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Untwisting timbers #72 11/03/99 12:57 AM
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tony begg Offline OP
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I am building a small timber frame house using green timber (white fir) in a low humidity climate. Timbers check and twist alarmingly - it seems impossible to slow down the drying. Also can only work on it weekends so am perforce slow. I have planed and aligned reference surfaces on timbers that seemed dry, cut the joints, then had more twisting occur. Too much work and timber to just discard and try again.

Are their any techniques to untwist timbers at raising time. Would soaking them and then
applying torsion work ?

Next time and for the replacement timbers I am going to use already dry timbers !

Thanks for any help.

Re: Untwisting timbers #73 11/03/99 09:51 PM
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Brian Wormington Offline
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Sorry to hear about your problems.

Green timber has a moisture content that is higher than 28% and much of the distortion will occur as it initially dries for the first time. Re-hydration can never raise the moisture above 28%, so there is no way you can force the cells in the wood back to their initial green condition. The benefits of twisting the joinery together are almost nil because it will certainly result in an out of square frame as the torqued joints would probably not stand up to forces they are not designed to resist.

Thus, I think that your only hope is to modify the joinery using scribe rule techniques so that it will go together as nearly square as possible.

Sorry I can't think of a better solution, but you are facing the same problem that furniture makers encounter with air-dried timbers.

Re: Untwisting timbers #74 11/10/99 01:20 PM
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Brian:

I'm having the same problem as Tony - twisting hemlock. I'm building a 14' x 24' timber frame cottage using 8" x 8" hemlock. I have four 24' hemlock timbers which I'm using for the sills and the plates. Three of them are straight as a pin, but the fourth is starting to twist in the last 4' or so. I'm building it myself, and I don't anticipate getting to the raising stage until the spring.

Can you tell us a little more about the scribe rule technique? How much twisting can be handled in this way before I'm better off cutting the timber and splicing it with two shorter ones?


Bryson

Re: Untwisting timbers #75 11/12/99 11:54 AM
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Brian Wormington Offline
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Bryson:

Scribe rule is just like the process trim carpenters go through when fitting a base board or crown moulding.

The timbers are aligned as they are expected to mate in two dimensions (generally in plan) and offset in the third dimension(elevation). You could think of this as a virtual assembly. Then, the the joinery is created on one piece and its outline is transferred to the mating piece with scribes, calipers or plumb bobs. Generally, the process it to cut the first half of the joint on one piece and then transfer the outline to the mating piece. The first half is usually the tenon and the second the mortise because it is easier to project the outlines from the tenon to the mortise rather than vice versa.

Before the advent of sawmills, entire structures were created this way from crooked timbers (AKA the cruck frame). In the French scribe method, the timbers are drawn full-scale as mated on a level surface below the timbers and then the joinery and alignment is projected up on to timbers with a special plumb bob with a built-in cross hair.

Good luck.


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