How do you check a square with no reference square?

[Richard King]

You can make a 90 degree reference rectangle which is as accurate as your best indicator using nothing but the indicator, if you have some cast iron and care to scrape it.

The version I made measured 14 inches tall, 8 inches wide and 1 inch thick.

First the left and right sides must be scraped exactly parallel to the best you can get them, in my case <0.002mm as that's what my indicator reads to.

Once they are parallel you stand the thing upright and use the comparative indicator method to check if the sides are vertical, since you already know they're parallel you only need to scrape the base until they become vertical. An explanation of this method is in this video https://www.youtube.com/watch?v=0tu9uyRG8ZM but it may not be too clear at first.

This part can then be used for checking any other squares either by bluing it or by making a little jig so you can slide an indicator up and down it.

Cheers,
Rich

Thanks Rich,

That's the way I check angle plates when I am scraping them, but Insert a 3/4" dia, x 3/4 dowel pin or a 3/4" ball bearing with a flat spot ground on one side so it doesn't roll. I put them in the V in front of the surface gage and not use the little flat bar he uses. Jeff Theile one of the MN class students from Missouri showed me how to use the round ball on the end of the shaft on a surface gage like that and not use a hardened steel ball or dowel pin. It worked slick too. He also made up a device made to slide the blade square under it. Sort of a bridge with 2 uprights and a 1,2,3 block on top straddling the parallels and a gage with indicator on top of the 1 2 3 block. I hope he can send some pictures to me tonight. It is slick like that. I hate to say it, but when I scrape the 4" x 6" x 8" cast iron blocks I make the students scrape them to be .0002" in 4". That is a AAA lab grade I guess. I need to start to take pictures so I can share them with you. I generally hope the students take the pic's.

Thanks everyone for helping. Rich

 

[Bill C.]

Or how are the reference squares generated?
Thanks,

Tadd

Could use a 1"x2"x3" block and look for light between the ruler's edge and the surface of the block. There are several ways to check a square. Good Luck

 

[Walt]

That's only good enough for wood working,really.

Thanks George, I appreciate the correction.

Walt

 

[Round in circles]

another way to check is with a turned to true and faced cylinder on a granite surface.

Edited to add pic:

you turn the cylinder to be true (mic'd to same diameter all across it's length so that it's sides are parallel), then face off the bottom so that it is 90 to side. then you can use it like so:

View attachment 56886

Undercut the bottom of the turned bar so you only have a thin raised ring around the edge . It gets rid of the center that might be slightly out of true.

 

[John Hasler]

Or how are the reference squares generated?
Thanks,

Tadd

You can do it in sets of three like straight-edges and surface plates. You need a straight-edge or surface plate.