Revisiting loose tenon joinery

[Derek Cohen]

I built a little jig to align the ends of the 10mm mortices to be made with a Domino DF500 ...

https://i.postimg.cc/MGDYkP6D/12.jpg


The stretchers are 125mm wide and 26mm thick Jarrah.

The loose tenons are 58mm in total length (29mm each side), made in the same Jarrah as the stretchers ...

https://i.postimg.cc/ZKGH6vsr/13.jpg

The fit is tight (not too tight), which is important and the strength lies with the faces and not the ends. The is about 3mm each end for wiggle room ...

https://i.postimg.cc/y6rvYbFp/14.jpg

This is going into two single beds ...

https://i.postimg.cc/fLRfMckh/15.jpg

More on the joinery later.

Regards from Perth
Derek

[Kevin Jenness]

One thing to consider when using that wide of a spline is that you may need to clamp the rail mortise cheeks to get a tight glue joint there. The post mortises are not likely to need it due to the greater thickness around the mortises. Your photo shows no problem but I have seen wide mortises open up in relatively thin material. I would probably use two narrower splines in the rails rather than one wide one.

[Edward Weber]

I would add that although you state that the "strength lies with the faces and not the ends", there is no reason I can see to leave such a large gap in the fit. Loose tenons need not be literally loose.
The tenon and the mortised material are of the same species and will move together at a similar rate. You can fit a much tighter tenon to the rails, which would more closely mimic a traditional tenon and have the added strength.
I would also opt for two smaller tenons rather than one, as Kevin mentioned, in this configuration.

Just another opinion, there are many ways of building the same joint.

[Kevin Jenness]

there is no reason I can see to leave such a large gap in the fit. Loose tenons need not be literally loose.

[/COLOR]

Agreed. I like to fit the splines fairly tight for width to get some mechanical locking and definite location in addition to the glue bond. If there is room for corner blocks they are good insurance as well. I am repairing an old Morris style rocking chair with failed m&t glue joints in which the corner blocks kept the chair loose but useable.

[Derek Cohen]

Thanks Kevin and Edward

My plan has been to make the faces tight, leave a little wiggle room to fit, and then double pin (from the inside) both ends of the tenon to prevent any movement. Would the latter make a difference, or should I remake the loose tenons?

Regards from Perth

Derek

[Kevin Jenness]

If you've already cut the mortises and splines, I think the joints will be just fine as long as the rail mortises are clamped sideways. There's no reason for those glue joints to let go with or without pins. There's not going to be that much racking force across the ends of the bed. If I had not yet done the mortising I would change to two mortises and recut the splines for a close fit.

[Cameron Wood]

One thing to consider when using that wide of a spline is that you may need to clamp the rail mortise cheeks to get a tight glue joint there. The post mortises are not likely to need it due to the greater thickness around the mortises. Your photo shows no problem but I have seen wide mortises open up in relatively thin material. I would probably use two narrower splines in the rails rather than one wide one.

That's a good point in general about the mortise cheeks possibly spreading, but his material is considerably harder than hard maple, so shouldn't be an issue in this case.:)

[Edward Weber]

That's a good point in general about the mortise cheeks possibly spreading, but his material is considerably harder than hard maple, so shouldn't be an issue in this case.:)

Joints don't always open up due to stresses put upon them or because they're a soft species. Wood can move on its own, regardless of what species or how hard it is. If you cut a long mortise like the OP, you can relieve tension (potential energy) in the wood and the joint may want to open on its own. As the wood moves, the joint can get tighter on one side and begin to open on the other. This is less likely to happen with a pair of shorter length tenons.
I doubt anything bad will happen in the OP's case, but there is a reason why certain joints are made the way they are.

[Carl Beckett]

If you made the spline tight to the width of the mortise, any concern about glue getting trapped in the bottom and hydro-lock on the way in (or creating some pressure that pushes the joint apart again).

If not tight to the width, I am not sure I see any mechanical advantage since even a small movement means it failed/moved.

[Kevin Jenness]

If you made the spline tight to the width of the mortise, any concern about glue getting trapped in the bottom and hydro-lock on the way in (or creating some pressure that pushes the joint apart again).

If not tight to the width, I am not sure I see any mechanical advantage since even a small movement means it failed/moved.

It appears Derek has milled his splines leaving flats on the edges, as I do. The rounded parts of the edges can mate tightly to the mortise ends while the flat allows excess glue to escape. Standard dominos achieve the same result with flutes and a central spine on the edge. Some people do a full roundover and mill a groove in the spline face for glue relief.

[Derek Cohen]

I need to remind all that these are bed ends. They do not carry any load from the mattress. The unglued-double-mortice-and-tenon (plus-bolt) on the side rails will be tight fitting at the faces and ends. The side rails carry all the load. I built in wiggle room for the end mortices, and plan to pin these anyway.

Any concerns about this?

Regards from Perth

Derek

[Carl Beckett]

It appears Derek has milled his splines leaving flats on the edges, as I do. The rounded parts of the edges can mate tightly to the mortise ends while the flat allows excess glue to escape. Standard dominos achieve the same result with flutes and a central spine on the edge. Some people do a full roundover and mill a groove in the spline face for glue relief.

Ah got it.

Derek - I can not see these coming apart as you say, the load is minimal (perhaps handling or sliding the bed across the floor would be the worst it would see) - and your execution is always flawless so never a need to accommodate sloppy workmanship when it comes to your work.

Does the wood you are working with take glue well? (some exotics are dense and oily and dont take glue well) Even so, you plan on pinning so extra margin even if the glue did fail.

[Tom Bender]

Very nice, the joinery will be fine. Just a quibble with the edges of the end pieces. When tucking the bedding under the mattress those edges might be a little hard on the knuckles.

[Derek Cohen]

Very nice, the joinery will be fine. Just a quibble with the edges of the end pieces. When tucking the bedding under the mattress those edges might be a little hard on the knuckles.

Tom, good comment - that would be correct ... if the edges were a factor :)

The beds are planned to be platforms, that is, the mattress will lie flush with the top of the bed. No lifting of mattress to tuck in anything.

Regards from Perth

Derek

[Kevin Jenness]

I need to remind all that these are bed ends. They do not carry any load from the mattress. The unglued-double-mortice-and-tenon (plus-bolt) on the side rails will be tight fitting at the faces and ends. The side rails carry all the load. I built in wiggle room for the end mortices, and plan to pin these anyway.

Any concerns about this?

Regards from Perth

Derek

No, they'll be fine. Your work is so meticulous, I am surprised you asked for input in the first place. Remember, my free advice is worth every penny.