# Squareness/Perpendicularity Checker



## EmilioG (Nov 7, 2017)

How are most home hobbyists checking squareness/perpendicularity when building something?
I'd like to make or modify  a stand that holds an indicator for checking squareness.
Can a bearing ball be used with a surface gage? I have vintage Starrett and B&S surface gages and they all have a V notch.

What is this V notch for? I've seen some nice checker stands with radius-ed metal "bumper" for checking squareness. Or, can this radius be machined and added to
an existing stand?  

A cylindrical square would be nice, but the Murkens is rare and the Suburban tools is pricey and no magnet.
A Murkens or Hermann Schmitt stand can probably be modified but again, very pricey.  

One of these tools can be made but the stand itself must have a very square shaft to the base.  How do you check how square your part is? 
Attached are images for OxTools home made stand. Tom Lipton.  Very sturdy looking. (of course, Tom has every tool in the book to make these things.) 
What is good enough for a home shop machinist?


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## RJSakowski (Nov 7, 2017)

Here is what I did for checking squareness.  http://hobby-machinist.com/threads/verifying-an-angle-plate.36384/#post-310490
The catch 22 is you need a known good square to calibrate it but I believe that was true for Tom Lipton as well.
A good 1-2-3 block or better yet, a 2-4-6 block could be used.  While the blocks aren't necessarily ip the precision square standards, they can be self calibrating.  First, you would verify that the sides of the block were indeed straight.  If that is true, then the sum of the four angle must equal 360º.  Furthermore, if the sides are parallel to each other, the diagonally opposite angles must be equal.  By measuring all four angle, it is possible to actually determine the individual angles using the method described in the linked thread.

Here is what I found for one of my import blocks.


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## s_vanhoveln (Nov 7, 2017)

I've seen a video where someone (can't remember who) used a polished steel ball in the notch you describe, bit I've never tried it. Tom Lipton also has a good video showing how to verify squareness using the comparator above and a known parallel. Seems easier to me than the angle method and cheaper than buying a reference square, but maybe I'm missing something.


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## Ed ke6bnl (Nov 7, 2017)

I tried my starrett surface gage with a bearing in the Vee worked but not Ideal. Didn't Tom take a pretty square/parallel plate and check it from one side  and the other and set the indicator mid way from the difference of both sides.


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## Asm109 (Nov 7, 2017)

How close to do you need to verify?  .001"/6 inches?  .0001"/6?  what?

I use a ground engineers square and feeler gages for a lot of things.

You can make your own cylindrical squares if you have a lathe and can turn between centers.

A chunk 2-3 inches in diameter and 6 inches long will work great.
If you can turn the OD to a variation of .0006 over the length, you will have a square that is good to 0.0003in/6 inches. Pretty darn good.


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## RJSakowski (Nov 7, 2017)

Ed ke6bnl said:


> I tried my starrett surface gage with a bearing in the Vee worked but not Ideal. Didn't Tom take a pretty square/parallel plate and check it from one side  and the other and set the indicator mid way from the difference of both sides.


That is basically what I did with the 1-2-3- block.


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## Grandpop (Nov 7, 2017)

When I worked in the die shop we always checked a parallel block side to side and set the indicator mid point. Everything after that is direct reading. I built 2 stands similar to above with a radius across the one side, the stem (thompson shafting) is about 18" high, base about 3 x 5 x 2.5 high, so it has some heft, and no adjustment screw needed. It always worked well for me then, and I use it at home now. Highly recommended.


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## EmilioG (Nov 7, 2017)

A gage stand like the Murkens or Schmitt has an array of screws in front. Is this to calibrate it to the main column?
I don't need my work to be aerospace accurate but would like to be able to check my work.  I suppose a simple radius on a surface gage should suffice. Along with an Interapid or Compac.


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## Bob Korves (Nov 7, 2017)

EmilioG said:


> I suppose a simple radius on a surface gage should suffice.


Most of the ones you see have been modified from a standard surface gage.  It is not too difficult to make a horizontal slot in one end of the surface gage to fit a radiused plate which is then pressed in, glued in, or whatever.  The radius is not critical, but should have a smooth curve.  Tom Lipton shows how to calibrate it, as s_vanhoveln pointed out above.


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## EmilioG (Nov 8, 2017)

I would have to buy a new stand or surface gage to modify. I won't drill or mill my vintage, hardened steel Starrett or B&S surface gages.
I see them on Ebay all the time, un hardened B&S surface gage.  Stefan came up with a simple design w/o a knob.

http://gtwr.de/projects/pro_squareness/index.html


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## EmilioG (Nov 8, 2017)

Asm109 said:


> How close to do you need to verify?  .001"/6 inches?  .0001"/6?  what?
> 
> I use a ground engineers square and feeler gages for a lot of things.
> 
> ...


Not an easy task. The ends must be ground to exact tolerance and the steel is usually stabilized.  I like the ones with a magnet. The older Murkens design was the best imho 
Thank you


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## Asm109 (Nov 8, 2017)

You turn a recess in the end of the cylinder. Then one turning pass across the remaining 1/4 inch wide band.
Lathes are scraped in to cut a concave face.  That means your part is at the maximum length right at the outside. 
That circle is by definition square to the length of the cylinder.  No precision grinding required.


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## EmilioG (Nov 8, 2017)

You need precision gages to verify your square. How would you verify your results?
.00005” at 6” possible?


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## Grandpop (Nov 8, 2017)

if I understand you correctly, you are thinking that the screws in front of the Herman Schmidt height gauge are for holding the item to be checked a fixed distance from the indicator? That is not why the screws are there. They are only to attach the flex plate that allows the upright stem to tilt for the fine adjust. We had those stands were I worked and they are very nice, but only way to check squareness with them is the slight strip that is on opposite end near the fine adjust screw (not shown in photo).

You do not set the indicator to zero then change the height location of the indicator. Once indicator is set to zero you leave it there and run the part against the radius of the stand. If you need to adjust the height, then you need another block of correct height to use to reset the indicator to zero.

The block to be used for setting the indicator does not need to be perfectly square, but it does need top be parallel and flat for the 2 sides you will use. I generally used a angle plate square. Get a reading on one face, then rotate 180 and get another reading on opposite face. Zero will be midway between the readings. We typically worked to .0002 per 12" high for squareness without any precision set blocks.

difficult to use something like a precision try square to set zero, as no opposite face to use for the double check. If you trust the try square you just use it.. 

These are some old photos of the gauge I built, one for me and one for my dad (now both mine). The hole that the upright stem fits into was jig ground square to the base and flat on bottom, and the radius was ground square to the base. Theoretically the stem is perfectly square to the base so you could change the height of the indicator without affecting zero, but I never trusted it and always reset zero every time. Base is releived on bottom about .03 deep so there is 3/16 lip around entire outter perimeter with one small air slot thru that wall to help it slide.

base




fine adjust feature


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## EmilioG (Nov 8, 2017)

Yes, I'm sorry that you misunderstood GrandPop. I was asking what the screws were for and did some research and found out that they are for the flexure plate.
Oxtool made his from .094" thk. blue shim steel.  Seeing his drawing, I saw that the shim plate flexes. A bronze screw moves
the flex plate. There is a space between the bottom base and the top part.  Your gage looks good.
I like Tom Liptons design. Carbide bearing balls ground flat and pressed in to the base.  I'll work on something simple.


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## Optic Eyes (Apr 9, 2021)

s_vanhoveln said:


> I've seen a video where someone (can't remember who) used a polished steel ball in the notch you describe, bit I've never tried it. Tom Lipton also has a good video showing how to verify squareness using the comparator above and a known parallel. Seems easier to me than the angle method and cheaper than buying a reference square, but maybe I'm missing something.


I use the bearing ball trick, works great


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