Custom Thread Basics
Custom Thread Basics
(OP)
OK, I'll start this off with an apology, as I know this is a basic issue. I will also state that I have searched, both here and google with no real success. I suspect I can find the answer in the machinery handbook, however, I am off site and cannot get to one easily. (Is there an online version?)
I am currently working on a design where 2 pieces will thread together. Because of packaging restrictions the threads will have to be "custom". I've decided on 3.125" X 12 TPI X .75" deep thread. Now my questions:
How do I design the tolerance between the male and female threads? Once the tolerance between the two is figured out, how do i notate that on a drawing?
I assume I can't just point to the male thread with a 3.125-12 - 2A dimension and 3.125-12 - 2B on the female and expect the machinist to get the clearances right so everything fits. Surely it is more complicated than that.
Like I said, I've done searches here and on google with no real results. I suspect what I'm asking is pretty much common knowledge, plus I'm sure i'm not using the best search terms. So sorry for that. This is my first design with "custom" threads, obviously, so any links on the subject are appreciated.
Thanks in advance!
I am currently working on a design where 2 pieces will thread together. Because of packaging restrictions the threads will have to be "custom". I've decided on 3.125" X 12 TPI X .75" deep thread. Now my questions:
How do I design the tolerance between the male and female threads? Once the tolerance between the two is figured out, how do i notate that on a drawing?
I assume I can't just point to the male thread with a 3.125-12 - 2A dimension and 3.125-12 - 2B on the female and expect the machinist to get the clearances right so everything fits. Surely it is more complicated than that.
Like I said, I've done searches here and on google with no real results. I suspect what I'm asking is pretty much common knowledge, plus I'm sure i'm not using the best search terms. So sorry for that. This is my first design with "custom" threads, obviously, so any links on the subject are appreciated.
Thanks in advance!





RE: Custom Thread Basics
"Art without engineering is dreaming; Engineering without art is calculating."
Have you read FAQ731-376: Eng-Tips.com Forum Policies to make the best use of these Forums?
RE: Custom Thread Basics
As I stated, I'm off site and can't get to one easily/quickly. I'm kinda hoping this is a fairly simple answer that someone here can supply faster/easier than getting to a book.
RE: Custom Thread Basics
See also h
RE: Custom Thread Basics
Try these for reference:
ht
http://www.sae.org/technical/standards/AS1338
ht
Chris
SolidWorks/PDMWorks 08 3.1
AutoCAD 08
ctopher's home (updated Aug 5, 2008)
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SolidWorks Legion
RE: Custom Thread Basics
What thread form are you interested in?
If you are talking about a unified thread (since you mention class 2A & B) form then consult ASME B1.1-2003 it gives you all the information you need.
The fact that you specify thread depth as well as pitch is confusing me a little.
Based on your OP, if you can't get to machineries I doubt you have B1.1 to hand.
http
Section 6.5 talks about threads with unified form but different tolerances.
If you aren't looking at unified form then you probably want to get the relevant spec for whatever form you are considering.
Please excuse any typos but you do get what you pay for
KENAT, probably the least qualified checker you'll ever meet...
RE: Custom Thread Basics
The .75" thread depth is, I'm sure, referring to the threaded portion length.
RE: Custom Thread Basics
Still, the rest of what I put above is correct, I hope!
KENAT, probably the least qualified checker you'll ever meet...
RE: Custom Thread Basics
"Art without engineering is dreaming; Engineering without art is calculating."
Have you read FAQ731-376: Eng-Tips.com Forum Policies to make the best use of these Forums?
RE: Custom Thread Basics
3.1250-12 UN is one of the 12 TPI series.
KENAT, probably the least qualified checker you'll ever meet...
RE: Custom Thread Basics
3.125-12 UN-2A
Hope this helps.
Don
Kansas City
RE: Custom Thread Basics
Thanks for the help here, I knew I had to be making this more complicated than I needed to be.
Your assumption that I wanted to use Unified standard is correct.
.75" is referring to the thread depth, i don't know why i threw that in the OP. Sorry for the confusion.
Next time I will be sure to take my machinist handbook whenever I work off site. The one time you leave it at home...
I hadn't run across efunda.com, thanks for that link.
Thanks for the link to the bolt calculator; I think I saw that link in another thread here just before I posted this topic, I'm guessing it was you that had posted it. Shame on me, I didn't scroll down past the stresses and get to the sizes. Also thanks for those standards, as I'm sure I'll be doing this sort of thing again in the future.
Again, Thanks thanks thanks, you guys saved me a headache.
RE: Custom Thread Basics
"Step 1, verify it is indeed a special"
KENAT, probably the least qualified checker you'll ever meet...
RE: Custom Thread Basics
RE: Custom Thread Basics
KENAT, probably the least qualified checker you'll ever meet...
RE: Custom Thread Basics
It basically lists every standard UNC, UNF, UNEF and UN (and common UNS) thread from #0 to 4" (22 pages). It gives the major, minor and pitch diameters for internal and external threads of each fit class. Anymore it's virtually the only chart I use.
Don
Kansas City
RE: Custom Thread Basics
So...
Step 1: Verify you truely need a special and cannot use one of the standard sizes. There are many more standard sizes than just the typical hardware sizes you find at the store or in a hardware catalogue. Advantages of using standard sizes is that mating nuts/bolts, taps, dies, cutters, gages etc are more likely to be readily available. Look in ASME B1.1 or a general resource such as Machinery's Handbook.
Step 2: Some 'specials' are less special than others. Resources such as Machinery's Handbook may give values for certain select 'special' combinations. Also check vendors catalogues for mating parts in the required thread, for instance many small adjuster screws with matching bosses are available in 1/4-80 or even 1/4-100 sizes.
Step 3: For specials you must specify more than just the Nominal ID, pitch and class, see ASME B1.1...
Step 4: The following link will help you calculate the required information. As with anything (especially anything free) on the internet for critical applications you should verify its accuracy.
KENAT, probably the least qualified checker you'll ever meet...
RE: Custom Thread Basics
I suggest adding the link CorBlimeyLimey posted to the efunda.com UN standard chart.
h
Also, where will that FAQ go? Is this the correct place? There are so many categories and sub catagories, its hard to know where to post or look for answers.
RE: Custom Thread Basics
It would also be relevant to other threads such as Machines & Machining engineering; QC, Inspection & Testing engineering.
It is possibley to cross link FAQs (I think I recall) so that would fix most of that problem.
Good call on the efunda link.
Busy right now I'll see if I can tidy it up and submit it soon though (faster than my idea of a faq on picking CAD systems anyway).
KENAT, probably the least qualified checker you'll ever meet...
RE: Custom Thread Basics
http://closetolerancesoftware.com/METhreadPal.html
Software For Metalworking
http://closetolerancesoftware.com
RE: Custom Thread Basics
KENAT, probably the least qualified checker you'll ever meet...
RE: Custom Thread Basics
KENAT, probably the least qualified checker you'll ever meet...