Making pins for pinned M&T joint

[jonathan snyder]

Hi Folks,

I like to tap into your collective wealth of knowledge once again.

How do you make pins to pin a mortise & tenon joint?

I would like to use maple pins on a walnut side table at the apron to leg joints. I would like the visible ends of the pins to be square.

I made a couple practice pins yesterday, but it was time consuming. There must be a better way.

What diameter pins do you recommend for a table apron to leg joint?

Thanks
Jonathan

[Jamie Buxton]

If you use square pins, making the pins themselves is easy: a couple passes with a table saw makes long sticks of the correct cross-section, and then you whack 'em off at approximately the correct length. The challenge is to make the square holes for them to go in. A hollow-chisel mortiser is a fast way to do it. A muscle-powered way is to make a template with a square hole in it, and use it to guide your chisel as you start the hole. To make a square hole in the template, I use a table saw. I hold the blank down on the table and against the rip fence, and plunge the saw up through the blank. Four cuts, and you have a square hole. The saw kerfs continue beyond the hole, but that doesn't affect the functionality at all.

[Jim Becker]

Jamie, you can take the "square dowels" and whittle them round from about 1/4" or so beneath the intended end, drill a round hole slightly smaller than the whittled stock, square the "mortise" with a chisel about 1/4" deep and then glue and pound the sucker home. This may very well be faster than dealing with the hollow chisel mortiser and can be done after the joint is already glued.

[Mike Cutler]

To make just a few can be a little tedious. I make them just like Jamie posted. Rip some long stock on a TS and then use a bandsaw or a backsaw to cut them to length. The easiest way to cut them on a TS,and the safest for me, is to "practice" cut a rabbet in the edge of the board that leaves me with a perfectly square tenon waste piece.

The size of the pin is kind of up to your visual aesthetic. I'm thinking 1/4" or 3/8" square should be fine.

[Alan Turner]

To make a square ended dowel you can use a dowel jig, as from LN. Cut your stock right at the finished dimension, say 1/4" square, cut to length, hand taper one end to fit into the jig hole, and pound away a bit, stopping a bit short of pushing it all the way through. Then, back it out.

Depending upon the wood of the table leg or door stile, you can drill a hole, and then just hammer in the dowel, and the sqaure section will cut its own hole deep enough to appear to go into a square hole. But for larger holes, you will need to mortise a bit. You can mark this mortise with a hollow chisel bit, and then just remove a bit, say 1/4" deep or a little less, and hammer away. To hold the dowel straight as the square section enters the square hole, use an open ended wrench on the square section.

[Greg Robbins]

You may find this hard to believe, but you can take a square peg and drive it into a round hole. Just drill your hole the so it is the same size as the width of your square peg. Now line the peg up to the orientation that you want it on the piece, because you only get one shot at this. Now take a hammer and drive it in. Try it on a piece of scrap and you'll be a believer.

Regards

[Ernie Hobbs]

I drill a round hole and take square pegs and whittle the entry end just enough so it will fit in the hole, leaving the rest of the peg square. This way, as you drive it in, only the square end is visible.

[Pete Bradley]

I'd probably put in a round dowel with a square plug over the top. Simple, strong, and it also eliminates the risk of that sinking feeling when a pin stops before it hits bottom.

[Cliff Rohrabacher]

Pins are for looks not strength. Keep that in mind. A pinned M&T is weaker than a non pinned one.

[Michael Fross]

Pins are for looks not strength. Keep that in mind. A pinned M&T is weaker than a non pinned one.
Hmm. Is this true if the joint is drawbored? I would think that the process would result in a stronger, tighter joint. However, I agree that a purely decorative pin would slightly weaken the joint, but I wouldn't think it would matter that much.

Thoughts?

Michael

ps. I supposed I should describe the technique. Drawborded MT joints involve drilling a slightly offset hole in both pieces and then when you pound in a tapered hardwood pin, it draws the joint tightly together.

[jonathan snyder]

Thanks Folks,

I got a few made. I ripped square stock, established a shoulder with a chisel, and whittled away. When it looked close, I pounded it through a hole I drilled in a piece of 3/16 steel.

Jonathan

[Mike Cutler]

Hmm. Is this true if the joint is drawbored? I would think that the process would result in a stronger, tighter joint. However, I agree that a purely decorative pin would slightly weaken the joint, but I wouldn't think it would matter that much.

Michael.
Mechanically, Cliff has a point. If I drill a hole through a Mortise& tenon joint I have created a weak area in the tenon behind the pin, extending towards the end of the tenon. I have also put a hole in the mortised memeber that can exert some amount of stress. I don't think that the amount of strength compromised is very significant though. The pin isn't that big. A square pin would create greater weakness areas that a round pin due to the direction of force and how the pressure is eqaulized.

Pinned M&T's have been around for centuries. They were actually the mechnical connection prior to adhesives. The original adhesives weren't that great and didn't have long lifespans, and or were not impervious to water, ergo the pin(s) were for longevity of the mechnical properties of the joint. Modern adhesives have negated the need for the pin(s) because they are so strong and the chemistry of the products aren't going to break down as readily as other adhesives that have been used throughout history.

I guess an argument can be made for drawbored pins to relieve some of the force on the adhesive component alone by tightening the joint prior to the adhesive setting. The cross sectional area of glued surface is probably stronger than the shear strength of the pin and M&T material though.

Personally I think they look nice when used properly, and add a design element that says that the builder cared enough about a piece to add them. I also avoid relying on glue alone to hold a joint together. I wasn't taught that way, so I add them in case the glue in the joint should fail for whatever reason.

The M&T joint is the workhorse joint of woodworking, and I believe that the pin still has merit in adding some additional mechanical aid in the reliability and longevity of the joint.

[Cliff Rohrabacher]

Hmm. Is this true if the joint is drawbored? I would think that the process would result in a stronger, tighter joint. However, I agree that a purely decorative pin would slightly weaken the joint, but I wouldn't think it would matter that much.

Thoughts?



There was a series of stress tests done by Woodworking Mag (I think it was them) in which they they found that a pinned M&T fails way sooner.
I think it's because the hole in the tenon weakens it and introduces a physical means of splitting it.
There was a link to it on this forum.

[Jake Helmboldt]

It was actually Wood that just did the test a couple issues back. And yes, the pinned ones failed at a much lower stress applied.

I think the other point made is primarily relevant; that pinned M&T joints will remain together if/when the glue dries and fails over time, and was most applicable prior to modern adhesives.

That said, I don't think the weakend joint is compromised that significantly if the joint won't be subjected to considerable stress.

JH

[Mike Henderson]

Based on what Jake, Cliff and Mike posted, maybe what you should do, Jonathan, is just put in square plugs to make it look like there are pins in the M&T (for decorative purposes), and leave the actual pins out.

Mike

[Bob Smalser]

Square pegs into round holes...Beall Tools and other sell dowel plates, or you can make your own:

http://pic20.picturetrail.com/VOL12/1104763/7099973/104689778.jpg

And if I were gonna pin it, I'd drawbore it. If you're gonna do it, it might as well be useful.

http://pic20.picturetrail.com/VOL12/1104763/5536778/70922369.jpg

[jonathan snyder]

Hi folks,

This has turned into quite an interesting discussion. This is what I like about the creek.

This is the first table I have ever built. Its a small end table with two drawers. I have 9 3/8" wide aprons with two tenons approximately 3" wide each. Based on a discussion in another thread (http://www.sawmillcreek.org/showthread.php?t=47169) (http://www.sawmillcreek.org/showthread.php?t=47169)) , my plans are, to glue to upper tenon only & draw bore the lower with an elongated hole across the grain in the tenon to allow for wood movement. I plan to put faux pegs in the upper tenon so it looks pinned.

In the above referenced thread, Martin S. mentions that he did not draw bore the lower tenon on a similar table, and now has a bit of separation at the joint.

I have already drilled the holes, so this is my plan and I'm sticking to it!!

Live and Learn I guess! I'm well entrenched in the learning stage.

Thanks to all

Jonathan - who is really enjoying the winter solstice today. Tomorrow the days start to get longer!!