# Machinist square quality



## daviddoria (Dec 18, 2007)

I've been using a combo square to square things (table saw blade, etc.) but I've heard that it is much better to use a machinist square (something like this: Amazon.com: Robert Larson 885-1004 4-Inch Engineer Square: Home Improvement). Is there really a difference? Is the idea that the combo square just may not be actually square since is adjustable (theoretically always square in every position, but maybe not?)? Also, inside the realm of machinist squares I've heard that there are some brands that are cheaper and not-so-square. Can anyone suggest a good-but-not-a-million-bucks square to go with?

Thanks!

David


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## cabinetman (Jul 5, 2007)

daviddoria said:


> I've been using a combo square to square things (table saw blade, etc.) but I've heard that it is much better to use a machinist square (something like this: Amazon.com: Robert Larson 885-1004 4-Inch Engineer Square: Home Improvement). Is there really a difference? Is the idea that the combo square just may not be actually square since is adjustable (theoretically always square in every position, but maybe not?)? Also, inside the realm of machinist squares I've heard that there are some brands that are cheaper and not-so-square. Can anyone suggest a good-but-not-a-million-bucks square to go with?
> 
> Thanks!
> 
> David


I just use Stanley combo squares, a variety of try squares, and framing squares. I check them for square. I don't get carried away with what "perfect" should be. Either they are square or they're not.









 







.


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## Gene Howe (Feb 28, 2009)

I bought a set of three for $21.00 several years ago. I can't remember where, though. But, they've remained square and so have my two old Stanley combos. 
It's easy to check squareness if you can hold the square in your hands. Just lay it across the counter, draw a line and flip the square over. See if it matches.


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## Dave66 (Apr 6, 2012)

Because they're adjustable, combo squares can get a bit off. Not always a problem, but if you really need dead-on square, it's a hassle.

I use drafting triangles to set common angles. They're easy to find (school supplies are fine) in 30*, 45*, 60* and 90*. I've seen 22.5* in drafting supply stores. I made one from some 1/4" ply with some very careful layout. Bisect a 45* and you get 22.5*.


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## Roger Newby (May 26, 2009)

Grab a plastic drafting square from the office supply store. If you get a 30/60/90 and a double 45/90 you will have most common set ups under control with minor investment, and cheap replacement when necessary.


I was typing while Dave66 was posting..............still applies.


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## RogerInColorado (Jan 16, 2013)

I bought an engineering square several years ago. I don't actually remember where I bought it, but I do remember taking it to a machine shop and asking them to verify it for me. They did, it was accurate to some ridiculous number of decimal points. It was in a small town, the guy had nothing else to do and probably was just happy somebody stopped by. He did the verification gratis. If he would have had to set up and machine it into a useable specification I'm sure he would have had to charge for it. It came with a wooden storage case. When I got home I used it to verify two machinist squares I had. One was square, one went into the trash (turns out the blade was tapered). The engineering square went into the box and only comes out when I am verifying my other tools.

I suspect that choice of a machinist's square vs. an engineer's square is more matter of preference and perception more than documented differences in accuracy. I'm pretty sure that if anyone had ever demonstrated that one type is absolutely more accurate than another that we would have heard about it by now. My recommendation is to use what works for you, but the most important thing is for you to have confidence in the tool. Get one verified and then store it away so you have a reference tool to verify the other tools in your shop.

I don't think you have to spend a lot of money to get a square that does what you need it to do. I wouldn't buy one on-line, though. I think it is one of those things that you have to see, touch and feel because you are going to have it a very long time.


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## GeorgeC (Jul 30, 2008)

cabinetman said:


> I just use Stanley combo squares, a variety of try squares, and framing squares. I check them for square. I don't get carried away with what "perfect" should be. Either they are square or they're not.
> 
> 
> 
> ...


Absolutely agree. As long as it is square I do not care just what it looks like.

George


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## Alchymist (Jan 2, 2011)




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## HowardAcheson (Nov 25, 2011)

What you really need is one square that you use as a master square to check your other squares. Keep your standard in a separate box or protected place. Take it with you when you go to purchase any new square. You can find lots of measuring tools that are surprisingly accurate if you match them against your known accurate master square.

So, what to use as your master square? You can spend a $100 or more for a Starett or Brown & Sharp machinist square which goes out of square the first time you drop it or you can go to an art or drafting supply store and get a $10-12 plastic 30-60-90 drafting square. To prove it's exactly 90°, take two to a glass counter, put the shorter legs on the counter and face the longer legs at each other and butt them together (like a teepee). If the legs exactly butt, you have two perfect 90° angles. Buy one of the triangles and that becomes your standard or master. Now you can check your other working squares--or any you want to purchase--and determine if they are accurate. Keep your plastic master square some place where it doesn't get banged up and you will always have a perfect reference. 

Use inexpensive squares as your working squares. Check them from time to time. It they get banged up and out of tolerance, cheaper to replace the inexpensive ones than the high priced machinest square.


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