# Squareness comparator from a 1-2-3 block



## jeremysf (Jun 9, 2022)

I finally got around to making myself a “bumper style” squareness comparator.

I machined it out of a piece of 4140 round bar (it’s the only tool steel I had lying around). First step was to machine the round bar into a rectangular prism.







Once squared up in the mill, I ground the faces on the surface grinder, and proceeded to mill away material to create the the “L” shape. I drilled, chamfered and tapped two holes for 1/4-20 threads to attach to the 2”
face of a 1-2-3 block.

I machined the radius on my small rotary table, taking a cue from Stefan’s video where he uses a gage block against a pin in the center of the rotary table to set the radius distance. I machined the radius and added a very generous chamfer to the top edge. Then a thorough debur pass and the machining work was done!






The bumper is shorter than the 1” face, so I used a 0.005” gage block on the surface plate to set the offset (so the bumper floats above the surface plate) and bolted the bumper on to the 1-2-3 block with some 3.25” 1/4-20 bolts. I completed the comparator with a Noga magnetic indicator stand and a 0.00005” DTI.






It works super nice! Previously, I was checking squareness with steel Starrett try squares, a number 3020 for kicking around the shop and a number 20 for “special occasions”.

For those that aren’t familiar with these types of squareness comparators, you butt the bumper against a known square object, adjust the indicator to also touch and rotate back and forth looking for the high spot on the indicator. After zeroing out the indicator on the high spot, you repeat the process on the part to test, and the high spot found there indicates the relative squareness of the part.

Testing random stuff lying on the bench and I’m kind of amazed that I had got this Windy Hill Foundry casting machined square to within 0.0002”! I guess my mill tram jobs aren’t total trash after all, lols.






Testing another project in progress and…not so square. I’m pretty sure the culprit is not deburring well enough before putting it on the surface grinder. Yikes.






I’m pretty excited about to have this comparator, since I can grind in shims to fix squareness and using this tool, now I know just how much to grind!

Very satisfying afternoon project!


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## Ecosta777 (Jun 10, 2022)

Very cool! It can also be done with a surface gage, used it that way many times 
	

	
	
		
		

		
		
	


	




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## jeremysf (Jun 10, 2022)

Nice! I have seen that done before, but the rod on my surface gage does not have a ball at the end, just a straight cylinder. I did think about machining a new rod, but decided on this approach instead.

What I am seriously jealous of is Stefan G’s custom base and stand, for both its rigidity and precision fine adjust. My setup is juuuuust a bit shaky/fiddly


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## wachuko (Jun 10, 2022)

So much to learn, so much to learn…


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## GT-6 Racer (Sep 18, 2022)

A good squareness comparator is a must have on the surface plate.  Here’s my take on it. Cast iron base with shaper finish on top.  Linear bearing shaft.  An old short travel tenths indicator.  Nice project works fantastic


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## twhite (Sep 18, 2022)

GT-6 Racer said:


> A good squareness comparator is a must have on the surface plate. Here’s my take on it. Cast iron base with shaper finish on top. Linear bearing shaft. An old short travel tenths indicator. Nice project works fantastic
> 
> 
> 
> ...



I just picked up 3 tenths indicators today. You have given me inspiration for my next project. 


Cutting oil is my blood.


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## GT-6 Racer (Sep 19, 2022)

Fantastic!!  Best of luck.  Also check out Tom Lipton of Ox Tools.  He has some great  ideas on his version of the Taft-Pierce tool.


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## twhite (Sep 19, 2022)

Scrounging around. I found some material to make one. It will be made from Aluminum for base and holder. 5/8” shaft stock and a 1/2” tooling ball. 

I drew up a basic design 






Cutting oil is my blood.


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## twhite (Sep 19, 2022)

Here is my real one I have at work. 














Cutting oil is my blood.


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## GT-6 Racer (Sep 19, 2022)

The second dial indicator mount is a nice add too.  I’ve been thinking of making one so I can use it as a height gage, but I found a proper electric gage head and amplifier with a height gage recently at auction so that project probably won’t happen. 

T white, I would strongly suggest cast iron or steel for the base unless you inset 3 points of ball bearings and surface grind them flat. Aluminum will wear rapidly on the granite. The weight of the iron base is helpful during use too making it more stable.


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## twhite (Sep 19, 2022)

GT-6 Racer said:


> The second dial indicator mount is a nice add too. I’ve been thinking of making one so I can use it as a height gage, but I found a proper electric gage head and amplifier with a height gage recently at auction so that project probably won’t happen.
> 
> T white, I would strongly suggest cast iron or steel for the base unless you inset 3 points of ball bearings and surface grind them flat. Aluminum will wear rapidly on the granite. The weight of the iron base is helpful during use too making it more stable.



What I will most likely do is machine 3 small pockets to accept ball bearings. I have a mess of 9/32 then swedge them in. I made a spherometer like that for measuring curvature of telescope mirrors. Works great and very little resistance moving around. 

I would use steel or iron if I had some. I just utilize what I have laying around. It is more fun that way trying to make things with what you have on hand. 

I have had my real one for 30 years. The man that I apprenticed under made it. He unfortunately passed away at the age of 35. That was the one tool I was able to acquire. 


Cutting oil is my blood.


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## GT-6 Racer (Sep 19, 2022)

Sorry to hear about the loss of your mentor.   The tools we make surely will far outlast us.   That’s why I do an engraving on the nice stuff


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## twhite (Sep 20, 2022)

Done just needs to be cleaned up. 















Cutting oil is my blood.


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## GT-6 Racer (Sep 20, 2022)

That looks very nice.  Excellent job.  It should be a good addition to the surface plate.


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## twhite (Sep 20, 2022)

The only drawback to the 3 ball base is. It is ULTA sensitive to any plate imperfections. A flat base can overcome that. 


Cutting oil is my blood.


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## GT-6 Racer (Sep 20, 2022)

Might try surface grinding the balls to a flat leaving enough below the body say 0.030”.  Will then span pits on granite.  Just a thought.


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## twhite (Sep 20, 2022)

Good idea. Unfortunately I have no access to a surface grinder. I could mount a cup wheel to the mill and use it as a primitive Blanchard type grinder. i might do that if I find I have an issue. My surface plate at home is much better than the one in the shop. I could use inspection’s surface plate if needed at work. 


Cutting oil is my blood.


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