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Running in reverse with screwed chuck.

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  • Running in reverse with screwed chuck.

    I thought I would address the shortcomings of the old style threaded lathe spindle. All of the chucks which are used with the Smart & Brown model A have backplates using a 1 3/4"W thread, and I decided to investigate the possibility of using some type of drawbar. Only one chuck looked to be a likely candidate, there was a space between the backplate and the rear of the chuck. Also the backplate overhung the end of the spindle by about 3/16". With a boring bar, I produced a recess in the backplate 2" diameter stopping about 0.02" short of the spindle and made a steel disc with a 3/4" hole to fit inside the chuck assembly.
    I used a large rod with nuts at either end which had been laying in the metal junk/stock for years which was exactly the right length. It had a strange thread on it which was found eventually to be 1.5mm pitch. The right hand nut was turned top hat shape to fit in the disc and a bush for the left end was made to keep the drawbar central. The bar even had spanner flats on one end, I'm so glad I hadn't cut it up for another job.
    Of course, you loose the hollow spindle although the S&B only has a 15/16" bore anyway.

  • #2
    How about making a hollow tapered piece that matches the taper of the spindle and also the bore of the chuck. Use set screws on the chuck to secure it, and have it also extend through the spindle bore and use external LH threads and a matching nut to pull it tight. The walls of the "pipe" could be fairly thin, maybe 3/32", so you would lose only 3/16" and you'd still have a 3/4" bore.

    My HF 9x20 has a groove on the OD of the spindle for a locking clip that screws onto the "neck" of the chuck, and that is another option.



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    • #3
      Most for whom this is a concern put in a setscrew or other friction arrangement (with suitable padding material on a setscrew) and report that it is effective.

      The latch shown by PSTP is also used and seems effective
      1601

      Keep eye on ball.
      Hashim Khan

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      • #4
        A reversing spindle on a lathe is such a handy feature I wonder why the lathe makers of olde even bothered with threaded spindles.

        I've seen many threaded spindle work-arounds like draw-bolts, keys, locking collars etc but there is still no positive drive. The work-arounds merely introduce a high break-away friction to inhibit disengagement of an otherwise free running thread. The chucks etc all have to have some modification for the work-around to engage.

        My long standing suggestion is a huge PITA to implement but solves the reversing spindle problem forever: Lock-Tite or high-strength soft solder an L-series long taper spindle nose hub and lock collar onto the spindle and equip the chucks with suitable back plates. My vote is for the high-strength soft solder because it's 4X stronger than Lock-Tite.

        Select the L series spindle nose size to suit your threaded spindle. Design the hub to minimize overhang. Ideally the the small end of the L series spindle nose will finish flush with the threaded spindle but alas many threaded spindles are too short.

        Fully machine the hub leaving finish stock on the taper and finish the taper on the spindle to ensure concentricity. I strongly recommend 4140 HT to Rc40-42 as hub material and regular 4140 HT stock for the retaining ring.

        If you elect to go with soft solder I suggest a 96tin/4silver alloy, having 11 KSI shear strength. Hard steel solders very nicely provided the faying surfaces are scrupulously clean, tinned, and assembled hot with additional filler applied at assembly to brim the joint. Use an acid zinc flux followed by a hot water and washing soda scrub.

        Naturally careful gentle heat is important to protect the spindle's properties and ensure a strongly bonded joint.

        Lock-Tite, thoroughly clean the threads, use the strongest grade, and follow the package directions.

        All the above said the soft solder approach is probably over-kill. Lock-Tite properly cleaned and primed is for all practical purposes bullet proof in normal cutting regimes. High shock cuts on large diameters (dressing off a lumpy weld on a large diameter for example) may be enough to disturb the bond so stay away from that situation running in reverse.
        Last edited by Forrest Addy; 03-13-2016, 03:17 AM.

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        • #5
          Or use collets when in reverse

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          • #6
            There is an old joke:

            A guy walks in to his doctor and raises his arm above his head. "Doc, it hurts when I do this." He says.

            "Don't do that." The doctor replies.

            If running the lathe in reverse carries the danger of the chuck coming loose, don't run the lathe in reverse. I spent quite a few years in a shop with threaded chuck lathes, and all of my lathes have been so equipped as well. I have never seen a need to run a threaded spindle lathe in reverse in a condition that would cause the chuck to unscrew. I do occasionally reverse to run a tap out or on the rare use of a TP grinder.
            Jim H.

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            • #7
              Cutting external threads with the boring bar on the back side of the
              spindle with the lathe in reverse is kinda handy, but ya know.

              --Doozer
              DZER

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              • #8
                Last week we had a long thread on what a PITA it is to get chucks unscrewed with breaking the back gears, now we've got a thread on what a PITA it is when chucks unscrew when running backwards. To be honest, when I had lathes with threaded spindles, I only used to use reverse to take the carriage back when cutting an odd thread and I didn't want to open the half nuts. Speed was low, no load on the chuck to unscrew it, no problem. If I'd needed to cut a thread when in reverse, I'd have made up a long bolt with big washers on each end, one end inside the chuck, one end at the left end of the spindle. No chance of accidental unscrewing that way.
                'It may not always be the best policy to do what is best technically, but those responsible for policy can never form a right judgement without knowledge of what is right technically' - 'Dutch' Kindelberger

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                • #9
                  Yah, well, donchaknow...........

                  If you run the lathe in reverse, EVER, the chuck will unscrew and roll around in the shop damaging things.....

                  There.... it's been said, and the Nervous Nellies don't have to say it.... we've got THAT out of the way.....
                  1601

                  Keep eye on ball.
                  Hashim Khan

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                  • #10
                    No, it won't do that unless you forgot you were running in reverse and fell asleep. But, even if your reflexes were quicker than they are, it could unscrew enough to ruin the work.

                    You don't have to be a Nervous Nellie to want to prevent that, and so far I don't see any Nervous Nellies posting on this thread.

                    Maybe you could dispense with the supercilious attitude and contribute something useful.

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                    • #11
                      Originally posted by Richard P Wilson View Post
                      Last week we had a long thread on what a PITA it is to get chucks unscrewed with breaking the back gears, now we've got a thread on what a PITA it is when chucks unscrew when running backwards. To be honest, when I had lathes with threaded spindles, I only used to use reverse to take the carriage back when cutting an odd thread and I didn't want to open the half nuts. Speed was low, no load on the chuck to unscrew it, no problem. If I'd needed to cut a thread when in reverse, I'd have made up a long bolt with big washers on each end, one end inside the chuck, one end at the left end of the spindle. No chance of accidental unscrewing that way.
                      Clearly we need everyone who posted in one thread to swap lathes with everyone who posted in the other thread. Problem solved!
                      Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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                      • #12
                        Originally posted by Richard P Wilson View Post
                        Last week we had a long thread on what a PITA it is to get chucks unscrewed with breaking the back gears, now we've got a thread on what a PITA it is when chucks unscrew when running backwards. To be honest, when I had lathes with threaded spindles, I only used to use reverse to take the carriage back when cutting an odd thread and I didn't want to open the half nuts. Speed was low, no load on the chuck to unscrew it, no problem. If I'd needed to cut a thread when in reverse, I'd have made up a long bolt with big washers on each end, one end inside the chuck, one end at the left end of the spindle. No chance of accidental unscrewing that way.
                        I like that idea and I'm going to try it next time. But I think it needs left hand threads on the bolt to be reliable.

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                        • #13
                          The usual number of sensible suggestions and the usual number of the other kind. I did think about changing the fitting altogether but it's not easy to get the part which normally comes integral with the spindle. Cost is a big factor for me, I don't have much to spend and the owners of the lathe, a museum has more important things to spend it's limited budget on. There is only about 1/16" of the spindle showing to the left of the backplates , so there is no room for locking devices. I have 3 three jaw and 2 four jaw chucks and all have bores equal or less than the spindle thread which is why I couldn't use a simple type of drawbar. I did contemplate making a special hollow collet with the same dimensions as the S&B collets, maybe at a later date. Iv'e only seen one chuck come off, back in the early 80's when I was an instrument mechanic, our firm had a small workshop where odd fixtures were made. We had an old Myford 7 , a pillar drill, press and odd things such as an induction heater and ultrasonic cleaning tanks. The boss bought us a brand new Myford Super7 long bed with all the extras. With a single phase motor, it was ready to run straight away. The chargehand who was a prat turned it on in reverse without checking anything and the 4 1/4" chuck dropped off, bounced off the bed and unfortunately missed his foot by a couple of inches. So I stoned the bruise on the bed of a lathe that had never been used.
                          Last edited by old mart; 03-13-2016, 02:56 PM.

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                          • #14
                            My Myford ML7 has a 1 1/8" X 12tpi threaded nose. I've never had a case of it unscrewing when taking light cuts in reverse or reversing when cutting metric threads.

                            My Hardinge HLV has a taper fit nose with an ejector cam track. That'll quite happily plug reverse from 1000rpm forward to 1000 rpm reverse, when threading, without throwing the chuck off.

                            Do folks forget to fit chucks properly???

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                            • #15
                              Originally posted by old mart View Post
                              ...Cost is a big factor for me, I don't have much to spend and the owners of the lathe, a museum has more important things to spend it's limited budget on. There is only about 1/16" of the spindle showing to the left of the backplates , so there is no room for locking devices. ....
                              The idea is a zero-space locker by a setscrew in the backplate's thread spigot. If there is no spigot (my preference) or the chuck is directly screwed on, then obviously that is less possible.

                              In that case, you may want to try "Vibra-Tite" reusable threadlocker. McMaster has it in bottles and small tubes. The tubes are a LOT easier to use. It is not a glue like other threadlockers, but a high friction material. I have not used it for this, but in general use it is about as effective as the "blue patch" type threadlockers that are applied to screws by specialty places.

                              the advantage is that unlike others, it never "breaks loose", but continues to provide friction even after the screw or nut moves a bit. So it would prevent the chuck spinning off.

                              Originally posted by cameron View Post
                              No, it won't do that unless you forgot you were running in reverse and fell asleep. But, even if your reflexes were quicker than they are, it could unscrew enough to ruin the work.

                              You don't have to be a Nervous Nellie to want to prevent that, and so far I don't see any Nervous Nellies posting on this thread.

                              Maybe you could dispense with the supercilious attitude and contribute something useful.
                              I believe the point WAS that it would not..... and as for the last sentence, you need to read the thread.... which you didn't.
                              Last edited by J Tiers; 03-13-2016, 07:09 PM.
                              1601

                              Keep eye on ball.
                              Hashim Khan

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