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machining a tailstock feedscrew.

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  • BCRider
    replied
    Originally posted by old mart View Post
    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.
    Difficult but not what I'd call impossible by any means. And while small in size the tool needed to cut the internal threads on just a short nut won't need to be overly long. Maybe 3/4", or 2cm or so? So even with the smaller size needed to clear it would still be well within the less than 4D stickout.

    I think I'd make my own single point tool from some 10mm drill rod then harden and temper it. To keep some additional height while still achieving the front and back fitting needed I think I'd do a bit of off center machining along the lines in the sketch.

    For getting the nice sharp and correctly relieved cutting edges from this, which comes out tangent, marker the metal and then with a good head mounted magnifier and a small rotary grinder sneak up on the cutting reliefs until there's the smallest still visible line of marking dye. At that point a couple of strokes with a fine sharpening stone will remove the last of the dye and give a nice edge.

    The angle on the inside of the relief will need to be the most aggressive. When we fold out a 1/2-10 angle the trig tells us that the angle of the helix at the smaller diameter root size is pretty small. Like 0.36" diameter and the 10 TPI.

    So the minor diameter is 0.36 which times pi = 1.13 And we have 10 TPI. So that's a triangle with 1" on one side and 11.3" on the other which gives us an helix angle of just over 5°. So to give yourself the cutting relief you need you need to make the side of the tooth in the relief angled at around 10°. The other side and the end can get by with something like 4 to 5°.

    That's better... I was thinking it was something like 45 and had to stop and pause for a second.

    Click image for larger version  Name:	Small Acme internal single point cutter.JPG Views:	0 Size:	36.6 KB ID:	1959207
    Last edited by BCRider; 08-28-2021, 06:20 PM.

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  • nickel-city-fab
    replied
    Originally posted by plunger View Post
    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.
    I think you are on the right track with the 12mm drill rod and trapezoidal thread. You could thread say 300mm all in one go, and then cut it in half to use one for the tap and the other for the screw.

    The cold weather is like any other weather, long clothes, in layers. Say 2 or 3 shirts, etc. You do get used to it, believe it or not. Mechanic's coveralls are great in cold weather. I know, I work at a truck shop... whatever the weather is that day, that is what I have. And in the summers, 40C.

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  • old mart
    replied
    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, 05:37 PM.

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  • plunger
    replied
    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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  • deltap
    replied
    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.

    Leave a comment:


  • nickel-city-fab
    replied
    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.

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  • old mart
    replied
    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.

    Leave a comment:


  • mattthemuppet
    replied
    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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  • plunger
    replied
    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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  • plunger
    replied
    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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  • BCRider
    replied
    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.

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  • J Tiers
    replied
    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, 12:10 PM.

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  • mattthemuppet
    replied
    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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  • plunger
    replied
    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.

    Leave a comment:


  • SLK001
    replied
    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.

    Leave a comment:

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