Timber envelope versus re-cutting when dry

[grweldon]

Please pardon if this has been asked before.  I searched on recutting and got a few hits that didn't answer my question.

As is normal for me, I'm thinking 3 projects ahead of myself.  Got a barn to construct, a house to finish and a runway to create.  Somewhere in there I want to build a small (say 16 x 20) TF structure.  In the process of clearing the land for the barn, I have some SYP logs than will end up as timbers for this barn.

When milling these timbers (pith centered) should I mill them oversize (1/2", 3/4", 1" ???) while I let them sit around and dry somewhat, then re-cut them to final dimension after much of the warping/twisting has taken place, or do I just cut them on-size and use the "envelope" process (not sure of the technical term) to envision the true timber inside the rough-cut timber when cutting the joinery?

I suspect these timbers will dry outside for 6 months to a year then will be brought in to the barn to better protect them from the elements before cutting joinery in another 6 months to a year.  In any case, I've got a few that have been laying on the ground for a month or so that I have to do something with soon or they will be unusable.

Now that I mention it, how long can a 12-14" diameter SYP log sit on the ground before it's unusable?  Is it still good when the bark just starts to loosen?

Thanks y'all.  I really wish I had more time and more years.  I got in to the sawmill and TF thing just a little late in life...

[beenthere]

Saw them asap and a bit oversize for truing up later.

[Dave Shepard]

I would just saw them and sticker them with some large stickers. I use 3"x4" dunnage, but that's just because that's what I have around for other purposes. The layout method you mention is called square rule, where you envision a perfect 7.5" square timber inside an 8"x8" timber. I haven't sawn any SYP, so I don't know it's drying characteristics, but square rule will accommodate a certain amount of movement. If they move a lot, then you can do what is called snapline square rule, where you snap a line on each face, and use that as your reference instead of the corner of the timber, which may have moved. I've never like resawing beams. It doesn't seem to leave a nice finish in white pine, and the pitch that comes out of the timber really gums up the band. Keep in mind that drier timbers don't work as well as fresh. Year old white oak is a bear to work. I've worked on some reclaimed dense SYP that was over 100 years old. That was some really bad stuff to work.

[grweldon]

Beenthere,

Can you be more specific than "a bit oversize"?  I'm an engineer.  We can't help it, us types prefer specifics over generalities.  It leave much less room for error!  ;)

Dave,

Obviously re-sawing timbers is almost twice as much work, however I wouldn't be concerned with finish much unless it affects layout for joinery.  The SYP I'll be sawing is between 30 and 70 years old with a tree or two in the 100+ range so no dense "old growth" wood to work with.  Regarding "square rule" layout, is the size of the timber envelope usually 1/2" (7.5" working dimension for a 8" timber) or does it chance with the size of the timber?

Thanks folks for taking the time to respond!

[beenthere]

Enough oversize to account for most warp from drying, which is near impossible to know precisely until after the timbers dry.
And the warp will depend a lot on the quality of the wood in the trees cut, how straight they are now and were when they were young.
No clear answer.  Cut extra so you have several to choose from when the time comes. But I would plan on re-sawing a bit. 
I know, it is tough to be an engineer in this business.  ;D

[Dave Shepard]

Typically you would choose the amount that you reduce the timber in each frame. Most of the small shed frames that I work on that use 6"x6", 4"x5" etc are reduced 1/2" from the nominal timber dimension. So, a timber with a target sawn dimension would be reduced to 7.5", even if you didn't quite hit the 8" dimension when sawing. This allows the timber to be undersized a 1/2" and not affect your joinery. Also, it could be quite a bit oversize and still not affect the final result. If you were working on a frame with larger timbers, say a lot of 10"x10", or bigger, then using a 1" reduction from the nominal would have a better proportion. The 12'x16' shed frame in Jack Sobon's "Timber Frame Construction" is mostly 8"x8" and uses a 1" reduction. I recommend either of Jack's books for a great introduction to square rule joinery and layout.

These Samson beam assemblies are hewn 12"x12" timbers and used a 1" housing. I thought I had a closeup of the joints to show the proportion, but I must not have uploaded one. Because they are hewn, I used snap line square rule and did all of my layout off of a chalkline. Personally, I would just saw your timbers and use them when you get to them. If any of them move too much to layout from the reference edge, then you can do snapline layout on those timbers. At some point I can do a thread on snap line square rule, but I don't think I have enough of the right photos uploaded to do it.



 

[grweldon]

Thanks Dave.. I have Sobon's book "Timber Frame Construction".  I read it a year or more ago and decided it was too much work but I still can't seem to get this type of structure construction from creeping back in!