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Thread: Lathe half nut

  1. #11
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    Quote Originally Posted by Carld
    Black_Moons, I'm just having a little fun with you, no harm intended but threading with a dial is not that hard.
    I tried that once, and I couldn't get it to work at all.
    So I gave up and put the toolbit back in, and that cut them just fine.


    Peter

  2. #12
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    Quote Originally Posted by Carld
    I just don't see what is so hard about using the half nuts.
    Ever cut a metric thread with an imperial lead screw, or vise versa?

    Even if you've rigged up the right gear for the indicator, you might be waiting a long time for the marks to coincide.

  3. #13
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    Yes, and you don't have to release the half nuts, in fact you can't release the half nuts but what has that to do with finding the right number on the dial.

    Black_moons, that's a good one, I like that, it make me chuckle after I caught what you meant.
    Last edited by Carld; 02-01-2010 at 09:15 AM.
    It's only ink and paper

  4. #14
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    Quote Originally Posted by Carld
    Isn't that what the half nuts do? Don't they engage the lead screw at the point you released them if you just look at the number on the thread dial? What is so hard about watching the number on the thread dial and engaging the halfnuts?
    ...
    I just don't see what is so hard about using the half nuts.

    As the OP noted, there is usually an issue with the half-nuts when the leadscrew isn't the same language as the thread being cut, e.g. cutting a metric screw using an imperial leadscrew.

    Plus, metric lathes generally need several little gears (interchangeable) for the threading dial to handle all the metric threads.

    I added a dog clutch to my 7x12 and combined with a retracting tool holder it makes threading much faster and easier for both imperial and metric. I used to thread to a shoulder using a hand wheel, now I rely on the dog clutch and often thread at 300+ RPM. Higher speed seems to produce nicer threads on this little lathe.
    See: http://www.gadgetbuilder.com/Dog_Clutch.html

    John

  5. #15
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    Black_Moons, I have to agree that it seems like in several hundred years they could come up with an easier way to engage the lead screw and all the manufacturers could use it.

    When you look at the lathe we use now and the lathes they used in the 1800's there is little difference except in the head stock. That is belt drive versus gear drive while the rest of the lathe is much like the early ones.

    The more complicated it becomes the higher the price and failures of the mechanism can increase because of complicated workings. Sometimes trade off's are necessary.

    In trying make it easy the makers that put all the marks on the dial only make it worse and complicate things. It would be much easier if they just made a simple dial with four marks and put all the rest on a chart.

    I guess no matter how you do it if your confused your confused and I must say I have been confused by the chart too. For that reason I mostly use the number 1 when there are several to choose from. On the other hand, if you using a lathe with a worn lead screw you best use the same number all the time because if you engage a number that is supposed to work for that thread the worn lead screw can put you in the wrong spot in the thread and spoil the thread. Been there, done that. I don't trust old worn lathes and that is what most shops I worked in had. I guess it's a habit I developed to save my butt from slopping up a thread.
    It's only ink and paper

  6. #16
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    Electronic, or virtual lead screws exist and have replaced the half-nuts. CNC is not a requirement.

    An example case study:
    http://homemetalshopclub.org/project...screw/els.html

  7. #17
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    Wouldn't it be easier to dog gear and have a reverse gear for the drive motor for the whole lathe? Assuming we are talking about single phase lathes here.

    So leaving the half nuts engaged and all and just releasing the dog clutch for the whole lathe drive and than switching to reverse gear much like a tumbler and than engaging the clutch to reverse the lathe spindle and carrige back to the thread starting point again.

  8. #18
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    GadgetBuilder, yes, reading the first post he is mostly talking about metric on an imperial lead screw or vice versa but to make a system to do that could be something subject to failure or to difficult to make for the standard lathe.

    The following is my take on this and is not intended to be arrogant in any way so please don't take it that way.

    It's not really that hard to leave the half nuts engaged and cut a thread. I have done it on lathes from 9" to 18" and all you have to do is pay attention to what your doing and know your lathe.

    The problem is an comparing home shop to paying shop and the machinist doing the work. The average home machinist doesn't have the experience a working machinist does and many times he has to learn stuff on his own. Hand eye coordination and experience go hand in hand. A person who does machine work day in, day out has a better feel for threading. So, when the home machinist having little experience cutting threads, tries to cut a thread, imperial or metric, he has issues and until he cuts enough threads to become very comfortable he will continue to have issues. At some point he will master thread cutting if he persists.

    If they put a mechanism on the lathe to make threading automatic it will increase the price of the lathe and expensive to repair. One of the essential parts of doing machine work is understanding the machines and mastering the methods to use the machine.

    There is easy way to do the imperial/metric issue, at least easy in some ways. They could put two lead screws on a lathe and you engage the lead screw for metric or imperial as needed. Now, at face value that seems simple but to do it would require lots of gears and shift levers and complicated instructions. Guess what, we're back at something that will confuse an untrained machinist or any machinist for that matter.

    Machine work is not easy and if it was everyone would be a machinist.

    Why not just buy a CNC lathe?
    Last edited by Carld; 02-01-2010 at 10:00 AM.
    It's only ink and paper

  9. #19
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    If your concerned with how long it takes to reverse the carriage when you can't release the half nuts then learn your lathe.

    When I got my current lathe I tested it and found out I can change speeds without disengaging the spindle from the lead screw as long as I didn't use the high/low shift lever. This is something I did with all the lathes at work, that is I experimented to learn them.

    Knowing that I could thread forward at 75 rpm, stop the chuck with the foot brake, back out the cutter, shift to 300 rpm and reverse the spindle back to the starting point and begin the next pass at 75 rpm.

    With that knowledge I can also speed up or slow the spindle rpm if I want to while threading.

    Isn't it nice to know exactly what your lathe can do that is NOT in the instruction manual?
    It's only ink and paper

  10. #20
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    Smile

    Yeah the half nut just took over other designs, but certainly many other systems have been around a long time.
    I dig the threading system on my old Artisan which is probably 100 years old or so. It'll cut every thread my South Bend model A will and faster.
    It has a dog clutch on the leadscrew and a cone clutch for the spindle drive.
    Threading is done quite differently than on a typical half nut lathe by using the dog clutch on the .5" pitch leadscrew and the spindles cone clutch.
    For threads divisible by 16, it's a no contest win in speed for the Artisan over the half nut, it's not even close. For all other threads, it's still quicker but you have to brake the spindle and count 1, 2 or 4 revs of the hand crank when returning (depends on the thread pitch).

    These are the original threading instructions that were included with this lathe.


    I removed the cover for this photo to show the hand crank and dog clutch setup. A lever beneath the hand crank controls it.


    This shows the cone clutch on the jackshaft. A lever at the base controls it. It stops the spindle very fast.


    And yes, I do actually use this machine.


    Steve

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