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  • Dual scales on slide dials.

    My lathe has dual scales on the dials, imperial and metric. The leadscrew seems to be 1/2" x 10TPI, and the dials I have are graduated as .100"/turn (.001" per graduation) and 2.5mm/turn (.02mm per graduation). Obviously the two don't relate perfectly .100" being 2.54mm, so one or the other (I'm pretty sure the metric one) is .016" inaccurate over a turn of the handle. Is it normal for makers to do this or standard practice?
    Peter - novice home machinist, modern motorcycle enthusiast.

    Denford Viceroy 280 Synchro (11 x 24)
    Herbert 0V adapted to R8 by 'Sir John'.
    Monarch 10EE 1942

  • #2
    Peter,

    Are you *sure* that the two dials rotate at the same speed? My lathe also has dual dials, made by CMT. The feedscrews are imperial, the imperial dial is fixed to the feedscrew. The metric ring is driven by internal tooth ring gears at a 125:127 ratio, and rotates at a slightly different speed. This exactly compensates for the "inaccuracy".

    Regards,

    Ian
    All of the gear, no idea...

    Comment


    • #3
      Hi Ian.

      Never thought of that. This isn't a 'high-quality' lathe, having been made for the schoolroom market, so I doubt it. All of the lathe is metric bar the slide screws as far as I have seen. I'll go and check it out.
      Peter - novice home machinist, modern motorcycle enthusiast.

      Denford Viceroy 280 Synchro (11 x 24)
      Herbert 0V adapted to R8 by 'Sir John'.
      Monarch 10EE 1942

      Comment


      • #4
        No, the scales are fixed together. By using my vernier and measuring across 20 divisions on the metric scale at various points and either side of 0 all I can conclude is that they must have simply spread the error across all of the 125 divisions on the dial.
        Peter - novice home machinist, modern motorcycle enthusiast.

        Denford Viceroy 280 Synchro (11 x 24)
        Herbert 0V adapted to R8 by 'Sir John'.
        Monarch 10EE 1942

        Comment


        • #5
          The best solution is to rig an indicator on the slide and see what one turn of the screw actually equates to.

          Some of the cheaper imports use either metric or imperial thread and fudge the dial graduations of one system to make it work while others graduate the dial correctly in both systems, leaving one with an odd finish count.

          There are also a few with metric leadscrews and imperial dials that are fudged and don't relate to anything at all.
          Jim H.

          Comment


          • #6
            That's a good idea.

            I figured it's an imperial screw because the OD is 0.500". According to the machine plate the leadscrew is 3mm pitch and it has a metric quick-change threading box.
            Peter - novice home machinist, modern motorcycle enthusiast.

            Denford Viceroy 280 Synchro (11 x 24)
            Herbert 0V adapted to R8 by 'Sir John'.
            Monarch 10EE 1942

            Comment


            • #7
              If it's an import it could be anything.
              They often decide on a diameter and then add the pitch needed so you could have a 1/2" x 10 tpi and also 1/2" x 3mm pitch. It means the build up for the family of machines, bearings etc, is still the same.
              Often even using the same dials.

              Of the cheaper fixed dual dials only one is right and the other fudged. Some times it's easy to spot as they religiously keep to an accurate division but at the end it may read 73 and a bit.
              Other times they stretch the reading to get a full dial and then you have to indicate to see what's what.

              Better class machines have the internally geared dials so they do read accurately
              .

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



              Comment


              • #8
                This is no import!

                Denford Viceroy made in Brighouse. Don't get much more British than that

                1st pic is the model I have - 280 synchro: http://www.lathes.co.uk/viceroy/page6.html
                Last edited by Peter.; 01-10-2009, 10:08 AM.
                Peter - novice home machinist, modern motorcycle enthusiast.

                Denford Viceroy 280 Synchro (11 x 24)
                Herbert 0V adapted to R8 by 'Sir John'.
                Monarch 10EE 1942

                Comment


                • #9
                  Of course it's an import, it came from Brighouse, that two continents away from Kent

                  You will have to clock it out and then see but if they are equal division one is out. Not a good way to do it, the unequal divisions are better as once you are close, lees than full turn you can use the divisions accurately.

                  I think my metric TOS has unequal thou markings, not certain as in 8 years I have never looked at them

                  Yup



                  This is direct reading so each imperial division is actually 0.001"
                  .

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



                  Comment


                  • #10
                    I think this is going to be 'one of them days'.

                    Using the dial gauge, four turns of the cross-slide screw moves the slide 9.98mm. Since there are 100 one-thou increments on the imperial dial if it read correctly it should have move .400" or 10.16mm. I guess it must be a 2.5mm pitch screw.

                    What I can't understand, is why on earth someone would turn a thread with 2.5mm pitch and an OD of .500". More to the point where the heck will I find a tap to make a new cross-slide nut when the time comes?
                    Peter - novice home machinist, modern motorcycle enthusiast.

                    Denford Viceroy 280 Synchro (11 x 24)
                    Herbert 0V adapted to R8 by 'Sir John'.
                    Monarch 10EE 1942

                    Comment


                    • #11
                      Bite the bullet now.
                      Replace the screw and nut with standard 1/2" x 20 thread and fit one of these.



                      Digital dial from Arceurotrade.
                      reads imperial or metric at the touch of a button, ability to zero at any point and you don't have to count turns.

                      It's not a DRO it's a digital dial and doesn't take care of backlash but neither does a dial.

                      [EDIT] it needs 20 tpi no matter what diameter to work the encoder correctly.
                      .
                      .

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



                      Comment


                      • #12
                        What do those dials cost?

                        Appears to be a workable solution so long as the dials plus the required new screws don't cost close to a cheap DRO.

                        As far as the screws and dials, early 1980s chinese import machines apparently sometimes had metric screws with an english dial just put on... the "nearest" metric was used, with no real thought as to whether the dial would be accurate.

                        Maybe the makers thought the dial would "convert" the machine by itself. Or maybe they had seen a picture of the dual geared dials, and didn't realize they were geared.
                        1601

                        Keep eye on ball.
                        Hashim Khan

                        Comment


                        • #13
                          I find myself using different lathes on different sites and never try to figure out the scale language used.

                          I keep a sticky back (magnetic) long travel dial gauge. Stick it on and read it!
                          "...do you not think you have enough machines?"

                          Comment


                          • #14
                            MAAAKKEEEITTTTT!!!!!!!

                            If it is that large you might single point internal it.

                            Comment


                            • #15
                              Originally posted by John Stevenson
                              ...it needs 20 tpi no matter what diameter to work the encoder correctly.
                              Just wondering if with 20tpi it works in radius or diameter mode? Hence, might there be the possibility of using it in the other mode with 10tpi (sod's law says it will require 40tpi - a bit fine for a leadscrew)?

                              P.S. For anyone interested in dual dials, have a look at UK patent 1 192 831.

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