Timber Framers Guild Forums General Barns and Traditional Timberframing Mill Rule v Square Rule

Hi Rudy,

Is there really a fundamental difference between what is called mill rule and square rule ? and if yes what are the key differences.

Regards

Ken Hume

Ken,
There may be those whose opinion differs but my learning says mill rule and edge rule are the same - of course this implies perfect timbers too. Square rule inserts a virtual beam inside the physical log so you have a constant to measure from.
Emmett

The timber I've bought so far (for braces) has been correct +/- 2mm (between 1/16" and 1/8"). If I can be assured of the same tolerances for the big stuff, is that good enough to use mill rule?

Ken,

Not really.

With square rule you are truing the timbers at the joints to make them perfectly dimensional and square.

Now if you have the saw mill or planer mill do this work for you by accurately sawing or sizing with a planer and you either use timber free from or assume your timber is free from wind and bow and un-square faces, then that can save you a bit of work as you don't have to size and square up the timbers at each half of each joint. That's mill rule.

Both rely on perfect geometry at the joints, the difference is whether that is accomplished by milling the whole stick perfectly or by perfectly cutting reductions, gains, and housings at the joints.

Griffon,

As for your question. There is not a simple answer. Some would say yes, some would say no.

For me to mill rule, the timbers need to be better than 1/16 of dimension and 1/16 of square (on an 8 or 10" face). Just as critically, you must have minimal sweep and no wind. And you always need to adjust things with mill rule when you are putting them together -- you just haven't accounted for irregularities up front, so you must pay at assembly.

The short answer is that if 2mm is good enough for you on this particular project, then mill rule is fine. (No value judgment intended, everyone has their own tolerances and values.)

Mill rule is fast, I will say that.

GH

Hi Emmett and Gabel,

Your advice and understanding is fairly simple and straightforward and so makes perfect sense.

Thank you for that clarification.

Regards

Ken Hume

mill rule contains structural housings, square rule contains lots of housing to that perfect timber. housings that are required for braces in square rule, may not be required in mill rule.

Thanks Gabel, thats very useful. I'm scratching my head to know exactly what are 'wind' and 'sweep' but I wouldn't trouble you to respond; I can see that any error from squareness or trueness will call for adjustment or result in un-even faces.

I think mill rule will be good enough

Wind as in a winding river, not as in the wind cries mary



and sweep as in not straight.

i hope this terminology is right

mo

I surveyed a barn which had a very small percentage of the joints relieved in the square rule method. That is, it was mostly mill rule. However, I still called it a square rule frame even though only two or three members needed the square rule to find the "inner timber" of the "out of tolerance" timbers. Just my opinion.

Jim

Griffon,

Wind is twist. Something that has wind is said to be wound as in "wound up like a spring".

Sweep is bow, as in long bow, not ship's bow.

gh