Joinery question, one domino or two?

[nerfball]

Like a genius I put this in the wrong forum  [tongue]

Hi guys,

I'm building some table legs out of 1-½" Maple. The table top is going to be very heavy, and I'm concerned about shear strength in the legs. I was going to use (2) 6mm dominoes in each joint, but I wonder if one larger domino will give me more strength. Normally I wouldn't be concerned too much but the table top is roughly 300lbs (live edge maple). What would you do?

Just looking for some thoughts or reassurances. 1st time post, long time lurker, and I'm not sure if I've uploaded the image of the legs properly.

I should say there are two pairs of legs shown in the drawing.

[attachimg=2]

 

[ear3]

The image is at the end of the message, but you might want to insert it inline in the message.

 

[nerfball]

I seem to be struggling with the photo uploader, and my question might be unclear.

Here's a picture of the table with the legs. My wife is showing it off  [laughing]

It's just a mockup at this stage, and the legs as shown are skinnier than they will be once built:

[attachimg=1]

 

[nerfball]

That's better.

So again, the question is:

What would be stronger (2) 6mm dominoes per joint, or (1) 8 or 10mm domino per joint?

 

[duburban]

I would use one bigger domino or use the tool in multiple passes and mill your own custom size domino to suit. 10mm by X wide.

 

[jbasen]

Just to throw in a slightly different point of view.  Looking at the photograph I personally think the thin legs are a little out of scale with the beautiful, but pretty massive, top. I would beef up the legs a little to make them a better match for the top.  Then you could use a couple of 10 or 12 mm dominos and  create a joint that will really stand up to a 300 lb slab. 

 

[Dane]

Man, I'm not sure any size tenon is going to make that sturdy enough.  Someone leans hard on that assembly at a party and it could get real exciting.  I personally would weld up some steel legs if you are committed to the skinny look (which I think looks great).  If you really want the legs to be wood, you could box the steel with wood.  I've done that before, lots of work to make it seamless, but it works.

 

[Jesse Cloud]

The key element is how much long grain is glued to other long grain, expressed in area.  I'm not near the shop so I don't have the relative widths of 6, 8, and 10 mm dominoes, but if the widths are close, two sixers would be my choice since we are talking 24 mm of glue space (4 sides x 6) vs. 16 and 20.  Also you have the requirement that two joints have to fail to cause a problem.

Still another issue is that shear is not generally the issue for tables.  The arch enemy of tables is the twist and torque when people move them by dragging instead of lifting.  Pins are your friend in that scenario.  Corner brackets help greatly here, too.

One last thought, any of the three scenarios would probably work just fine.

 

[Birdhunter]

Both from an engineering view and a visual perspective the legs are far too spindly for the massive top. I think, without scientific analysis, the table would be subject to both racking failure and twisting failure.

I would suggest you rethink the support structure (legs et alia) for the table. Not just thicker legs, but rethink the entire design.

Something as heavy as that top collapsing on top of a person could be dangerous as well as embarrassing.

 

[GarryMartin]

Looking at the photograph I personally think the thin legs are a little out of scale with the beautiful, but pretty massive, top. I would beef up the legs a little to make them a better match for the top.

Man, I'm not sure any size tenon is going to make that sturdy enough.  Someone leans hard on that assembly at a party and it could get real exciting.

Both from an engineering view and a visual perspective the legs are far too spindly for the massive top. I think, without scientific analysis, the table would be subject to both racking failure and twisting failure.

I think you guys may have missed nerfball's earlier comment...  [wink]  [poke]

It's just a mockup at this stage, and the legs as shown are skinnier than they will be once built:

Jesse Cloud is on the money for me, but I understand the concern regarding the engineering of the legs in relation to the size and weight of the top. Perhaps combining some of the thoughts above, you could use fabricated steel legs but wrap them with the wood of your choice to get both the engineering and aesthetics you may desire?

 

[rvieceli]

Think about the problem in a different way.

From your drawing the table top is resting on six vertical legs that go from the top directly to the floor. Even at an inch and a half that should have no problem in holding up the top.

The problem is how to keep those vertical legs vertical. The design you have for them now seems destined for failure if there is racking of sideways force from either the side of the table or the ends. If you keep it in wood, I'd think you need to design some bracing to counter act the racking.

 

[BMH]

I concur vertical support is not the issue but becomes a major issue when any lateral force is applied. Collapsing 300 pounds becomes a dangerous event to anybody around. I would recommend googling large live edge table and look at images. This will give you a better idea how professional furniture makers addressed this problem.

You are going to have a beautiful table when done.

 

[nerfball]

Thanks guys for the good feedback.

Couple things:

a) - These Maple legs are a temporary measure until we can have stainless legs made, which will likely be summer time. I could wait, but we are buying a house soon and I want the table 'ready' for the house.

b) - I was thinking about adding braces/gussets at the top of the frames where they wouldn't be seen. I agree the twisting is a major issue. I'm very glad I posted the question because you guys confirmed my thoughts.

I think that most twisting/racking would happen at the top, rather than the bottom, so I think I'll add the braces.

Thanks again! 

 

[shaun.mcc]

Nerfball,

I think this is going to be beautiful! I agree with others about engineering the legs...and can totally see metal legs...I actually would think brushed brass would be cool to as that style is coming back and looks upscale i.e. Jeff Lewis Design. SS is cool too.

Back to the issue...are two smaller tenons likely to hold up better than one larger tenon to shear forces...I  don't think so (one of two might break...then the other)...but with that weight I'm not sure anything will hold...unless you engineer it. I have in my office at work both the little black book (engineers book) and a much larger engineering handbook that cover various strengths/shear etc. Might look at one of those...the second one about a $100 book...but every engineer or machinist has that one (if you know anyone).

Shaun

 

[nerfball]

Thanks for the comments! We are looking forward to having this table complete. It's wood that has been salvaged from our recent home in British Columbia from a tree that had been felled over 100 years ago.

We are going to inlay cast glass into some of the defects to give the appearance of having a couple lakes
The glass will be coloured a translucent light blue-ish and we may put some stones in the bottom of the largest one.

[attachimg=3]

[attachimg=1]

[attachimg=2]

 

[GarryMartin]

We are going to inlay cast glass into some of the defects to give the appearance of having a couple lakes
The glass will be coloured a translucent light blue-ish and we may put some stones in the bottom of the largest one.

Sounds great.

Here's something I came across recently that may or may not be of interest as an alternative - Photoluminescent (glow) powder mixed with clear casting resin...

http://www.instructables.com/id/Glow-table/

 

[nerfball]

Sounds great.

Here's something I came across recently that may or may not be of interest as an alternative - Photoluminescent (glow) powder mixed with clear casting resin...

http://www.instructables.com/id/Glow-table/

Interesting! Thanks for that.