Are these squares worth it?

I have a couple PEC squares and they're decent. Not Starrett, but 9/10 as good for 1/3 the price.

Modern B&S is China import crap :-(



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Squares are one of the few metrological instruments that are self calibrating. It is fairly easy to verify the accuracy of a set of squares using a surface plate or other known flat surface or a known good straight edge. Place squares A and B back to back with blades touching. Using feeler gauges, measure the gap and record the size and location (top or bottom). Next, place squares A and C back to back and repeat. Finally, put squares B and C back to back and repeat. Here is an illustration of the process along with the calculations.
If you have been out of school for some time, it may test your algebra skills.
Calibrating Squares.JPG
 
Finster said:
Well, I was just looking at some browne and sharps that are supposed to be accurate to .0006 but the reviews were horrible. one guy said a .005 feeler went under the 6".
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My first question is by what method was the square checked? Did they use a surface plate or detail how they checked the square?
 
RJSakowski said:
If you have been out of school for some time, it may test your algebra skills.
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I agree, and I've been out of school a long time. It doesn't take a lot of math to place a square against a straight edge, scribe a line along the blade, flip it 180° and see where the line is in relationship to the blade. Of course this only gives us a rough indication of the blade accuracy measuring the inside and outside 90°. With that said; we need to check the beam and blade for width accuracy too.
 
Solid squares are typically made to a DIN standard. The ebay ones say this but do not state their accuracy class so who knows. The beveled edges are typical of tool makers squares and are useful for scribing and aligning with reduced parallax. My Tesa solid square has an accuracy class 00 rating - less than 0.00003" over the length of the blade.

Solid squares have limited utility. They are good for layout work and preliminary alignment before using a DTI for final alignment of a work piece. They're also useful to get something aligned at roughly a right angle, like a boring tool post or some such thing. Personally, a hardened combination square is more useful to me.
 
I have a hardened Starrett four piece 12" combination square set, a hardened Lufkin four piece 12" set, and an additional hardened PEC 18" rule that fits both. I find combination squares quite versatile and I have always thought that they are repeatably accurate for doing decent layout work, but not for anything requiring tight and repeatable accuracy tolerances. I must confess to never testing comprehensively a combination square other than an old Stanley one which was not even in the ball park, and which I fit to be a lot closer, but still too far off for peace of mind. I go to tested, solid squares and my Starrett bevel protractor when I need accurate work. Am I missing something?
 
Bob Korves said:
I have a hardened Starrett four piece 12" combination square set, a hardened Lufkin four piece 12" set, and an additional hardened PEC 18" rule that fits both. I find combination squares quite versatile and I have always thought that they are repeatably accurate for doing decent layout work, but not for anything requiring tight and repeatable accuracy tolerances. I must confess to never testing comprehensively a combination square other than an old Stanley one which was not even in the ball park, and which I fit to be a lot closer, but still too far off for peace of mind. I go to tested, solid squares and my Starrett bevel protractor when I need accurate work. Am I missing something?
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I did not mean to imply that solid squares are not accurate; just that they have tolerances and we have to understand what those tolerances are. As long as they are accurate enough for the work we do then, okay. My milling T-square is shop made and was aligned with my Tesa square. The T-square is accurate enough to be very, very useful but it is not dead nuts; I still get a tenth or so deviation on stock I square with it if I measure the stock on a surface plate with a DTI. This is in keeping with my reference square so I can accept that.

I think a lot of us think that a solid square is balls on accurate; they are not. They are good enough for most work we do but if something has to be dead on, then an indicator is still the best bet.

I guess we have to decide when good enough is good enough.
 
Bob Korves said:
I find combination squares quite versatile and I have always thought that they are repeatably accurate for doing decent layout work, but not for anything requiring tight and repeatable accuracy tolerances.
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I have multiple squares for multiple uses and I put my 18" Starrett combination square up against any in regards to accuracy and I handle it accordingly. A fixed inaccurate machinist square is no better than a worn combination square. I think it best to think of a combination square like we do a piece of equipment with ways. They need to be kept clean, wiped down, grime and grit free, otherwise they wear on the bearing surface and become inaccurate. Knowing the tolerances of each measuring tool we work with should come first. I have three framing squares, one I use for layout, the other two for checking square when I'm welding.

I'm not sure how many folks know the likelihood of having two measuring tapes of the same brand, model, etc. measure the same is close to slim and none. Somewhere within 10' they will not match up at least once and sometimes multiple places by 1/16".
 
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