does this join exist ?

[stef]

and will it be suited for my writing desk ?
the writing desk (more or less like the picture)
will have (in my mind)wobbly leg. I therefore need a strong join at the top of the leg,
which should prevent the leg from being pulled out of the mortice.
so i thought of this one:

will this work ?

 

[crazylilting]

Looks like an interesting one to do. Do a test one and see how it fairs.

My suspision is it is like a lever. A desk is what? say 28" being held by 1". I'd be afraid of it failing. But one doesn't know until they try it.

It looks like a lot of work.

 

[seaco]

Hi Stef

I hope you don't mind me saying but this joint appears to be far to complicated and extremely difficult to get exactly right time after time?

How about a wedged tenon after all it appears there's two points of contact for each leg and would be just as solid but much easier, just a thought!

 

[crazylilting]

Just curious...

What software are you using?

 

[TheTiddles]

I think the top needs to be thicker and if so, there should be plenty of material for a through tennon

Aidan

 

[StevieB]

Just curious...

What software are you using?

Looks like sketchup to me.....

Steve.

 

[OPJ]

I agree with Aidan's comment. Regardless of whether you want to use a through tenon, I really think you should consider making the top thicker.

That joint you have 'designed' looks very complicated indeed - there's a lot to get right and, equally, a lot that can go horribly wrong! :? I guess you could consider using less 'fingers' - perhaps five and a three? With all those fibres, there should be a good enough surface for glue contact and bonding.

I like the overall look of the design though, especially those legs. It's gonna be a very interesting build to follow.

 

[arminiusrex]

Hi Stef.

I really like your design.


Is this for A level or is it a Degree Project??

The reason that I ask is that the joint you propose, although attractive, will not be seen when the construction is complete.

If an A level project, despite the extra work involved, you will not receive any additional marks for a complicated joint.

If, however, this is your degree project, innovation is valued.

Can I make a suggestion?

Rather that hide the joint that you have described, project the combs/tenons through the surface of the work and make a feature of them.

I hope this helps.

I'm a D & T teacher, by the way.

 

[arminiusrex]

Sorry Stef.

I have just seen that you are resident in Normandy.

Probably not a student then.

Still if I can help, please ask.

 

[Night Train]

I think by making the top part of the joint as a sort of cap you have make the usable table top thickness even less then it is.

If the cap is end grain to look like the end of the leg then it will have a rim of short grain which will not add anything to the strength of the joint.
If the cap is long grain then the fibres between the fingers and the cap will be very weak as the fibres will not pass from one to the other but lie parallel.

I would not do this except to look pretty at the expense of strength but as it will all be hidden then there is no benefit. It will also be very hard to make well.

A wedged through tenon will be strong but make sure your wedges push against end grain in the mortise and not against the long grain as it will split the panel.
If you don't want the joint to show like then you can always route out the end of the tenon after the joint is complete and lay in a veneer to give the impression of a different joint type or other effect.

I have seen a table where the legs are screwed to the table top, for speed of construction, by long screws from above and then an end grain veneer is inserted to the table top, covering the screw heads, to give the impression of a neat contrasting wedged through tenon in the same timbers as used in the leg.

 

[Night Train]

The other thing you can do, having had another look at your drawing, is to put the table top onto a frame that is connected to the legs.

You already have a drawer under there and that will need some sort of construction to support it so that may be designed to incorporate the strong leg joints in such a way as to still achieve the visual effect that you want. You could do this by having a rail joining the top of the front leg to the top of the back leg, on each side and then these side rails can be joined across the width of the table inboard of the legs and incorporating the drawer pocket, or opening, with slides.
Imagine seeing the construction from above with the table top removed and it would look like a very wide and short letter 'H' with two cross bars. The cross bars would hold the drawer and the legs would be tenoned to the top and bottom ends of the 'H'.
The table top can then be fixed to this frame with buttons or slotted screw holes to allow for timber movement.

 

[Racers]

Hi,

That joint looks imposable to do and not very strong to much short grain, like the others have said make the top thicker it looks un-balanced at the moment, you can put a wide chamfer on the edge if you like it thinner.
A stretcher high up between the legs will also help, and diagonal wedges in contrasting wood in through tennons are nice.

pete

 

[stef]

Thank you all for the response.
thinking about it with the helpof the comments, i do agree, it wont be taht strong.
i was thinking of cutting the cap so that the finger would be perpendicular to the grain, which means they would be weaker.

overall, the cap does not add to strength: i can see that by thinking this way: imagine i could route the fingers in the top from the underside (and the corresponding ones in the legs, and not make a separate cap.
The effect on the strength would be exactely the same as having the cap done in the way i drew it.
yet, it just means having 5or 6 thin tennons, rather than a think one.
would this be stronger ? i doubt. and infact, probably worse. if the thin tenons fail (breaking along the grain), that would be more catastrophic than the fat tennons coming unglued.

on the question of difficulty to make the join. i dont think it is that difficult.
a good table saw and some jigerry would make the fingers easy to cut.
the rest is not anymore difficult than a through tennon.

I am still left with the problem though. How to make the leg stronger.
I cannot have a thicker top without compromising the design.
Similarly, the H braces underneath is also a compromise i cannot make just yet. The top needs to look feather light.

the back legs (or at least the inner leg braces) will rest on the rear drawer/compartment thing, but not the front ones.. the front drawer will be much smaller, and should just be big enough for a pen, or two.
The back compartement will be almost invisible when standing in front of the desk.
The more i am thinking about this, the more i think i will use "forbidden" techniques. I am thinking of a tennon, reenforced by a steel thread, through the leg and the top, with a washer and nut either side. of course, this will have to be built in the leg, with just the thread sticking out at the top. Then a block to cover the thread and nut in the top should hide the trickery.

Not for A levels or degree, btw.. just for the fun of it !
and of course, it is sketchup 7.0

 

[stef]

Hi Stef

I hope you don't mind me saying but this joint appears to be far to complicated and extremely difficult to get exactly right time after time?

How about a wedged tenon after all it appears there's two points of contact for each leg and would be just as solid but much easier, just a thought!

what do you mean by wedged tennon ? a couple of wedges glued and forced through the top to "lock" the leg tennon ?
I can see that would work...

 

[Racers]

Hi, Steff

I used wedged tenons on the front rail of my chairs

It makes a really strong joint.

Pete

 

[seaco]

Hi Stef

I hope you don't mind me saying but this joint appears to be far to complicated and extremely difficult to get exactly right time after time?

How about a wedged tenon after all it appears there's two points of contact for each leg and would be just as solid but much easier, just a thought!

what do you mean by wedged tennon ? a couple of wedges glued and forced through the top to "lock" the leg tennon ?
I can see that would work...

Yes Steff something like this http://www.iverswoodshop.com/Articles/W ... age015.jpg

 

[stef]

yes, that's what i understood you were saying.
so at the moment, i am still unsure between this wedge, and the threaded rod..
I am feeling the thread a bit more, tbh..

 

[Night Train]

The other thing to take into account with a steel thread is any movement in the timber. The timber will move and the steel won't. Also a veneer, nut, washer and table top material in the joint all adds up to quite a lot of thickness in itself and still won't be as strong as a wedged through tenon.

You come back to the desire to have a thin, light looking top. To look thin and light doesn't mean it has to be thin.

I made this chair seat and although it looks really thin it is really 30-40mm in the centre.

You could easily feather the underside of your table top to the thickness you want while retaining the substance where it matters for sound joints.

To be honest, though it is great to be innovative in your design there are reasons why some joints have been used for table and chair construction since the 1660s.

You could use a lot of the top of the leg to make a substantial double tenon that is also blind (doesn't go all the way through) and fox wedged (wedged inside the joint as a part of the assembly). That would give you an easier joint to make and is very strong despite being shallow for your thin top.
If you are uncertain about a blind mortise and tenon joint then you could make it a through joint and then veneer the whole surface in the same timber.

Your legs also have a diagonal brace at the top, that would double the number of joints and so increase the strength too.

 

[xy mosian]

Hi Stef and All,

Any thoughts about the use of a long dovetail joint. The tail groove, on the underside of the top, being shared by the top of the leg and the top of the brace? A routed pocket, on the underside, would be needed to aid assembly of course.

xy

 

[stef]

Hi Stef and All,

Any thoughts about the use of a long dovetail joint. The tail groove, on the underside of the top, being shared by the top of the leg and the top of the brace? A routed pocket, on the underside, would be needed to aid assembly of course.

xy

Oh yes.. i think i see what you mean..
a V shapeed pocket throught the top (Widest part on the top side, narrow on the underside), and a rectangular pocket right next to it. The leg is cut with a dovetail, sliped through the top through the rectangular pocket, and then inserted on the V socket...A regular tenon piece then fills the rectangular pocket, as it's done its job..
That would be neat..but pretty tricky to get accurate, i reckon, as the angles of the V and the dovetail would have to match perfectly. and i'd have 8 to make...mess one up, and the top is scrap.

I take the point for the top looking thinner than it really is. that is still a compromise i may have to make.
so, the best candidate so far would be wedge through tennon.