21 December 2014

Lure and lore of the framing square

Open post #4 dating back from September

Framing squares with their sides filled with tables and numbers are attractive.  Maybe because in my mind they share something with rune swords.  And that's of course my mistake,  I want magic and it's mainly about math.  To get the swords part right, swords are in medieval literature supposed to rely on relics not text:  E! Durendal, cum es bele e seintisme! En l'oriet punt asez i ad reliques:  La dent seint Perre e del sanc seint Basilie, E des chevels mun seignor seint Denise, Del vestement i ad seinte Marie. (Turold 1080)  That's the fantasy part, in real they probably relied only on a hard edge.  I can imagine that rune swords are just like framing squares mainly a 19th century invention.

Now OK, I did look at the framing square maths.  As I was curious enough I studied the tables and numbers.  It's interesting but it doesn't relate to anything I ever did.  Stairs for example are mostly made here with steps between the stringer,  not on top.  The advantage of seeing inches on the square as scaled down feet is also probably lost if I use a metric square.  So I have a book, but not the square.

When making structures with diagonals nowadays things have changed.  Compared to 40 years ago I now have calculators, excel sheets, tape measures of more than 2m and no need for a plumb bob. I would probably be better served with something like an alpha square to solve angled framing problems.  There is a good video about precise measurement cut with a chainsaw using a long tape measure and an alpha square.

Looking for framing square information on youtube I discovered Mark Harmon implementing a low math framing square for framing composed hip roofs: The adjustable hip square.  The square is made to set out 45° hip and valley rafters. To simplify calculations the frame scale is offset by a √2 factor so that the orthogonal values can be used when measuring diagonals.  And by keeping that scale and measures to the horizontal, the roof angle doesn't change the values either.  The only problem is that the measures are stepped,  giving most probably cumulative errors.  A specialized jiggery,  but it looks like an attractive low math solution for one type of problems.  

Of all that lure I acquired a Stanley adjustable quick square to serve as a sliding bevel. I offers me a locked angle together with its complementary angle (90°- angle).  It's jiggery, but I know I sometimes miss the complementary angle on a sliding bevel.  Now what about my next problem, the halved angle?  There is certainly a jig about that too.  Maybe all I needed was a good protractor.