Squarness Comparator

[rossbotics]

I built this dedicated Squarness Comparator (squarness checker) to take the place of a surface gage that I normally would convert over to a squarness comparator for checking something after grinding, having a tool that is made for a certain application speeds up the machining process, no more fumbling around with a surface gage a hand full of yokes and a dial indicator, this tool is dedicated for this purpose and will never be altered.

This tool will check the squarness of something from 1 ½” to 6” in height, the same height as my cylinder square, for those of you that don’t know what a cylinder square is, it is one of the masters of squares.

The Comparator has a 7/8” thick cast iron base, a 7/8” round TG&P 303 Stainless steel column, an aluminum yoke with a brass thumb screw and a used but not abused .0005” graduated Federal dial indicator with .125”travel.

The base has been fine ground on the bottom (will be lapped later on) with a milled out pocket to reduce friction on the surface plate, there is also a machined radius (not hand ground) on the nose of the base for rotating to find the high point with the dial indicator, the column has a 3/8” hexagonal hole broached in the upper end for tightening, I have included multiple photos of the machining and grinding processes it took to manufacture this tool.

As always thanks for looking and happy machining.

Doug

[Paul Jones]

Doug,

Great work as always for this useful tool. I also learned something new with the term "TG&P" meaning "Turned, Ground and Polished" and found lots of metal suppliers for TG&P steels.

Thank you,
Paul

[DIYer]

Thanks rossbotics! We've added your Squareness Comparator to our Measuring and Marking category,
as well as to your builder page: rossbotics's Homemade Tools. Your receipt:

Squareness Comparator by rossbotics

tags: measurement, comparator

[rebuilder1954]

Very cool, Doug.

For the benefit of this newbie, how is squareness checked with this tool? Do you look for the same high spot reading at several different heights? Is there a ‘best practice’ for how you make the test?

Thanks,

Bob R

[rossbotics]

Very cool, Doug.

For the benefit of this newbie, how is squareness checked with this tool? Do you look for the same high spot reading at several different heights? Is there a ‘best practice’ for how you make the test?

Thanks,

Bob R

Thanks Bob
Yes you are looking for a high spot, you rotate the squareness checker left and right up against the cylinder square watch the needle on the dial indicator it will get to a high point and then the needle starts to go back the other way, rotate the squareness checker till you find the highest point and rotate the dial on the squareness checker to zero, you are now ready to compare that to anything you sit on the surface plate for squareness. here is a video of how to use a squareness comparator.

Thanks, and hope this helps

Doug

[mklotz]

Hi Doug,

I have two questions. Assume that I have your device and a surface plate but don't have a precision cylinder square or other high accuracy orthogonal reference.

1. Is it possible to test the squareness of an ordinary machinist's square - the L-shaped style? In particular, is the outer edge of the square's blade perpendicular to the surface plate when the square's body (the chunky part of the square) is placed on the plate?

2. Is it possible to test the squareness of the inner edge of the blade to the inner edge of the square's body ?

I have my own ideas about how to do these tasks but I want to hear how an expert would do it before prejudicing the discussion. If either of these is doable, could you describe how you would do it, please?

[rossbotics]

Hi Doug,

I have two questions. Assume that I have your device and a surface plate but don't have a precision cylinder square or other high accuracy orthogonal reference.

1. Is it possible to test the squareness of an ordinary machinist's square - the L-shaped style? In particular, is the outer edge of the square's blade perpendicular to the surface plate when the square's body (the chunky part of the square) is placed on the plate?

2. Is it possible to test the squareness of the inner edge of the blade to the inner edge of the square's body ?

I have my own ideas about how to do these tasks but I want to hear how an expert would do it before prejudicing the discussion. If either of these is doable, could you describe how you would do it, please?

Hi Marv
with this tool I call a squareness comparator you could only check one side of the machinist square, and that would be the side where the body of the square is pointing away from you, but then you have to check the other side as a reference to the adjacent side, this is where the cylinder square comes into play, there is another way to check your square but not with the squareness comparator, instead of me explaining to you how to do this I attached a video of how to do this operation, this is how we use to it.
Thanks for asking
Doug

[mklotz]

Hi Marv
with this tool I call a squareness comparator you could only check one side of the machinist square, and that would be the side where the body of the square is pointing away from you, but then you have to check the other side as a reference to the adjacent side, this is where the cylinder square comes into play, there is another way to check your square but not with the squareness comparator, instead of me explaining to you how to do this I attached a video of how to do this operation, this is how we use to it.
Thanks for asking
Doug


https://www.youtube.com/watch?v=baqCWk4OmwU

Yes, the video describes exactly the procedure I've used in the past. Building the little "bridge" to go over the body of the square when the blade is reversed is the nuance that novices may not immediately grasp.

Thanks for finding the video. It will be very helpful for future readers of this thread. I suspect that most of the non-professionals who frequent this forum don't own an expensive cylinder square.

[mklotz]

Now that I've thought about it in the shower, I have two remarks concerning the video procedure.

1. In the beginning of the video, he checks that the square's blade has parallel edges by miking it at several locations. However, he does not make the same check of the body of the square (the bit that sits on the surface plate). Even if the both blade edges turn out to be perpendicular to the plate, the internal angle of the square might not be a true 90 degrees if the inner surface of the body is not parallel to the side that sits on the plate.

2. It's important that the "bridge" bar over the body not move during this procedure. He puts his hand on it while testing but that could lead to movements imperceptible to him. I would rather the bridge were a heavy structure (or suitably weighted) so that gravity would assure it stays fixed and the operator's hands not touch it.

[rossbotics]

Now that I've thought about it in the shower, I have two remarks concerning the video procedure.

1. In the beginning of the video, he checks that the square's blade has parallel edges by miking it at several locations. However, he does not make the same check of the body of the square (the bit that sits on the surface plate). Even if the both blade edges turn out to be perpendicular to the plate, the internal angle of the square might not be a true 90 degrees if the inner surface of the body is not parallel to the side that sits on the plate.

2. It's important that the "bridge" bar over the body not move during this procedure. He puts his hand on it while testing but that could lead to movements imperceptible to him. I would rather the bridge were a heavy structure (or suitably weighted) so that gravity would assure it stays fixed and the operator's hands not touch it.

You're right, if the body of the square isn't in fact parallel like the blade then that method would only work for the outside edges of the square, someone buying a cheap square would run into this problem, but you know as well as I do most people don't even worry about .002" much less a .0002", where as you and I take that into consideration, it all boils down to the quality of tool you buy to start with.

Doug