Tenon shoulders on Trestle table stretcher. - Woodworking Talk - Woodworkers Forum
 
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post #1 of 18 Old 04-05-2015, 03:32 PM Thread Starter
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Tenon shoulders on Trestle table stretcher.

For a through MT to join the stretcher to table uprights should I make shoulders on all four sides or would shoulders on the narrow top an bottom be sufficient? The stretcher is 7 x 6/4 so I am thinking a 6 inch long mortise would do but I am unsure about the number of tenon shoulders and corresponding mortise width.
Thank you.
Here is a sketch

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post #2 of 18 Old 04-05-2015, 03:34 PM
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my vote is no. 1 .....

For strength no. 1 is fine. To hide any "mistakes" in the mortise .... shoulders on all 4 edges will cover them best.

No. 2 is confusing. The shoulders need only extend to the body and be all the same location, not run the length as shown. For a through tenon, you mortise must be accurate and clean on the end that is visible.

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 04-05-2015 at 03:37 PM.
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post #3 of 18 Old 04-05-2015, 04:10 PM Thread Starter
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Quote:
Originally Posted by woodnthings
For strength no. 1 is fine. To hide any "mistakes" in the mortise .... shoulders on all 4 edges will cover them best. No. 2 is confusing. The . For a through tenon, you mortise must be accurate and clean on the end that is visible.
I am unsure what you meant by "shoulders need only extend to the body and be all the same location, not run the length as shown".

Here is another bad sketch.

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Thanks for your help!
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post #4 of 18 Old 04-05-2015, 04:40 PM
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your sketch is fine

You have sketched what I was referring to. IT's more a matter of choice I guess. The larger the tenon coming through, the better in my opinion. A wimpy tenon doesn't look all that strong, being reduced on all 4 surfaces, rather than just the two sides. JMO.

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #5 of 18 Old 04-05-2015, 04:44 PM Thread Starter
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Quote:
Originally Posted by woodnthings
You have sketched what I was referring to. IT's more a matter of choice I guess. The larger the tenon coming through, the better in my opinion. A wimpy tenon doesn't look all that strong, being reduced on all 4 surfaces, rather than just the two sides. JMO.
I like that also. Was just checking for soundness of design as far as strength was concerned. Two sides it will be!
This is great I appreciate all your help.
Regards
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post #6 of 18 Old 04-07-2015, 11:27 AM
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Bluefilosoff, I'm enjoying the threads you've started and the questions you've asked, since I too am in the process of building a trestle table. I've opted for shoulders on all four sides of the tenons on the stretchers. Although it's not a big deal, the shoulders on the vertical sides provide some rotational stiffness about a vertical axis. The stretchers are 1.75"x6" in cross-section, and the top edge is 14" from the floor. The top cross pieces, the feet, and the pedestals are all formed from two pieces glued along the center-line, so that the mortises can be cut on the table saw with a dado set. As others have pointed out, the mortises on the outside of the pedestals need to be nice and clean, since they will be visible. In my case, I undersized those mortises by about 1/8" in each direction, and will finish them off with a router using a template and pattern bit. As always, there are many ways to get things done.

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post #7 of 18 Old 04-08-2015, 10:56 AM Thread Starter
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Quote:
Originally Posted by terryh
Bluefilosoff, I'm enjoying the threads you've started and the questions you've asked, since I too am in the process of building a trestle table. I've opted for shoulders on all four sides of the tenons on the stretchers. Although it's not a big deal, the shoulders on the vertical sides provide some rotational stiffness about a vertical axis. The stretchers are 1.75"x6" in cross-section, and the top edge is 14" from the floor. The top cross pieces, the feet, and the pedestals are all formed from two pieces glued along the center-line, so that the mortises can be cut on the table saw with a dado set. As others have pointed out, the mortises on the outside of the pedestals need to be nice and clean, since they will be visible. In my case, I undersized those mortises by about 1/8" in each direction, and will finish them off with a router using a template and pattern bit. As always, there are many ways to get things done.
Hey terryh,
This is good information thanks for that.

I wish I would have a cut the mortises on a dado but chalk it up to experience. I ended up hogging them out with a Forstner bit and cleaning them out as well as I could with a chisel. As it turned out I will also leave a narrow shoulder on the face side on each side of the stretcher in addition to the top and bottom like shown in your drawing.
May I ask, are your vertical pieces made up of a single board or are they also laminated face-to-face to thicken them up?
Additionally how are you planning to attach the tabletop to the supports of the trestles? I haven't figured that one out yet.
Finally will you be doing a through tenon tightened to the vertical with a key or are you planning another type of join say maybe a wedged tenon set up?
Here is a diagram also.

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.

Thanks for your help!
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post #8 of 18 Old 04-08-2015, 02:25 PM
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Bluefilosoff, the vertical pieces on my pedestals, are full thickness boards (1.75"), but they are formed from two boards edge glued. The glue line coincides with the center line of the mortices, hence I could rough cut the mortises on the table saw. I'm using Douglas fir boards from trees that we had to take down when we built our house 10 years ago. At the time, I had them sawed up into 8/4 boards, so I was able to get a milled thickness of 1.75".

The table is going to have a 30" middle extension, so I will be attaching a set of table extenders (type B below) on top of the pedestal assemblies.


Lastly, I plan to attach the stretchers using a horizontal wedge. When I was designing the table, I did give thought to attaching them to the inside of the pedestals using bed rail hardware like these.



In that case, I would have attached a dummy tenon and wedge on the outside of the pedestal to get the traditional look. In the end, I opted for the real meal deal -- i.e. a through mortise and tenon connection.

I hope you'll keep posting on the progress of your project. I'll follow it with interest. I'm taking lots of photos and plan to post a "start to finish" thread once I'm done. I work slowly, so it may be a while, especially with fishing season happening soon.
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post #9 of 18 Old 04-08-2015, 02:51 PM
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Quote:
Originally Posted by Bluefilosoff View Post
For a through MT to join the stretcher to table uprights should I make shoulders on all four sides or would shoulders on the narrow top an bottom be sufficient? The stretcher is 7 x 6/4 so I am thinking a 6 inch long mortise would do but I am unsure about the number of tenon shoulders and corresponding mortise width.
Thank you.
Here is a sketch

Attachment 147025
Shoulders on the top and bottom are sufficient. I've made several tables of this design including one we eat on everyday.
Jim
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post #10 of 18 Old 04-08-2015, 04:27 PM Thread Starter
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terryh
Those extensions look really nice. Maybe I will try on my next table.
I'll look forward to seeing your build video. I will try to post something when I'm done mine also.
Thanks again!
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post #11 of 18 Old 04-08-2015, 08:07 PM
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Keep in mind. On the tenon it's best to have 4 bearing sides to butt against the mating wood for more strength against
the wood crushing. Having only the top and bottom to bear leaves the joint prone to early wobble if the fibers crush or compress.

Al


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post #12 of 18 Old 04-08-2015, 08:16 PM
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Quote:
Originally Posted by Al B Thayer View Post
Keep in mind. On the tenon it's best to have 4 bearing sides to butt against the mating wood for more strength against
the wood crushing. Having only the top and bottom to bear leaves the joint prone to early wobble if the fibers crush or compress.

Al
Al
I agree with you on this for many projects and many types of wood, but this is a large dimension Red Oak trestle table. The two surfaces are sufficient for this. You don't have to worry with compression on a large piece of Red Oak. My own table is 10 years old and sturdy as the day I brought it inside. It can be disassembled in just a few minutes to move if necessary.
Jim
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post #13 of 18 Old 04-08-2015, 09:19 PM
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2 vs 4 sided tenons

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Originally Posted by Toolman50 View Post
Shoulders on the top and bottom are sufficient. I've made several tables of this design including one we eat on everyday.
Jim

With 2 shoulders, top and bootom you'd have the best leverage against racking, but the least amount of surface area for "crush".

With 2 shoulders on the sides, your have more surface but somewhat less leverage.

With 4 shoulders you would have the best of both worlds.

What works in practice is always good to know from someone who has first hand experience.

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #14 of 18 Old 04-09-2015, 05:58 PM
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Here is another viewpoint. This is from a 1979 Fine Woodworking book called Tage Frid Teaches Woodworking-Joinery Tools And Techniques

"A mortice and tenon joint should be designed and made so that it has the maximum long grain to long grain glue surface. The strength of the mortice and tenon joint depends entirely on the interplay between the cheek and shoulder of the tenon, which is the projecting part of the joint."

That said, Frid shows two side cheeks and no top cheeks and also two side cheeks and a top cheek that steps down in his examples.

He also says-"Four shoulders should never be used unless absolutely necessary. The joint becomes more difficult to fit because all four shoulders must be precisely located in the same plane. Also, glue surface is lost. On the other hand, if the design calls for carving and material will be removed around the joint, four shoulders ensure that the joint will not be revealed."
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post #15 of 18 Old 04-09-2015, 07:11 PM
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there's the mechanical and there's the glue

To get all 4 shoulders in the same plane is not that difficult. Just set a stop and use the crosscut sled. To get the faces in the same plane, is a bit more difficult but, not impossible. I use the bandsaw or a tenon jig on the table saw, IF they aren't too long.

A strong mechanical joint will take the strain off the glue joint. Long grain to long grain is the best glue bond obviously. I used a bunch of 4 shoulder tenons on this Mission quilt rack:
http://www.woodworkingtalk.com/membe...on-quilt-rack/


The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #16 of 18 Old 04-09-2015, 11:38 PM
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I think we're discussing two different things here. A glued mortise and tenon joint is one thing, a through mortise with a wedge is something else completely. In the latter case, the only thing holding the joint together is the tension on the stretcher arising from the wedge. Therefore, issues like bearing surface become important, and glue surface becomes irrelevant, because there isn't any glue. I don't have strong opinions on subject, since I'm sure shoulders top and bottom will work just fine (as Toolman50 argues) because the main objective is to prevent racking in a vertical plane. I also think shoulders on four sides, while requiring more work, will be even better, because those additional bearing surfaces improve the racking resistance in both a vertical plane and a horizontal plane. Both work, it's just a matter of choice -- I choose 4 shoulders.
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post #17 of 18 Old 04-10-2015, 11:20 AM Thread Starter
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More considerations have arisen in my fevered brain,
1. The stretcher is about 6 feet long to start with. I will reduce it once I have sized up the tenons but I want to give myself enough play (the tabletop is 9 feet long therefore I will be leaving about 2 feet on the outside of the trestles). Because I am going solo with this, the board will be too long and unwieldy to manipulate on a tablesaw so I imagine the best way to craft the tendons would be with a circular saw? Or maybe a router? Or would there be a jig that could be built?
2. I have already cut the mortises on the vertical pieces and I am practicing fitting the tenon with a practice piece. Should I work solely on the tenon to make it fit into the mortise or would one work on both? I find myself continually going back-and-forth between the two elements. I have a feeling that's not the right thing to do. Is there a rule of thumb about this?
Thanks everyone for your valuable assistance.
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post #18 of 18 Old 04-12-2015, 01:38 PM
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Quote:
Originally Posted by Bluefilosoff View Post
2. I have already cut the mortises on the vertical pieces and I am practicing fitting the tenon with a practice piece. Should I work solely on the tenon to make it fit into the mortise or would one work on both? I find myself continually going back-and-forth between the two elements. I have a feeling that's not the right thing to do. Is there a rule of thumb about this?
Thanks everyone for your valuable assistance.
The rule of thumb is to always fit the tenon to the mortise. It's much easier, and more accurate to adjust the size of the tenon, rather than to try and adjust the mortise. Going back and forth between the two will cause you nothing but headaches!
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