Square accuracy

[cambournepete]

Following on from Eric's thread about digital angle guide accuracy, how many people check the accuracy of their squares?
I've got a T square for marking out large sheets and it's 3 or 4 degrees out and therefore useless.
I check it against a normal try square which I've since checked against another so I know which is wrong.

 

[deserter]

I check my squares before using it every time, I have to for the work I do.
The best way I know to check it is to square off a straight face then turn the square over and make sure it squares the same line.

 

[Eric The Viking]

For DIY, I check my spirit levels every time - a moderate bump is enough to put them out, and the consequences can be expensive! Squares get checked a few times each month, but as I'm the only user, I know if I've dropped or bumped them!

FWIW, I have a couple of "Soba" brand engineers' squares, that most definitely aren't, but I think its down to the way the butt is swaged onto the blade (the metal has spread a bit). Possibly fixed with a diamond stone. The only genuinely right angled one I have is a BS-marked one by Fischer. I take great care of it!

Cheers,

E.

 

[Phil Pascoe]

The BS mark maybe shouldn't be taken for granted - as far as I know, it refers to the inside of the square not the outside, which (for a woodworker at least) is the edge least used.

 

[Eric The Viking]

The BS mark maybe shouldn't be taken for granted - as far as I know, it refers to the inside of the square not the outside, which (for a woodworker at least) is the edge least used.

That's useful to know.

My BS-marked Fisher one is the only one that tests square though - the others don't (and didn't when new, either :-( ).

Cheers,

E.

 

[Benchwayze]

How do you check a spirit level, without a known, dead-level surface?
The only way I know is to plonk it down, take the reading, and then twist it end for end to compare.
Is that right? I think it must be, because all the shelves in my garage look level; but then my eyes aren't level. (homer)

 

[Eric The Viking]

That's it - as long as it gives identical readings, no matter which way round it is, it'll do. They're usually adjustable.

Of secondary importance is flatness (straightedge check) on the bottom, and the linearity of the bubble (how much it moves for a given tilt).

The one on top of my Gem Red bevel box is a PITA though. It's supposed to be a range of 1/2 degree, and it probably is, but it's very static-sensitive - you can move the bubble just by wafting a charged object near to it. I *think* it's set up properly, but I rarely use it as it doesn't settle easily.

 

[Benchwayze]

Thanks Si.

My 4 foot level is doing well. A Rabone-Chesterman, with a body of Meranti. (Straight from the factory, which was on my beat, Circa !965) I bought it when I taught myself to lay bricks. Wouldn't be without it, although I don't lay bricks anymore. Just drop one occasionally! :lol:

 

[ossieosborne]

Here is a method of checking and adjusting a framing square. The technique uses a couple of thin knives to place against the blade, once in position, before turning the square over. This is more accurate than relying on the Mk I eyeball to sight against a pencil line:

Construction Square - checking & adjusting to 90*

With thanks to the late "Niki"

Oz

 

[DTR]

I hardly ever check mine Having said that, my "go to" square is an engineer's square from Moore & Wright, who I like to think are quite trustworthy. I don't have much trust in my combi square as it only takes one shaving or chip between the reference surface and the ruler to throw the accuracy way off.