I was wondering the best way to drill, or chisel the angled side of the mortise for this joint. I have looked a the drill guides that timberwolf tools sells and the chain mortisers, all look like great tools but a little pricey for me right now.

You could go ahead and drill perpendicular to the face where the tenon runs through so all that is left is the wood running to the angle. Then you could simply chisel the remainder. I would recommend transferring that "interior" angle to the faces of the post for alignment ease. If you clean out the cut part of the mortise just mentioned I guess you could take a hand rip saw to the sides and cut to the angle as well. That might make the chiseling easier

tack or clamp a straight board on the timber to (visually) guide your drill. on the end of the timber works pretty well, or on the adjacent face to the mortice.

with a boring machine you can prop the base of the machine up with a wedge. the angle of the wedge is then the template for the dovetail tenon. easy. whistle a song while you're drilling. yet another reason why boring machines rock.

How many do you have to do? Is this for a personal project house or are you trying to feed your family by cutting these? Do you currently use a mortiser or drill for mortises?



One thing to help with the cleanup is to cut a block the required angle to register the back of your chisel on while tapping.

GH

In Doug Fir anyway, you can angle a hollow chisel mortiser to cut the taper with minimal clean up.

Gabel were you suggesting that the wedged half dove tail requires extra time and there for not worth a client or your families valuable time, when you typed this...personal project house or are you trying to feed your family by cutting these?. I have seen two examples in production shops where they don't use this joint, due to the fact it " takes to much time". This bothers me in some way. The wedged half dove tail is a very strong joint and there for is the joint of choice over one with out a wedge and half dove tail,when used on a tension member. I believe it was the joint which broke Ben Brungrabers hydraulic press.
Other details I am interested in is the direction the wedge goes Inside/outside and why? Number of pegs, size and placement? Where else is this joint used King post and Tie beams?
I have read that the wedge goes in from the outside. The shrinkage issue is solved for the most part by having the small end section of the timber (the tenon) naturally/pre dried in comparision to the rest of the timber so on assembly there isn't much drying left and very little shrinkage after that. There for the wedge is inserted from the outside not the inside where it can be tightened later by taking up the flooring and driving the wedge even more. I also don't use anchor seal on any of my joints, this would prolong the drying process.
I have gone to one 5/4" peg in addition. I was looking at a old barn and noticed the tying joint had had pulled away by about 2" on closer inspection there was no peg as back up, but the building had great amounts of stress added to it as it was in a state of collapse.
Futher comments would be great. Tim

Tim,

With my questions, I was trying to get a sense of how many of these per week/year/lifetime the original poster was going to need to cut, as well as what tools he currently had.

To my mind that pretty much determines whether to use tools he has, even if they are slow, or spend money on an expensive tool.
There is a big difference in how I approach cutting 2 vs. cutting 200.


I have no issue with the wedged half dovetail tenon. I think it is a great joint. We don't use them often, but that isn't because they are hard to cut or take too much time.

I'm also interested in what the best way to detail this joint is. As well as how much tension capacity can be developed if it is properly detailed.

I have seen an old frame where the wedges could be removed easily by hand. They were loose. I have also seen an old frame where the wedges were gone in some trusses. They had fallen out because they were loose. It seems to me that you want those things tight -- that is why I think it best to have the wedge on the inside as mo drew it in another topic. If the wedge is taller than the floor is thick, you could tighten it without taking up the floor. But if it is hidden in the wall, you'll never know how tight (or loose) it is.

I like these discussions about detailing joinery -- I would like to hear more people's point of view.

Gabel

Hi Gabel,

Having been through thousands of domestic and agricultural buildings, I have yet to see one of the joints that is described above. That is not to say that these do not exist but that their usage is not immediately obvious in the vernacular building landscape.

You have identified its major weakness i.e. the possibility for wedge loosening, or worse still loss, and that just about says it all. I would suggest that unless you are dealing with a structure that is known to need to be taken apart, aligned and / or tightened on a regular basis e.g. a like a mill, then this type of connection is best avoided.

Ken Hume P.Eng.

I think Ken may be suggesting the WHDT is an American joint. Which makes sense, being, it is used mostly in the dropped tie configuration, with common rafters. Ken, do you see that set up on your side of the pond? I have a book, Recording Timber-Framed Buildings: An Illustrated Glossary By N.W. Alcock, M. W. Barley,.... It shows a half dove tail with a wedge. No detail so I am guessing but the wedge looks like it has no taper. This book is a recording of English joints. It is on page F-28. So there may be examples on you side of the pond, Ken just rare.

On one of my own first buildings I used the WHDT on the foot of the king posts (6 trusses 30') In the recient past I noticed one of the wedges was not present! I can look right up through the wedge slot, the joint shows no gaps to speak of. There is no floor loads either. I should jam in a new wedge. These joints were cut incorrectly. My wedge side had no taper, and some of the wedges went in from the top, some bottom, it is a bottom wedge which is missing. In a king post set up, I put the wedge in from the top now. This is the same as going in from the inside as with a dropped tie. I also like the ratios Jack Sobon talks about 1:5. I would think a wedge with even less taper would be better yet. So, on a 10" post the wedge would be something like 2"-2-1/2" in 10". How about putting a nail in the wedge so it can't fall out? This would have to be pulled to tighten later.

Another situation I have come across is where the king post was square ruled into the top of the tie by about 1", this housing prevented the half dove tail from fully contacting its seat before being completely assembled. The joint needed some futher adjustments. I had to extend the housing/reduction on the tie to allow the king to seat onto and than slide over to the half dove tail. A haunched shoulder eliminates this problem on the dropped tie. I now only use the top of the tie as reference in a king post truss. For futher info on that, I used the bottom as ref. so I wouldn't have to reduce at the posts, Trial and error. Tim

Remember the dovetail's weakness lies in geometry: If the slope is 1 in 8, then 1/8" of shrinkage in the height of the tenon allows a whole inch of withdrawl. CB.

Man O man, geometry is every where, even in the arc of the sledge hammer used in driving the wedge. If you just place the wedge so as to make contact, home, than the above statement of 1/8" of shrinkage would be more than likely be true. Now apply some force behind the wedge and push it beyond home say 1" or until it just simply stops. Now how much withdrawl will you have? This should be calculatable, if we know how much futher the wedge is driven, this is still unknown. They very from 1"-3" beyond home. 3" is more likely due to a cutting error. I suppose one could even dry the wedge in an oven just before it is applied. Driving the wedge is different then driving a peg, there is no relish to blow out, this is when using a draw bore. These are just some thoughts bank around in my head. Tim

Yes, then you'd be counting on the compression on the top of the tenon to keep it tight, which may counteract the shrinking. Will the compressed fibers stiffen up, and lose their spring? Before the tenon is done shrinking? I don't know it that's calculable. But even if this results in a withdrawal of only 1/4", then all the bearing moves to the pegs anyway, and the dovetail stops helping. It's a cool joint, but I have my doubts about how well it works in practice. Of course there are historical examples where it worked well. I wonder if there are historical cases where it did not work so well, but no evidence was left behind :-) CB.

Is there an option for a joint on the end of dropped tie beams? The historic examples in my area show any other joint in the drop tie configuration has had to of been fixed at some time. Not all of them but most, they also far out number WHDT. Examples of fixes are the large iron staples, cables, and reenforcing nailed to the side of the tie and to the post. I have seen no repair work on WHDT, in other words they work where the simple through tenon is failing. How about in your part of the world. The only failed WHDT I have seen was the one I mentioned before. It had pulled apart I think mostly due to the structures state of being. Tim

Hi TIMBEAL,

Re reverse assembly (tie below wall plate)- this is quite an archaic form of construction and is found in a few very early and mainly aisled buildings in England (think 1100's till early 1300's) and of the examples that remain most of these are liable to be found in quite large important buildings like Great Coxwell Barn. I suppose that these buildings are of similar dimensions to the relatively large modern mid west American barns and so there might just well be a correlation between size and preferred joint design (research study ?). The dropped tie approach is much more likely to be a continental practice imported into the States by mainland European migrants. Without checking my reference books I seem to recall from correspondance with John Macfarlane that the German "Liegender stuhl truss" exhibits this type of construction and thus American practice might well be more related to a cultural design melting pot approach than evolutionary design progression.

Take care re drawing widespread conclusions on English practice from The CBA "Recording Timber Framed Buildings" book. This is a serious attempt to document joints encountered during academic study of timber framed buildings but it gives no indication as to the widespread use and practice of specific joint types. A well known Timber Frame Building book author once said to me that this book smacked of "stamp collecting" and I now know what he meant. English timber frame style and practice is not universal across the country but more specifically related to regions or even just county wide practice which might not travel very far.

Regards

Ken Hume

Ken, the U.S. is a melting pot, that is for sure. Our historic building methods alone reveals that. In my area I have a theory based on the last names of folks in this area, the Scotch/Irish, and how the area was settled starting from the early 1600's to a firm settling around the mid 1700's. I am trying to figure if there is a connection with building styles and the Scotch/Irish. I'm not sure how exactly to go about this it will take a while and a bit of poking around, mostly taking pictures and getting familiar with the local buildings.

That was the only joint of that type I found in the book. I'm not sure I made a conclusion, more like a thought in print. What is meant by "stamp collecting"? I like the book for it's simple drawings which translates into joinery options. Please elaborate with your opinion of this book. How about some suggestions on other books which could be helpfull. Thanks, Tim

Hi TIMBEAL,

Being a natural born Scot (and emmigree to Canada) I suppose that I am at liberty to reveal a few home truths about the country of my birth and its people. I am not aware of any great traditional timber building tradition being present in Scotland. That is not to say that it does not exist - more that what does exist is hidden from view behind masonry walls unlike the south of England and the continent where everything is on show. There is rude jointed cruck buildings to be found in farm settlements but a considerable number of these were raised (burnt) during the Highland clearances (in favour of sheep) when the resident population was forced to consider opting to migrate to the new world. Scotland's oldest ally is France (not England) and therefore it is not surprising that English framing traditions tend to be absent in Scotland with French design influence being dominant in many of the more important early buildings. Ireland has a similar story to tell with many of its old buildings destroyed by Cromwell and their own desperate exodus experience due to the potato famine. These countries are both windy, wet and rocky so it is no surprise that since timber does not survive well in wet external situations that masonary construction should be favoured. I doubt that very much timber building tradition translated to the new world from Ireland or Scotland but equally since both of these proud celtic nations are intelligent and highly inventive they no doubt adapted quickly to the new set of circumstances that they found in the new world. Personally, having some experience of both sides of the big pond, I have seen little in America that reminds of home grown building practice but the story in Canada is different where French, Scots and Irish styles are evident in the many masonary buildings present in that country - especially in the east.

I think that it is important to draw from personal observation and experience as well as that information contained within the pages of books and articles. Not all authors are created equal. I shall leave you to ponder about "stamp collecting".

I was recently faced with the question - "If limited to a choice of 5 (timber framing) books what would they be" ?

Answer :

1 Discovering Timber-Framed buildings by Richard Harris.

This little book can easily be purchased by those persons operating on a tight budget and having sufferred (in the biblical sense) under his marking hand on my Masters Degree essays I can vouch that he knows his stuff and rarely will he be found to be wrong or defficient in his thought processes.

2 English Historic Carpentry by Cecil Hewett.

Cecil employed his artistic skills to good and great effect in combination with his analytical skills to produce this master work. Many are critical of Cecil, quick to point out his errors here and there but this must not be allowed to detract from the value of this corpus of knowledge.

3 The Framed Houses of Massachusetts Bay (1625 - 1725) by Abbott Lowell Cummins.

This is a well researched, beautifully written and illustrated book that provides a snap shot in time that can be employed equally on both sides of the Atlantic since at that time we were the same nation.

4 Timber Frame Construction by Jack Sobon & Roger Schroeder.

Jack's knowledge, enthusiasm and understanding of his subject is hard to beat. His Garden Shed must be the most built timber frame structure in the world and it has now spawned many variants. I learned directly from Jack that sometimes it is important to see and interpret the detail in order to understand the bigger picture.

5 Building the Timber Frame House - the revival of a forgotten craft by Tedd Benson, James Gruber and Jamie Page.

This was the first timber framing book that I bought and it is notable for its inspiration and achievement in helping to set a whole industry in motion.

Regards

Ken Hume

Thanks Ken, I appreciate the input in the Scot/Irish area. Rocks, we have rocks, they probably felt right at home. I belive they moved into this area from the other parts of New England, they did not move here directly from Scotland. So they picked up building types from the south. I need more time to put some thoughts together.

I am going to the TTRAG meeting and will look those books up with Summer Beam Books. Tim

HI evryone on this thread

I do have a good slide of a half dovetail connection used in an early (1865) bridge truss. It was part of the ceiling structure of a 45 foot span framework. It shows clearly the wedge protruding on the upper surface having been driven from underneath, and only one being used.

I also contemplated if the wedge bore against a taper cut into the side of the mortise that was in line with the slope of the wedge, in my books that would have to be the case. The wedge protruded about 3 " above the surface of the 14" timber, and the shoulder of the post had raised slightly out of its original position about 1\2" due probably to its age and the steady pressure applying to the connection.
NH