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Squares. Cyl;inder squares, to be more precise

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  • Squares. Cyl;inder squares, to be more precise

    I've read a lot about precision squares, and especially how the import machinist squares are often not too accurate. I've also read about cylinder squares, which raises the question.

    If my lathe has no taper, is making a high precision cylinder square as simple as turning a cylinder on the lathe and facing off the bottom?


  • #2
    Ah, just found a thread about making these. A needless post. I apologize.



    • #3
      Originally posted by jcaldwell View Post
      is making a high precision cylinder square as simple as turning a cylinder on the lathe...
      As always, this depends entirely on tolerance, that is, on what you consider "high precision" to be. I'm not sure what thread you found, but in one of Moore's precision books there is an important discussion of checking out-of-squareness for precision tooling such as a cylindrical square. For many home shop lathes, the best surface finish you can attain might not be up to acceptable standards for an old school toolmaker. It might, however, be adequate for less demanding projects.


      • #4
        Are there any advantages, in use, to a cylinder square, as compared to a regular square of the same precision?


        • #5
          A cylinder square can be rotated back and forth a bit on a surface plate, which drives out dust, etc- allowing the end to sit flush quickly and easily. Once you are set up and have oriented something square using the cyl sq, you can rotate the square to see how the gap may change. This is a means of assuring yourself that the square is indeed square.

          If using the cylindrical square on a mill table, it affords an easy means of bolting it down. Use can use only one, or several at a time to hold workpieces, and because they are so easy to make (after assuring that your lathe isn't cutting a taper) you can have a process of making a kit of various lengths. For holding items on a mill table, you would probably want to make them from thick walled tubing, or solid with a through hole so they can resist crushing if you'd be clamping across them.

          I have not referred back to the original discussions, but I'm sure it was mentioned that wrist pins from large engines can make very serviceable cylindrical squares.
          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


          • #6
            Rather than machine a pair, with attendant problematic results, why not visit a shop that overhauls diesel engines? A pair of wrist pins from a good-sized engine will make a lovely pair. When the engines are rebuilt, the wrist pins are usually replaced, damaged or not. I got a pair that appeared to be "as new," all I had to do was chamfer the ends so that they sat on a narrow edge. Somebody went to a LOT of trouble to make them parallel, and that is the essence of a cylindrical square, (I think!)
            Duffy, Gatineau, Quebec


            • #7
              A cylinder square is a reference tool. It's used in combination with a dial indicating comparator square and a reference flat for calibrating hard squares, validating and quantifying perpendicularity of part features, etc. Home shop guys seldom have need of a cylinder square except for keeping their squares up to snuff and even then, only if the work requires unsual accuracy measured in tenths per foot or seconds of arc.

              A cylinder square to be worthy of the name has to be a good cylinder. That is it has be a Eucludean cylinder one whose surface is generated by a rectangle rotated on one edge. Another way of putting it the square's reference surface has to be round and free of taper its full length and its ends have to be perpendicular to its axis of generation. The square's axis is generated from the center holes in the recess machined at each end. On other words, a good cylinder square is very simple in design but carefully executed as an item of manufacture.

              One of the complications of making a good cylinder square in the home shop is the quality of the lathe spindle where circularity error is measurable in the range of millionths up to half thousandths of an inch. Then there is the tracking error of the carriage along the bedways affecting the parallelism of the reference surface to the generating axis. A good hand possessing full and detailed knowledge of the machine's errors and quirks can halve these errors using skill and a little technological jiu-jitsu.

              A cylinder square is well within the abilities of the beginner as its nothing more than a straight round piece turned between centers whose ends are faced square. Therafter it's a matter of tracking down error and reducing it to accaptable limits.

              I'd hazard a capable home shop machinist with a 10" lathe in middling condition could make a cylinder square 2 1/2" dia x 6" long whose cylindrical surface is within 0.0002" total error and perpendicular to its ends within 0.0001" with no more than 20 hours of "inspecting in" accuracy.

              Just for comparison and without intending to intimidate or dismay a wanna-be gage maker, an equivalent good quality working grade cylinder from a reputable tool manufacturer will be 0.00002" of a perfect cylinder and register square within 1 arc second. A lab grade cylinder square will be 8 times as accurate.


              • #8
                I have sometimes cheated a little and made a cylinder square for specific purpose by just undercutting the center portion of its length, as the lathe is was made on tended to make a small taper on long parts. Just turned two same diameters and faced the end with a small undecut on the end too.

                Better ones I've done with a cylindrical grinder, but this is not usually available to a home shop guy.
                Amount of experience is in direct proportion to the value of broken equipment.