Morris Chair Arm Tenon--Dowel or Screw

[Jan Bianchi]

Cross posted at General Woodworking--no answers there. I thought I might find the answer to a mortise and tenon person over here.


In a previous post I asked about what joint to use in place of the traditional raised through joint on the arm of a Morris Chair Rocker. Several of you commented that I should just go ahead with a tenon on the end of the leg going into a mortise under the arm and pin it with a screw or dowel. Having read up on this, I now need to know what's better, dowel or screw and if the latter, then what size screw--6, 8, 10? Next time I will use a wedged through joint, but I'd already cut the leg too short to do that.

The purpose is to pin the joint so the arm doesn't pull up and away from the tenon on the leg. This chair is really heavy and if someone picks it up by the arms, there will be a lot of stress on that joint. I've read up on dowels and these sources say just to put the dowel a short way into the tenon because putting it all the way through would severely weaken the tenon. But the downside is that if the joint does fail, the dowel will be a problem to remove. I can't find any information about how far a screw should go through the tenon or what size it should be. I'm tempted to just use a 6 since I'm only pinning. But if memory serves me, which it rarely does, I usually see really big screws in this position. Maybe they're only there because the arm failed and someone added them in an attempt to fix it.

The front arm pin has to go through 1 1/4" of arm before it reaches the tenon, which is 1 1/4 inches in diameter, centered on the leg. The arm is 7/8" thick. The back arm tenon is 3/4" in diameter and there is 1/2 inch of leg the pin has to go through before it reaches the tenon. The book I'm using suggests putting a plugged screw there. Also if using a screw should I do a clear hole through the arm and only screw the tenon?

So what are the pros and cons of dowels versus screws as pins, and what size and how far through the tenons?

I sure is nice to have you all around to ask questions of.

[Kent A Bathurst]

I don't know that it matters structurally - in general - re: dowel v. screw. One thing about a dowel - as the arm gets thinner it gets more difficult for me to get a dowel in there. For example, I wouldn't try to put a 3/8" dowel through a 5/8" thick arm, but maybe that's just me. [EDIT - duh - you put the dims right in front of me - 3/8" dowel easy thru 7/8 thick].

If you were to use a screw (which is how I handle it), I'd suggest you consider sinking it into a counterbore, and then putting a plug on top - matching the grain as best as you can - can't really do this with a long dowel (but you could sink the main dowel into a counterbore then plug it).

Screw size - I would select the dia based on the length - maybe #6 up to 1-1/4" - 1-1/2" or so, #8 above that to maybe 2-1/2", and then a #10. Of course, my decision would be influenced by the size plug cutters I have on hand also. [EDIT - repeat duh - on the front I'd prolly use a #8 x 2-1/2", with a 3/16" or so counterbore for a plug. In the back, I'd look at #6 x 1" with 5/16" counterbore. THese would get the screw holding the arm on both sides of the leg].

The original Stickley, et al stuff often used pinned joints, and I always kinda figured they were screws and plugs - easier and cleaner to assemble, and easier to get a grain match. Could be wrong on that, though.
FWIW - I have a Stickley Morris chair from the 19-oughts IIRC. Legs have tenons through the arm mortises, no wedges, no pins, no problems. Glue does hold in a well-fit joint.

You could even veer off track a bit - I've used screws with square-cut ebony plugs sitting proud and with chamfered corners - you've seen that a lot. I'm going into my foxhole now, before the Authenticity Police begin the barrage about mixing styles - G+G with A+C.

[Jan Bianchi]

Thanks Kent. So far, no authenticity police are out today. Sounds like you'd put the screw almost completely through the tenon rather than just in a quarter of an inch or so?

Thanks a lot for the info.

[Kent A Bathurst]

Took a quick peek over the top of the foxhole - no incoming rounds, so far.......

Yep - that's what I would do - as long as you are going to reinforce the joint, might as well REINFORCE it, ya know? I'd put the screw completely through the tenon, and exit the far side of the tenon into the arm again (that's what my math was intended to convey, but I could have messed up the fractions). Putting in a longer screw is no harder (as long as you remember to wax the screw). I don't think there will be enough thread on the far side of the tenon to cause any appreciable cross-grain expansion problems.

[Jan Bianchi]

Thanks Kent. So far, no authenticity police are out today. Sounds like you'd put the screw almost completely through the tenon rather than just in a quarter of an inch or so?

Thanks a lot for the info.

[Jan Bianchi]

Sorry for the repost. Thanks for your help.

[Pam Niedermayer]

To get more responses, perhaps it would be a good idea to post some photos.

Pam

[Kevin Groenke]

Hey again Jan,

Have you thought about a wedged blind tenon?



You can use this joint even though you've already cut the posts to length.

You could even go for some structural redundancy by employing both a wedge and a peg/screw. Orient them 90 degrees to one another and you'll get the strength of both without compromising either.

-kg

[Jan Bianchi]

This I really like, Kevin. Unfortunately, I glued up yesterday and I assume I can't do this not having cut a space on the tenons for the wedge. If there is a way to still do it, I'd practice on the extra arms and legs I have for this project (not because I was prudent, but because I kept making mistakes). I really like the idea of wedges on the arms.

I'd try to post a picture, but that tests other skills I lack.

[Pam Niedermayer]

Hey again Jan,

Have you thought about a wedged blind tenon?



You can use this joint even though you've already cut the posts to length.

You could even go for some structural redundancy by employing both a wedge and a peg/screw. Orient them 90 degrees to one another and you'll get the strength of both without compromising either.

-kg

Great idea, Kevin, too bad it's too late for Jan. I was thinking of something similar, as seen at John Alexander's site, essentially a draw bore, not exactly what I'd call a dowel. In fact, if you (Jan) really mean a purchased dowel instead of a home made peg, I'd recommend against this.

John/Jennie Alexander's Green Woodworking

This approach would probably require one wet and one dry piece for maximum effectiveness.

Pam

[Jan Bianchi]

Thanks for the idea Pam. Looks like I've got a lot of ideas for the next project. I make my own dowels, but I'm going ahead with the screw on this one.

I tried to send you and Kevin a picture, but I can't locate Microsoft Picture Manager in my browser to add it as an attachment and pasting doesn't seem to work. I'm half way there. I can get the picture into my computer--I just can't get it out.

[Pam Niedermayer]

In Manage Attachments make sure your file size is not greater than the stated allowable sizes. To compress them you'd have to use some basic photo handling software that allows you to set the quality of the jpg, or whatever.

Pam