Is your square truly square

Date 08-07-2006 20:41

Good tip, another is the ole three, four, and five rule. Draw a straight line with the square on both legs, measure up three and over four, the diagonal should read five. For better accuracy use multiples of the 3,4,and 5. (ie. 6,8, and 10 or 12, 16, and 20) You can recheck by flipping the square over and draw the lines again and they should match up if the square is really square, like aevald stated.(keep your soapstone sharp)

By Shane Feder (****)

Date 08-07-2006 23:31

Hello guys,
If you weld 2 long lengths of pipe on either end of an elbow it is impossible to stand the spool up and check levels.
That is where the 3,4,5 calculation comes in handy to check squareness of spool.
When doing 3,4,5 on pipe spools the top centre of the pipe needs to be found first.
Take a length of angle and lay it diagonally (roughly 45 degrees) over the 2 pipes
Using the back edge (sharper the better) of the angle scribe backwards and forwards along the top of the pipe and this will give you exactly top centre.
Regards,
Shane

By swnorris (****)

Date 08-08-2006 11:04

John,

We use the 3, 4, 5 method too. Since measuring instruments that are used to perform final inspection have to be calibrated, the auditor asked us how we calibrate our QC framing squares. We showed them the 3, 4, 5 method, which was supported by procedure and periodic calibration documentation. Also, we use a brand new 24" framing square that never leaves the QC office. They were fine with all of that.

By thcqci

Date 08-08-2006 22:05

Having been the manager of a calibration lab before, I have verified granite master standard squares to machinist squares to framing squares. I would like to suggest another simple way to check squares used at this level of performance. If you have 3 squares and a flat surface at least as long as two legs, you may compare each of the squares to the other two squares by standing them up with the legs opposing each other. If all 3 squares (A to B, B to C and A to C) agree with each other within what ever tolerance you assign, they are all square. Save one as the standard and use the other two.

A quick way to make a good square standard is to cut a 2'1" or slightly longer piece of pipe. It should be large enough diameter to be stable as you place it on a flat surface and put a square against it. Cut (good) or machine (better) a square end on the pipe and place it on a flat surface, and go around the outside of the pipe at different points with the square. If the pipe is cut square and/or the square is square, the square will be verified square all the way around the pipe. If either are not square, it will become obvious also.

Here, all the fitters use aluminum squares. I have a steel square that I have confirmed square and it is mounted on a wall on the shop floor as a standard so anyone can place their square inside or outside it at any time to verify their own square. Also, in the handrail shop, we have a framing square that the outside corner of the square has been removed so it will fit inside the radius of a bent pipe or tube. It was verified after the removal of the corner and is verified periodically as a maintenance check.

By CHGuilford (****)

Date 08-11-2006 22:11

You know, I like the idea of mounting a known-good square on the wall for the fitters to use to check their own. I normally use the 12-16-20 (3-4-5 x 4) method that John mentioned but I get a "deer-in-the-headlights" when I explain it to others so they can do the check themselves.
It seems that screwing a square to the wall is a lot easier to explain and removes reasons that people can't do their own. I might just do that.