How to allow for expansion & contraction in a wide door rail?


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I'm building a full-light exterior door, with a triple-glazed window unit.  I’d like this door to last hundreds of years, so I’ve bought some quarter-sawn 8/4 white oak, and I’m planning on a 12″ bottom rail to take the weight of the glass.

My plan is to give the bottom rail a double tenon, 3-1/2″ per tenon, with a full haunch, and pin both tenons. Single pinned tenon on the top rail.

What’s got me worried is thinking about expansion and contraction of the bottom rail, and how to allow for it in the joints.  I’m thinking that perhaps I could just pin one of the double tenons and leave the other one floating.  Or perhaps I could relieve the base of one tenon to allow for some movement.  Is there a better way, or am I overthinking it?

What did the old-timers do?  I haven’t been able to dig up anything on the subject, and it seems that it’s been almost unheard of to use such a wide rail for quite some time.

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That is one gorgeous door, curlyoak!  It's good to know about your issues with mold on the white oak -- I live on a river in Ontario, there is a lot of humidity in the summer here, and it's very dry in the winter.  Since I've already bought the oak for my door, I'm going to proceed, and my current thinking is to use Cutek oil on it rather than a varnish.

According to the numbers, my bottom rail may easily expand & contract 1/4" or more in our humidity extremes, so I will definitely have to account for it!

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3 hours ago, Oberon said:

According to the numbers, my bottom rail may easily expand & contract 1/4" or more in our humidity extremes, so I will definitely have to account for it!

That's for QS white oak or flat sawn? Seems high for QS, even at 12" width.

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Quartered oak is typically tight grain. If yours is then I think I would not make accommodations for movement. I'd pin the tenons.

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These and other doors just like these has a 10" bottom rail.   One deep continuous tenon that is dowel pined from the other side. The bottom rail is exactly even with the bottom of the styles. The doors are 18 years old. 

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It sounds like I may have been overestimating the movement of the wood -- I had assumed a yearly swing of around 10% moisture content winter/summer in Ontario.  But reading through the USDA Wood Handbook, it sounds like it may be as little as 3 percentage points.  That gives more like 1/16" movement over 12".

@curlyoak I'm no expert, but I wouldn't really say it's tight grain, I count between 6 and 8 rings per inch.

I appreciate the input as I try to get this figured out!

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@Oberon, I am currently building a 36” wide interior door from air dried walnut. It will have 5 ea. horizontal glass panels/lites. My bottom rail is 8”, top rail is 5” and 4 ea. center rails at 3” each. Stiles are 5” wide. I used double inline 3” floating tenons on the bottom rail, a single 4” on the top rail and 1 1/4 “ wide on the center rails. I came up with these measurements after much research on the net from those with multiple opinions. Mine will be used on new construction which just got permitted so won’t be installed for another 6 weeks but was hell bent on building it now. So far, just a glue up. Again, after much research, I did find that the floating tenons offered great help in making sure the rails and stiles joints were baby butt smooth and needed almost no sanding. Good luck with your door.

@curlyoak, those are beautiful doors! 

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