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

On the Swiss structures that I have studied, the use of half laps v. mortises depends on how the building is to be finished out, it seems. If the building is to be infilled between the timbers and the timbers left exposed, then long slanting braces (streben) are used, which are mortised and pegged. If the building is weatherboarded or enclosed by means of heavy boards between the timbers, the half dovetail lap is more common (with the profile a bit different than the English version of this joint) The lap joints on these building are pegged as well, some dating back to the 1600's and possibly earlier.

I think more than anything it depends on WHERE the building was built. In Switzerland building style, joinery, etc. varies a lot from one valley to the next. Folk in the Gürbetal (A valley that lies between the cities of Bern and Thun), for example would build a house that looks something like this:

(This picture is of the old Bähler farm near the Swiss village Kirchenthurnen)

Whereas people the next valley over would build something like this:

which is "blockbau", built of squared logs, not timber framed aside from the roof structure.


Mortised and tenoned roof bracing, from a farmhouse built in the late 1700's


A half lap version of the same basic roof system, I don't have a date on this one


half lap wall braces from a day laborer's house built in 1803



Pegged Streben from a Bernese farmhouse built in 1797

I have some better pictures, but don't feel like uploading them right now. Maybe some day I will post the results of my studies into this style of framing and then you can see more pics (That is if anyone actually is interested in seeing that)

There are examples of mortised and tenon/pegged braces in this style that date all the way back to the late Middle Ages, including some of the oldest timber framed houses in Switzerland (which seem to be often located in castle complexes)
There are also examples of hap lap joints built within the last century or two. There are even examples of Streben style long braces with half lap joints, which seems somewhat odd really.

Also note that the short corner braces are not at 45 degree angles, but rather go to the third point of the post, and the third point of the adjoining timber.

This is kind of a long winded answer to your question, Tim, but It's easier to get the whole thing out at once to avoid some confusion.

Why did they use half laps? A lot of it I think has to do with their tradition, and also what they intended the joint to do.

As I understand it, there are times when a half lap dovetail was intentionally chosen in a situation where the joint would be subject to tension, even though it was still primarily a compression member. An example of this would be scissor trusses, all examples of which in English Historic Carpentry seem to use this joint, which the author explains is due to the fact that a mortise and tenon would have failed in this task.







-all pictures aside from the first are from buildings in the Ballenberg Museum in Switzerland, a Museum of rural Swiss buildings, the oldest being a farmhouse dated to approx. 1330. Pictures courtesy of J B Dowse, jbdowse.com, used by permission.-

Great Pictures. The Xbracing in the roof plan is good stuff. And the thatch.

I'm interested in seeing more pictures and analysis.

P.S. As echoed here, shouldn't the pegs in a well built frame just provide assistance in the fit-up? Only good tension joint I've have noticed is the anchorbeam through tenon.

Hi Guys,

As Simon Cowal would say - "I knew that this was a good question" and the follow on questions and comments are equally thought provoking.

Re the original blind pegging question :-

There are some places in timber frame construction where a concious effort was made not to show pegs coming through to the interior of the building. This still applies to day and typically might include where a common rafter is pegged to a clasped purlin and where floor joists are tennoned into a spine (summer) beam.

Re mortice and tenon joints not being being employed on scissor braced trusses :-

This is not quite true. The scissors can and are joined using M&T at each end to the rafters but the ovelap joints are generally made with unpegged lap joints.

See photo of Bishop's Camera roof at Farnham Castle [dd 1375, Moir]:- Scissor braced trusses with collars

It is of course possible to use lap joints at the scissor / rafter connection points but one has to consider the sequence in which the rafters, scissors and collars are to be laid up, cut and assembled and especially where slightly twisted timbers are being used. This can lead to less than tight lap joints. These are some of the most difficult timber configurations to frame. The roof illustrated was a "cost not an issue" construction and employed only the best timbers to form 39 sets of scissor braced trusses set on 16" centres. The rafters feet are not pegged and simply butt into a shallow locaton socket on the wall plate with no overhang beyond the plate. There are no purlins or windbraces i.e. a "sans purlin" roof.

Re Ommitting pegs

It's probably worth examining the interupted butt rafters employed in an early 17th century butt purlin roof in Farnham, Surrey.

See :- Butt Purlin Roof & interrupted Rafters

You will note that the lower sections of the common rafters have been deliberately omitted where a lean too dormer roof has been framed. The lower rafters were designed to be mortice and tennoned and pegged to the underside of the butt purlin but the upper section of the rafters only to be mortice and tennoned with no peg. There is no ridge or windbraces in this roof. I have seen this on other buildings in this town so this practice of completely omitting the upper peg is quite deliberate. Your thoughts on this practice would be much appreciated.

One must consider how a joint is expected to work. It is not just about tension or compression it is also about moment connection. A M&T joint functions well largely as a result of the shoulders being pulled up tight by the use of a tapered draw peg. It is the shoulders of the joint that are important as this is where load is transmitted so even if a member goes into tension providing there is sufficient preload applied by the peg then the joint can continue to act as a moment connection. A single three quarter inch dia oak peg can sustain a double vertical shear load of nearly 10 tons which means that a significant degree of preload can be applied. Its worth keeping in mind that the preferred mode of joint failure is in peg shear such that tenon relish shear and mortice cheek pull out are avoided. Replacing a peg is cheap and easy.

Re Lap Joint versus Mortice and Tenon

It is highly likely that Tim's surmise about the evolution of timber joints probably progressed hand in hand with tool development. This is true today with certain joints now being made on CNC joinery machines being impractical to achieve by hand (housed taper curved dovetail floor joist to beam joints).

That said there are still places where a lap joint is preferable e.g. as in the case of a cruck mantle beam (low tie cross beam). These joints are generally skew pegged and though the carpenter might anticipate that the lap shoulders will do most of the work it is more likely that this is actually done by the pegs since cross grain shrinkage will gradually loosen shoulder contact.

There is also the well known lap dovetail found at the end of a tie bean where an English tying joint is employed. These unpegged lap joints are known to shrink back and frequently come apart over time requiring the addition of some metal strapping to arrest any further movement. This is classically illustrated at The Olde Bell public house in Henley-On-Thames, Oxfordshire [dd 1325, Miles].

See :- English tying joint failure

Conclusion

It appears that carpenters were and probably still are prepared to rigidly stick to tradition regardless of whether or not there is a well established history of failure in service of a particular type of joint.

What is the alternative ?

Regards

Ken Hume

With the English tying joint, I have gone to a cog, still a lapped joint but removing the shrinkage of the dove tail. This is an exception to the lapped joints missing in my area, and in breaking tradition, I see far more dropped tie configurations.

I hope the OP sees that a through peg hole is the way to go. And if not then a deep blind hole just shy of the other side. If a blind hole is used take care not to drive the peg deep and blow out the other undrilled side.

Tim

Now were cooking.

Hi Tim,

I concurr with your warning about the potential to blow the back face of a timber containing a concealed peg and it would appear that this is not a new problem. Please attached blown back face of a cruck purlin circa 1390's.

See - Blown Cruck Purlin

Regards

Ken Hume

Ken- could you explain that joint, seen in failure there in the picture , please? is it a lapped dovetail brace- or specifically its absence, that we're looking at there?

big spikes make excellent one-side blind pins, in that application and others.

Hi Toivo,

This is a particularly difficult joint to decipher. The purlin "extension" (to the left) is a short length maybe 3 or 4 ft long that is tacked onto the end of an 18 ft boxed heart elm purlin. Its very difficult to say whether this is original or added later because of the smoke blackening and limited access around the joint but it is positioned above a fairly narrow 6 ft wide bay (at ground level) which is still open to the fully hipped roof. To determine exactly what is happening inside this joint would require a little more in the way of joint forensics and unfortunately that window of opportunity has now closed. This is not a perfect world or a subject where everything is or can be revealed on demand in crystal clear detail.

I rather like the full text version of advice clarification given by Donald Rumsfeld :-

"... as we know, there are known knowns; these are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns - the ones we don't know we don't know1...”

Are you now ready for the analysis ?

The large peg that has blown the joint is the "singles" rafter peg and hence the 2 other smaller pegs (to the right of the large peg) appear to relate to the scarf joint. These 2 pegs have been driven from the outside in. To the right of these 2 pegs there appears to be 2 peg hole "shadows" which might relate to this joint and if they do then these would be for 2 pegs driven from the inside out. This might well be a simple step lap joint with the mating faces in the centre of the purlin in a plane parallel to the roof. We must keep in mind that there might well be other features of this joint that we cannot currently see.

Which stage in "Rumsfeld's progress" have you now reached ?

Maybe Mike could produce an "X-Ray" specs view of the likely configuration of this joint using Sketchup.

Regards

Ken Hume

Mike, I think something might be burning to the bottom of the pot, as we read quotes from Rumsfeld.

I have also seen draw bored holes that had a tad too much draw in them, and with a green peg driver not paying attention, pounded the peg through the start of the hole into the tenon and at which point the pointed peg was driven, not through the remaining hole but into the timber and out the other side. This done by the owners teenage son. If you need a sledge to knock the peg into place, at least don't force it. I could not get the peg back out, I left it as it was.

Tim

Hi Toivo,

Comme sa ?

Face pegged half lap scarf joint

Regards

Ken Hume

Even with xray vision we couldn't find those WMDs!!!!

Respectfully, I would appreciate if politics didn't sour our discussion. That's a subject that can easily get out of hand and upset people, especially on the internet where it is difficult to tell whether someone is simply joking or insulting another.

Now, on topic (at least sort of)

First, I need to retract a previous statement. I was in error on my comment about scissor trusses. I had another system in mind when I said that, and got the two confused. There is an older style of truss joinery employed during the Anglo Saxon, Norman, and transition periods that relies heavily on half dovetails, because there are members that are designed to at times be in tension.

The subject of the development of joinery is interesting. One of the appendices to English Historic Carpentry contains a discussion of the development of the unwithdrawable lap joint, it discusses it as a sophisticated, important joint. It is a joint that serves a purpose that the mortise and tenon cannot. And the mortise and tenon functions in ways that this brace cannot.

I think we do well to remember this joint, and what its advantages are.

Lapped dovetails also provide an advantage in that they can be inserted after other framing members have been assembled and pegged.

And as a side note, are there enough of you that would like to see some of my conclusions regarding traditional Swiss (Lower Bernese) carpentry to justify writing it up and posting it on these forums? (I don't have a website, guess I am behind the times. Which is OK I guess for an Anabaptist, right?)

Hi DHL,

I thought that you might enjoy this picture of the Master at work taken at Cressing Temple, Essex, England in January 1993.

Cecil Hewett at Cressing Temple Jan 1993

I do not appear in the picture. There are 2 possible explanations.

Regards

Ken Hume

Fully housed bracing can be also inserted after raising with the use of a filler block under the brace mortice, the mortice just needs to be a little longer.

Tim

I know what you mean there, Tim, but I've never been a fan of that method really.

There's a 100 year old barn directly behind my house that has braces inserted into extra long mortises, and I just don't like the whole system that well having seen it first hand.

Personally, I like the look of a refined entry lap dovetail brace, and some of the examples I have seen in my study of Swiss buildings make this joint quite attractive. The Swiss have a tendency to make everything both wonderfully functional and elegantly beautiful.

That said, I realize that the mortise and tenon has certain advantages over the lap dovetail. It really depends on what the joint is designed to put up with as much as anything. Obviously if your joint is not expected to be under heavy tension then you do not need to engineer it for tension, and a lap joint in compression might have more of a tendency to 'pop out' of its housing.