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Lead screw wear, when is it time to replace.

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  • Lead screw wear, when is it time to replace.

    The deeper I get into cleaning up this Clausing 5914 the more is seen that causes concern. I don't mind spending some bucks but do not want to unnecessarily. My guess is, presuming it is factory available, that it will be costly, alternatives to factory are probably available though. It is not standard TPI being 7/8-8 if recalled correctly.

    Does wear cause any significant issues?
    What I call substantial wear is seen in the drive slot and the thread both.

    What about the thread dial gear wear, the worm gear that drives the carriage or the split nuts, should these be replaced at the same time if/when a lead screw is replaced?

    If pictures would help let me know.


    In the left mostly unused area

    You can see the slot wear

    Does not show up well but this is in a high wear area showing sharper thread crowns.

    Thread dial gear, the gear tooh crown is almost to a knife edge.
    Last edited by Ken_Shea; 12-25-2009, 10:11 PM.

  • #2
    Both look fair to me. Any wear in the leadscrew keyway will be picked up through backlash. The thread dial gear looks like it needs a good kerosene bath and toothbrush clean-up.

    Both are hardened quite well.

    My eyes would be on the drive key for the leadscrew, this is a soft steel part that could have wear or swedging, and the half nut, which is bronze of brass. These are the primary wear parts or chip embedding parts on all lathes I have seen


    • #3
      Probably didn't need told of the parts needing cleaning

      I haven't got to the split nuts as yet, but will soon, I am curious as to what condition they are.

      I have seen lead screws much worse but none of them have I ever used, so I am unsure what difference it really makes.


      • #4
        Ken I run a 5914 at work, I've also done alot of work on this machine. The 1/2 nuts are not badly priced but still not cheap new. IIRC about $120 from the factory. The nuts are a bit different, at least on mine they were Cast, not Bronze.

        I'd not worry much about that leadscrew, it looks mostly alright, but check the support on the tailstock end and make sure it's in good shape. I ended up having to drop a bronze bushing in mine as it was flopping about.


        • #5
          Well, that's two for two being serviceable, that's good.\
          The looks of it bugs me but I can live with it as long as it doesn't impact the quality of the turning or threading.

          Walter, I had checked the end support, very little play but it will still be getting new bushings, front end had essentially no play.

          spope14, are those drive keys a separate item?


          • #6
            I have to wonder if that threading dial gear was kept in contact when not threading.

            One of the weakness of this unitized system is that the drive key working in the slot can cause wear and distortion to the acme threads that can cut your half nuts.

            I'm not being critical. I have a 6903 out in my shop.

            I'd just run it and deal with what ever issues that come along. The feed slot groove isn't going to hurt your turning.

            The acme section looks pretty good from your pictures.

            I'm not sure what rides in the slot, checking that as already mentioned might be a really good idea. My machine is pretty low wear so I haven't been into that part of the machine.

            Last edited by clutch; 12-25-2009, 11:12 PM.


            • #7
              I can tell you that the threading gear was locked into the engaged position, unlike the proper practice of rotating it out of contact with the lead screw when not in use.
              I guess in all fairness, could be the last thing done with this lathe was threading so not sure if it remained engaged or not.

              If it wasn't so late I would tear into the carriage assembly a bit more yet tonight to take a look at that drive key and split nuts.


              • #8
                I kinda would suspect the threading dial gear could of been made like that. The thing has absolutely *0* force on that gear so id really doubt it would wear that badly. also as its just an indicator, untill it starts wearing to the point of skiping teeth positions its still fine.

                As far as the acme leadscrew, Wear can cause threading problems, in that as you move from a worn to an unworn area, you cause a small error in the pitch. try threading a really long fine thread and see if a 'coupleing' nut (those 2"~ long ones) will still fit without binding anywhere. if it will you surely have little to worry about in thread accuracy as long as your only making mechical threads and not leadscrews for other machines.

                Ideal with a machine like that, the leadscrew teeth itself are not used except when (rarely) threading, so its likey while that slot has a lot of wear, the teeth themselfs are still unworn. This is why its important to buy a lathe that does not use the lead screw for feeding, but at the very least has a keyed lead screw (like yours) and a rack gear for feeding, and idealy a completely seperate keyed shaft for feeding.
                Last edited by Black_Moons; 12-26-2009, 02:30 AM.
                Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.


                • #9
                  What is the function of the slot on the leadscrew? You have a pair of half nuts in the carriage which close over the leadscrew to begin pulling the carriage along. The threading dial gives you an indication of when you can slam the half nuts closed to keep things in sync with the thread you're cutting, otherwise it does nothing except help jam swarf into the leadscrew threads. I can think of nothing that requires being keyed to the leadscrew, except the drive gear which would only need an inch or so of slot if a key was used. The slot that runs the length of the leadscrew is just a place for swarf to go when the half nuts and the dial gear are engaged.
                  I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


                  • #10
                    that slot on the leadscrew likey drives a worm gear inside the carriage and that drives another gear, and THAT drives the standard feed (via rack gear along the bed) or the cross feed (Via driving the cross slide lead screw)

                    Some lathes have an entirely seperate rod for this perpose.

                    This prevents every day turning from wearing out your acme threads, as well as allows you a handwheel on the carriage to move the carriage around.
                    Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.


                    • #11
                      erm ... Just beacuse it doesn't have a feed rod doesn't mean there isn't a handwheel on the apron to move the carriage around - that is supplied via a rack and pinion set up.

                      I would make a new gear for the thread dial. That is worn out and yes, they wear out. You'll find that you'll be making a really critical thread and the dial will skip a couple of teeth at the worst possible moment. Don't ask me how I know this

                      Usually, they are made out of bronze and keeping them engaged all the time results in wear, even though they don't have any significant load on them. I think they getted loaded with chips and dirt. Anyhow, I made a new gear for a WWII era Cincinatti Traytop lathe. I only had a piece of solid copper and some SS to work with, so I made a hob from SS and the gear from solid copper. Not the best material choice, but ... it's what I had and it was a "charity" project for a student lathe.

                      It's a fun and easy project. Grinding the tool to cut the acme thread might take 20-30 minutes to get it done properly if it's your first time. Otherwise, it's not tough. I say put the lathe back together and once it's working, your first project should be a new gear.


                      (also see the link DP posted)
                      Last edited by Fasttrack; 12-26-2009, 03:14 AM.


                      • #12
                        Ok, I see there is a function for the slot- it drives a gear that slides along the shaft with the carriage. My bad for not seeing that earlier.
                        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


                        • #13
                          Id highly recommend cleaning that leadscrew at least
                          if done in place iv figure out a few good cheats...

                          Like take a wire brush and naptha, dip in naptha, brush leadscrew, repeat (grit hopefuly sticks to brush and transfers to small can of naptha)

                          Once that stops taking a whole lot of dirt out, buy some COTTON string (not nylon or any of that other trash) but just some old crappy soft cotton string that fits the thread groove, soak it in way oil (or whatever you want all over your lead screw) and start the lathe with the string at 1/2 to 1 turn around the leadscrew

                          NEVER wrap the string around your hand or anything, just grasp it beween fingers, or wrap it around a small tool like an allen key and hold that.

                          then just pull on the 'loose' end so you are constantly feeding fresh string across the leadscrew, it will suck most of the remaining grit into the oily string. You may have to wipe it down a few times with a cloth as the grit will also tend to move out of the groves and smear over the top of the thread.

                          half hour to an hour and you can clean a 30" long leadscrew to spotless if that carriage is not in the way and the lathes feed is assisting you.

                          The half nut should be removed and just repeatly wire brushed and rinsed in naptha. I just submersed my half nuts and other feed nuts in naptha and shook them violently underwater beween brushings. (Wear nitril groves)
                          Last edited by Black_Moons; 12-26-2009, 08:34 AM.
                          Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.


                          • #14
                            "Id highly recommend cleaning that leadscrew at least "

                            What is with this advice about cleaning
                            My post starts with "The deeper I get into cleaning up this Clausing 5914" , I mean really, who would take a lathe apart to clean and inspect, just to put components back filthy.
                            But... I do like the string method you mention.

                            Making that gear would be very good experience and I have another lathe that can be used, I have put into Clausing an email asking availability and pricing on that gear and other items. we will see how that goes before taking the time to make a hob to cut it, especially since I would have to purchase a length of 7/8-8 acme rod, or make that too is also possible but still more time.
                            Last edited by Ken_Shea; 12-26-2009, 09:49 AM.


                            • #15
                              Check the feather that rides in the leadscrew keyway as well.
                              It is likely worn.