Table: Will a wedge-joint be strong enough for the table leg

[Ctech83]

Hi,

I'm in the process of building this table of white oak. The length of the table is 150 cm, with a width of 50 cm. The table thickness is about 1.9 cm. The turned table legs is planned to be 3 cm in diameter where the joint with the table will be. The table legs will be slightly angled outwards from the center with 6 degrees.

Then to my questions. Will a 3 cm diameter table leg, into a 1.9 cm thick table, with a wedge joint be strong enough for this table? It will be used as a sofa table. So it will never have a lot of force on it - general use 0-10 kg. That said, if someone was to accidentally sit on it it probably need to withstand around 80 kg.

If the above is too weak - what are your suggested options.

 

[Jacob]

I would think OK but flimsy and not strong enough to sit on. The depth of the hole needs to be at least as much as the width of the leg i.e. needs thicker top or cross battens, or for this modern style of table a set of metal socket plates.

 

[Ctech83]

I would think OK but flimsy and not strong enough to sit on. The depth of the hole needs to be at least as much as the width of the leg i.e. needs thicker top or cross battens, or for this modern style of table a set of metal socket plates.

To get the depth of the hole the same as the thickness of the leg. i will then have to reduce the thickness of the leg to 1.8 cm.

Do you know where they sell socket plates with a 6 degree angle/slope?

 

[dzj]

I also think it would be too flimsy.
You could attach legs to dovetailed cross battens. (only to the battens, to avoid crossgrain-longgrain issues)
Or as suggested, some metal hardware...

 

[Jacob]

I would think OK but flimsy and not strong enough to sit on. The depth of the hole needs to be at least as much as the width of the leg i.e. needs thicker top or cross battens, or for this modern style of table a set of metal socket plates.

To get the depth of the hole the same as the thickness of the leg. i will then have to reduce the thickness of the leg to 1.8 cm.

...

I meant increase the thickness of the top! It's not a 'rule' I just thought it felt better.

 

[transatlantic]

Looks like a very weak design to me, especially at that size. If you're going to go ahead with the design then you could double the thickness and just have the chamfer around the edge be more set in ... you probably wouldn't even notice.

 

[Ctech83]

Hi,

I'm struggling to find a mounting plate with a 6-degree slope. I've found only 10 and 11 degrees.

Is threaded inserts an alternative that I epoxy directly into the table top? or is this a lot weaker than a mounting plate?

 

[Racers]

The thickness of you table top is the main problem of the design.
Two battens under the table top running the full length will stiffen it up and give you a thicker part to fix the legs into.

Pete

 

[Phil Pascoe]

^^^ or of course you could turn four rounded edged discs, say 100mm x 19mm if you have any more of the same timber, and glue them underneath before boring the holes. It might look a bit neater and lighter than a strip and it would achieve the same thing.

 

[Ctech83]

The thickness of you table top is the main problem of the design.
Two battens under the table top running the full length will stiffen it up and give you a thicker part to fix the legs into.

Pete

My calculations, based on http://www.woodbin.com/calcs/sagulator/ indicate that the thickness of the plate is not a problem. Should be ok up to ¨~80kg. I've already milled these to size, and tested the strength. Very little sag even on a single plank 810cm), so would expect a full width table of 50 cm is even stronger. Though being new to furniture building, I don't find the thickness of the plate to be an issue. Aesthetics are also more important to me than that it holds the weight of a person. I rather build new or repair the table, if someone unlikely will brake it. I like the simple and clean look of the table pictured, so i would prefer not to have battens strengthening the underside of the table.

I assume that the thickness is sufficient to hold a threaded insert at an angle of 6 degrees (seem to be about 1.2 cm deep only - https://www.rockler.com/steel-threaded-inserts-select-size) . I can use my drill press to make an accurate hole. Alternatively I can mount an angle top plate to screw the hanger bolt into. However that wouldn't be as nice. I know it is under the table, and no one will see it, but I will know it is there, so would prefer the threaded insert or through-hole wedge joint.

 

[Phil Pascoe]

It wasn't the top that's weak, it was the joints.

 

[Ctech83]

It wasn't the top that's weak, it was the joints.

Ok, i see. Thickness needed for the joint, and not the thickness in general. That makes sense.

Thanks for

^^^ or of course you could turn four rounded edged discs, say 100mm x 19mm if you have any more of the same timber, and glue them underneath before boring the holes. It might look a bit neater and lighter than a strip and it would achieve the same thing.

Thanks for confirming that this is a viable option. Then I only have to decide whether I want a through-hole wedge joint design, or if I want the table top to be clean without the wedge showing.

 

[paulrockliffe]

You could make the top without the outer edge strips, fix your legs, then bore through the top from the side, through the joint and then fill with epoxy/cascemite and a metal rod, threaded bar would work OK. A draw-bore effect might be useful to get the joint tight. Then fit the two edges.

Fundamentally the joint is strong enough if you entirely fill the hole and the leg cannot be moved so that it's not longer filling the hole entirely. Achieving either of those states is the tricky bit, which is why the above will make a big difference. The metalwork would stop the joint working loose or ovalising under load.

 

[dzj]

Looks like a very weak design to me, especially at that size. If you're going to go ahead with the design then you could double the thickness and just have the chamfer around the edge be more set in ... you probably wouldn't even notice.

Probably the best course of action.
You'd have to buy a bit more oak though.

 

[Ctech83]

Thanks for a lot of great input.

Do anyone have any experience with using brass as the wedge material in the joint? Anything challenging with this worth considering?

 

[Racers]

You would have to use PU glue to hold it in even then it might not last.
Bog oak would be nice, or any dark hard wood.

Pete

 

[Phil Pascoe]

Or epoxy.

 

[rafezetter]

If you wanted the brass effect at the top of the wedge you could use a normal hardwood wedge cut below the surface and just add a thin strip of brass to the top?

Or, if you used a solid brass wedge maybe you could drill a hole down the centre into the leg from the top once it's set in place and flush then use a screw to secure it instead of relying on glue?

If you wanted a clean look to the top you could try the invisible wedge joint where the joint is cut almost the same a few mm short of going through, but the wedge is placed inside and the action of driving the leg home forces the wedge into the groove in the top of the leg and driving out the sides at the top into the corresponding shaped hole. (a circular dovetail essentially)

Complicated, but way stronger than one of those threaded nut things you screw into the wood.

 

[Phil Pascoe]

Fox wedging. You'd still have to level the strip, so you'd just as well level the wedge. I'd have thought, anyway. If you epoxied the wedge in it wouldn't go anywhere. Still best to build up the thickness of the wood in the first place - probably simpler, too.

 

[Sheffield Tony]

Rare to see so many principles of woodworking ignored in one thread. Screws into end grain mentioned now ! A thin top, with no cleats, rails or breadboard ends will not stay flat. If the sun gets on it, it will surely cup. Legs joined into a 20mm thick top - no chance of blind tenons having enough purchase, even if you can find a drill bit to bore a blind hole without a centre point penetrating the top. Even wedged through tenons are a bit weak.

Someone on here has often advised looking at existing furniture and how it is built, and why. Good advice.