WIP: trestle kitchen table
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I agree Andy, the more faces in a glue joint the stronger the joint. So if the mortise is shouldered, you have a potential 9 faces.
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The mortise is what I suggested at first but I like the lap joint. Any faces which include end grain are basically write offs as far as strength so in a mortise and tenon joint you still really have only two good gluing surfaces. With the strength of glues today, the wood will be weaker than the glue joint I doubt you'd have any problem with the lap. If you wanted to maintain the the look of the lap (which I like) but you want to add some mechanical security to the joint in addition to the glue, you could do the dovetailed thing. Bevel the sides of the parts so the legs will only slide in from the top.
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@dave r said:
Bevel the sides of the parts so the legs will only slide in from the top.
Great idea, I like it! Now I understand what you mean about dovetailing. I was trying to figure out what the orientation of the dovetail would be. So this way, you would see the profile of the dovetail from underneath. -
Yes. Exactly. Fromt the front it would look basically the same as it does now.
I should have draw it up for you. Sorry about that.
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There certainly is nothing wrong with the lap, and as Dave say's with the glues we now use there should be no problem.
However I would like to discuss why I think a shouldered tenon is a stronger joint. This would be and end grain to side grain joint, which is stronger than an end grain to end grain joint, but weaker than a side grain to side grain joint.
An end grain to side grain joint is quite strong in compression and tension. It's weakness lies under racking stresses. This is where a (well executed) shouldered tenon comes in and supplies the mechanical advantages needed to not allow the joint to rack.
On the other hand the 1/2 lap, although essentially a side grain to side grain joint except that in this situation the grains are running perpendicular to each other. According to my Hero Bruce Hoadley..."The conflict between dimensional change along the grain and across the grain (especially where tangential opposes longitudinal direction) may become more important than the stress/strength of the original joint. The potential self destructiveness of such joints should always be anticipated"
This is extreme, and most likely will not take place in the joint of the trestle table, but what may take place is the differences in the way the woods dimensional properties change in response to changing moisture conditions, may cause the joint to open up slightly because the legs will shrink more "across" their grain, than the feet will "along" their grain.
Sorry, don't want to take this too far sideways, but my cabinet making teacher, my father, pounded stuff like this into me. -
PS
As for the dovetail, that's a great idea.
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Dale, yeah, I certainly get the cross-grain issue. Seems like a joint that shouldn't rely exclusively on glue. I've got a bit of an unconventional idea - doing something kind of like a double mortise, but with a lap/ mortise combo. Here is my model file, I drew the joint in SU. Also, in looking at it, there doesn't seem to be a good way to do the dovetail - since there's not much material between the verticals, and it would take extra material to dovetail on the outside sides. Anyhow, curious what you think.
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Andy, I really like this now. I haven't had time to download the SKP but I'll look later.
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I agree, that looks great!
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Very nice design. I did not see in your model how you are planning to attach the table top. There will be a great deal of expansion and contraction and I am a big fan of furniture buttons. They are small clips, shop made that screw to the underside of the table top and slide in a groove in the rails. Also you might consider a wedged tenon,not much more work and then you never have to worry about the joint having any issues.
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never did do the trestle design in the end. My wife nixed it as she had a trestle table growing up and hated the crossbar underneath. Here's a photo of our table. Simple 4 legs and solid top. Can't say enough nice things about maple butcher block!
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Very nice work.
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