Tuesday, January 27, 2015

What A Well Fitted Post And Rung Chair Joint Looks Like

An important part of chairmaking is knowing how tight to make a joint in order to get a proper fit. How tight I make a joint will depend somewhat on the type of wood used but, essentially, I want it as tight as possible without splitting the joint - and having to use a little force to bring it together is not necessarily a bad thing.

A good rule of thumb for testing a windsor chairmaking mortise and tenon joint is if you can put the joint about half way together with only hand pressure then you are about perfect. Then during assembly you can force it togther with a few hammer blows.

In windsor chairmaking, you are not often putting multiple joints together at once so a tight fit like this is possible without complicating a smooth assembly. On the other hand, with a post and rung assembly, I will back it off just a hair so I can have a bit more control on an assembly. When you add up a lot of joints that have to come together at the same time on one of these chairs then the extra give can be the difference between success and a struggle or failure.

Here is a short (and very out of focus) video of how tight I try to make the joints for a post and rung chair joint.


Enjoy!


6 comments:

  1. Great post Caleb. I find it really interesting as Curtis taught me essentially the same as what you suggested above, with the joint too tight to fit together by hand and requiring a good pounding together. I saw a few joints assembled like that on my trip to the U.S. last July and more than half had splits in the leg below the mortise where obviously the leg tapers away. On talking to Curtis when I visited with him, some 5 years after my initial class, we talked a lot about those particular joints. Curtis now sizes them essentially as you have in the video. Which is how I fit my windsor stretchers. Ironically, when learning how to make one of Brian Boggs side chairs with Jeff Lefkowitz, the pressure exerted on those leg and stretcher assemblies ( with multiple sash clamps ) is so great it almost makes you wince, thinking they may explode any second…...but they didn't fail and it was pretty impressive. I find the whole thing fascinating…. Cheers mate.

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    Replies
    1. Nice to know what Curtis is doing now. I have split those legs from too tight of a joint so I make some good test joints on a few before going ahead with the assembly. Splitting a joint will about make you cry after all that work. ;)

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    2. Caleb and Glen. I have seen lots of joint failures at assembly when we were using very tight joinery (± .002") and were pounding the joints together with a 3 lb. dead blow. I even saw a student completely destroy a front panel assembly and not even know it until he went to clean off the glue. That is why I use an assembly jig with two heavy duty I-bar clamps that provide even, smooth clamping pressure and a great deal of control over the process. I rarely have failures using this method, even with very close tolerances.

      I am curious if you have a tolerance you are going for between the size of the tenon and the size of the mortise, or is it something you a feel for.

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    3. Jeff,

      I don't have an exact tolerance that I aim for. I find that somewhere right near that nominal size of the bit seems to be about perfect since the bit usually drills a slightly larger hole than it measures.

      Also every different type of wood will result in a slightly different sized hole even with the same drill bit so I just make a test joint and go by how it feels when I fit it by hand.

      I mostly just use the dial caliper to judge how my test joint should effect my adjustments to my caliper on my tenon cutter.

      Delete
  2. This was a very good post! i also really liked the video! The narration in article and video made understanding it all much easier.

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