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Thread: Home shop solution for a reasonable master square for the surface plate?

  1. #1
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    Default Home shop solution for a reasonable master square for the surface plate?

    So this is a hobby with a hobby budget. What is a good solution for a good square to use on a home shop surface plate? Something that can be used to set up a squareness comparator.

    Tom of Ox Tools on YT had one grand idea for using a 1-2-3 block where if the ends are truly parallel according to a DTI in a stand and the squareness comparator is zeroed to one face then the block flipped "flat" to that face to the other end and the comparator set against it then any difference noted can be split and the comparator is then calibrated.

    But it would be nice if one could make in a reasonable time or buy at a reasonable cost a known square item to use as a "master". Options?

  2. #2
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    Optical flats? Cheap optical flat, i.e. Plate glass? Bot 50 years ago, I was instructed to use several pieces of float plate glass, checking them against each other to find the flattest, then cut the diagonal out of the best one. Monocromatic light was a s.o.b. to set up, green LED,would be way to go .
    Last edited by Corbettprime; 01-15-2019 at 06:09 PM. Reason: Needed to add

  3. #3
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    I would opt for some form of cylinder square. Relatively easy to make, Harold Hall details this in his Lathework course book. I would opt to make one out of an old engine cylinder liner, just to get a decent size and somewhat square and pre-machined already.

  4. #4
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    Make your own!

    I made a set of three, only one of which is to be actually used, the others were the other two of the three used to compare in order to get a true right angle. Took a bit of time, but less than I thought. The key is to cheat a bit and use the flat to generate plane surfaces, instead of relying on the comparing between angles to do BOTH angle and flatness.

    Mine is 4" long, and I am somewhat sorry I did not make it 6".
    1601

    Keep eye on ball.
    Hashim Khan

  5. #5
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    Quote Originally Posted by nickel-city-fab View Post
    I would opt for some form of cylinder square.
    I second this. As long as you machine all surfaces on the lathe in one setup it doesn't even matter if the facing cut is perpendicular to the long side. It just creates a cylinder with a tapered end cut that is still square.

    Dennis

  6. #6
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    I made a cylinder square.

    First I worked hard to get the lathe trued up. Turns out I managed to do a good job.

    I took a piece of 4140 (not because it's "best", it's what I had) and turned it between centers. Instead of using a lathe dog, I drilled two holes on each end. One in the center, and the other off center as a driving hole. I tapped that one and used a bolt to engage the driving dog on the lathe spindle. After I finished the square I put in hex grub screws to plug the holes. I also painted the ends so I could know which was the "master" end and which one wasn't.



    I checked the diameter using a 0.0005" indicator attached to a height gauge. It came out to be within +/-0.0003" end to end. Not bad.



    Later I checked it against a starret square using single slit laser interferometry... which is danged cheap nowadays with laser LEDs selling for a few bucks. I got roughly the same number.




  7. #7
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    Quote Originally Posted by Corbettprime View Post
    Optical flats? Cheap optical flat, i.e. Plate glass? Bot 50 years ago, I was instructed to use several pieces of float plate glass, checking them against each other to find the flattest, then cut the diagonal out of the best one. Monocromatic light was a s.o.b. to set up, green LED,would be way to go .
    Sodium light source is just as easy.

  8. #8
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    I would lean towards buying a proper ground cylindrical square.. import of course so you don't need to sell a kidney. There are good quality options out there. Then you truly have a master that is
    plenty accurate for a home shop. You can make your own stuff from that point on and test against the master.
    If you do make your own, ground and hardened stock would be my choice. This is worth a watch: https://www.youtube.com/watch?v=Ofhek3Lbxkc

  9. #9
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    When I did my concrete block for the lathe I was bragging at how tight I was able to get my skim cuts down to on the test bar. So I think I'd give that a try as a starting point. The finish is the thing for doing a job like this on the lathe. I'll have to play with what I've got for materials and hopefully one of the lumps is a nice free machining steel and perhaps with a bit of work on the cutter and maybe a shear cutter I can get the sort of finish I want and need.

    I've got an 8" long piece of 2" hot rolled cutting as I type this. Aiming for a 6" long by 1 7/8's diameter for finished size. It's "mystery metal" that has a 6" long 2in-4.5 thread on the other end...... More as it develops.

    Jerry, your post reminded me about making reference squares in an article in one of the Lautard Machinist's Bedside Reader books. Is that the same thing? It makes flat squares but I was hoping for something that would stand up on it's own.

    It also occurs to me that if I were to get a good flat face on some heavy bar and mount it to a base with a joint that can be set then if I'm really careful with it that could then be my master reference for setting the comparator. As long as I can find something that is true enough to set the master....

    I'm not needing lab grade here. Just something where I can get the comparator set so it can be within a few tenths. I'd be quite happy if I were able to get to within 5 tenths over 5 inches. And overjoyed if I could actually get to where it's a needle wiggle over 5".

    How is the optical flat going to help me with establishing a square? Are the edges ground optically and accurately to 90? One of us may be missing something on that aspect.

  10. #10
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    I did try an Ebay and searched Shars for cylinder squares but we're still talking $300 and up for something I'll use rarely. But I've got a need for one now so thus the interest.

    Also it's fun to make this sort of stuff. It's a hobby after all. So if I can turn out something that works it's a double win.

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