Jan Bianchi
01-01-2010, 12:45 PM
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.
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.