Floating Tenon Grain Orientation Query - Woodworking Talk - Woodworkers Forum
 
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post #1 of 7 Old 07-09-2012, 02:59 PM Thread Starter
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Floating Tenon Grain Orientation Query

I am going to use wedged floating tenons to secure my workbench stretchers to the 4" x 4" legs. Having said that, I would like to have a few opinions on what some of you believe the correct grain orientation of these floating tenons should be.

I have done a little testing with the grain going in two directions: Parallel (tangential) with the face of the tenon and perpendicular to it. The perpendicular being 'quarter-sawn'.

What I was trying to determine is how 'flexible' either tenon was in the different orientations. Not having any scientific gear to make a real comparison, I will just say that I thought that the quarter-sawn tenon felt a bit more flexible.

To be clear: The kerf in the tenon with extend 3/4's the length of the leg. In this case I am using 4" legs, so the kerf will be about 3-1/8" in length. However, the kerf will only extend down 3". The extra 1/8" is just a safety measure to trap glue and keep my wedge from bottoming out. I am marking my wedges, so this should not happen, but still I will take this precaution.

Photos are:
The test stretcher showing the double mortises (each 3-1/2" x 1/2")
A test floating-tenon with wedge
A test floating-tenon with grain in tangential (parallel) orientation
A test floating-tenon with grain in quarter-sawn (perpendicular) orientation

Does anyone have any experience with these? If so, I would like to know what you think. All thougths and suggestions are welcome.
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post #2 of 7 Old 07-09-2012, 03:18 PM
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Both of those will offer more strength than ever needed, provided the fit and glue is done properly.

But if you want to get technical, the link below will give you full answers. Once those are glued, the elastic deformation is no longer relavent.

If you tried to shear without the joinery, the first example will fail easier.

I usually keep my joinery lighter, but resort to calculation should there be any doubt.

http://www.fpl.fs.fed.us/documnts/pdf2001/green01d.pdf

Pure mathematics is, in it's way, the poetry of logical ideas. - Albert Einstein.

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post #3 of 7 Old 07-09-2012, 03:41 PM Thread Starter
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@WillemJM

Thank you, sir.

After reading the info on the link you provided I remembered that I have Bruce Hoadley's great book - 'Understanding Wood'.

I will take a close look at both.

Thanks for your comments.
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post #4 of 7 Old 07-09-2012, 06:58 PM
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Would these tenons be through tenons?
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post #5 of 7 Old 07-10-2012, 08:56 AM Thread Starter
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Quote:
Originally Posted by woodbutcher360 View Post
Would these tenons be through tenons?
Yes, wedged tenons go completely through the leg. Each side of the tenon has a kerf cut into it with a bandsaw/saw to about 3/4 of its entire internal length. A 1/8" hardwood wedge is driven into both kerfs to spread the sides of the tenon against the mortise. The tenon takes on a dovetailed shape.

Prior to this, the wood worker would have relieved the mortise about 1/8" at each outer edge (where the wedge is driven into the tenon) and tapered back to about 3/4 the length of the mortise to match the dovetail shape produced by the driven-in wedge. IOWs, the most internal 1/4 of the 4" mortise is left undisturbed. This section is not tapered in any way.

The attached photo shows a prototype (partial) tenon with its wedge. The black horizontal lines are incremented in inches. From this it can be seen that the wedge only extends into 3/4 the lenght of the mortise.

Several years back I built a mobile bench for my INCA bandsaw. Beneath the bandsaw I keep my Craftsman tool chest. This whole contraption (see photo of big blue) is very heavy, but it is extremely sturdy because it has held up for longer than I care to remember.

The point is that the base is held together with wedged-tenons. These were made with a mortiser and hand chisel. The joinery looks very sloppy to me (now), but in spite of my poor crafstmanship back then, the base has held together perfectly. And it has survived being shipped from NM to IL.

The Man must have been looking over my shoulder on that project.

Bottom line is that wedged tenons are IMHO, the toughest joinery except with the possibility of dovetails or pinned tenons.
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post #6 of 7 Old 07-10-2012, 12:45 PM
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You have answered your own question. That is exactly how my Grandfather showed me how to make a through tenon joint that will not pull out.
The orientation of the grain of the wedge is immaterial to the strength of th joint, but keeping the grain the same as the length of the stretcher will make it easier to drive with less chance of breaking when struck. He always used two wedges to form the dovetail.
The other joint he liked was the same but was a normal mortise and tenon and he tapered the mortise to a dovetail shape, cut his slots, started the wedges and when he drove the tenon home the joint was made. No room for error for sure, but you'd never pull that joint apart.
So, that's how I do it.
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post #7 of 7 Old 07-10-2012, 03:24 PM Thread Starter
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@woodbutcher

Quote:
Originally Posted by woodbutcher360 View Post
You have answered your own question. That is exactly how my Grandfather showed me how to make a through tenon joint that will not pull out.
The orientation of the grain of the wedge is immaterial to the strength of th joint, but keeping the grain the same as the length of the stretcher will make it easier to drive with less chance of breaking when struck. He always used two wedges to form the dovetail.
I was afraid you guys were going to think I was splitting hair. So, OK, I won't worry about the grain orientation of my floating tenons and use whatever hardwood I be happy about it.

Thanks for your help. I appreciate it.
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