DIYbanter - View Single Post - How Square is Your Squa A dial indicator method

Doug Miller[_4_]

wrote in news:bc9297af-00ce-44cd-8f63-cfff2cea2c50
@googlegroups.com:

I like to have at least one master square that I know is balls to wall accurate. I had no way
of checking before and I do now. The Draw-A-Line and flip method will never tell you how
far out of wack your square is

Pfui. Of course it will. The more the lines diverge, the more out of whack it is.

- only that it might be out of wack. There is no way to quantitate the angle error unless you
can measure the distance betwene the lines/knife marks with a caliper (good luck).

That'll work. Feeler gauges will probably work better.

How much of a gap in between the marks is considered unacceptable? You can't easily
answer that question so why bother checking in the first place?

Of course you can easily answer that question. Decide what percentage error is
acceptable in your project, and you can easily calculate the permissible gap between the
marks. Suppose you want accuracy to one part in 1000 (99.9%). The gap between the
pencil lines at a distance of 8" -- double the error in the square, remember -- must be no
more than 8 * 2/1000 = 0.016", which is easily measurable with feeler gauges, a dial caliper,
or a mike.