Tenon size?

[stuartpaul]

As per usual I'm probably over thinking this!

Dining table with 90mm square legs. Rail is 20mm thick and 140mm wide.

I'm familiar with the rule of thirds and this would give a tenon of just over 6mm thick and 95mm wide. I was going to go for 60mm 'deep'.

I'm feeling that 6mm is to flimsy and I'm tempted to increase to 10mm.

Anyone see any problems with the dimensions quoted? I really don't want a failure as the boss would give me considerable grief!

 

[Jacob]

It's just a rule of thumb, which you have misinterpreted. It applies to the mortice, not the tenon. A big mortice weakens the leg as it exceeds 1/3 of the width with increasing risk of breaking the sides out. A fat tenon obviously is stronger than a thin one.
So in your case the tenon could be the full 20mm without an over sized mortice, but a shoulder would reduce the tenon to 18 or 15 say, and make a better joint. At 140 the tenon depth could be say 100 with a 40mm haunch

 

[Steve Maskery]

Wot Jacob said.
S

 

[RobinBHM]

If your table is rigid, ie tenoned on both end rails and side rails, be careful to set out the joints on the legs as 2 mortices at 90 degrees can go in to one another depending on position of mortice on the legs.

Most tables are made for disassembly otherwise it limits the table width to less than a standard door.

Jacob's suggested dimensions would create the strongest joint. You may want to make the joint to suit mortice chisel sizes, typically 1/2" , 5/8" , 3/4", with some compromise on strength.

 

[stuartpaul]

Thanks all, - useful information.

Now the work starts!

 

[Fat ferret]

Should be fine. I usually use 33mm stock and make my tenons 25mm for 90mm legs. Just cut a cheek on the inside.

The rule is all very well but can't remember last time I actually used it. For instance 45mm stock for say a door would require a 15mm tenon but cause my router bits are dear I only have 1/2 and 3/4 same with chisels. Doesn't matter.

 

[Racers]

I would be inclined to do a barefaced tenon leaving the back of the rail with out a shoulder for maximum strength.

Pete

 

[Steve Maskery]

I'd do it the other way round. I'd do an (almost) barefaced tenon, (i.e. a tenon offset towards the outside). That way I'd increase the tenon length before the two tenons get in each others way.

I hope the pint is still on, Pete
S

 

[Eric The Viking]

Out of curiosity Stuart...

... are you planning to drawbore the joints in the traditional way, or do you intend that the M+T plus glue will be enough to keep everything together?

A kitchen table is high on my "want to make" list, but it's going to get far more dragging about than a dining table should. That said it's not on carpet, and the apron will be taller as I intend to put either a drawer in one end, or a pair of drawers in one side.

I can appreciate that drawboring might not look good, depending on the design you're going for.

E.

 

[stuartpaul]

Eric,

Wasn't planning on drawboring although that could change!

It is a dining table and won't get moved around very much at all so I think I'm comfortable without. However I'm going to use some wenge inlay to match an existing piece so it might actually look quite nice if I did (although that piece isn't drawbored so this might look strange).

It's a flip top jobby (see attached). The white bits show the overhang when open (about once a year!) which is 485mm.

I know this is not the way to do it but even as I sit here I'm thinking of reducing leg size from 90 to 85mm to relieve some of the chunkiness.

 

[Eric The Viking]

The arched apron will give you stronger M+Ts I'd guess as there's more area for the joint.

I wonder if a double tenon (vertically) would be stronger too, as it would be stiffer in a vertical plane and should reduce the tendency toward racking - Jacob, what sayest thou?

Also, might you taper the legs below the joints, if you want it to look lighter?

Having similar thoughts about the kitchen table, but I haven't got as far as drawings yet.

 

[stuartpaul]

The legs are tapered it just doesn't show in the drawing (10mm from just below the rail). This may increase depending on how it ends up looking.

I tend to find drawing gives me the basics but then I find myself changing bits and pieces as work progresses as there's nothing like 'in the flesh' to give you a proper feel for how it's going to look. In the past I've even found that full size drawings still lead to changes!

Hadn't thought about a double tenon. From my simplistic approach I wouldn't have thought it would add much extra strength compared to a single one?

More than happy to learn if others know better (which isn't hard!).

This mornings thicknessing has resulted in 22mm thick rails. A bit of hand planning should still give me 21 ish.

Onwards!

 

[Phil Pascoe]

I'm with Pete on the tenon. I suspect even 85mm is a bit "chunky" unless the top itself is quite thick, and they will need tapering to look right. You could of course run a rounding over bit down the legs which would lighten the appearance and helps stop chips and digs in the outside sharp corners, which will inevitably happen when you have people seated on the outside of the frame.

 

[stuartpaul]

This is my interpretation of Jacobs comment above. With just about 22mm rail thickness and 2mm shoulders at the sides (20mm at the top and bottom) I have a tenon of 18mm 'thick'.

 

[Eric The Viking]

Don't forget Steve Maskery's comment - mortice nearer the outside of the legs: it lets you have longer tenons before they meet each other inside the leg. Also, you're making work for yourself if you put the the apron pieces central on the side of the legs. You can have them planar with the leg faces, so that marking out is much easier, and if the tenons are to the back of the apron pieces, you only need cut three shoulders (the fourth won't be seen).

I appreciate, though, that having the apron flush with the legs is a design choice not everyone will like.

 

[Woodmonkey]

Most tables are made for disassembly otherwise it limits the table width to less than a standard door.

Jacob's suggested dimensions would create the strongest joint. You may want to make the joint to suit mortice chisel sizes, typically 1/2" , 5/8" , 3/4", with some compromise on strength.

I have a kitchen table build planned which may need to be disassembled, what construction would you recommend for this?

 

[Jacob]

Most tables are made for disassembly otherwise it limits the table width to less than a standard door.

Jacob's suggested dimensions would create the strongest joint. You may want to make the joint to suit mortice chisel sizes, typically 1/2" , 5/8" , 3/4", with some compromise on strength.

Most tables aren't made for disassembly in my experience and you can get wide ones through doors on edge (with a bit of a weave if the door is narrow).

I have a kitchen table build planned which may need to be disassembled, what construction would you recommend for this?

Stub tenon to locate the aprons (though you could get away without them at all) and corner fixing brackets. There's lots of variations on this.

 

[Giff]

What about mitred tenons (where they meet) in the leg ?