I suggest referring to the June 2008 issue of Timber Framing for an article on snap line square rule.
Offsetting the line from a reference face keeps all the timbers (roughly) flush to that face, which is desired for outside walls or top of floors, for example. Using centerlines would center the timbers, and for timbers of varying thicknesses would require some mental gymnastics to offset them back to the flush face or snapping the line to some new datum other than centerline, hence back to "square" one. Unless you want all of your timbers of varying thickness centered.

Hello everyone tonight:

To each his own I guess, but I agree with Will B. unanimously!

I was always taught to not use a centre line unless for some reason it was necessary, A centre line usually will confuse things big time, because in hewn material layout, you would need to snap more lines than necessary, and mistaken lines could cause mistakes.

As an instructor I would not consider using a centre line layout, but rather start with the 2" offset line from one face (usually the otside) as I referred to in my earlier post. I use 2.25" to allow for rough surfaces in reality.

As Will B referred to above it always keeps the outside surfaces of hewn material (nearly) flush which is normal.

In historical work all braces and girts were set to the outside surfaces of timberframes, even on interior surfaces only occasionally would you see ceiling girts crossing the centres of frameworks set to the middle of the supporting wall posts

The large anchor beams of Dutch barns are one of the occasional centre lined connections with the braces being in line with the large tusk tenons

NH

DL, have you ever used square rule for working timber? One of the premises to square rule is knowing which face is where, and having the reference edge/snapped line closer to this best face is not confusing, in fact it makes the system more clear.

So, two advantages to snapping lines off center are highlighting the reference sides and delineating the joinery locations.

I am still not convinced a center line is the best location, perhaps there is an occasional exception. And it can be done without pre leveling of the timber, as has been mentioned, pre leveling is just an extra step as is center lines.

An interesting description of traditional square rule is in Hodgson's Light and Heavy Timber Framing Made Easy from 1909.

Here's a link to it on google books: http://books.google.com/books?id=kkk1AAA...ber&f=false

The relevant section starts on page 162, third paragraph.

I agree Tim, referencing the edges/faces is much more important than finding the center lines. When I snap lines for laying out a wonky square rule piece, or for scribing, I level and feather mark the timber, then plumb my top line down on either end, and then put a level line either 1.5" or 2" down on either end and connect the lines. Now I have marks delineating two planes at 90 degrees to one another.

Tim et al,
I should say, I was playing devil's advocate here. I am not necessarily a proponent of center line square rule. I was pointing out a conceivable advantage to some. I have never done center line square rule, but I have dabbled with it in the form of setting out from a primary corner/face. Just a thought I threw out there. Sometimes I do throw out opinions I don't necessarily agree with because I still think they merit consideration!

For the most part, however, I am content to sit back and listen to what you all have to say on this. I don't consider myself any kind of authority on square rule, not even close! SO keep the information flowing, I am certainly soaking it all in.

DLB

Hi,

So far the conversation would appear to revolve around using either square or rectangular section timbers. When round, polygonal, moulded, profiled or tapered timbers are employed then the ability to establish offset lines from references faces will become more problematic and so this might well demonstrate the ultimate value of using centre lines as a method to establish reference planes.

Regards

Ken Hume

Hi Ken, that is a good example for why we should not get locked into one method. When a certain problem arises we should have a variety of methods to deal with it.

Hello everyone tonight

Thanks for stepping in Ken with those examples, I thoroughly agree with you.

These types of unusual shapes and conformations might appear and could be handed to you for your attention, in that instance one needs to have alittle something in your experience manual to deal with it.

I once said to my father--"what would I do if I come up against something that I have never done before"--his reply was "when you have enough experience you will be able to figure it out"

How true a statement that was and it carried me through many first run situations, and my Aunt told me as a young man to always listen carefully to your mind when it came to hard calls or problems.

I found that as my career developed and various new challenges emerged I drew on past experiences to solve problems, "Historic Millwrighting" while specialized in itself contains certain aspects of carpentry and timberframing, mainly the getting down to brass tack calculations, common sense and good accurate workmanship.

Anyone of you guys could become a good Historic Millwright--working with wooden drive wheels, line shafts, mill frames, flumes, wooden machinery of many different types--I know this from listening to chatter from all of you!.

NH

Hello,

This seems roughly similar to the way I create guide lines for squaring up timbers with axes.

Greetings,

Don Wagstaff