How much of a bow in a timber is too much?

[beetle]

A couple of my Timbers have " taken off " slightly, maybe a 1/8" over the 14' lenght. These timbers are intended to be used as posts so I cannot use them for plates and put the crown up.

Is there a rule of thumb as to how much bow will cause a problem during fit up? Or any advise on how can I deal with this?

[Jim_Rogers]

We have discussed this issue, here at my workshops, and at other raisings, several times.
The general option on a bow in a post is too put the bow inward toward the center of the building.
If the post is a corner post towards the center of the gable or the center of the broad wall. That way vertical wall sheathing will span the gap created by the bow.
If the post is an interior bent broad wall post then place this bow towards the center of the bent/building. Same reason, vertical wall boards will span the gap.
If the bow was out in either location, then the sheathing will be bowed out.
If the post is an interior bent and interior post, therefore no sheathing, then it might not be seen at all.
One eighth of an inch over fourteen feet isn't that much at all.
Setting these posts up on saw horses with the bow up for a few days might settle the bow right out of them all together. (I've been told this will work).


Solutions during fit ups.
If you're into the fit up stage and you are boring your holes in the mortises, you bore these holes dead on the mark.
Then after you have placed the tenon into this pre-bored mortise, with the intended hole location on the tenon drawn in by pencil, but not bored, you can site the hole, from the layout face and see how far off the intended hole location is. If it's off a lot then you might need to find out why and fix that. Once fixed, then bring your drill bit down into the mortise hole and just prick the tenon a little, to create a mark where the hole should be.
Remove the tenon from the mortise and create the draw bore location based on the prick point mark, not the lines drawn.
This is allow you to compensate for irregularities in the frame caused by bow, drying, and undercuts.
If the fit-up shows an alignment problem and you've determined it is because something is too long, you can take the bent apart and trim it back, hopefully to the correct size and try it again.
I like to try to either cut right on the correct line or leave a little of the line in order to have enough later to use for final fitting just before raising.
Depending on the location of other things in the bent like tie beams and braces, girts, girt braces and nailers, an eight of an inch might not be a big problem at all. Because in the distance from the end of the timber to the first joint you may be able to bend this timber into line during the raising.
Good question.
And good luck, with your frame.
Jim Rogers

[beetle]

Thanks again Jim.... I have been steadily sawing and chippin for 6 weeks and I am about 1/2 done, so I am estimating I should be all carved out by the end of August or mid September. Then I will have to make the decision to raise or wait till spring, which I preffer not to do.

Still no electricity to date, using a finely tuned old Disston 8pt for crosscutting and a Atkins 5.5 for ripping, the old boring machine sure beats twisting your arm off. Hope to post some pics here soon.

[ARKANSAWYER]

  I have taken down frames of old buildings that were plumb and square for the most part and when looking at the timbers I can not figure out how that was.  They were no way near straight or square.  Like Jim said it is a matter of where you place them.  I only worry about the corners and door jams being of truly square  timbers and just deal with the rest.  You should look up into a Japanese temple for they use any stick they find and make it all work.  It is working with these minor defects and making a work of art that is called a building that makes timber framing so much fun.
ARKANSAWYER

[beetle]

My concern is that if my timber is slightly bowed or twisted, and I take all my measurements for the tenons from the referance face and edge of the sawed timber, then they will not match up true and square to the corresponding mortise? I know I can get around this by using the " finding the inner timber " on a hewed timber method. Where do you draw the line  before switching methods?

Maybe I am reading too much into this?  As I have read somewhere......." it aint furniture " its a Barn.

[Jim_Rogers]

When you're in the process of sighting a timber for crown, you look for twist as well.
One way to do this is by using sticks, sometimes called winding sticks. You place one on one end of the beam and then the other on the other end of the beam. Then stand back and site over the tops of the sticks. If these sticks are somewhat longer than the beam is wide the longer length of the stick will increase the amount they are out of line and show the twist more easily.
If the beam is twisted a lot you have two choices, ignore the twist and cut the tenons as drawn off the reference face or compensate for the twist.
If you want to compensate for the twist the easiest way to do it is to plane off the side that has lifted up and created the twist.
This side that is planed off should be the outside of the building and then the surface planed won't show in the finished "barn".
Then the timber should be true from one end to the other.
Then layout your tenon off of this straightened end.
How do you determine whether to ignore the twist or correct for it?
That all depends on the size of the beam. If the beam is large and you don't think you can straighten any twist out of it by assembling it in the bent then plane it straight.
If some of the joinery is up close to the tenon, therefore preventing the beam from being able to twist then plane it off.
If the some of the joints are in the middle of the beam and the beam is long and it can be twisted by using come-a-longs and straps during the raising then cut them without planing off the twist.
There can be other factors that can play into the decision.
Do you have a timber wrench?
I had one made for me.
It's a large fork made out of tube steel with a long round pipe handle on it. It's made to slip over a timber in order to induce some twist to the timber.
Here is a shot of mine:




This one is made for 5" timbers as I needed it to twist some 5x5 rafters into their seats. You can use this on smaller pieces by adding a spacer block of wood in between the wrench and the timber.
Some of the guys have made them out of plywood by cutting out the two shapes on a sheet of plywood and then gluing and screwing the two halves together. Then they rounded off the handle end to make it smooth to the touch.
I don't think I have a photo of one on file, but next time I go to a raising and one is there, I'll take a photo of it.
You can create your own by simply attaching a standard 4' or longer bar or pipe clamp to a timber and then use the left over bar or pipe as the handle to twist the timber.
Most of this twisting is done as the frame is being assembled. Either at the time of the bent assembly or at the raising.
Once the timber is twisted, using the wrench, and aligned to it's pocket, it is held in place, by the wrench operator, as the other timber is slid into position, once the timbers are together they should hold it there.
Sometimes this requires using a commander to help it slide together. Or wax. Or both.
At a raising of an old barn, that was disassembled, repaired, restored, and reassembled, it was necessary to put a twist into a 36' long plate.
As we were assembling the barn, the plate was lowered over the tenons on top of the posts, by a crane. One end was started and as the worked their way down the plate inserting post top tenons and brace tenons the twist was apparent.
To induce the twist to align the mortise to the post top tenons the crew chief used a pair of straps and a come-a-long. He placed the strap so that when the come-a-long was tightened up the strap connection would twist the timber.
Very interesting to watch, and it worked. Once the timber was twisted back into line, the plate was pounded down onto the post top tenons and held in with new pegs. Then the come-a-long was released. Once released you couldn't even see the twist.
This barn was assembled in 1856, and is fine and still standing, only now in a new location.
Hope this helps.
Jim Rogers