Sometimes Engineer's Squares aren't

[routercnc]

Hi Peter,

Surely a square must be within a certain limit, albeit a fairly tight one. Otherwise you are suggesting that every atom is perfectly in line, and that they are all perfectly at 90.00000 recurring degrees relative to the other part. Not only would that be difficult to build, it would be extremely expensive. As soon as you picked it up you would have to reject it due to the heat from your hand distorting the frame if that was your pass or fail criteria.

We need to use limits all the time in Engineering - think of all those tolerances we put on dwgs. They aren't to make it perfectly square, they are to make it square enough for the intended application.

[AdieR]

squares:

A quick way to check whether a square is "square" is take a piece of material with a straight side, put the square against it, and draw a line, then turn the square over and draw on top of the original line - both lines should line up with each other, if you see what I mean.

No square (or indeed any other measuring instrument) can ever be "perfect": temperature, the material its manufactured from, how the item is treated (in manufacturing, transport/shipment, and also treatment by end user) all affect accuracy (a square can only be accurate to a given tolerance over its length).

Cost is obviously a factor (items mass manufactured in the far east to keep cost down are obviously never going to be as accurate as more expensive items where more care is taken in manufacturing / handling).

Personally, when I buy new measuring equipment, I try it on a known standard, and if possible I'll try to compare it to other measuring equipment which I have.