# Setting the left/right position of DTI on a squareness comparator



## digiex_chris (Jan 30, 2015)

I'm interested in making a squareness comparator, the kind that's like a surface gauge, but with a ball or curve on the front edge. My question is how do you adjust the tip of the DTI to be in the middle of that ball or curve? I would expect having it offset would throw off the test, because if I have the pointer to the left of the center of a ball bearing, if I were to have the base at an angle to the left of perpendicular with the the surface I was testing, it would have a larger reading than if I'd had the base at an angle to the right.

I see the column type seems designed with a radius on the front that matches the radius the indicator would be at, so that solves that, but what about the ball bearing in the V-groove type?

Set me straight!


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## nobog (Jan 30, 2015)

Sorry, this is really confusing -  never heard of a squareness comparator??

jim


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## digiex_chris (Jan 30, 2015)

http://oxtool.blogspot.ca/2012/11/squareness-comparator-part-1.html?m=1
Like the second photo down.


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## awander (Jan 30, 2015)

Wherever the DTI point happens to be, will become the "center".

You rotate it and test for the point of max deflection. This is the spot on the radius that lets the work approach the closest too the DTI.


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## rgray (Jan 31, 2015)

Awander has it right...........The tool & die guy uses a surface gauge like that(phil kerner). I can remember watching some of his videos using it and thinking how would I make one of those and get the radius right......................... He explains it and builds one in one of his videos................ It is just a sanded edge nothing fancy and as you roll the piece, that you are testing for square, it will find the high spot so the reading is correct................ Made one...very handy and a nice upgrade to my surface gauge.............I like the ball bearing idea also....Being off center makes no difference as long as you can roll the edge past the indicator tip to find the high spot..... If off center far enough you could run into the side of the surface gauge before finding the high spot, but that would be extreme.....The ball bearing would add places for error if the ball is not fitting on a nice hardened place in the gauge or dust or grit in the way.


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## rgray (Jan 31, 2015)

digiex_chris said:


> http://oxtool.blogspot.ca/2012/11/squareness-comparator-part-1.html?m=1
> Like the second photo down.




Not sure if I was understandable in my reply.....I say roll the part across the piece you are testing for square....in the web site you linked on the first picture...they state "self proving by rotation"......the indicator is not set up with any effort for center.....the rolling past it or rotating past it is what finds the high spot...then simply remember the reading or set a zero.....turn your measured piece around to a different side, and the difference in the reading is how far off square it is.


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## digiex_chris (Jan 31, 2015)

Thanks a bunch! I guess with a small point like a ball bearing in a v, close enough that the highest measurement isnt past hitting the side is good enough. Maybe I'll go with the curved edge style. Off to make one!


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## 4GSR (Feb 19, 2015)

Here's one I bought a while back.  Paid more than I wanted to, but knowing what they sell for, I didn't do too bad.  The indicator had a busted point on it.  Had to do emergency surgery to fix the indicator and bring it back to life.  The original contact point was an odd length and did not have a match for it.  But had a matched set of carbide points I've had for many years that I used.  The lower contact point has some adjustment that allows you to align it up with the upper indicator point.  Still working on fine tuning the lower point.  Its close but not close enough.  Just thought I share the one I have here.


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