Project: Squareness Comparator

[dian]

what is a "pitch lap" and what does a "pin hole tester" test?

[nickel-city-fab]

First principles:

First, you need a flat surface: For this, the three flat method is used. The only surfaces that will exhibit intimate contact when three surfaces are checked against each other in ALL COMBINATIONS AND IN ALL ORIENTATIONS are three flat surfaces. The second half of that condition (in all orientations) is just as important as the first but it is often forgotten. Scrape or lap to bring them into that condition.

You will need some kind of linear measuring instrument to then make a block with two parallel surfaces. This measuring instrument does not need to be an absolute measure, just a means of comparing two distances. DIs have been made from scratch: only calibrating them in conventional units (inches, mm, etc.) requires an external standard.

You can then use one of those flat surfaces and the means of comparing linear measure to assist in making a "square". First create a block with two parallel surfaces that are flat. Check them against one of the three flat surfaces you created above and check them for parallel with the linear measuring instrument.

Then, make a squareness checker as has been described here. This does not require any great precision. The DI that was created from scratch can be used in it's construction.

Finally, that squareness checker, along with one of the original flat surfaces can be used to create a third surface on that block that is square to the original two, parallel surfaces.

That is how it is done from first principles. All of the above can be done without any machine tools and without any purchased measuring instruments.
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Paul -- thanks for the education. I knew about the three-plate method from reading Moore's "Foundations of Mechanical Accuracy". I was not sure about the rest of it, so it's good to have your explanation. For better or worse, I have nothing but time on my hands this year -- the docs want to do another surgery in April. So I decided to spend the year by asking myself how to rebuild civilization from scratch. Just for practice. It's much, much easier to simply open my wallet online and get a piece of granite from a far away country and trust them that they say its flat. But simply buying things doesn't teach as much.

[JoeLee]

Here is another idea I came up with the other day. I've been using the straight toe for direct readings for squareness but a ball bearing could be placed in front of the toe so the part could be pivoted like with the surface gauge set up. A notch the dia. of the ball could be milled into the edge of the toe with a ball end mill to keep it from rolling away.

JL......................

[nickel-city-fab]

Here is another idea I came up with the other day. I've been using the straight toe for direct readings for squareness but a ball bearing could be placed in front of the toe so the part could be pivoted like with the surface gauge set up. A notch the dia. of the ball could be milled into the edge of the toe with a ball end mill to keep it from rolling away.

JL

Make it even easier by ordering a tooling ball from https://www.mcmaster.com/tooling-component-balls

[JoeLee]

Well that makes it even easier. Just drill a hole.

JL....

[nickel-city-fab]

Well that makes it even easier. Just drill a hole.

JL....

Yep. And no more rolling away or having to chase something all over the surface plate. I may actually redo this project idea in the future.

[alanganes]

I'm not sure that the world is ready for this, but here is the super ghetto version of the quick and dirty use what's on hand squareness comparator:

Yes, that's a large steel fender washer stuck the the base with some of those small neodymium super magnets. Laugh if you wish.
Stays put just fine so long as you don't ram it into your work piece. Not very elegant, but quick to deploy and allowed me to do what I needed without having to start and complete (yet another) project, so that I could complete my project.

[nickel-city-fab]

Love it! Another one that makes me wonder "why didn't I think of that??"