I have switched to using cogs in the normal assembly. I think it was the perceived difficulty of cutting the half dovetails in the end bents that first drove me in that direction. I get turned inside out very easily and the cog, in my eyes, is an easier joint for me to figure, I also like how they are cut, no finicky corners to deal with.

Typically principal rafters and common purlins are used but I have seen common rafters and principal rafters used, I see this could apply additional forces on the dovetail and the cog. Which joint would work best to resist these forces?

Raising is also a deal. In a large building you need a larger crew to stand the long walls up and the difficulty of assembling the truss or a large gin pole set up to get it up in place. Of course with todays technology it is no problem. I have read this is part of the reason they switch to bent raisings it makes for a more friendly raising. And a segway to other tie configurations but let's not go there yet.

Tim

I am almost finished cutting the joinery for a covered porch.
This will be for my house. I tried something different with the Tie Beam as it was going to be too low if I made it the standard below the plate method.
I'm not sure if it was applied correctly but it should be plenty strong.



What would you call this Tie Joint as it is different at each end.

Hi Will and Everybody;

Thane, collars do not affect this discussion, that I can think of. But, while we are on the subject, collars are normally in compression to try not to call them a tie. The only time they are designed to be ties are when they are near the bottom of the rafters, usually they are half of two-thirds the way up the rafters and keep the rafters from sagging rather than spreading.

I would call your porch frame assembly "Thane's Assembly"!! I like it. The tapered or gunstock posts in old frames in the North always taper into the building in the direction of the tie, but in the South, sometimes they put the taper in the direction of the plate like you did. Since your rafters are supported at both ends there will be no outward rafter thrust so maybe I wouldn't even call any timber in your frame a tie...."Tieless Assembly"! Sort of like a hammerbeam truss!

Thanks Jim, I did not know HATJ was on the web. Yes I was referring to that drawing. Here is a link: http://www.tfguild.org/joinery/part2.pdf

By the way, if anyone sees joiinery which is not in HATJ, let Jack know so he can add it in the next edition. I think he has about 13 more joints to add.

Tim, I know dovetails are very strong but they allow some slippage as they shrink. I do not know how strong a cog is. This is a good engineering question which would depend on the wood species, size of the cog, roof load etc.

Here is a normal assembly barn which was taken down after a wind storm blew a rotten gable end completely off. It had common and principle rafters which tenon into a five-sided ridge. The beam directly below the tie is a binding beam. This barn was one of two 40' x 40' barns next to each other on a farm of German-American decent here in Waldoboro, Maine.



Here is a normal assembly house frame in Waldoboro, Maine with the tie and plate flush and an "eaves purlin" tenoned into the ties.


Jim

I tried editing but ran out of the time limit and then the edit button dissapeared. Sorry about the typos in the last post.

Jim

Jim
In the Collar Tie frame I am refering to the Collar tie is located near the bottom and the end brace extends from the post to the collar tie. In this example the collar is indeed in tension and is hold things together. Even though it may not be part of this disscusion I thought it worth mentioning. Keeping in mind I am building smaller structures.

I did have a look at the on-line book of Historic American Timber Frames and am looking forward to some lively debate.


Thane

Hi Jim,

I find it hard to believe that a barn in such good condition as per your photos could have been allowed to be pulled down.

Why was the gable end not just repaired and placed back in position ?

Regards

Ken Hume

Hi Thane, could you clear this up a bit? Are you referring to the depiction you posted or another one, if another could you post that picture? It sounds of interest.

Tim

Tim & Jim
Here is an example I am refering to. Though I think the king post may have an affect on this one.




I appoligize for straying from the original topic of the six Tie connections.

Jim,

That is a great picture of the normal assembly. On that post I can't tell if it is checking or actually splitting from shear forces. If it splitting, could it be because the thrust from the rafters between the bents is causing the dovetail to slip (this could be from the ridge falling)?

The tie does have a dovetail on it right, or is there another connection from tie to plate? I could look up in my yellow book, but I have lent it out to some architects for their referencing.

ASIDE ROOF FRAMING: Is there any reason that the builders would not have used a purlin system into the principal rafters? Would this not reduce the thrust? Do you think they did not have the proper material for such a set up?

I see the check as a natural formation, it easily runs down the post from the square corner which the top plate sits in, many are like this. I also see the principal rafters holding up the majority of the roof, it is a complete unit. If you were to cut the boarding right at the principal rafters and disconnect them from the unit I could see thrust being applied to the walls. I also suppose the bay spacing could have an impact on this as well. Think of it this way if the check was due to thrust we wouldn't be looking at a picture of it now, a crack that long would not be much good with some thrust on it.

As for purlins, it could be a time issue, simpler to install rafters, the frame seem to be square ruled? and purlins were more commonly let in to the tops of the rafters and scribed. It is a newer barn and newer approaches to framing were used. It may even have been reworked 100 years ago, I am starting to guess now.

Tim