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Precision Machinist Square at a reasonable price

11K views 9 replies 7 participants last post by  Holbs  
#1 · (Edited by Moderator)
Products Engineering Corp. - 7000-006 Solid Square (Rating: 5)

I have been looking for a precision square to align may machines and also my combination squares. I found the PEC tools solid square on eBay. Un like most other low cost squares, it comes with a squareness specification : 0.0006"/6". I checked it using a dial indicator, it indeed looks to be within that accuracy.

You can find this square for sale here.

Made in the USA, High precision all for $26! The only downside (if you could call it that) is that it does not come in a case. But that is just an excuse to make a custom wood box! My unit is going to live in the house only to be pulled out when I want to check my working tools. However for $26 it is inexpensive enough to use on a daily basis.
 

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#6 · (Edited by Moderator)
Thanks for all of the comments. The method I used to check the square is a variation on the method of reversing the square against a straight edge. In this case I made sure that the blade sides were straight and parrellel. Then using a straight edge I placed the square against a pin in one direction and placed a dail indicator at the end of the blade.

I the flipped the square over and repeated the process. I had a varation of about 0.001".
 
#8 · (Edited by Moderator)
Small squares are easy enough to check with calipers as long as they open far enough to measure the hypotenuse. If A-squared plus B-squared equals C-squared then you have an accurate square. Just remember that the leg lengths change depending on how you use the square! I made a quick diagram showing the different ways you can measure to confirm accuracy.
Image

This method removes any error in the straight edge used in the flip and compare method, so the only error involved is the accuracy of your calipers.
 

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