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Author Topic: How much bow is acceptable?  (Read 4426 times)

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Offline VictorH

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Re: How much bow is acceptable?
« Reply #20 on: March 01, 2014, 01:43:31 PM »
The workshop will be over Memorial weekend.  Here is the thread for it

http://www.forestryforum.com/board/index.php/topic,71929.0.html

Brad - he's planning on a post and beam so square rule won't really apply, although I'm trying to pull him over from the dark side  :D :D

Victor

Offline oe_alex

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Re: How much bow is acceptable?
« Reply #21 on: March 01, 2014, 02:58:32 PM »
Back in 2009, I wrote up a paper on definitions from NeLMA's rule book. And included some pictures to show that these definitions meant.
I have attached it as a pdf so you can download it and keep it on hand to understand what they mean.
I hope you find it useful.

Jim Rogers

I should clarify myself then. The "bow" is very minimal, is the "crook" that I'm worried about. 1/4" in the center on one, 3/8"-1/2" on the other.

Offline PaAnkerbalken

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Re: How much bow is acceptable?
« Reply #22 on: March 02, 2014, 08:55:06 PM »
You might want to check with FF member Rooster.  I sorta remember him patching in pieces into beams that had rot, damage, etc.  There were pictures as I recall.
logosol M7

Offline PaAnkerbalken

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Re: How much bow is acceptable?
« Reply #23 on: March 02, 2014, 09:10:20 PM »
 It's under re-facing a rotten beam by Rooster.....might give you an idea. smiley_thumbsup
logosol M7

Offline oe_alex

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Re: How much bow is acceptable?
« Reply #24 on: March 22, 2014, 10:36:49 AM »
So we have footings going in for this project sometime early next week.

My staff and I are still planning out the stages on how we're going to do this whole project. As we were discussing yesterday, the question came up about cutting the rafter seat cut. The two beams that have the 1/4 - 3/8" 'crook' to them are going to be the plates on which the rafters will sit. Will it be wise to get the beams up first and cut the rafters, individually measuring each one? The reason I ask is because the rafters are going to come together on top of the ridge with a 2" deep seat cut, my thinking that is if we cut them all the same that where the crook goes out on the plate beams, the rafters won't come together at the peak, leaving an open gap that will be seen. We also discussed maybe taking a strap and pulling them straight once in place, attaching the rafters, then letting it loose, but I would think that they will want to pull out, maybe taking the rafters with them.

Offline Jim_Rogers

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Re: How much bow is acceptable?
« Reply #25 on: March 22, 2014, 11:26:44 AM »
Ok, well maybe we should go over this again.

Bow is a deviation from a flat plane of the wide face of a piece of lumber from end to end
Crook is a deviation from a flat plane of the narrow face of a piece of lumber from end to end.

You're telling us that you have a "crook" timber. That means the narrow face is higher on the ends then in the middle if crown is down or lower on the ends if crown is up.

If you want the rafters to sit on the timber all the same then you either cut all the rafters the same and shim the ones that sit on the low spots or cut the rafters to match the crown so that they all sit at the same elevation for a flat roof.

Now, you have a bow and the middle of the beam is either further away from the ridge or closer to it, then you may have to custom cut each rafter to fit.

What I have done, in the past, to test fit all my rafters to my plates before they are up in the air is to put the plate on the foundation/floor system in the exact spot where they will be except not up in the air. Basically remove the elevation of the posts. Check that they are true and square. And then sit the rafters onto the plates to ensure that the seat cuts are right and the rafters will sit correctly when they are up in the air.
I don't know if you can do this as you are using a ridge beam as well. You'd have to "mock up" the elevation of the ridge beam in between the plates to make sure it will all go together once up.

Good luck with your project.

Jim Rogers
Whatever you do, have fun doing it!
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Offline oe_alex

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Re: How much bow is acceptable?
« Reply #26 on: March 22, 2014, 11:46:10 AM »
Thanks for the further clarification Jim. As a matter of fact, I have a little of both on them. I think the best way to go about this is to cut each one individually like you said.

Thanks


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