chart for rod diameter for threading?
Largest Manufacturing Technology
Community On The Web
Close
Login to Your Account

Results 1 to 18 of 18
  1. #1
    Join Date
    Nov 2010
    Location
    Rochester, MN
    Posts
    1
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    0

    Default chart for rod diameter for threading?

    This question may seem very elementary to many here, but I've been trying to find some kind of chart that will tell me what the starting diameter of a rod should be for threading with any given size die. For example, I learned the hard way that a 1/4-20 die really struggled when I tried to thread a full 1/4 " diameter rod with it. Apparently, the starting diameter needed to be smaller. Any tips as to where I can find a chart that might cover this for the popular size threads? ( 6-32, 8-32, etc...)

    thanks
    Knipper

  2. #2
    Join Date
    Apr 2004
    Location
    Spring,Texas, USA
    Posts
    223
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    0

    Default

    Machinery's Handbook.

    Ford

  3. #3
    Join Date
    Feb 2008
    Country
    UNITED STATES
    State/Province
    Illinois
    Posts
    1,065
    Post Thanks / Like
    Likes (Given)
    30
    Likes (Received)
    269

    Default

    The starting dia. for any thread is the nominal size of the thread. You put a chamfer (lead) on the end to start. Cutting a thread free hand is not easy and requires some experience.
    The main thing to do is keep your threading die at 90 deg. to your work. Also look at the die from each side. One side will have a longer starting chamfer. That is where you start.
    Practice! But is is best to have lathe, vertical mill or a drill press to help you get started.
    Good luck and use cutting oil.

  4. #4
    Join Date
    Oct 2006
    Location
    San Leandro, California
    Posts
    528
    Post Thanks / Like
    Likes (Given)
    1
    Likes (Received)
    53

    Default

    If you look at Machinery's Handbook, you'll see that the major diameter tolerance allows the diameter to be a little smaller than nominal. For average work, making the outside diameter about .005" smaller than nominal works well. This reduces the torque required to turn the die.

  5. #5
    Join Date
    Mar 2006
    Location
    Cape Cod, Massachusetts
    Posts
    4,329
    Post Thanks / Like
    Likes (Given)
    823
    Likes (Received)
    1319

    Default

    In addition to the advice already offered, if your die is adjustable, make sure it is fully open when you make your first pass. You can close it up a bit and take a finishing pass afterwards.

  6. #6
    Join Date
    Oct 2010
    Location
    Burton-on-Trent, UK
    Posts
    117
    Post Thanks / Like
    Likes (Given)
    1
    Likes (Received)
    3

    Default

    I think I'd also add, as an amateur, that the quality of the die makes a lot of difference, and yet it's not generally obvious (to me) from looking at it. I've collected a lot of dies over the years and they really are very variable. I've got dies with reputable names on them which I wouldn't trust to put a thread an a piece of brass, and one particular 5/8" die nut which puts a beatiful thread on a piece of (reasonably) hard steel at full diameter.
    So, what's the secret from the Professionals?
    Alan

  7. Likes Bobw liked this post
  8. #7
    Join Date
    Dec 2005
    Location
    Auburn, Alabama
    Posts
    1,438
    Post Thanks / Like
    Likes (Given)
    114
    Likes (Received)
    120

    Default

    Quote Originally Posted by AlanBeckett View Post
    ...
    So, what's the secret from the Professionals?
    Alan
    Using a thread cutting lathe. Or a Geometric threading head (never used one myself)

    I've also been guilty of starting a thread in the lathe, and doing a "finish pass" with a die (for 1 or 2 pieces).

  9. Likes Bobw, Matt_Maguire, wheels17 liked this post
  10. #8
    Join Date
    Jun 2006
    Location
    Beaverton, OR
    Posts
    5,448
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    45

    Default

    Send the parts out and have them rolled?

  11. #9
    Join Date
    May 2009
    Location
    Canandaigua, NY, USA
    Posts
    2,146
    Post Thanks / Like
    Likes (Given)
    81
    Likes (Received)
    656

    Default

    There are also threading dies and re-threading dies. I think this is or once was indicated by the shape, round or hex. Make sure you have the right one. My experiences with modern dies have been less than wonderful. Single point or a die head ($$) is way better.

    CH

  12. #10
    Join Date
    Mar 2016
    Country
    UNITED STATES
    State/Province
    Illinois
    Posts
    1
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    1

    Default

    Old thread but I found this one that does everything I want to do.

    http://engineershandbook.com/Tables/threadlimits2.htm

    Mike

  13. Likes t.jones liked this post
  14. #11
    Join Date
    Oct 2003
    Location
    Bonners Ferry, Id
    Posts
    2,833
    Post Thanks / Like
    Likes (Given)
    448
    Likes (Received)
    342

  15. #12
    Join Date
    Dec 2008
    Country
    UNITED STATES
    State/Province
    New York
    Posts
    5,776
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    1512

    Default

    Quote Originally Posted by Knipper View Post
    This question may seem very elementary to many here, but I've been trying to find some kind of chart that will tell me what the starting diameter of a rod should be for threading with any given size die. For example, I learned the hard way that a 1/4-20 die really struggled when I tried to thread a full 1/4 " diameter rod with it. Apparently, the starting diameter needed to be smaller. Any tips as to where I can find a chart that might cover this for the popular size threads? ( 6-32, 8-32, etc...)

    thanks
    Knipper
    .
    1) .003 to .006" undersize is not unusual. larger number for coarser threads
    .
    2) not all thread dies have same starting taper. almost exactly like starter tap, middle or plug tap and a bottom tap. often i find a larger thread die like 1.5" has more starting thread taper than a 1.0" thread die.
    .
    3) i find it is easier to cut most of thread on a lathe and then just finish threads with a thread die. cutting just last .005" with a die is like reaming a hole.

  16. #13
    Join Date
    May 2003
    Country
    UNITED STATES
    State/Province
    Iowa
    Posts
    9,292
    Post Thanks / Like
    Likes (Given)
    2408
    Likes (Received)
    3075

    Default

    Quote Originally Posted by jbltwin1 View Post
    Old thread but I found this one
    Mike, instead of opening and hijacking a 6 year old thread, start a new one. I know that it's your first post so I won't be too hard on you. After all, you did read the rules and posted your locattion, which is more than some do.

    As for the chart, it starts at 1/2". Everything that you need on threading is in Machinery's Handbook. Also, it has pretty much all the sizes, standard or not.
    JR

  17. #14
    Join Date
    May 2010
    Location
    Kolding Denmark
    Posts
    14,609
    Post Thanks / Like
    Likes (Given)
    2890
    Likes (Received)
    4057

    Default

    Quote Originally Posted by Knipper View Post
    This question may seem very elementary to many here, but I've been trying to find some kind of chart that will tell me what the starting diameter of a rod should be for threading with any given size die. For example, I learned the hard way that a 1/4-20 die really struggled when I tried to thread a full 1/4 " diameter rod with it. Apparently, the starting diameter needed to be smaller. Any tips as to where I can find a chart that might cover this for the popular size threads? ( 6-32, 8-32, etc...)

    thanks
    Knipper
    First re AllanBecket's post #6 is important. There is a vast difference between a cheap die and a "professional" die.

    As also has been mentioned then for a standard 2A tolerance on UNC threads the max diameter is a little under nominal diameter.

    These might be useful as to OD tolerances:

    6-32 max 0.1372 min 0.1312
    8-32 max 0.1631 min 0.1571
    10-24 max 0.1890 min 0.1818
    12-24 max 0.2150 min 0.2078
    1/4-20 max 0.2489 min 0.2408

    Hope you have a good micrometer

    Nothing against Machinist Handbook but for threads then I suggest buying ASME B1.1. As far as thread information goes ASME beats the handbook hands down.

    Oops noticed post #11 after I posted and also how old this thread is.

  18. #15
    Join Date
    Dec 2008
    Country
    UNITED STATES
    State/Province
    New York
    Posts
    5,776
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    1512

    Default

    i have cut fine threads up to 127 tpi by using front of cutter to push or form threads before
    .
    what happens is since metal is pushed around the outside diameter gets bigger and often a wire edge or sharp edge forms at top of vee. when you use a dull thread die i believe it pushes metal around a bit and the outside diameter can change. that is
    ..... you might start the threading .005" under size but when done threading you can easily measure less or it might be .000 to .003" under size after threading.
    .
    some early fine pitch threading dies or plates actually cut not threads but formed the threads by pushing metal around. thus you had to start with under size outside diameter. very very similar to using thread forming tap. you start with bigger tap hole size and after threads formed if you measure you will measure hole size closed up a bit
    .
    by the way if you think thread forming is odd or new that is how henry maudslay first created threads over 200 years ago. it actually is a very very old thing forming threads in soft ductile metal

  19. #16
    Join Date
    Apr 2007
    Location
    mays landing NJ
    Posts
    384
    Post Thanks / Like
    Likes (Given)
    355
    Likes (Received)
    104

    Default

    Multiply the threads per inch X 13. Add 60. This is the stock size for threads less than 1/4-20.
    2/56 thread= 2x13=26+60=86 .086 is the stock size for 2/56 thread
    3/48 3x13+60 =.099
    4/40 4x13+60 =.112
    5/44 5x13+60 =.125
    etc

    This formula works up to but not including 1/4/20
    There is another formula for larger threads,I have it written down in the shop.I'll post it tomorrow.I think if you do a search ,you may come up with it yourself.I wrote down formulas for metric as well.also in the shop.
    mike

  20. #17
    Join Date
    Dec 2004
    Location
    uk
    Posts
    10,627
    Post Thanks / Like
    Likes (Given)
    2426
    Likes (Received)
    4332

    Default

    Quote Originally Posted by AlanBeckett View Post
    So, what's the secret from the Professionals?
    Alan
    Ditch the button dies and use a die head, will take off a fair over size in one hit - one pass. Resulting thread will be accurate and beutifull :-)

  21. #18
    Join Date
    Feb 2008
    Country
    UNITED STATES
    State/Province
    Illinois
    Posts
    1,065
    Post Thanks / Like
    Likes (Given)
    30
    Likes (Received)
    269

    Default

    Where can you buy steel rod under size? I can see a turned dia for threading to be 0.002 to 0.004 undersized, but threading standard rod should be used as it is. May be it comes 0.001 to 0.002 undersize - fine. Nobody will take foot long sections of 1/2 inch dia rod and turn it down. A good die will have no problem cutting a thread on a rod 0.500" in dia. I have never has a problem with running a 1/4-20, 5/16-18, 5/16-24, 3/8-16 or any other die over a full size dia rod.


Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •