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  • Tailstock Rant

    Tailstocks seem to be the topic today so in keeping with that, here is my tailstock rant. My lathe is a chicom BVB25L (Tiffie, it’s the same as yours) As a hobby lathe it is adequate except for the tailstock. Whoever designed it for this lathe should have it tied to an ankle just before he goes for a swim. The saddle on this lathe is so wide that the tailstock will not reach across it . In order to use the tailstock I have had to add an mt2 to mt2 adaptor. So although I get no rotational deflection I do get lateral deflection. A few pictures to show you what I mean.

    Here is the tailstock right up against the saddle with the ram retracted:



    And again with the ram at full extension:



    The ram with the adaptor. Way too unsupported, hence the deflection.



    What a POS eh? One day when I feel capable to do so, I am going to bite the bullet and cut off the top of that tailstock and try to make something better. John, Brian, Anyone??? Have you got a good design???
    Ernie (VE7ERN)

    May the wind be always at your back

  • #2
    Any chance of a picture of the saddle without the toolpost and tailstock in the way ?
    .

    Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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    • #3
      Originally posted by John Stevenson
      Any chance of a picture of the saddle without the toolpost and tailstock in the way ?
      Sure.

      Ernie (VE7ERN)

      May the wind be always at your back

      Comment


      • #4
        Dockrat,

        What about making an extended ram for the tail stock, I'd think you'd probably eliminate some of that deflection at least...

        Comment


        • #5
          Hardinge is guilty of doing the same thing.

          Comment


          • #6
            Many makers are, my small TOS is very similar.
            There are some machines that have remedied this by overhanging the tailstock nose.
            .

            Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



            Comment


            • #7
              Looks like the total range of movement is like 40 mm. That is just really strange. The tailstock body looks like it would be about 150 mm.

              Maybe the screw is just too short, and the guy who assembled the machine just didn't care.

              Take the thing apart and see if you can't fit a longer screw inside.

              .

              Comment


              • #8
                What is the ram length? How far in can it go?

                Some of the old-time lathes that came from a watchmaker's lathe background had some WAY long rams, with really long supports as well.

                Of course, the whole tailstock ram is a kludge, its about the only part of the machine that should have some sort of gibbing, but it does not due to being round.

                There is NO adjustment for wear. And it is difficult to see how to make one that is sensible. One could do a design somewhat like an ER collet, clamping inwards as an adjustment collar is tightened. I've never seen one, but I;d be surprised if it was never done.

                But most machines don't have that, and don't even have ram wipers. So from day one, the ram gets looser and looser, more and more wiggly, sloppy, and imprecise. Bellmouthing is the order of the day.

                Now, there is NO particular reason that the ram HAS to be round, and no particular reason it must be enclosed in a tubular part of the tailstock, either. It never turns except in a watchmaker's type lathe, all others have some form of key.

                It could easily have been made like the ram of a shaper, with dovetail ways , or square ways. That wouldn't bother the action at all, but that is not the traditional way to do it.

                This is a case where tradition should have been broken long ago. But as far as I know, not ONE lathe maker ever made a non-round tailstock ram. If any did, I'd love to see a picture, because they would be the only maker that had the brains to see past tradition and easy manufacturing and focus on function. But they were probably punished by the market for being so sensible.
                1601

                Keep eye on ball.
                Hashim Khan

                Comment


                • #9
                  Originally posted by J Tiers
                  Now, there is NO particular reason that the ram HAS to be round, and no particular reason it must be enclosed in a tubular part of the tailstock, either. It never turns except in a watchmaker's type lathe, all others have some form of key.

                  It could easily have been made like the ram of a shaper, with dovetail ways , or square ways. That wouldn't bother the action at all, but that is not the traditional way to do it.
                  Actually, I was trying to think of ways to improve the side-to-side adjustment on my little 7x SIEG lathe and after looking at it for a while and reviewing the many different ideas on the ole WWW, I've decided that I am going to rebuild from scratch.

                  Now keep in mind, I haven't done it yet (haven't got me one of them round-tuit's!), but my idea was to use dovetails on the side-to-side adjust (with a screw for movement) and dovetails on the ram-in-out. I was originally thinking a square ram, but figured the dovetails would be better since they are adjustable and (reasonably) easy to make.

                  Great minds think alike!

                  Andrew

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                  • #10
                    Smart man!
                    1601

                    Keep eye on ball.
                    Hashim Khan

                    Comment


                    • #11
                      Iv thought of replaceing the pin in the tailstock with a wedge shaped key that would be held in a precision slot in the tailstock with gib screws behind it.. that would compensate for wear and help wedge the ram in place against the top of the ram bore. But I like the dovetail tailstock idea more
                      mmmm.. very temping to make my own tailstock sometime in the future.. if I only I had the castings
                      Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

                      Comment


                      • #12
                        Hmm. That's got me thinking- I was actually needing a support, a steady rest I suppose, where there could be some motion like a dovetail slide. For my use, I would have machined the business end of that with a tool held in the chuck. Anything turned to fit that business end would be about as on-axis as you could get.

                        And guess what- the thing I did make has a round ram just like a tailstock. Sometimes its hard to see out of the box.
                        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                        Comment


                        • #13
                          Dr. Rob....the total travel is 1 7/8" (47.6mm)

                          Jerry....over all length of the ram is 5" and it will retract into the tailstock body by 1/4"

                          I don't think a longer screw is the answer. With that 5" ram I think you would need at least 3" of the ram inside the tailstock for support. The real answer is a longer tailstock body WITH a longer ram.
                          Ernie (VE7ERN)

                          May the wind be always at your back

                          Comment


                          • #14
                            Originally posted by dockrat
                            Dr. Rob....the total travel is 1 7/8" (47.6mm)

                            Jerry....over all length of the ram is 5" and it will retract into the tailstock body by 1/4"

                            I don't think a longer screw is the answer. With that 5" ram I think you would need at least 3" of the ram inside the tailstock for support. The real answer is a longer tailstock body WITH a longer ram.
                            The Logan has a 5.25" ram, and the housing is 6". The ram does not retract inside, it only goes to flush, which is enough. Total travel is about 2.375", at which point slightly over half the ram is still inside. It isn't enough, the slop gets rapidly worse near full extension, although it is nearly non-existent in the first 0.75" of travel. I've been meaning to do something about it, but I actually have not even assessed the conditions yet. I just do my work-arounds.

                            I'm with you on both points.... the ram needs as much as possible inside teh barrel for stability. The lever is a multiplier for slop..... if you have only 0.002 slop, and the ram extends half it's length, the slop at full extension is 0.004. More is clearly NOT needed.

                            A considerably longer ram would have to wear a lot more to get to the same slop. But it would have less force on it, and therefore might actually wear slower, due to the reduced lever arm.

                            yes, the longest ram, with the longest tailstock barrel is best. That would give the smallest 'slop multiplication" possible, and the best performance of a round ram.

                            It would be the same with a dovetailed ram, but at least there you could adjust the slop with gibs.
                            1601

                            Keep eye on ball.
                            Hashim Khan

                            Comment


                            • #15
                              It sounds like J Tiers is describing a bed turret, see the second picture from the bottom. http://www.lathes.co.uk/hardinge/page4.html

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