Might have been easier using an electric drill but at the time I didn't have a drill press and I liked the idea of using the old B&B that my father gave me - feels like he's contributed to the work.

EDIT: Just re-read your OP, for 90x50x14mm mortice, given I now have a big router and 50mm long 1/2" cutter, it would be easiest and most accurate for me to use the router with guide bush and template. YMMV.