Enhancing mortise/tenon joint with nuts and bolts? - Woodworking Talk - Woodworkers Forum
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post #1 of 28 Old 02-09-2012, 11:29 AM Thread Starter
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Enhancing mortise/tenon joint with nuts and bolts?

Hi!

I am fresh here. I have played carpentry my whole life but always in the wrong way. As far as I can remember every time I made something I tried to burn steps and get the final result in a rush, what means meh stuff.



So you can imagine that my "carpenter life" has a toolbox with dull chisels, wood corners attached with drywal bolts or nails (no joints) and projects with an absolutely lack of blueprints or plans. LoL! I know, a nightmare!



Anyway, now I am trying to start over the right way and the SECOND project in my new woodworking life is a decent workbench. The FIRST project is a wood mallet.

The case is that I have an ugly and wobbly workbench (yeah, no joints!!!) that I have used so far, but it's time to say goodbye to her.

The new one supposed to be made of thick roof beams and will have glued mortise/tenon joints for extreme stability and strength.
Since I am new in the joints stuff, I am still not totally convinced that they can do the job, so (here we go) I was thinking on trespass the joints with bolts and tight everything together with a nut the other side to achieve extra strength, but I am not sure if this is a smart idea.

Question is... Pinning the joints with bolts and nuts will:

1) Enhance the strength of my joints?
2) Weak the joints?
3) Do nothing?



Thanks!
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post #2 of 28 Old 02-09-2012, 11:43 AM
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On a properly designed and executed M&T it's my own opinion that a bolt probably wouldn't weaken it but would be altogether pointless... A redundancy.

What are your concerns with executing the joint?

~tom
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post #3 of 28 Old 02-09-2012, 11:59 AM Thread Starter
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Quote:
Originally Posted by firemedic View Post
On a properly designed and executed M&T it's my own opinion that a bolt probably wouldn't weaken it but would be altogether pointless... A redundancy.

What are your concerns with executing the joint?

~tom
Hey Tom, thanks for such quick response!



As I have mentioned I have ZERO experience with joinery, so I am a complete idiot about this.

My real concern is that I am tired about wobbly workbenches (in my opinion it is specially irritating when you have to perform tasks such as handsaw, planer, etc), so I want that my new workbench be REALLY steady.

I don't know, maybe you will roll over yourself in the ground while piss in the pants laughing of what I will say, but... being a M&T joint just attached and glued to each other I am afraid that someday the pieces will just detach -- or get loose and the workbench start to wobble.

But as for you have mentioned above, I think that this is just a silly supposition as the joint will keep it strong enough, right?

Sorry for my ignorance!

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post #4 of 28 Old 02-09-2012, 12:17 PM
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No reason to apologize. We all start somewhere. Modern glue has come so far that glue is far stronger than the wood that glued together. The joint will be the last thing to fail.

That said, glue joints most be well fitting not so tight that all the glue squeezes out and not so loose that there is a gap filled with glue.

Also glue is only strong when gluing long grain to long grain. What that means as a simple example is the sides of the board not the end.

Hope that helps! The great thing is solid joinery can be as simple or as complex as you like. It can all be done with hand tools too!

~tom
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post #5 of 28 Old 02-09-2012, 12:28 PM Thread Starter
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Quote:
Originally Posted by firemedic View Post
No reason to apologize. We all start somewhere. Modern glue has come so far that glue is far stronger than the wood that glued together. The joint will be the last thing to fail.

That said, glue joints most be well fitting not so tight that all the glue squeezes out and not so loose that there is a gap filled with glue.

Also glue is only strong when gluing long grain to long grain. What that means as a simple example is the sides of the board not the end.

Hope that helps! The great thing is solid joinery can be as simple or as complex as you like. It can all be done with hand tools too!

~tom
Thanks again!



Yeah, you really put a bunch of light over that!

:)

I am too much more confident now. And, yes, I am going to make the mortises manually (after to sharpen my chisels, of course) as I really have to practice carving, and also I don't have a plunge router yet -- going to buy one in a very near future.



Anyway, since we are here, I have another quick question about carving the mortises. Every time I install door locks I use to start making some holes with the driller to speed up (and make easier) the process. Is this feasible when doing mortises too or since I am going to make it by hand is safer (for the sake of the mortise quality) do the whole job with the chisel?
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post #6 of 28 Old 02-09-2012, 12:54 PM
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Taking away a majority of the waste with the drill is a very acceptable way when hand cutting mortise.
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post #7 of 28 Old 02-09-2012, 12:58 PM
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By all means use a drill if you care too. Much quicker! Forstner bits are typically preferred for mortises as they leave a relatively flat bottom. Drill away as much waste as possible be be sure to stay inside the boundaries of the mortice and drill straight.

Also, I should mention that there is some confusion surrounding glues due to all the advertising hype. Yellow glue, such as titebond, is more than sufficient. Don't get sucked into the foamy expanding gorilla glue tizzy... It's an absolute mess for joinery and really any furniture building for that matter.

I use to be in construction and guys acted like gorilla was the holy grail of glues, lol

~tom
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post #8 of 28 Old 02-09-2012, 12:59 PM
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post #9 of 28 Old 02-09-2012, 01:03 PM Thread Starter
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Originally Posted by Chuck M View Post
Taking away a majority of the waste with the drill is a very acceptable way when hand cutting mortise.
Cool, thanks a bunch!



It may seem to be a stupid question with an obvious answer, but as mentioned in the starting post, I have done DIY empirically my whole life, and mostly of times it has shown that my solutions were wrong. So since I am starting over and want to do the right way this time, I think that it won't hurt to ask even if I look an idiot!

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post #10 of 28 Old 02-09-2012, 01:11 PM
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wobbly benches

Imagine a card board box with no back or front panel, it will fold over easily. Now fold the flaps in on the back. It doesn't collapse as easily. If you fold the flaps over on the front, it's even more rigid.

So your bench with it's legs extending down, is similar. All the strength and resistance to "racking" is in the joints....not good. To prevent racking and wobble, the joints either have to be incredibly strong, braced with blocks or frames ...or have a back and side panels.

A triangle won't collapse, a rectangle will. We don't make triangle benches because it's hard to balance things on a point. We use slabs and rectangles to make benches, but they are stronger if triangles or solid panels are used for braces. Bridges have a million triangles because of this.

http://images.search.yahoo.com/searc...c7&fr2=piv-web

The type of joints will matter far less if the frame is properly braced. Any pins in a joint that want to collapse will either shear off or destroy the surrounding wood in the joint, neither of which is good. bill


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; 02-09-2012 at 01:23 PM.
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post #11 of 28 Old 02-09-2012, 01:20 PM Thread Starter
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Quote:
Originally Posted by firemedic View Post
By all means use a drill if you care too. Much quicker! Forstner bits are typically preferred for mortises as they leave a relatively flat bottom. Drill away as much waste as possible be be sure to stay inside the boundaries of the mortice and drill straight.

Also, I should mention that there is some confusion surrounding glues due to all the advertising hype. Yellow glue, such as titebond, is more than sufficient. Don't get sucked into the foamy expanding gorilla glue tizzy... It's an absolute mess for joinery and really any furniture building for that matter.

I use to be in construction and guys acted like gorilla was the holy grail of glues, lol

~tom
Hey Tom,

Great points, thanks for all the explanation!



For the glue, I should use a Brazilian yellow wood one that normally works fine for me, although by your other post I figured out that I have using glue wrongly too. Seems that gluing grain directly to top doesn't provide a very strong bond. I have to review it too.

Cheers!
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post #12 of 28 Old 02-09-2012, 01:36 PM Thread Starter
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Quote:
Originally Posted by woodnthings View Post
Imagine a card board box with no back or front panel, it will fold over easily. Now fold the flaps in on the back. It doesn't collapse as easily. If you fold the flaps over on the front, it's even more rigid.

So your bench with it's legs extending down, is similar. All the strength and resistance to "racking" is in the joints....not good. To prevent racking and wobble, the joints either have to be incredibly strong, braced with blocks or frames ...or have a back and side panels.

A triangle won't collapse, a rectangle will. We don't make triangle benches because it's hard to balance things on a point. We use slabs and rectangles to make benches, but they are stronger if triangles or solid panels are used for braces. Bridges have a million triangles because of this.

http://images.search.yahoo.com/searc...c7&fr2=piv-web

The type of joints will matter far less if the frame is properly braced. Any pins in a joint that want to collapse will either shear off or destroy the surrounding wood in the joint, neither of which is good. bill
So, let me understand this.

Are you telling me that even with joints, unless I use braces as complementary pieces to increase the stability my workbench still may wobble -- that's right?

I have seen in the link you provided some metallic braces -- could they be replaced by wooden triangles made of wood scrap and screwed/glued to the internal corners? Would it provide the same strength?

Thanks!
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post #13 of 28 Old 02-09-2012, 01:54 PM
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Quote:
Originally Posted by yankleber View Post
So, let me understand this.

Are you telling me that even with joints, unless I use braces as complementary pieces to increase the stability my workbench still may wobble -- that's right?

I have seen in the link you provided some metallic braces -- could they be replaced by wooden triangles made of wood scrap and screwed/glued to the internal corners? Would it provide the same strength?

Thanks!
No, not exactly. There are a million workbenches that rely entirely on precision mortise and tenon joints and date back a few hundred years. They are made with massive beams and heavy slabs and are incredibly stout/strong. The joints are strong because of the shoulders on the wood that resist rotation. Unless you want to make your joints accurately and use sufficent width material you...may not have a wobble free bench.
Mass is also important when planing and moving against the bench. The Japanese use pull saws because the the force is a pull rather than a push. They hold the work on the floor with their legs and feet and generally don't use a "bench" but rather a planing plank.
I'm not saying what you should do but rather suggesting other options to make a rigid bench, regardless of the joinery you choose. Look at other benches for ideas. The old English benches are incredible examples of woodworking joinery. bill

Any braces or blocks you use will certainly add to the stability of the bench rather than relying strictly on the glue strength and the mechanics of the joint to resist rotation....wobble.

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 28 Old 02-09-2012, 01:58 PM Thread Starter
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Cool, thanks!!!

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post #15 of 28 Old 02-09-2012, 06:19 PM
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Another very good option, and easily executed by beginners, is to pin the joint with a wooden dowel. Since a mortise and tenon joint relies on good contact area for the glue if your mortise is even a
Ightly bigger than your tenon the strength is reduced dramatically. Add a dowel to it and brawbore it, basically drill your holes through the mortise, slip the tenon in and a slight whack with a drill it to get a centerline, remove the tenon and drill the hole about 1/8" closer to the shoulder. When you pound the peg in it will bring the joint tight and add good strength.
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post #16 of 28 Old 02-09-2012, 11:56 PM
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sounds like your question answer is....

....

Last edited by user27606; 02-24-2012 at 12:35 PM.
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post #17 of 28 Old 02-10-2012, 10:52 AM Thread Starter
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Just be sure that I got right what you mean, I made a drawing. Please let me know if this is the idea!


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post #18 of 28 Old 02-10-2012, 03:28 PM
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Quote:
Originally Posted by yankleber View Post

Question is... Pinning the joints with bolts and nuts will:
accomplish nothing at all.
The strength of such a joint is dependent on the tenon and it's fit in the mortise. If the fit and glue up is correct then the tenon is the limiting factor and no amount of steel will change that unless you are wrapping the wood in steel.
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post #19 of 28 Old 02-10-2012, 03:56 PM
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Seems as if you have good advice already.

For knock down (something you can assemble and un-assemble) my favorite is a tight fitting mortise and tenon with a bolt and a barrel nut. It is very strong and stable.



For a work bench, this one was built with 2 x 4 pine studs purchased from Lowes, for the entire base frame, with a Maple top. Mortise and tenon, glued, no dowels, no pins, that was 2001 it is still rock steady.

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post #20 of 28 Old 02-10-2012, 05:25 PM Thread Starter
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Thanks for all the replies, fellows!

In the meantime I have found this interesting workbench project where the guy didn't use any joint for the main structure. Instead he used 3/8" threaded shafts along the horizontal beams trespassing the legs and tighten with nuts. What do you guys think about this?

For whose has interest and curiosity, the project can be checked out at:

http://www.angelfire.com/music2/construct/bnchthmb.html
http://www.angelfire.com/music2/construct/benchpln.html

I didn't know this technique and would like to know how strong and stable it can be if compared with a traditional M&T joint.

Thanks!
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