I've started cutting my first english tie joint frame, with the help of our workshop students.
My co-instructor and I started looking at the dovetails and he suggested we wedge them to help deal with shrinkage.
I haven't seen this done before, but this building is a good place to try it, as it is a pavillion and the wedges will be accessible in future (no siding)...
Has anyone wedged this joint before?
I'm using 8x8 white pine as a tie beam so I'm assuming there will be around 1/4" of shrinkage, and would design the wedges to be driven in enought to take up this much slack.
It would be great to hear any feedback on this idea, and on cutting the ETJ frame in general.
Thanks in advance,
-Mark in Ontario.

Mark –

With very few exceptions my frames tend to be English Tieing, usually scribe but I have SR’d a few also.

I know this speaks only indirectly to your main question, and won’t help being at the stage your at, but I long ago abandoned the dovetail for the cog & clasp, it just doesn’t share the same shrinkage issues. Interestingly while at the Clumps event I asked a number of our Brit friends about this, and it seems to be a common practice on their side of the Atlantic also.

As far as cutting goes, be sure to connect your datums and draw your teazel’s end before you make the end cut for the plate tenon. Usually the Jowl is too large for the clamp of the mortisers, so I deal with this by screwing a two by block, ( aligned parallel to the datum ) which has a three inch wide slot cut in it, to the post and clamp the mortiser to that ( tending to grab the HCM if we’re working pine ) and use this to cut the crotch between the front of the plate tenon and the jowl.

I tend to hand pick saw logs ( my main supplier indulges me and lets me cruise his log yard even though he wants nothing to do with milling them )with very heavy butt flair to mill the jowl posts, so the grain flows back into the posts as was traditional. and even often opt for the English type true jowl ( when a project merits it ) instead of the taper more typically found here in New England.

Hope some of this helps.

Best with it,

I'm unfamiliar with the word datum, could you explain?
the posts are eastern cedar, from our own forest, and yes with ample flair for the teazle tenon. We are using snaplines for layout.

we have already laid out and cut the dovetails into the plates, so I spose we'll stay with the dovetail version, though really there is nothing stopping us from straightening out the cuts and screwing in a cog. I assume the clasp happens outside the plates?
thanks for the reply, Will.

Datum/s – is simply a word commonly used to describe those unwound planes of reference running through your timber, represented on it’s imperfect surface by those snaplines.

I wouldn’t change your dovetails at this point, and your thoughts on wedging seem worthy of a try. Keep us posted on how it works out over time.

The cog is placed at or near the inside face of the plate to max the relish behind it

Mark:
When considering the shrinkage remember that the angle of the dovetail in the plate and tie changes with shrinking and that any wedge would have trouble dealing with this geometry. 1/4 inch shrinkage would allow how much withdrawl and what possible failure modes, can the teasel deal with this extra loading? If there is a bent brace loading this post in a leeward condition what will happen to the system?
The dovetail has served reasonably well when it has been cut in dry materials and the joint is not dealing with much tension. Many modern joiners forget both of these things when they select this joint.

Joinery all needs to be designed with moisture content and differential shrinkage in mind.

Best,
Curtis

yes, the dovetail shrinks more at the wide side than the narrow side. So the wedges should be initially tight on the wide side and a bit loose on the narrow side. I'm thinking of wedging both sides of the dovetails, so the change in geometry will be split in half.... It's a lot of to-do to deal with the dovetail and next time I'll be checking out the cog. The English Tie Joint frame is quite rare in my area.
This building is 12'x15' and we are using a kingpost with principal rafters and ridge so there will not be too much tension.
I plan to leave a gap between the teasle tenon shoulder and the tie beam seat.(and milton,your post tells me there should be a similar gap on the upper shoulders of the post/tiebeam braces) Also a gap on the plate side of the teasle tenon mortice.
The question that remains for me is pegs.
I don't mind leaving out the pegs in the teazle tenons(we have common rafters running from ridge to plate that will tie down the tiebeams), but would like to peg the post/tiebeam brace....

Will, how do you deal with plate shrinkage in the post/tiebeam brace?

and by the way Will, have you not picked up the fine art of standing on the mortiser base?(grin... don't tell ontario workplace comp I said that....)

Hi Mark et al,

This thread is in great danger of getting out of hand.

You should cut all of your English tying joints tight using green timber and fit all pegs as if this joint would work perfectly now and evermore.

We know that over time it does not stay together as originally intended but it is doubtfull that you will still be hear when this joint needs a bit of reinforcing. When this time eventually comes a simple metal strap nailed to the side of the tie beam twisted through 90 degrees and bent over the wall plate is the standard solution. Probably up to 50 percent of old joints will eventually require this treatment but not all joints exhibit this tendancy.

Listen carefully to the advice given by Will Truax re the flow of grain at the post head to help avoid shearing down the inside face of the jowl.

You MUST fit the teazle tenon peg. When the cross brace is working in compression it will try to lift the tie beam thereby pulling this joint apart.

This joint design has been around for over 600 years and has a proven track record. It's aplication seems to be fairly peculiar to England and east coast North America with minimal use on mainland Europe where other systems are employed.

The English tying joint is part of a system of building and if you elect to use this joint then you should also be using all the other attendant frame design features that can be seen on typical English frames like cross sills, intermediate studs, etc. A pic n mix approach to timber frame design is unlikley to achieve an optimal result.

Regards

Ken Hume
visit www.kfhume.freeserve.co.uk

thanks, Ken.
That's what a farmer likes to hear, don't fix it if it ain't broke....
the main point I'm picking up is that the cog is a better tie than the dovetail. And thanks everyone for the input. English Tie Joint is a frame I've been studying for a long time, I'm happy to have a chance to build one.

I have been wrestling with these issues for a good while now and would summarise as follows.

It may seem sacreligious to say so but in my opinion (despite a very long track record);The English tying joint does not work that well!

There; I've said it! And this from an Englishman too....

Ken says it all with his accurate observation that about half of the historic examples have been reinforced with iron bands. Now this could be down to other factors found in historic frames; such as subsidence of foundations (what foundations?) placing undue stress on areas of the frame. However you think about it, the shrinkage of the dovetail will losen the joint and compromise it's ability to tie.

If you are dead set on authenticity, one way to deal with the shrinkage that I have learned from historic frames is to cut the dovetail at very steep angles (tapering from full width of the tie beam to say 1 1/2" or even nothing. This will reduce the amount of spread at the plates for any given amount of shrinkage on the tie beam but it will still move a bit.

One should consider the forces at work within the frame when deciding whether to use the dovetail joint. For example; if the design of your frame puts significant thrust on the wall plates then you need a strong tying joint. If however you have purlins taking much of the rafter thrust them you don't need to be as cautious.

Then there's the question of whether to leave a gap at the teazle tenon shoulder to allow the tie beam to settle when the plate shrinks. The theory is good but what about the top shoulder of the brace? If you leave a gap here then you have a loose brace and a wobbly frame.

If you don't leave gaps at the shoulders then the plate shrinks away from the underside of the tie beam and is left fairly loose and at the mercy of what ever the rafters want to do to it.

You also end up with all of the loads from the tie beam (and in a traditional English purlin roof frame this generally means all of the roof load) bearing on the teazle tenon shoulder. Hence the need for good swept grain in a jowl post and the large number of historic examples which have splits runing down the length of the jowl. OK; I know that this is also due to heart shakes at a very inconvenient location but you really have to pick & saw your logs well to avoid this.

Even a cog joint instead of a dovetail doesn't get you away from these issues.

When choosing this joint much will depend on your customers expectations about tightness of joinery over time. It is unlikely that the frame will fall down due to your choice of dovetails or cogs.

So there you have it; a character assasination of the English tying joint. It's certainly not a perfect joint but it does stand the test of time sometimes (with a little help).
Having said all of this though, I agree with Kens approach. This is house carpentry in green wood we are talking about and it is possible to obsess about details.

Best wishes
Steve

"one way to deal with the shrinkage that I have learned from historic frames is to cut the dovetail at very steep angles"
how about 90deg?
using the cog takes care of one element of shrinkage, the problem of shrinkage in plate depth could be taken care of by not bracing between the post and plate, instead bracing between post and foundation(though I cannot recall any examples of this, tension braces often seem to be in the sidewalls).... not an option for our little building, as we are landing on 4 concrete piers.
I can't see building this frame without leaving a gap at the teazle/plate shoulder.... so what to do with the braces???
tight? loose?
one good thing about this pavillion, is that the work is divided into several sessions, as it is being built by our workshop students. This gives some time to think about things and work out changes in layout.
thanks again for all the feedback