Hi Don & Jim,

I am sorry about the delay in replying to the draw bore question. This topic has probably been done to death elsewhere on this forum but yes indeed draw boring is well proven to be a very early practice that predates the founding of the American Colonies at least by 2 or 3 centuries and probably much more.

The important thing to recognise from and engineering standpoint is that drawbores are employed in conjunction with tapered pegs (or is that pins) and so when a peg is being driven it pulls the joint together up the inclined slope of the peg. Driving home the peg is thus somewhat of a "musical" or resistance based process. Knowing when to stop driving is therefore very much an experience based affair in order to prevent tenon relish pop.

Old draw bore pegs that are removed exhibit parallel deformation over the span of the tenon though whether this happens straight away or over prolongued periods of time is difficult to say.

One other understated factor that comes into play is mortice "slop". Most american timber framers employ engineers squares to ensure perfectly parallel and straight sided mortices but examination of old frames reveals that mortices tend to be more bellmouthed starting at say 1.25" opening up to 2" at the bottom with all the load being taken on the tenon shoulders and peg. This means that the tapered peg is actually unsupported over a short length either side of the tenon and thus is able to deform elastically rather than fail in shear. I have a wonderful photos of this practice taken in Laurie Smith's cruck framed house in Wales (Gwernfyda - dd 1552) where a tie beam was partially sawn through to create less of a step over and into an inserted upper chamber. See Fig 24 in TF 70 [Dec 2003].

I shall risk being a little controversial here in stating that I think that the current "tight" fitting parallel mortice side practice is probably techically misguided and certainly less forgiving.

Regards

Ken Hume

Ken, are you saying we can be a little more slack in the fitting of our joinery? The bell shape at the bottom of the mortice is difficult to avoid with hand tools. When working, say hewn timber you don't have a easy reference to gauge the walls of the mortice, it can be a guess at times. It is sure easy to create the bell effect rather then the opposite result let alone a perfect fit. Which goes along with a perfect pre drilled peg hole, it won't happen. Did the old timers build the bell shaped mortice on purpose? I believe they did, but it wasn't for the benefit of the peg. That is a bonus.

My example was with a small oak peg. A recent small frame I helped move had soft wood pegs, tamarack. It wasn't stressed, it sat on a slab, it had draw bored pegs and they were deformed, just sightly, enough to tell. It was 8 years old. The old frames with stress placed on joints could confuse the subject. Tim

Ken,

This happens fairly quickly as we have removed pegs from a frame we built only a few months earlier and the pegs had the parallel deformation, or as Tim mentioned the tenon impression, just like pegs I have seen that are 150+ yrs old. It was interesting to dissassemble some of our work.

Hi Gabel,

Thank you. It is indeed fortuitous that we have been able to benefit from your relatively short time based and hence verifyable evidence, sadly however we cannot make the same comparative observations (i.e. before and after) on joint that is now several hundred years old.

Hi Tim,

It is the mortice face and tenon shoulder that does the work in a mortice and tenon joint and thus the face to face mating should be well aligned even if a hewn surface is the start point. Mating faces should be regularised (flatened) to provide reliable reference points that can then be transferred by scribing to create the mating tenon shoulder face cut lines.

As per the reply given above to Gabel is no longer possible to say with any certainty whether old time practices were technically driven or arose simply from working experience or even expedient shortcuts but since M&T face / shoulders are not necessarily at right angles when compared with the line of the joint then any slop provided in the joint will allow the tenon to slide in and will even accomodate a slightly "offline" tenon without the mortice sides interfering with the fit of the tenon in the joint.

I did not previously mention about the effects of drying of green timber i.e. on shrinkage & deformation of the joint but very tight and parallel mortice / tenon joints made in green timber must tend to promote cracking as the timber dries since there is no "forgiveness" in the joint and thus I think that slop is and was probably a necessary technical ingredient in making a M&T in green timber.

Your thoughts and observation are very welcome since what is in the process of being outlined here in this topic might be considered to be quite revolutionary (and maybe even a relief) to some when they compare what is being discussed herein with the standard "workshop" type approach that is generally taught to beginners and is also seen to be reflected in various "how to" timber frame books.

No offence intended to anyone.

Regards

Ken Hume

Thanks for the input, Ken. After yours and others comments I think we can agree that draw boring is/was historically widespread...an old technology ("old tech").

As to your comments about tapered pegs... To my mind, the fact we see tapered pegs reinforces the theory of draw boring even further. Fact is, as we know, because holes are offset in draw boring, you need a tapered peg to align/fit through everything... Seems this is why we see tapered pegs. Otherwise a chamfered peg would have been adequate to get it in the hole.

I know some assert that tapering is just a result of drawknifing them on a shaving horse, but there are also rived and turned pegs out there... It would be interesting to see if joints pegged with these were drawbored. I would guess not, given you need the taper for draw boring, etc.

Most all pegs I've seen here in old barns are tapered... ~ 90%

As to your sloppy mortise assertion, it sounds like a good practice to allow for stress/movement, esp. wracking. Old buildings weren't on frost walls. And like you say, a tight shoulder is really where the strength of the joint is. Slop can be done w/out infringing on that critical factor.

Putting "slop" in a mortise is probably counter-intuitive, as well as more difficult to accomplish w/ today's power equipment, however.

"Mating faces should be regularised (flatened)...

sounds like the begining of square rule, doesn't it?

I sure hope no one thinks my joinery is sloppy or crude by my comments. Although I do push it right up to the line at times, all in the name of efficiency. Which brings me back to why I draw bore, efficiency. Square rule is efficient, too.

This discussion reminded me of the French Snap. It is a fairly crude but efficient method in shaping a tenon and would leave the shoulder tight and the bulk of the tenon possible shy of the mark.

Ken, the article on daisy wheels was great. It kept my kids and I busy for a number of winter evenings playing with the compass. I just read about the "illegal" windows. Did you do work on the frame in Fig. 24? The tie has a patch. Tim

What's the magic number? 3/16ths?
Having just done a large frame with Mark, and no draw boring (or little) I can see the benifit. But dread the sound of "POP"

Hi Tim,

I did not work on the frame in Fig 24 - if I did that would make me about 480 years old ! I have however slept in the bed shown in Fig 24. The more observant of you will note that the leg of the bed appears to be propped up on books and that is because a large hump in the floor has developed due to subsidence in the front wall.

Don,

I agree your comments about modern day power equipment not providing adequate "slop" clearance in the mortice and thus I rather suspect that frames made thus will be much more subject to the development of large shrinkage cracks.

Regards

Ken Hume

Maybe there's another word for "slop" we can use... that way it won't sound like "sloppy," which as Tim pointed out, can lend a negative meaning.

What about

"tolerance"

or

"allowance"

Anyway, I was giving this some thought... seems like we're talking about two different animals, even two different time periods here.

What Ken seems to be asserting is that it made sense (long ago) to cut mortises with some "allowance" factored in because of the conditions, principaly no modern foundation, and green timber.

Settling of both wood and building were certianly going to happen.

So I'm wondering, and the question might now be, if we need to make mortises in frames today with "allowances" given we don't have those concerns in new construction: modern foundations and kiln-dried stock reduce movement issues considerably.

(I assume stock is often KD these days)

thoughts??