I am just about to start construction of a small (100 square metres) single storey timber frame house.The posts will be freestanding on stones,and the timber frame will be 105mm x 105mm throughout.
I have never built this sort of structure before,and I have a few specific questions related to the mortise and tenon joints.
1.I intend to pin all joints.With the through tenons I have no query,but there will also be stub tenons,where two tenons butt each other through the post.These stub tenons will therefore be half the width of the post,so 52mm.My query here is: I understand there should be 3 times the width or diameter of the pin left in the tenon,after the pin.I calculate that this would allow me a pin of not more than 10mm diameter,with a length of 105mm (so as to leave 30mm of tenon after the pin,and 12mm of tenon between the pin and the shoulder).The proportions of the pin seem fairly thin,for the size of the timber?
2.Further to that - any views on the relative merits of square versus round pins?
3.In my plans I have vertical through tenons extending from the top of some posts,onto which would be fixed a beam,with the other end of that beam being fixed into a post by means of a regular one third width rectangular horizontal stub tenon.The query in this case is: in the case of a vertical tenon,it seems logical to me to use a square centred tenon of 50mm x 50mm dimensions (105mm length)...........?

1. An alternative to two tenons butting in the middle of the post is to make an over and under tenon. This way they can be full length and have plenty of wood left for the pin diameter problem you are facing.
2. round pins are easier to bore a hole. square pins would require more work to make exact sizes.
3. You can center the tenons if you want to, but you need to consider the layout on both pieces, so that they align properly.
We use a method called "square rule" where you layout by using a standard framing square and offset the tenon by either leg of the framing square that way the layout is the same on both pieces as you use the same tool to layout both.
And you need to consider the amount of wood between the mortise in the beam and then end of the beam. It is usually stronger to leave some small section of wood between the mortise and the end of the beam so you wouldn't have a open mortise on the end.

There are good views of joint in the pdf files available from the guild website for free download.
Look for the Historic American Joinery series and you can view different joints, together and exploded to see how timbers can be joined.

Good luck and keep asking questions.

Jim Rogers
PS see over and under tenon example in my avatar, to the left.

For house framing, I believe the cross section of your members is far to small, my comfort level would increase greatly if the timbers would double in size.

Hello,

In the plan you have laid out you describe two tenons coming together and butting against each other mid way in a through mortice but you leave no room to accommodate for shrinkage and expansion of the post. The effect will be that the tenons bottoming out against one another will force a gap at each shoulder half the width of the amount of shrinkage or if pinned possibly even worse.

Your thinking on the pegs is correct and with that in mind but also the extra effort involved in the peg openings, the octagonal or six sided peg in a round hole is the best compromise solution.

Greetings,

Don Wagstaff

Thanks for the informative replies everybody.
An over and under tenon looks interesting,although at this stage I don't have the confidence in my woodwoorking skills to start considering more complicated joints.I'd prefer to keep the joints as simple as possible - as long as my dimensions allow for pinning.As for the timber dimensions (105mm x 105mm),these are the standard dimensions for posts in the part of the world where I live (Japan),and since our house will only have a light,low-pitched tin roof I feel no need to increase the beam dimensions.Things here are generally done on a smaller and finer scale than in the West,something that it's taken me a while to get used to.
Likewise the pin shape here is usually square,which probably reflects the fact that yesteryear's builders had no access to powerdrills - and neither will I.I'll be doing everything with hand tools,with no access to a power source.
The alignment of the square tenons with the ones on the other side of the beam is a point to consider,although I'm a little stumped by the meaning of the terms "square rule" and "layout"......?
Also the shrinkage of the posts and consequent exposure of the mortise shoulders is something to consider.I wonder if it would be worth shortening the blind tenons a little - although that would of course exacerbate my problem with the pins,which remains my main concern.
In case anyone is wondering why I'm asking these questions on this forum,when I live in a land that contains the oldest and most intricate wooden structures in the world - well,it's partly a matter of limited language skills on my part (this is not a simple subject),as well as the cultural difficulty of obtaining a direct,to-the-point answer in this part of the world.But most importantly it comes down to the fact that pure timber framing is a dying art here,and it is very difficult to find one of the few remaining old men whose craft it is,or was.

Regards
Iain Andrews

Could you explain the effect an octagonal peg in a round hole would have Don? (Please excuse my ignorance!)

Regards
Iain Andrews

When making your own pegs with out a lathe the end result is an eight sided peg. It is not necessary to shave off the eight corners making it nearly round, that would be superfluous. So, I would say that the corners are not the goal. The goal is to fashion a working peg, any farther beneficial benefits are gravy. The eight corners, compared to turned round pegs, do not hold any negative side effects. The peg should be tapered as well to aid in draw boring.

A square peg in a round hole will cause undue force on the tenon. It could crack it.

Hello,

Also because in Japanese timber building a round(ish) peg is thought of, (as it is), as inferior in both function and appearance.

Well not only is the 8 sided peg easier to make properly but it will always fit as there is a degree of cutting action. With a properly fitting round peg as you can imagine the fit is 100% compression and that requires more force to achieve the same surface contact. It's the same with round or wire nails and lets say cut nails - being also tapered - but because they cut through the wood fibers instead of pushing their way through they create the maximal surface contact with intact wood fibers and so grip better along the entire length.

Also a rounded off opening exposes a maximal amount of end grain, undesirable in any case but on the verge of offensive in Japanese woodworking.

An allowance for wood movement is also well accounted for in Japanese timber construction. Tenons never bottom out in a mortice. In Japanese joinery books I think a 5mm space is allowed for.

Greetings,

Don Wagstaff

Don:
I agree with many of your points, but I'm not following you on this one:

"Square rule" is the name of a method of marking lines on a timber so that all the joints line up from one timber to the next.

In Japan I believe they use center line layout.

Layout means drawing lines on the wood to represent the tenon/mortise and waste wood to be cut away.

We usually layout the lines first so that we can see what will be cut away and what will stay.

I can understand your need to do things with only hand tools.

To make pegs you can use a draw knife if you have one. And you can build your own simple shaving horse to hold the stock while you shave it to size and shape.

If you don't have a draw knife then you can use a plane or a chisel. It's a bit harder to do, but you have to use the tools you have on hand.

To bore holes without power drills you need to find a "T" handle auger bit. It is a simple but effective way to bore holes for removing wood from mortises or drilling peg/pin holes.

Jim Rogers