Joint placement question on timber frames.

[AJB Temple]

I am starting to get my act together to make two oak timber framed buildings, each about 6 metres square. This question is about setting out. It's been a very long while since I last put up a timber framed building (which was mainly a re-erection of one where I bought an old frame and re-located it) and I am wondering if my memory is playing tricks on me regarding joint placement. My recollection was that the mortice slots were cut in the centre of the posts / beams as appropriate.

However, I have been reading on the subject of framing. The books that I have are American and they suggest that the mortices should be cut offset. So for example, in an 8" post/beam joint, a 2" mortise cut 2" in from the face side - and not central. The rationale for this appears to be partly related to structural integrity (leaving some of the central fibres uncut presumably) and partly because they say it is very difficult to mate up the faces accurately if the mortise slot is cut central. They also double peg, with offset pegs, whereas most pegging I see over her is in-line.

Does anyone who has done some oak framing have any thoughts on mortise placement? Or can point me to a UK book or website (I have searched in vain for a forum) that will provide some advice before I get the chain mortiser going. I am in no rush as the timber is yet to arrive.

Adrian

 

[Jacob]

I don't know about timber framing but the general rule for mortices and tenons everywhere is that they are registered from the best face and/or edge and very rarely central. This ensures that the face of the structure will be in one plane with all error and variation on the back.
Two pegs in line are more likely to cause a split along the grain than if they are offset. They should also be close to the shoulder joint to keep the joint tight at that point - with any shrinkage or movement at the other end out of sight.

 

[AJB Temple]

Yes Jacob, I agree that in furniture M&T that is standard. But I have looked at a number of cheap (allegedly) kit oak frames from various suppliers and apart from using a hell of a lot of softwood, most of the M&Ts I have seen have been central. I have even seen them joint up with coach bolts and then hide it with fake pegs on top.

Anyway I have ordered a couple more books from the US and irrespective of what current makers seem to be doing over here who sell these ubiquitous timber framed double garages, I am going with traditional timber frame joinery.

 

[Jacob]

Yes Jacob, I agree that in furniture M&T that is standard. ...

And architectural joinery, and I suspect with trad timber frames as the logic is the same.

 

[Wuffles]

I read a book (albeit in my usual skimming way) before tackling my straightforward oak framed porch and I don't recall any mention of offsetting the M&T. All mine were done centrally.

It'll certainly be embarrassing if the book you have already read is this one, but here goes: Timber Frame Construction: All About Post and Beam Building - it's on Amazon.

It seemed to delve more into the history of the tools and as it was on a long haul flight there's every chance I nodded off and missed a chapter or two.

 

[HOJ]

I have 3 books I refer to for the types of joints and methods of construction.

Rupert Newman who runs this company: http://www.westwindoak.com/ his Book:http://www.amazon.co.uk/Oak-Framed-Buildings-Rupert-Newman/dp/1861087268

An American book which is very well detailed with sketches:http://www.amazon.co.uk/Building-Timber-Frame-House-Forgotten/dp/0684172860

And A Trada Book which has gone missing, I think I left it on a Barn coversion project: http://bookshop.trada.co.uk/bookshop/view/F53561CE-A0E6-4D17-B58C-2F4926E0E109/

There is the Carpenters Fellowship web site, with a forum, but not much on there: http://www.carpentersfellowship.co.uk/index.php

When I have worked on frames i use the method Jacob defined, always referenced to a face side, in order to allow for timber sections that are either under sized, out of square or bent, which could well mean a compromise on joint positioning.

 

[Bm101]

If you don't have it, Rupert Newmans Oak Framed Buildings might be worth a look at. It's a fairly comprehensive overview I guess aimed at people looking to self build or interested in the subject. I can't see any reference to offset joints in the section that covers it. Scribing seems to be done with chalk lines and bobs.
https://wordery.com/oak-framed-building ... GwodG8EPGA

Edit. Ah, beaten to it.

Chris

 

[Beau]

(I have searched in vain for a forum) that will provide some advice before I get the chain mortiser going. I am in no rush as the timber is yet to arrive.

Adrian

Try Arbtalk. Quite a lot of guys on there making green wood structures.

http://arbtalk.co.uk/forum/woodcraft-forum/

 

[Jacob]

The point is - even if you want to put the mortices central you'd still reference from the face side/edge.

 

[AJB Temple]

Thanks for the input gentlemen and the links. I have actually cut a couple of mortises in my time and do know to reference from the face. In any case green oak often only has 3 true(ish) sides. The query was about joint location.

The books I have currently are Oak Framed Buildings by Rupert Newman and Timber Frame Construction (all about post and beam building) by Jack Sbon and Roger Schroeder. The former is rather superficial and the latter is quite good. I also have a few historical books from earlier forays into timber framed buildings, but these are not construction tomes. On order are A Timber Framers Workshop by Steve Chappel (which I hear is very good- though American again) and Building the Timber Frame House, revival of a forgotten craft, which is reputed to be an interesting read.

I did look at The Carpenters Fellowship, but the forum is inactive with minimal content. I will have a look at Arbtalk thank you. I think I have allowed myslef to be misled a bit by some of these so called timber framing companies. Some are really good - others appear to be riding a bandwagon. You Tube has been very useful especially for some techniques for using chain mortisers. I do need to do the joints very well as I have limited labour available to me so the frames need to go together really smoothly.

 

[PAC1]

If you want a definative answer Steve Chappell - A Timber Framer's Workshop seems to go into the structural engineering side of joint design. Sadly there is no short answer as he points out the first consideration is whether the joint is in tension or compression. Thereafter it is a long read. But interesting!

 

[bugbear]

Thanks for the input gentlemen and the links. I have actually cut a couple of mortises in my time and do know to reference from the face. In any case green oak often only has 3 true(ish) sides. The query was about joint location.

IIRC there are some interesting timber framing techniques which don't rely on referencing from any face, since putting a true face on a sodding great oak beam is a lot of work, which can be avoided.

Full trad timber framing is really dissimilar to small scale joinery or cabinet work.

BugBear

 

[Jacob]

Thanks for the input gentlemen and the links. I have actually cut a couple of mortises in my time and do know to reference from the face. In any case green oak often only has 3 true(ish) sides. The query was about joint location.

IIRC there are some interesting timber framing techniques which don't rely on referencing from any face, since putting a true face on a sodding great oak beam is a lot of work, which can be avoided.

Full trad timber framing is really dissimilar to small scale joinery or cabinet work.

BugBear

Faces were roughly "trued" either at the saw mill, or by hand with saw pit, axe, adze etc. with every attempt to make a regular piece of timber. Even logs for a log cabin had opposite sides trued up to make a meeting surface.
Joints (central mortices or otherwise) are referenced from a face which allows you to use different sizes of timber (or imprecisely cut) but still to get one flat (ish) face on the structure.
It's a just a dead basic universal technique, throughout woodwork.

 

[Woody2Shoes]

Hi - this may or may not be helpful. Like you, I have found "the literature" to be relatively unhelpful in the details - I ended up buying a US book which I wouldn't necessarily recommend. What I did was look at existing examples around the area (a couple of old barns and cart sheds, I'm also a fairly regular visitor at the Weald & Downland museum) and then follow my own advice (based on an engineering training) - I ended up going against what seems to be "received wisdon" when scarfing horizontal beams for example, for what I think are perfectly logical and aesthetic reasons. You also have to go with what looks good/right in your own eyes.

The way I made my 48' long verandah was tenons central at the top of each 6X6 post into mortices in the centre of the horizontal 6X8 beams - the mortices were incorporated into quite a complicated Z-shaped scarf joint along with slightly curved braces on either side of each post. Everything using the centre of each piece as the reference, rather than a particular face. What I ended up with looked great as far as I'm concerned, and seems to be robust, but probably took far longer to make than most professionals would accept.

Cheers, W2S

 

[bugbear]

Thanks for the input gentlemen and the links. I have actually cut a couple of mortises in my time and do know to reference from the face. In any case green oak often only has 3 true(ish) sides. The query was about joint location.

IIRC there are some interesting timber framing techniques which don't rely on referencing from any face, since putting a true face on a sodding great oak beam is a lot of work, which can be avoided.

Full trad timber framing is really dissimilar to small scale joinery or cabinet work.

BugBear

Faces were roughly "trued" either at the saw mill, or by hand with saw pit, axe, adze etc. with every attempt to make a regular piece of timber. Even logs for a log cabin had opposite sides trued up to make a meeting surface.
Joints (central mortices or otherwise) are referenced from a face which allows you to use different sizes of timber (or imprecisely cut) but still to get one flat (ish) face on the structure.
It's a just a dead basic universal technique, throughout woodwork.

Not for low status and/or early work; certainly, once making squared beams became common, jointing techniques exploited the convenient reference surfaces, because it's easier.

But poor peoples houses, barns, store houses were made from simple branch wood. Whilst accurate reference surfaces allow joints to be cut using absolute measurement, scribing techniques can be used to make two pieces relative to each other; this is more work than making a joint relative to a reference surface, but can be less work than squaring a beam just because you don't know how to scribe. And the beams are stronger. There's also use of virtual references, such as the handy vertical plane provided by gravity; two vertical lines marked on the ends of a timber using a plumb line are parallel, regardless of any contortions the beam makes in the middle. This concept is central to "centre line" framing.

Search for "cruck frames" or "roundwood framing" to find out more.

BugBear

 

[Jacob]

Cruck frames were built to one fair face for two simple reasons: it's easier and the outer face of the cruck needs to be fairly flat.

...once making squared beams became common,.....

That'd be late neolithic to early bronze age.

Joinery techniques still apply with round wood construction - log cabins had flat faces to logs, joint positions are marked etc.

 

[AJB Temple]

Lots of different opinions on this. I am a fan of the Weald & Downland museum too - had forgotten about it as we have not been for years. I might well pay a visit.

Our house is actually oak timber framed - though not a lot of it is visible. Many of the beams are extremely irregular, often with only one or two reasonably flat faces and the rest being tree shaped! Some of the beams, for example the top plates are 16" deep at one end and 12" deep at the other - this in a 24 foot beam. I can't see how the joints were done but the irregularity is such that a scribing method must have been used I should think.

Pretty much whatever I do will work for the two frames I am putting up as they are only single storey and at 6m square they are not enormous. I have over specced the timbers anyway, for aesthetic reasons.

Back in 1987 (was it 87?) when we had a huge storm, we had a farm with some woodland, and lost quite a few mature trees (dozens), mostly oaks and a few elms. These were cut on site into beams and thick planks and mostly stored in a disused barn. I had intended to build a timber framed house from them and thought I might use a bit for these two small buildings. However, having looked at the costs, it actually makes far more sense for me to sell this fully seasoned English oak rather than haul it from Warwickshire, take it to a local timber yard for cutting to approximate size, then haul it again to home. Buying French green oak, fully dimensioned, is reasonably cost effective as I am able to source QP1 for about the same price as shifting and dimensioning my own timber for the smallish quantity I need. Green oak will be a lot easier for me to work with than my own timber, which appears now to be rock hard. As I am cutting the joints myself I am opting for the slightly easier life.