Thread: Loose tenon joinery

Originally Posted by derekcohen

Here's the issue: I have some Jarrah, but the ends will not be long enough to use mortice-and-tenons. I shall need to use loose tenon joinery. (And, no, I am not going to purchase more for the length - Jarrah like this is hellishly hard to find and Expensive!).

If you despair of the loose tenon idea, I have some long Jarrah lengths in 30/40mm that I'd sell / trade to you at a very reasonable rate. I can PM send you some pics when I get home if you like.

Cheers, Zac.

Thanks Zac. I am interested. Let me know what you have around 1100mm length in a nominal 30mm thick (which will be after jointing/thicknessing) and 130mm high. I need 4 lengths.

Edit to add: I have enough Jarrah to do the job as long at the end rails use a loose tenon. This may need to be the way to go since this timber is hellishly expensive, as you know.

Cheers

Derek

Derek, As a rule of thumb loose tenons are 1.5 times the width for depth with the grain. Therefore, a 100mm wide tenon would run 150mm into the rail. Not very practical for a router. Two ways to overcome the problem:1) Glue fix the shorter tenons into the rail. 2) Use two tenons (narrower) in the end of each rail thus reducing the depth required for the rail mortise.

Rusty, I have been searching for a Rule of Thumb for loose tenons. Traditional tenons are old hat to me, but loose tenons are not something I have used in the past.

I have made up stock for the loose tenons from an offcut from the same boards. These will be cut to length and width when needed.

Deciding that the "tenon" should be 35-40mm in length (into a 60mm square post) is the easy part. The 110mm wide mortice/tenon can be divided into 2 x 50mm tenons. The question then is "how deep to secure the loose tenon into the rail?". You are saying that this should be 75mm (for each 50mm wide tenon). That is unrealistic with regard boring the mortice.

For contrast, the Domino DF500 has a maximum depth of 28mm. The 10mm domino is 24mm wide. In other words, roughly 1x width. I've heard from some who say that large doors are strongly made with 10mm DF500 dominos, but we are talking about a bed joint, which is more demanding.

35-40mm is doable by using the Domino cutter first, taking the mortice to 28mm, and then drilling it deeper. I have looked at router bits, and they just will not get that depth of cut.

Another idea I had was to reinforce the sunk tenon by pinning it as well (from the inside of the rail) to prevent movement.

Thoughts?

Regards from Perth

Derek

I've done a repair like this on the head and end of a queen size bed, using 1/2" loose tenons. Mortises were cut using a 100mm long upcut bit, which allowed a mortise >65mm deep in the rail. As a guide and support for the router a template made from 10mm MDF to be used with a 3/4" template guide bush is screwed to the end of the rail. The screw holes in the rail end will never be seen as they are inside the joint once assembled. 5 years later the bed is still going strong, and the timber wasn't a strong hardwood like Jarrah it was recycled oregon. I did use hardwood tenons though.

Most of the stresses on bed joinery are end to end, not side to side.

If a short/stub tenon is your only option I would go to my option (1) Glue tenon into rail. I mortise my rail ends on a horizontal mortiser so depth is only restricted by the bit length which, of course, is considerably longer than a router bit.
I have found unglued loose tenons require the extra length to prevent mechanical fixings splitting the tenons or, sometimes, the rail itself due to the parallel grain. I guess thats why we were told minimum of 1.5 times the width as apprentices.
The third tenon thickness is not adhered to in bed frames. Often the rail is full size mortised into post or almost full size into post with only a 5mm shoulder all round. A cross fixing runs from inside face of post and on through the tenon.

Hi Derek,

Traditional term was slip tenons if you want to check the old English books.

I'm working on a deliverable and logged in quickly after a google search and this came up. Sorry for rushed reply.

The legs look approx 60mm square?

Depth of the blind mortice is 40mm into the leg, as you said.

I'd make them 40-60mm deep into the end grain of the rail as well. Then glue the slip tenon into the end of the rail, let the glue dry, then cut in the mortices for the bed stiles, in case there's overlap in the mortice slots. Being 125mm rail width, you could get away with gluing in a single 80mm tenon - upper limit of allowing for shrinkage, but I think it'd work, and save you cutting a castellated tenon. If you are worried about movement, only glue the upper 2/3 (edit: or make 2 x 50mm twin/castellated tenons with a joining haunch.)

To answer your question, I think 28mm deep slip tenons is too shallow. There's a lot of moment on the rail due to their width, and Jarrah isn't the easiest to glue (but I know you have lots of experience.)

Do you have a horizontal borer? Or a lathe you could mount a drill chuck in to the head of?

This may be a better option with a 10-12mm forstner bit.
https://www.brwoodworkers.com/wp-con...ng-Machine.pdf

You'd have to do a bit of cleanup of shoulders with a chisel, but no biggie.

The other option is mortising bits and a slot mortiser, but they're expensive.
RH Rotation | Carbatec

Saw a cheap horizontal mortiser advertised in Perth. PM me for details if you want. I'll check in Mon morning.

A
[edit - saw rusty nail's comments - you could go 15mm thick tenon into your 60mm legs as he mentioned - I personally wouldn't go thicker as it leaves you 8mm meat on the mortice cheeks. The only guide for me is that I'd leave enough meat on the mortice cheeks so the rail doesn't split if it warps. Assume the rails are centred on the legs? His rule of thumb on unglued tenons makes sense to me too - if they weren't glued and being used with KD fittings, my gut says 100mm min depth, but I'll defer to his experience here.]

[edit II - a.k.a. false tenons - one more term to look up if you want details in old books.]

Thanks. I have moved on quite a bit since my original post. Go here to see what was done: Hidden bed bolts

Regards from Perth

Derek