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Building a Cylindrical Square

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  • Building a Cylindrical Square

    I would like to build one or more cylindrical squares. I've seen several different types and styles and would like some input as to which are more useful. I would also like some opinions as to what material would work best for this application. The ones I've seen range from a solid cylinder to those made from precision thick wall tube. They range in height from 4" to well over a foot and are generally 3" - 4" in diameter. Some include features like one end at a fixed angle to the sidewall and a series of hash marks to determine the exact degree of squareness of the object being measured.

    Here's an example of a basic one offered by MSC:

    Thanks, projectnut

  • #2
    Make a bunch of 'em! The overall accuracy depends on the squareness of the base to the cylindrical surface and the degree of taper, so a good method would be to turn the cylindrical OD, mic' to ensure it's parallel, then *without taking it out of the chuck* face the "bottom" end - if made from solid bar rather than tube all of this can be done with tailstock centre support, as you'll want to recess the base to leave a narrow ring contact (to ensure it doesn't rock) once you're finished. They're precision tools, so if they turn out good, make a nice wooden box to keep 'em safe too

    I have a few of 'em ranging from tiny (a 2-stroke engine's gudgeon/wrist pin 1/2" diameter by 1-1/2") up to a scrapped lathe tailstock barrel (12" tall x 3" diameter, trued up in the lathe to eliminate wear and taper) - it's handy to have the small ones as they can be used in awkward places.

    Checking how far out of square a workpiece is is pretty easy if you slip a feeler gauge between work and square, see how far from the base and do a little trig...

    Dave H. (the other one)
    Rules are for the obedience of fools, and the guidance of wise men.

    Holbrook Model C Number 13 lathe, Testa 2U universal mill, bikes and tools


    • #3
      Rudy Kouhoupt wrote an article about how to make these in the Sept-Oct 1997 Home Shop Machinist magazine. The ones in the article are smallish, 1 inch diameter I think, but the method applies to any size you care to make. Reprints may be available or it is likely published in one of the Village press compilation books.


      • #4
        The good material is tool steel, either thru hardening or carburized grade. The goal is to achieve high hardness (not less than HRC 60) on the cylindrical and face surfaces. After hardening it needs cylindrical grinding, followed by stress relief and lapping. This is how I believe the professional tools are made.

        Any soft material would next to useless since it would not be able to maintain its accuracy over time.



        • #5
          In Guy Lautard's Second Bedside Reader, he describes the process a friend used to make cylindrical squares from heavy wall stainless steel tubing (surplus submarine periscope standard) that had been precision ground on the OD.



          • #6
            Originally posted by mikey553 View Post
            Any soft material would next to useless since it would not be able to maintain its accuracy over time.

            you described the text book and preferred method, but only a small percentage of home shop guys will have cylindrical grinding capabilities. How long soft material lasts is a function of how much its used and with what level of care. Since a home shop guy's works isn't subject to ham fisted knuckle dagger treatment and its used less often, soft materials can work very well.

            The thing to make a cylindrical square on the lathe is super consistent diameters. tweak things until its to a tenth over its length and you've got a high class square. Of course undercut the end that is held by centre so you can face a 1/4 land or so that becomes the base. Now turning to a 10th ( or bloody close there to) over any length is not simple, but that's the exercise and what you need for good square.

            I've got one that won't budge a tenths indicator needle. just dead on. I got another that is out a tenth and half and another that is out several tenths. All are hardened ground and made by tool and die makers, one good and and two not so good. I don't think I could replicate the good one the lathe, but I could probably do as well as two hacks
            Last edited by Mcgyver; 02-08-2013, 08:25 PM.
            in Toronto Ontario - where are you?


            • #7
              I've considered this a few times. For a working grade cylindrical square, you could use some precision shafting. Mount a short section of aluminum tubing in the chuck and bore it until the shafting will make a very close slip fit into it. Without moving it from the chuck, insert the end of a suitable length of the shafting. The other end of the shafting gets held by a steady. With the piece in place, tighten the chuck jaws. This should get that end about as well centered as possible. Now face the end and turn a recess also. You should be left with a lip that will seat flat against a surface plate. Reverse the piece and machine the other end the same. Make two. You can test them against each other on the surface plate. I know from experience that they will be better than many items that are supposed to be square.

              I would use something that's at least 1-1/2 inches in diameter to give it a wide enough stance to be usable. It will be heavy enough to stand some feeling around with shim stock or paper. You can polish them up with nevr-dull or something like that, and as dave suggested you can keep them in a protective box. Throw a silica gel packet in the box to help keep moisture at bay.
              I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


              • #8
                I have a Wrist Pin from a Catapillar Diesel Engine
                It is perfectly round, and square and ground all over and it is hard.
                Couldn't be better

                Green Bay, WI


                • #9
                  Another thing I remember from reading about cylindrical squares is the working ones should have a central hole so they can be bolted to a fixture plate or mill table or a face plate. This hole does not need to be bored or reamed or a precise diameter, just a clearance hole for a bolt.
                  Paul A.
                  SE Texas

                  Make it fit.
                  You can't win and there IS a penalty for trying!


                  • #10
                    Screw the version of cylinder square with the "calibrated" out of square end and the scribed etc. It's a PITA. Make a universal comparator square you can zero with the cylinder square at the preset "reckoning height" you wish to verify. The virture of a comparator square is you can check features and quantify errors to the observable resolution of the dial indicator and do so over protuberant features.

                    The fixed comparator square has the heavy base whose R is coaxial with the mast. An adjustable dial indicaor attached to a clamp travels vertically on the mast. The base is bumped against the cylinder square and the indicator zeroed. The comparator square is then set against the work under test and the out of square is registed directly on the dial indicator. Dial indicating comparator squares were quite common. Taft Pierce made a dandy in their day.


                    The universal comparator square is similar but the base has no reference feature except the face on which it rests. It has an adjustable "fixed" jaw that slides vertically on the mast. The reference jaw and the dial indicator may be positioned at any height and separation to validate squareness of any vertically oriented feature once set with the cylinder square. I've jury rigged many an iuniversal ndicating comparator square from a transfer stand with a hunk of keystick dressed to a blunt point and clamped to the mast.

                    You don't see universal transfer squares. They are rare. The few I've seen were shop made or extemporized with shop made hardware clamped to a regular transfer stand.

                    You can construct a universal comparator square from a surface gage using the ball on the mast, a DTI and /or other dial indicator hardware and snugs but they are very sensitive to temperature and tiny bumps. If you are forced to assemble one be sure to use "repeat zero" technique to validate before and after zero settings.

                    I'll see if I can find some links.
                    Last edited by Forrest Addy; 02-09-2013, 12:26 AM.


                    • #11
                      Originally posted by darryl View Post
                      I've considered this a few times. For a working grade cylindrical square, you could use some precision shafting. Mount a short section of aluminum tubing in the chuck and bore it until the shafting will make a very close slip fit into it.
                      I thought that the idea of the cylindrical square was that once it was parallel to the lathe's spindle and faced, it was pretty much guaranteed to be 90 degrees.

                      What am I missing?
                      At the end of the project, there is a profound difference between spare parts and extra parts.

                      Location: SF East Bay.


                      • #12
                        Originally posted by danlb View Post
                        I thought that the idea of the cylindrical square was that once it was parallel to the lathe's spindle and faced, it was pretty much guaranteed to be 90 degrees.
                        that would be true if there was zero twist in the bed, no wear, the axis of motion of the carriage perfectly straight and the tailstock dead on the spindle axis. I reality it takes some doing to turn say a 6 inch length and have it mic the same to a tenth at each end.....and if its not the same dia, its a cone and it's surface wont be square when sitting on the surface plate
                        in Toronto Ontario - where are you?


                        • #13
                          What I'm talking about is not doing anything to the OD- you start with what might be called superior, TGP, or whatever it is that's already finished. You cut a length from it and face the ends.

                          The idea of the aluminum ring in the chuck is that it lets you bore a perfectly concentric home for one end of the bar chunk you start with. When you further tighten the jaws after the bar has been inserted, it grips it without throwing it off center. With a steady at the other end, the piece of bar is going to rotate with no wobble. When you then face the end, it comes out perfectly square.

                          The aluminum ring cannot be used again if it's removed from the chuck, as it won't remount with perfect concentricity. When you loosen the jaws to turn the bar around, you loosen only enough to relax the grip on the bar, not enough to let go of the ring. The ring is a jig, and goes in the scrap once you're done making your parts.
                          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


                          • #14
                            how do you get the lathe to face perfectly "square"? get a precision square, attach it to the shaft and adjust the compound, maybe? otherwise you will have a quare standing on an edge, that will wear rapidly.

                            by the way, did anybody (rich?) with the appropriate equipment really measure wrist pins, as i use them too.


                            • #15
                              Maybe I'm jumping to conclusions. Making a cylindirical square can be accomplished on a lathe of modest size and middling condition and it's not that tricky. However final finishing and certification is done post machining and calibration has to be carefully done.

                              Another point is the error in the square's cylindricity has to be 1/4 to 1/10 of the accuracy in the work to be tested with it. Centerless ground or turned and polished barstock may or may not have the cylindricity you may expect of it. Be sure you check the starting material by rolling it in a V block under a 0.0001" indicator before you commit.

                              Factory cylindrical squares are made of stablized hardened steel cylindrical ground between dead centers (not live) and lapped to finished cylindricity of 0.0001" or better. BTW cylindricity is a metrology term having a specific definition. It's calculated from the measured errors in taper, roundness, rainbow, and other deviations from a true Euclidean cylinder.

                              A pretty good cylindrical square can be made in the home shop on basic equipment but the work has to be carefully done. Chrome rod and TGP bar stock can be used provided you satisfy yourself that it's roundness etc is up to snuff. One can make a good cylinder on a shaky home lathe provided the finish cut is taken between dead centers. Think of locking the spindle and driving the work directly via a belt from a separate motor. Use a power drill or something variable to run the saddle feed. Take light cuts with a heavy feed and a flatted nose radius. Spend the money and buy a single Sunnen external honing stone to refine the finish, hone out residual taper, etc until your work is within 0.0001" of a common dia for the full length. Then face the registration end flat and square relieving the center to 60% of the outside diameter. The registration face should be a narrow rim, easily corrected by abrasive sheet lapping (400 grit!) should it be necessary.

                              Set your new square on end on a surface plate and check the squareness of the cylindrical body at 8 points on the diameter. If the square is tipped a trifle, determine the points of maximum acute and obtuse error and mark the upper surface. The square's diameter at 90 degrees to the plane of max error will be square.

                              Squares qualified to read 0.0002" in a foot can be made following this recipe. Remember that a dial indicating comparator square is an inescapable necessity for a cylindrical square. These are also easy to make. Maybe you chould make the comparator square first because you will need it at the end.

                              Relax the accuracy if my suggestions seem to be persnickity for your purposes but rememer that if errors are present they may loom up and bite you where you're least prepared. Know your equipment.
                              Last edited by Forrest Addy; 02-09-2013, 02:41 AM.