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  • machining a tailstock feedscrew.

    As some of you may know Im trying to help a mate fix his old southbend nine lathe. Living in S Africa its not a simple task of buying stuff off ebay. Ive made good progress on this lathe with many learning curves such as line boring and making backplates etc.
    My next problem is that the tailstock seems to have a homemade feedscrew . If you wind the handle clockwise the tailstock goes backwards. I would like to make a new feedscrew and tailstock nut.
    Does anyone know the original dimensions and pitch etc of the tailstock. Also seeing that we live in S Africa and dont understand the outdated imperial system does it matter if I do this in metric using a 60 degree v thread or would it be a compromise compared to a acme or trapezoidal thread.
    I also found this intersting and wonder what the thought are of the members on this forum. This guy 3d prints a crosslide nut for a southbend. What do you think. Would it work. I cant 3d print so its just for curiosity sake.
    https://pinshape.com/items/16566-3d-...ross-slide-nut
    Today is the coldest day of the year so far. I cant believe how cold it is. Yesterday was 36 degrees and today its 12 degrees. Its gonna be hard to get into the workshop.

  • #2
    If I recall correctly, the original thread would have been an Acme (trapeziodal) thread of 1/2-10 size. Nearest metric equivalent is something like 12mm x 2.5mm. Left-hand of course.

    where I live it routinely goes below zero temps in February with humidity through the year
    25 miles north of Buffalo NY, USA

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    • #3
      The tailstock definitely has a left hand, ACME 10 TPI thread. Whether it is 3/8", 7/16", or 1/2", you'll have to measure that yourself. If you don't use the original thread size, you'll also need to line bore out the old tailstock threads and insert a sleeve with the new thread size - not an easy task for the novice. You'll also need to obtain the corresponding sized left handed ACME tap to tap your new sleeve.

      As for not understanding the (not) "outdated" Imperial system, I would suggest that you study up on it if you intend to continue repairing an old South Bend - you'll need that skill.

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      • #4
        Being three km away from the Indian ocean which is on average 20 plus degrees Celsius in winter we fortunately will never go below freezing , . But I'm just not used to such cold weather. I cant imagine living in a place with snow, cant figure how you can work in such cold. But it does look beautiful.

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        • #5
          I have some 1/2-10 LH acme thread I can send you, but you'll need to sort out the quill threads some how. I borrowed a tap so I can't help you there

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          • #6
            I'm fairly certain the T/S screw is 1/2-10 LH Acme for those. IIRC that is what the one I refurbished had. If that one you are repairing has been modified with a RH screw, there is likely no evidence of the original left.

            Originally posted by plunger View Post
            Being three km away from the Indian ocean which is on average 20 plus degrees Celsius in winter we fortunately will never go below freezing , . But I'm just not used to such cold weather. I cant imagine living in a place with snow, cant figure how you can work in such cold. But it does look beautiful.
            BTW, he meant zero F, not zero C........-19C.

            Somewhere between about 5F and 15F (-15C to -10C) is ideal for skiing, either downhill or cross-country. Not very good for repairing trucks outside, but I have done that, back when my FIL had a water hauling business. A tad chilly...... but at least usually no pools of water under the vehicles.

            When it does not freeze, too many insects. Where I live now, there are termites. Temps get to -10C regularly, in winter, but that's not cold enough. Where I grew up in Minnesota, there were no termites, because the ground froze too deep for them. It would often get to -30C.
            Last edited by J Tiers; 08-28-2021, 11:10 AM.
            2730

            Keep eye on ball.
            Hashim Khan

            Everything not impossible is compulsory

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            • #7
              Back when I had my old Myford ML7 with the "external" lead screw the repaired brazed joint broke. I "fixed" it by totally replacing the old screw with a LH regular threaded screw and LH nut. There was more to it than that but the upside of this for you and your idea is that the regular thread worked just fine. So if you don't want to take on machining an ACME screw and nut in some sort of LH thread then by all means carry on.

              Technically there would be a slight bit more friction and slightly shorter life span on the thread. But for hobby use? No one will notice.

              The downside of regular triangular thread sizes would be the travel per turn. The nice thing about the Acme sizes is that you get a good amount of movement with each turn of the hand wheel.
              Chilliwack BC, Canada

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              • #8
                Originally posted by mattthemuppet View Post
                I have some 1/2-10 LH acme thread I can send you, but you'll need to sort out the quill threads some how. I borrowed a tap so I can't help you there
                Thankyou for the offer . I dont want to inconvenience anyone. Im just grateful for all the help. Luckily I'm the type of guy that might be clueless but I'm stubborn and dont give up so eventually get the job done.
                Ive machined a few left hand acme nuts. My first lathe I had to make a banjo for a tumbler reverse gear setup for my emco but my emco v13 doesnt have that problem. I just dont know if the hole is big enough to single point turn this one. But I could also make a acme or trapezoidal tap to do this one. I would like to try machine a left hand feedscrew. It will be a new experience for me

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                • #9
                  Originally posted by SLK001 View Post
                  The tailstock definitely has a left hand, ACME 10 TPI thread. Whether it is 3/8", 7/16", or 1/2", you'll have to measure that yourself. If you don't use the original thread size, you'll also need to line bore out the old tailstock threads and insert a sleeve with the new thread size - not an easy task for the novice. You'll also need to obtain the corresponding sized left handed ACME tap to tap your new sleeve.

                  As for not understanding the (not) "outdated" Imperial system, I would suggest that you study up on it if you intend to continue repairing an old South Bend - you'll need that skill.
                  I just multiply everything by 25,4mm . I have no doubt imperial is a dying language. It wont be long before imperial is a distance memory. But time is relative.
                  Do you really believe imperial will be around in a hundred years. ? I doubt it very much.
                  Thankfully metric is used in Africa. With the lowest IQ in the world statistically and a dna not wired for mathematical inclination and a poor education system coupled with a pass rate of 33 percent in schools(I kid you not .That's all you need to pass your exams)imperial doesnt stand a chance here in Africa. Its just far too complicated.

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                  • #10
                    no inconvenience, just some postage money and more than enough people off here have helped me for me to owe it to others. I should have a piece of bearing bronze around that you can have too if you need it.

                    Tapping the nut in bronze is not trivial though, took ALOT of effort to get it through. One of the cheapies of eBay should work if you're careful. Not sure I'd want to risk a homemade tap unless it was just for finishing the threads.

                    I think you'll need to get in there and see what's been done. It's quite easy to mate the new acme thread with the rest of the existing screw shaft, but the threads in the quill will be the challenge.

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                    • #11
                      Making the leadscrew is easy, the left hand thread is produced by threading away from the chuck. The nut will be the problem, it is too small diameter to singlepoint and taps could be hard to get hold of especially in South Africa.

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                      • #12
                        Originally posted by plunger View Post
                        I just dont know if the hole is big enough to single point turn this one. But I could also make a acme or trapezoidal tap to do this one. I would like to try machine a left hand feedscrew. It will be a new experience for me
                        That's probably the best way. Consider if you use brass for the nut, the tap won't need to be fully hard, especially if you only need to use it once. Some drill rod or even old axle steel would work for both the tap and the screw. And being a plumber I am sure you can get brass easily.
                        25 miles north of Buffalo NY, USA

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                        • #13
                          If you have machine tools in SA there must be suppliers to support them. Unless you must make one I would buy an acme screw. Evan posted a method of making delrin nuts by using heat and pressure. Might be worth a try.

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                          • #14
                            Originally posted by deltap View Post
                            If you have machine tools in SA there must be suppliers to support them. Unless you must make one I would buy an acme screw. Evan posted a method of making delrin nuts by using heat and pressure. Might be worth a try.
                            Its getting harder to get stuff as I notice alot of the engineering supplies have gone out of business. S Africa is just expensive but in terms of technology we arent too bad. Its just that its getting much worse very quickly .Alot of engineering businesses are shutting shop unfortunately.

                            I would think 12mm trapezoidal would be a good choice .I say this because I can get silver steel or drill rod of 12 mm diameter off the shelf.

                            Back to cold weather . It got as cold as six degrees c. I cant handle it. Its so weird. We are not used to wearing anything else but t shirts, slip slops and shorts in the dead of winter.I cant imagine living in a place below zero.

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                            • #15
                              In the UK, acme screws are much harder to get hold of than trapezoidal metric types.
                              6C would be much too cold for me too.
                              Last edited by old mart; 08-28-2021, 04:37 PM.

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