Myford Super 7b lead screw end float

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Myford Super 7b lead screw end float

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Viewing 25 posts - 1 through 25 (of 33 total)
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  • #441947
    Niloch
    Participant
      @niloch

      How critical is the amount of end float on the lead screw of my lathe (1956 vintage)? Mine appears to be excessive or is it?

      A thrust collar (part no 75/1115/1) fitted with a cup point socket set screw is fitted immediately adjacent to the right hand lead screw bracket.

      Should there be a gap between the two and if so, how much? How is the adjustment made, the presence of the grub screw would suggest that an adjustment can be made.

      The manuals by Myford and Ian Bradley are not helpful.

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      #27014
      Niloch
      Participant
        @niloch

        Adjustment

        #441949
        Mike Poole
        Participant
          @mikepoole82104

          Leadscrew thrust
          Hemingway do a thrust bearing mod for the Myford leadscrew. I would adjust for minimum float without any tight spots.
          Mike

          #441951
          ega
          Participant
            @ega

            The adjustment is simply made via the Nyloc nut.

            #441953
            Zan
            Participant
              @zan

              I don’t think it’s really important as you only drive the saddle in one direction at a time so any backlash is catered for each time you change the direction it’s being moved. It is of course consistent in value. As ega says, adjust the nylock nut in any case

              #441968
              ega
              Participant
                @ega
                Posted by Zan on 16/12/2019 23:09:41:

                I don’t think it’s really important as you only drive the saddle in one direction at a time so any backlash is catered for each time you change the direction it’s being moved. It is of course consistent in value. As ega says, adjust the nylock nut in any case

                However, in their "blurb" Hemingway do say:

                "Axial slip of the leadscrew is a common cause of thread inaccuracies. A slight oscillation imparted to the screw will cause a periodic error in pitch. Georg Schlesinger adopted a pass-off criteria of half of one ten thousandth of an inch of slip for the 1920's German machine tool industry. To adjust clearance in the right hand bearing of the Myford Series 7 leadscrew is a difficult balancing act, generally resulting in excessive thrust loads."

                What do others think?

                #441974
                Hopper
                Participant
                  @hopper

                  I think it's mighty fine marketing hype for the Hemmingway kit. The rolled thread on the Myford leadscrew was never as accurate as that when brand new and certainly has not improved with age. Then add in wear to the half nuts — usually considerable by now.

                  Set it to the minimum clearance you can with no drag and be done with all this overthinking and get on with lathing.

                  #441979
                  Tony Pratt 1
                  Participant
                    @tonypratt1

                    I had a super 7 for nearly 50 odd years & as has been said previously just adjust with the Nyloc nut to obtain minimum clearance & don't worry about it. I won't comment on the Hemingway blurb!

                    Tony

                    #441989
                    Michael Gilligan
                    Participant
                      @michaelgilligan61133

                      Posted by ega on 17/12/2019 00:29:08:

                      .

                      However, in their "blurb" Hemingway do say:

                      […] Georg Schlesinger adopted a pass-off criteria of half of one ten thousandth of an inch of slip for the 1920's German machine tool industry. […]

                      What do others think?

                       

                      .

                      I think I would like to see that in context … Schlesinger was brilliant [*], and his advice was generally very practical.

                      MichaelG.

                      .
                      [*] https://www.gracesguide.co.uk/Georg_Schlesinger

                      .

                      P.S. … I would instinctively distrust anyone who writes “a pass-off criteria”

                       

                      Edited By Michael Gilligan on 17/12/2019 07:36:54

                      #441995
                      Michael Gilligan
                      Participant
                        @michaelgilligan61133

                        With apologies for the digression:

                        I’ve just found this, which may be of interest to some: **LINK**

                        http://www.ebhsoc.org/journal/index.php/journal/article/viewFile/15/15

                        MichaelG.

                        #442003
                        Bill Davies 2
                        Participant
                          @billdavies2

                          Michael, that was very interesting, and similar to today's situation with products from China.

                          Bill

                          #442017
                          John Haine
                          Participant
                            @johnhaine32865

                            It's very easy to add needle roller thrust bearings either side of the LS bracket which allow more preload and give less friction.

                            #442019
                            Mike Poole
                            Participant
                              @mikepoole82104

                              The Hemingway sales pitch may be a bit over the top but the conversion should offer the possibility of zero float and improved feel, has anyone fitted the conversion? And could comment.

                              Mike

                              #442035
                              Nick Hughes
                              Participant
                                @nickhughes97026

                                From the Myford manual, dealing with replacing the Half Nuts, so ignore the reference to the Saddle and Carriage:-

                                annotation 2019-12-17 092702.jpg

                                #442045
                                derek hall 1
                                Participant
                                  @derekhall1

                                  Hi I have fitted the Hemmingway kit some years ago and it was a fairly straightforward conversion and it is an improvement on the original design.

                                  Regards

                                  Derek

                                  #442051
                                  ega
                                  Participant
                                    @ega

                                    Michael Gilligan:

                                    Thanks for the interesting links. At first glance they don't deal with "axial slip" and I suspect you are better than I am at locating the context for this.

                                    Derek Hall:

                                    Did you find the ability to reset the hand wheel index useful?

                                    #442057
                                    Michael Gilligan
                                    Participant
                                      @michaelgilligan61133
                                      Posted by ega on 17/12/2019 10:24:50:

                                      Michael Gilligan:

                                      Thanks for the interesting links. At first glance they don't deal with "axial slip" and I suspect you are better than I am at locating the context for this.

                                      .

                                      Although Schlesinger’s masterwork ‘Testing Machine Tools’ mentions “axial slip” … I cannot find the source for the improbable number quoted by Hemingway.

                                      My point was that I cannot trust their assertion until I see the source.

                                      … This may take some time.

                                      MichaelG.

                                      #442062
                                      Peter Sansom
                                      Participant
                                        @petersansom44767

                                        I have allos fitted the Hemmingway leadscrew thrust bearing as part of reconditioning a 60yo S7. Certainly improved the leadscrew movment, negligible now.

                                        Would say it is a worthwhile modification.

                                        Peter

                                        #442071
                                        John Haine
                                        Participant
                                          @johnhaine32865

                                          But just to note that Hemingway charge £27 for £10 worth of thrust bearings and some bits of steel and bronze. There's no need to replace the existing bush so you don't need the bronze; and the end caps to position and shield the thrust bearings can be made from a scrap of 1 inch steel bar that may well be in your scrap box.

                                          #442077
                                          ega
                                          Participant
                                            @ega
                                            Posted by John Haine on 17/12/2019 13:13:08:

                                            But just to note that Hemingway charge £27 for £10 worth of thrust bearings and some bits of steel and bronze. There's no need to replace the existing bush so you don't need the bronze; and the end caps to position and shield the thrust bearings can be made from a scrap of 1 inch steel bar that may well be in your scrap box.

                                            Fair comment but you also get a beautiful drawing, helpful instructions and support if you need it.

                                            Plus one for making use of the scrap box. I always get a kick out of using up "unusable" short ends.

                                            #442081
                                            not done it yet
                                            Participant
                                              @notdoneityet

                                              ​​​​​​£10? As much as that? Fymord charge £3.60 just for a single nyloc nut, so I don’t suppose some consider £27.70 as outlandish for an improvement kit?

                                              At least fymord include postage on that single nut.smiley

                                              #442119
                                              old mart
                                              Participant
                                                @oldmart

                                                The leadscrew end float is mentioned by Smart & Brown in the model A toolroom lathe instructions, so it would be equally important for any lathe.

                                                _igp2516.jpg

                                                #442139
                                                Howard Lewis
                                                Participant
                                                  @howardlewis46836

                                                  If you only want the needle roller thrust bearings, see if Arc Euro have any the right size. Might be less costly!

                                                  Howard (aka as Scrooge at this time of year )

                                                  #442147
                                                  Brian Oldford
                                                  Participant
                                                    @brianoldford70365
                                                    Posted by John Haine on 17/12/2019 13:13:08:

                                                    But just to note that Hemingway charge £27 for £10 worth of thrust bearings and some bits of steel and bronze. There's no need to replace the existing bush so you don't need the bronze; and the end caps to position and shield the thrust bearings can be made from a scrap of 1 inch steel bar that may well be in your scrap box.

                                                    For intellectual completeness could you provide a bearing part No?

                                                    #442164
                                                    Michael Gilligan
                                                    Participant
                                                      @michaelgilligan61133

                                                      The quest for a clear reference for Hemingway’s assertion continues …

                                                      I can, however, quote this verbatim from page 26 of the fifth edition of ‘Testing Machine Tools’

                                                      [quote]
                                                      .

                                                      (2) Axial slip.

                                                      We have to distinguish between axial (or end) play and axial slip of a spindle. End play means the indispensable freedom of a spindle moving in the axial direction to prevent it from seizing by heating. This end play, specially on high – speed machines, should be within the specified limits and uniform running.

                                                      Axial slip (axial sliding motion) is defined as the axial spindle movements which may repeat positively with each revolution as a consequence of manufacturing errors. It is only this axial sliding movement that is to be tested, and the specified tolerances apply only to this movement. To measure axial slip correctly, the spindle must be forced in one direction by an applied axial thrust to ensure that the end play remains the same throughout the test.

                                                      [/quote]

                                                      .

                                                      Please note Dr. Schlesinger’s careful distinction

                                                      MichaelG.

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