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What Size For Threading?

Discussion in 'A BEGINNER'S FORUM (Learn How To Machine Here!)' started by AR. Hillbilly, Jul 20, 2016.

  1. AR. Hillbilly

    AR. Hillbilly United States Active Member Active Member

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    I need to make a special stud. It needs 7/16" nc threads on one end and 5/16" nf on the other. I thought I'd use a 7/16 bolt and turn it down and use a die to thread the other. I have experience tapping holes and have a chart for what size drill to use. I have no idea what size to turn the bolt to to thread the other end. Is there a chart someplace I can copy to I don't have to keep asking dumb questions?
     
  2. 4gsr

    4gsr Global Moderator Staff Member H-M Supporter-Premium

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    For most threads, go with nominal OD, 5/16 or .3125" with a minus tolerance of about .005". This should be good for most of us.
    In industry, we have calculations and machinery's hand book that give you more information.

    You get it turn down to .312/.308", I would single point the thread to near depth, about .034". Then chase the rest of the thread with a die.
    BTW: actual thread OD is .311/.302" I always go about .001-.003" big (.314/.312) and at the end of threading, I dress up the thread with file to remove burrs and a little emery. By the time I do that, the OD always wind up around .310".
     
  3. Ulma Doctor

    Ulma Doctor Infinitely Curious Active Member

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  4. AR. Hillbilly

    AR. Hillbilly United States Active Member Active Member

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    Thanks for the information. I really do appreciate it. I have one more question. How do I chuck up the existing threaded end and not destroy those threads while I turn down the other end? And for the poster above I haven't learned to cut threads with my lathe yet. I have a friend that may come help me but he's always short of time and I don't like to bother him. I may have a few questions before I get to this. It wouldn't be a large cost to ruin one in trying but before this I had no idea where to start. Would a grade 8 bolt be hard to turn and thread?
     
  5. Wreck™Wreck

    Wreck™Wreck United States Active User H-M Supporter-Premium

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    An excellent choice is to subtract the thread lead from the major diameter, this will get you close, if you have reason to make a very accurate thread buy a thread gauge or measure over wires, this is unpleasant in many ways however.
     
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  6. T Bredehoft

    T Bredehoft Active User H-M Supporter-Premium

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    Put two 7/16 NC nuts on the big end and screw them together VERY tightly, then chuck on one of them in your three jaw chuck. If it wobbles, start with it chucked in the lathe, cut or turn the head off (holding on the unthreaded shank) and centerdrill the end. Then, when it wobbles, loosen the chuck, put a live center in the tailstock in the centerdrilled hole, tighten the chuck on one nut and go to work.
     
  7. Ulma Doctor

    Ulma Doctor Infinitely Curious Active Member

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    i'd try another bolt rather than grade 8 at first.
    a grade 5 will cut much easier and thread easier too.
    stainless bolts at the box stores are generally grade 7 or thereabouts, and still relatively machinable.
    grade 8 is harder and chews up tooling.
    to be honest i haven't really seen the need for 5/16 grade 8 bolts, other than aircraft or military spec
    a grade 8 proofs at 120,000 psi, grade 5 proofs at 85,00psi

    do you need more than 70,000 psi tensile? in a 5/16 bolt
    (i'm giving a kentucky windage guess that you'll have a 15,000 psi loss slop factor after machining for argument sake)
     
    Last edited: Jul 20, 2016
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  8. brino

    brino Active User H-M Supporter-Premium

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    I have an ER collet system for my lathe, with it I can grab onto the points of threads with good grip and no damage.

    If you have not single-point threaded before here's a few things I have learned:
    -make sure you use back gear; you want slow speed and slow feed!
    (to cut right-handed threads you have to cut towards the head-stock, and you do not want to "crash" into the chuck)
    -find/grind a 60 deg tool and use a gauge to get it "square" to the work, also be sure it is on centre
    -you need to cut the thread in multiple passes to get it to full depth
    -set the compound to 29 deg. and use the compound to advance for each cut pass; this way you only cut on one side of the 60 deg point, and you get less chatter
    -be sure you have a small recess on the work to stop the tool bit in and the end of the pass
    -if your lathe has a threading indicator use it to be sure you are "cutting in the same groove" on multiple passes.
    (if you do not have a threading dial, then you need to keep the half-nuts engaged the whole time even when bringing the tool back towards the tail-stock for the next cut)
    -set it up to what you think is right and then take an "air cut" without the tool touching the work, this will give you a feel for how fast you need to react to disengage the feed
    -for your first real cut pass, make it very light, just scratch the surface, then stop the lathe and check it with a thread gauge or known bolt, just to prove you have all the feed levers set right for your required TPI

    For the threading dial there are rules about when to use any number, or an even number depending on your lead-screw and the TPI being cut.......I can never remember them!
    I just use the exact same number for each pass.....I may spend a bit of time waiting for my number to come around, but I spend less time looking up the rules!

    -brino
     
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  9. Charles Spencer

    Charles Spencer Active User H-M Supporter-Premium

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    Since you're just turning down the end and not single point threading, I'd probably turn it between centers. You could put paper or thin cardboard on the threads while holding it in the dog.

    I agree with Mike (Ulma). I'd use a bolt that wasn't quite as hard.
     
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  10. AR. Hillbilly

    AR. Hillbilly United States Active Member Active Member

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    I do have a collet set that has a 7/16" collet. There will be a 7/16" dead space/shoulder between the 2 sizes appx 3/8" long. I shouldn't get too close to the chuck. I do have a threading dial.
     
  11. 4gsr

    4gsr Global Moderator Staff Member H-M Supporter-Premium

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    AR,

    You didn't mention how long the thread is going to be, the portion that you are turning down. If over 1" in length, center drill the end and run a live center especially if you use a grade 2 bolt! One problem trying to thread on a small part like that in a collet, it could slip. If running 5C or bigger collet, probably be ok. If your using a 3C collet, it'll slip on you while threading. ER collet, I don't know. Putting two nuts, tighten together and chucking on the two nuts as Tom mention works. That's how I do it.
     
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  12. rgray

    rgray Active User H-M Supporter-Premium

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    I usually use brass shim stock under the dog screw. .020 is usually heavy enough.
    Turning that between centers would make it come out real nice and accurate, but would cramp the work space and be a little tricky.
    Having a die holder for the tailstock would help and you would not need to single point thread at all. Hold with collet and thread from tailstock die holder.
     
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  13. AR. Hillbilly

    AR. Hillbilly United States Active Member Active Member

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    The 5/16" threads need to be near 1" long. It has to screw in to a lever and have a jamb nut. Once set it should never need to be adjusted. How could I hold a die in the tail stock? So far All I have is a dead center and drill chuck. I don't have a lot of tooling yet. I'm just getting started and my work is very busy right now. I soon hope to be able to get to some serious learning. How hard is a grade 5 or grade 2 bolt to turn and thread? As someone mentioned above I'd like to use stainless for this project.
     
  14. Ulma Doctor

    Ulma Doctor Infinitely Curious Active Member

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    to hold a die in the headstock,
    you'd build a simple attachment to put into a drill chuck or turn the tailstock taper present on your machine and put the holder onto it.
    if you have round dies, most likely they are 13/16" in diameter but do come in larger sizes for larger fasteners.
    if you have hex dies they are normally 1" hex, the holder will be a little more difficult to make but still completely doable
    grade 2 cuts like butter.
    grade 5 is tougher but still machines ok- use a dark cutting oil or anchor lube for better results, the new threads appearance may appear a little grainy- take relatively light cuts
    you'll want to use anchor lube for stainless if you go down that road, it's the cat's meow!
    when you machine stainless , use relative low speed for a relatively deep cut.
    i like carbide for stainless, but HSS will cut it
    i just yesterday rethreaded some 316ss studs that were operator damaged, from 16mm 1.0 to 1/2"-13 tpi to keep a processing machine machine running.
    during threading i'll take .010" cuts (per side) and 60-80 rpm spindle speed
     
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  15. Ed ke6bnl

    Ed ke6bnl Active Member Active Member

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    What is the thread lead? Thanks
     
  16. Wreck™Wreck

    Wreck™Wreck United States Active User H-M Supporter-Premium

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    Thread lead is the distance that a thread advances per revolution , for instance 17 threads per inch has a lead of 1/17 or .0588 lead for a single start.
    A metric thread such as M8 1 has a lead of one millimeter per revolution for a single start, The lead is important.

    I suspect that a discussion about multiple start threads will not help.
     
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  17. kd4gij

    kd4gij United States Active User Active Member

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    Just don't mic a 5/16 bolt from the big box stores. :angry no:
     
  18. Wreck™Wreck

    Wreck™Wreck United States Active User H-M Supporter-Premium

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    Why would you set up a lathe to turn a thread large then finish it with a die? If already set up why not finish it in the lathe.
     
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  19. benmychree

    benmychree United States John York H-M Supporter-Premium

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    Because it is easier for an amateur to get a fairly accurate size on his thread; the reason to rough out the thread with a single point tool is to get an accurate and non wobbly start for the thread, as it seems that using a die from the start usually ends up wobbly, even when using a guided holder. I have Geometric automatic dies and do not have the problem, but sometimes I have only one small thread such as AH describes, and I do exactly as suggested, single point it oversize, and finish with a button die, this procedure is best for small sizes of threads.
     
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  20. 4gsr

    4gsr Global Moderator Staff Member H-M Supporter-Premium

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    I made that statement in the support of an amateur as benny said. I've long since graduated from using dies to finish threads with. Occasionally, I will grab a die to chase a thread if needed or even the check a fit when I don't want to use a thread mic, too. Kind of hard to break old habits!
     
  21. benmychree

    benmychree United States John York H-M Supporter-Premium

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    In the future, call me John, my given name; I use the name benmychree as my e bay identity, it is after the ship of that name that plies between the Isle of Man and Liverpool; my dad's mother's family was from there; there is a part of me that identifies with the Isle.
    John York
     
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  22. savarin

    savarin Active User H-M Supporter-Premium

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    When I need to grip threads I slit some nuts and screw them on, tightening the chuck ensuring the slits are between the jaws and not under them squeezes the nuts to grip the threads.
    I know its not exactly centred but I've always found it close enough.
     
  23. benmychree

    benmychree United States John York H-M Supporter-Premium

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    Near enough is close enough! In my apprenticeship, our company, Kaiser Steel, had drawings that were tolerenced in a fashion that was "good enough for the times" (my words), nothing like today's drawings and tolerences; given that, if there was a "problem", that is something that did not meet the specs, there was nearly always a way to make up for it on the mating part; the drawing was something to aim at as the personification of perfection, but, finish and fit were what was important.
     
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  24. Tozguy

    Tozguy Active User H-M Supporter-Premium

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    For thread charts, littlemachineshop has some handy ones, for example http://littlemachineshop.com/instructions/UN_Thread_Data_Chart Rev D.pdf

    To hold the 7/16ths end in the chuck, I would jam nuts on it as already suggested but I would use as many nuts as will fit. Use enough torque on them to line up the flats of all the nuts. When turning it will be obvious if the stud is held enough.

    Once the stud bolt is turned to the .311'' to .301'' range, add a chamfer on the end to help in starting the die straight. Hold the die in the holder that came with your set but use the tailstock to push it onto the stud. The square end of the TS quill should keep the die square to the stud. Don't forget the lube.

    I would start it by turning the die handle by hand while using the other hand to turn the TS hand wheel to keep pressure on the die handle. Then when it gets harder to turn use both hands on the die handle and forget the TS. Lathe must be in its lowest gear but not running.
     
  25. RandyM

    RandyM United States Global Moderator Staff Member H-M Supporter-Premium

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    John, I suggest that if you prefer to be addressed by your given name on the forum that you add it to your signature for everyone to see.
     
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  26. benmychree

    benmychree United States John York H-M Supporter-Premium

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    One should always chamfer the end of a thread, whether one is cutting it with a die or single pointing it. The above procedure is by no means a guarantee of not ending up with a wobble in the thread, hence the suggestion to start the thread by single point and finishing with the die.
     
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  27. Tozguy

    Tozguy Active User H-M Supporter-Premium

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    John, based on the initial post my comments were aligned on using a die. There was no question about single pointing. If I got that wrong and single pointing is on the table then post 18 makes the most sense to me.

    Plus, my comment about chamfering the end was to ''help starting the die straight'' and not to guarantee anything. However, the chances of starting a die straight by pushing with the TS are pretty darn good in my experience.
     
  28. benmychree

    benmychree United States John York H-M Supporter-Premium

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    My experience in starting dies by pushing with the tailstock have not been good; perhaps it has to do with the die stock that I use. I recently got a Monarch 9" lathe probably from the 1920s or 30s, for it, I bought a set of button die guides; the shank fits in the tailstock taper, and there are sliding die holders that have a slot cut in their length behind the die that fits over the straight portion of the shank, which gas a tapped hole for the "key" that fits in the slot of the shank, so the tailstock remains stationary and the die with sleeve is slid into position to cut the thread; ,have not used it yet, made in China, kinda sloppy fits, but I guess it will work OK.
     

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