Joining Posts

[Radar67]

Hello all,
     I decided to ask the experts on this one. I have searched and found little info on it.

I am having trouble finding or making long posts (25 feet), could one use a mortise and tenon joint to extend a 15 foot post to 25 feet? I am going to build a gambrel style barn 24 x 40. I would like to hear comments on the best way to join the posts to get longer lengths. TIA

Sorry, I forgot to give the post dimensions - 8x8 and 6x6

[slowzuki]

Good afternoon,  I don't know off-hand any ways to join posts with wood joinery if they are structural.  Some type of steel connection would be needed if you want to stay close to the original dimensions and have a strong enough joint.  Or bracing near the joint to prevent buckling could be used.  Perhaps there is already bracing near the joint as a 25 ft unsupported column would be subject to buckling.

[hayton1960]

Hi Radar
I am a beginner framer, but for what its worth-
You can make long timbers out of two or more shorter ones, but a mortise & tenon isnt the best joint to use. Scarf joint is the method to use, but even then you need to position it carefully in the frame arrangement where it wont be under too much stress. Here in England we depleted our oak stocks many centuries ago, and we had to devise efficient scarf joints to fabricate long sills and plates from short stock. If I remember correctly, even a very well cut and assembled scarf will only acheive 50-60% of the strength of a solid timber of the same dimension. Check out Jack Sobons books or Cecil Hewitts English Historic carpentry; scarf joints have been used to repair rotten posts so I expect it should be possible to use one to make a new post. There are lots of variations and ways to set out a scarf joint. In fact I just cut my own first attempt recently; (there is a picture in my gallery if your interested) ;)
Hope this helps.
Cheers Jonathan

[mark davidson]

the simple and dirty way would be a straight scarf(halving) with steel bolts.
the scarf length should be 3x the timber thickness, and the bolts should be around 1/10th the timber thickness.
so for 8x8 you would use a 24" scarf with at least three bolts measuring 3/4"
6x6 needs 18" scarf w/1/2" bolts
buckling will be an issue if there is thrust on the post(probably would be on a gambrel style frame).... you may need to strap another timber along the side of the scarf.
If you're really unsure, you should get ahold of an engineer type or a real engineer.
I have rarely seen scarved posts in an older barn, except for repairs.

[hayton1960]

Hi Mark
Is it because at the foot (where scarfed post repairs are mostly made) that there is mostly compression to deal with, and it is really only suitable in that position?
Am I right in thinking that traditional english scarfs were designed to join horizontal members only (sills or plates)? Are they in fact unsuitable for vertical posts? Perhaps it may be necessry to re-think the design to avoid long continuos posts? (I am not sure what a gambrel is though, perhaps long posts are an important feature of its character?)
Cheers, Jonathan smile
smiley_fiddler

[Radar67]

Hello Hayton1960,
    Below is a link to gambrel barns.

http://www.barnmakers.com/gambrel_barn_kit.php

I may have to end up extending my sawmill rails to cut my own posts.

[hayton1960]

Mornin radar
(cold dark foggy day here)
I see now your trying to get the main central posts?
I hope you have good success extending the sawmill rails (and can find long trees!)
cheers jonathan

[Radar67]

I remember those days, spent three years in Germany back in the late 80s.

Yes, I am trying to get the central posts. I should have no problem getting the long trees as I have 20 acres of pines. I had planed to build a longer rail system eventually, this just moves my plans forward. Thanks for the help.

Stew