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Turning a long, thin taper

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  • Turning a long, thin taper

    Any suggestions on how to do this? Let's take a piece of steel rod, 3/4" diameter that has to be turned down to 1/2" diameter over 3 feet in a linear taper as an example. Long and thin enough such that support will be required near the cutting tool to prevent deflection.

    Offsetting the tailstock centre by one method or another will give the required taper. The problem comes with supporting the rod.

    If it were being turned parallel, no problems - use a travelling steady. However, this won't work on a tapered workpiece.

    Using the compound in short steps is possible but not elegant, and doesn't allow power feed to be used.

    Does an "expanding travelling steady" exist for this, any other suggestions?

    Ian
    All of the gear, no idea...

  • #2
    Ian

    The only methods can think of are hopelessly complicated!

    For example, have some mechanism to slowly move the cross slide 'out' while the compound slowly moves in to form the taper. The tailstock would not be off set and the travelling steady would be on the cross slide. Maybe if a wheel was fitted to the cross slide and there was a wire wrapped around that and attached to the lathe bed so that as the carriage moves the cross slide would move in or out, the rate of movement and hence the taper would be set by the diameter of the wheel.

    For what it is worth, I have an old lathe where the travelling steady holds a a wooden block which is drilled for the required work size.
    Last edited by The Artful Bodger; 05-19-2011, 06:48 AM.

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    • #3
      I think you have to ask what the component is going to be used for and what precision, strength, etc. is required before you can decide how to make it. Turning might not be the right way. It's easy to come up with things that can't be (or shouldn't be) made on a lathe.

      Tom
      Tom - Spotsylvania, VA

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      • #4
        Set up a roller and spring to push against the cutting force and mount on cross slide.
        Rotate compound to act as cross slide off set tailstock required amount and proceed slowly.
        As long as the spring loading is quite strong should be OK.

        Peter
        I have tools I don't know how to use!!

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        • #5
          +1 what Artful said about complicated but also +1 what Peter said in that some sort of spring tension/loaded method appears the most workable.

          Newbie answer but I would be tempted to use the steady rest, attach somehow to the normal place of the travel rest (assuming the travel rest is the type the bolts to the side of the carriage saddle), slack off all the adjustments and the spring load each adjustment bolt individually (on most you would end up with 3 springs sort of in a circle, each putting pressure on an adjacent finger).

          Even more newbie answer, you are making the male part, what would happen if you made a really thick wall female version (same taper I mean) but only a small portion of the total length? You could then make the very smallest part of the taper (male) without support then fit this "cone" over the bit you just made and have support to do the next section. Then as you go, bore the piece larger but because some of the taper will remain, you will still have some support. You may end up having to make a few of these cones.
          Like Artful said, it certainly seems complex

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          • #6
            What you need is a spring loaded steady rest with a ratchet mechanism, such that the spring force is very light (so it doesn't flex your workpiece), but as the bearing gets pushed out a little bit it can't be pushed back in because of the ratchet.

            The danger with a spring loaded steady rest is that you either have such a strong spring that it bends the workpiece defeating it's object, or, you have such a weak spring that it doesn't work as intended.

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            • #7
              A steady rest would not do too much good, a follow rest is needed with the support opposite the cutting tool. Hydraulic follow rests are used for turning gun barrels, a simple one could be fabricated or a pneumatic cylinder used to counter the cutting forces. A heavy spring could achieve the same result.

              Is there enough material available for some experimentation?
              Jim H.

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              • #8
                The deflection of the work piece results from the tangential component of the cutting force so you want to minimize it. A sharp pointed or properly relieved HSS bit that cuts on the left side is what you want.

                There have been numerous threads discussing chatter when turning rifle barrel profiles. Several types of spring type follow rests have been proposed. One that caught my eye was a lever and a weight that was a very novel approach. Haven't built one yet but it is on the to do list.

                In one of Brownell's Gunsmith Kinks books, A brass bar on the right side of the tool post that is brought into contact with the work after turning a short section of the taper is recommended.

                Frank Ford has posted a small folow rest that attaches to the right side of the tool post that would be very usefull on this type of project.
                Byron Boucher
                Burnet, TX

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                • #9
                  Originally posted by loply
                  What you need is a spring loaded steady rest with a ratchet mechanism, such that the spring force is very light (so it doesn't flex your workpiece), but as the bearing gets pushed out a little bit it can't be pushed back in because of the ratchet.

                  The danger with a spring loaded steady rest is that you either have such a strong spring that it bends the workpiece defeating it's object, or, you have such a weak spring that it doesn't work as intended.
                  How about a pair of roller bearings mounted to the toolpost and set level with the tool's cutting edge (on the "just turned" part of the taper) to stop the work being deflected - that way you could use a hefty spring and ratchet (pair of wedges behind the spring follower?) to stop the work deflecting away from the tool - I've used a pair as a follow rest, mounted on a piece of steel in the "other side" of my toolpost to stop deflection when threading a leadscrew, although that was stopping deflection away from the cutter (it was "?" shaped, and reached around the work).

                  An alternative would be to use a toolpost grinder - the force on the work would be really low compared to turning, but progress might be a bit slow...

                  Just my ha'pennorth,
                  Dave H.
                  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

                  Comment


                  • #10
                    It seems like you need a set of ball bearings on an (very heavy duty :-)) camera iris; this would be attached to the follower rest and spring loaded closed.

                    One way of realizing such a mechanism would be two disks w/ spiral slots and a center hole for the shaft being turned; these slots could engage the extended pins of the ball bearings, which are constrained to move in a radial direction around the shaft. If the disks are rotated about the follower rest, the ball bearings would move in or out. depending on direction.... The disks would need to be kept centered....

                    - Bart
                    Bart Smaalders
                    http://smaalders.net/barts

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                    • #11
                      Russ has the easy answer - for doing it in a lathe

                      Originally posted by RussZHC
                      +1 what Artful said about complicated but also +1 what Peter said in that some sort of spring tension/loaded method appears the most workable.

                      1 - Newbie answer but I would be tempted to use the steady rest, attach somehow to the normal place of the travel rest (assuming the travel rest is the type the bolts to the side of the carriage saddle), slack off all the adjustments and the spring load each adjustment bolt individually (on most you would end up with 3 springs sort of in a circle, each putting pressure on an adjacent finger).

                      2 -Even more newbie answer, you are making the male part, what would happen if you made a really thick wall female version (same taper I mean) but only a small portion of the total length? You could then make the very smallest part of the taper (male) without support then fit this "cone" over the bit you just made and have support to do the next section. Then as you go, bore the piece larger but because some of the taper will remain, you will still have some support. You may end up having to make a few of these cones.
                      Like Artful said, it certainly seems complex
                      No1 works for continuous shallow taper turning, [ use wood pads & grease ].
                      (Nb; don't offset tailstock, use a boring head in the tailstock & just dial in the offset, much easier ).


                      No 2 wont allow continuous turning so you could end up with slight steps, but its a good way to support the finished taper for supplementary work instead of using a Cathead (which can mark the surface).


                      I wouldn't do it in a lathe, I'd use the cyl grinder - set up taper, put on auto go & do something else - come back to finished job

                      john
                      John

                      I used to be indecisive. Now I'm not so sure , but I'm not a complete idiot - some bits are still missing

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                      • #12
                        Hydraulic self-centering steady bolted to the carriage but not the cross-slide. That may sound complicated, but it might be easier than figuring out a scissors follower setup.

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                        • #13
                          Thanks all - I also couldn't think of an easy way of doing it, but thought I might be missing something.

                          Not having a cylindrical grinder, and not wanting to use a toolpost grinder for the usual reasons, I'm thinking about hard rubber wheels on the traveling steady and a sharp HSS tool. Hopefully tihey'll give enough support for the machining, but will have enough 'give' to absorb the slight increase in diameter (maybe with a reset half way along)

                          But still wide open to other ideas!

                          Ian
                          All of the gear, no idea...

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                          • #14
                            Farm it out to a shop that is equipped to do such a job. You will be time and money ahead.
                            It's only ink and paper

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                            • #15
                              Originally posted by Ian B
                              Thanks all - I also couldn't think of an easy way of doing it, but thought I might be missing something.

                              Not having a cylindrical grinder, and not wanting to use a toolpost grinder for the usual reasons, I'm thinking about hard rubber wheels on the traveling steady and a sharp HSS tool. Hopefully tihey'll give enough support for the machining, but will have enough 'give' to absorb the slight increase in diameter (maybe with a reset half way along)

                              But still wide open to other ideas!

                              Ian
                              Ian,

                              You wont get a straight taper but part of a concave ellipse as the wheels push the bar into the tool.

                              You need 3 equaly sprung suports @ 120° coaxial with lathe centers & fixed to the carrage.

                              & dont use wheels.

                              guess how I know



                              I've just given this some more thought & coffee

                              If you use a traveling steady you cant offset the tail center to make the taper !!!!


                              Can you disconnect the cross slide screw, rig up a 3'6" long bar with a slider on it, to front or back of lathe & connect cross slide to slider giving you a full length taper attachment, that removes all the problems caused by offsetting, & you put the cut on with the compound slide.


                              john
                              John

                              I used to be indecisive. Now I'm not so sure , but I'm not a complete idiot - some bits are still missing

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