Do I need to bore a hole through BOTH sides of the mortise or just one? If just one, does it matter which one?

If you are sure the joint is in compression, then the pin really isn't doing much, but it's common practice to go through both no matter what. Going through only one side is fairly useless, in my opinion. A pin should be in double shear, not only for strength, but so that the pin is evenly supported. If it were only going through one side, it wouldn't necessarily be in single shear only. There would be a moment(torque) that would be applied to one side of the mortise. Why are you asking this question, something specific?

I suppose you could bore a blind hole in the second side of the mortise, if your intent is to not have a hole and peg visible on the opposite side, but you'd have to do some peg adjustment to make the peg fit correctly without bottoming out. There would be a slight reduction in the strength of the joint.

Hi Glane,

I too am not quite sure why you are asking this question but that's maybe what makes it such a good thought proving first principals question.

Everything Tim mentions above rings true but it does raise the tricky subject of lap joints which are effectively open mortices on one side and these tend to be fitted with a peg, sometimes skewed, which must work in single shear and cantilvered bending. This is a particularly ancient form of carpentry with some of the buildings constructed like this now in excess of 600 years old and so its a practice that does work.

Regards

Ken Hume

One aspect I find necessary for a through peg hole is that the draw bored peg can be easily knocked to its correct fit, otherwise the peg could be loose and the joint not fully seated in initial fitting. There are frames with some joints with no pegs at all, so a peg, only through one side of the timber and the tenon would be the middle ground. Draw boring rules.

Btw, that was Brad's ringing words.

Interesting Ken, your thoughts on the half lapped joints in comparison to a fully contained joint have me wondering how they work and can they be equally compared.

Tim

The answer can only come from the context of the joinery - tension? brace? frame taking lots of lateral load, etc.


Ken - your half lap example is anecdotal at best without reference to engineering context.

And, similar to Ken's example, I've pulled every peg out of a barn or two and was still unable to get it to topple / significantly move / etc., even pulling on a corner post with a truck.

Hi Mike,

Anecdotal at best ? - ouch !

Nice reward for trying to contribute to the thread.

Regards

Ken Hume

Ken - no harm intended, but as someone whose posts trend to the scholarly, I found it odd coming from you.

True, they work and have been around for a long time - but to me it was sort of like saying 'well, wood has been used in buiding for X years, so if you are using wood, it will work'. I've seen some lap joints pulled apart and not functioning anymore, in stateside buildings that are mere youths compared to structures on your side of the pond.

Seeing a few other posts by the same new member to the forum I thought that context would be important, as it appears that he / she has little experience with the craft and techniques used.

No harm intended. Apologies for sounding short.

Hey, everybody stop reading insults or condescension into everything. We're just talking here. I don't think Mike was jabbing you. And Mike could have put it a little differently, but I understood his point, that you need a context, that was the point, not a jab at you. In the words of someone famous, "Why can't we all just get along?". Don't have an ego, and it won't get bruised. Don't assume you can read someone's tone either, as often in the virtual world, you'd be wrong. And lastly, be conscious of the words you use so as to be as clear as possible and not allow for interpretation of your meaning or intent. Now go whack some wood!

I've seen pegged tenons pulled apart in buildings that are mere infants compared to the English frames, like only 100 years old or even less, on the topic of infant lap joints pulling.

The success depends on execution every bit as much and more than it does on theory. I could make a mechanically perfect joint but If I make it with a bad piece of wood or build the structure with a poor understanding of loading and structural forces and therefore give the joint stresses in multitude and direction that it simply wasn't designed for (or do the same by setting it on a poor foundation) then the joint will fail, sooner or later.

On the other hand, I could make a 'lousy' joint that in a well executed frame might last 1000 years or so. Or I could make a good frame and not bother to peg anything, and have absolutely no problems as a result. There are some old building traditions in Europe that don't rely on pegs very much at all, and incorporate many joints besides mortise and tenon. For example, look at the way the Germans handle the problem of tie beams. Google "Einfacher Kamm" or "Gerader Kamm" -they totally do away with the mortise and tenon for this altogether, and instead sandwich the timbers between two plates, which also allows them to get away with using fairly small timbers. (I know I reference the Germans and the Swiss a lot, but that's because it is something I am familiar with.)

In my study of the Swiss buildings, I find that nearly all of the very oldest buildings in the particular style that I have been studying employ lap joints for the braces, sometimes half dovetail laps, sometimes just plain half laps. It could, however, attribute some of its success to the fact that the builders of these buildings seemed to have braced them excessively, or at least to a higher degree than we might think is normal. However, it seems that in many cases these joints are designed to resist tension as well as compression, even though they are primarily in compression (wind loading causes that to happen at times to wall and roof braces)

Now back to the original question,

I would caution against single sided pegging, as that could potentially put a lot of stress on that one side of the mortise which could cause joint failure (COULD, not WILL) Even if you intend pegs as an assembly aid and not vital to the strength of the assembled joint (which in my opinion is how joints should be designed, although that is my opinion and I realize there are many others out there who feel differently than I do) the peg WILL at least on occasion put pressure on the mortise side. SO I would recommend going all the way, or at least most of the way, with your peg.

Brad has some good advice there, try not to read insults into things. And try not to make them inadvertently. I try my best to always assume that someone isn't trying to insult me, even if it's very hard to do that. I find that life becomes more enjoyable if you aren't offended all the time (which being offended is usually your choice)

Historically, were lap joints used more before the invention of the auger with the feed screw? Suggesting lap joints were more efficient to cut when you didn't have access to the fancy boring bits of today and yesterday.

I see almost no lap joints in the older barns in my area, dating back to the late 1700's and early 1800's on.

So, why did they use half laps.

Ken and DL, do you see more half laps in the older structures or do dates not play a factor?

Tim