(Acme) 29deg stub thread 9TPI - Thread dimensions & tolerancing and root dimension

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peterh

#1
We have an 'American 29deg stub thread 9TPI' and are in dispute with our supplier regarding thread dimensions & tolerancing, particularly the root dimension. Can anyone please advise tolerances/dimensions before I get a headache!!!

Many thanks

peterh
 
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Stijloor

Staff member
Super Moderator
#2
Re: American 29deg stub thread 9TPI - Thread dimensions & tolerancing and root dimens

We have an 'American 29deg stub thread 9TPI' and are in dispute with our supplier regarding thread dimensions & tolerancing, particularly the root dimension. Can anyone please advise tolerances/dimensions before I get a headache!!!

Many thanks

peterh
A quick Google search revealed this. I hope other will chime in.

Do you have the actual thread standard available? In the USA, we use The Machinery's Handbook quite often.

I believe that ASME/ANSI B1.8-1988-R2006 may be applicable.

Stijloor.
 

Wes Bucey

Quite Involved in Discussions
#3
Re: Acme 29deg stub thread 9TPI - Thread dimensions & tolerancing and root dimens

As Stijloor implies with his link, you are probably looking at an ACME stub thread (flat bottom of the minor diameter)

There are literally hundreds of sources to get the standard specifications - your only difficulty was in not having the word "ACME" in your search.

Bon chance!

Moderator note: I'm altering your thread title to include "acme"
 
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sitapaty

#5
Re: (Acme) 29deg stub thread 9TPI - Thread dimensions & tolerancing and root dimensio

please refer the applicable American or British standard for acme threads.
Sitapaty
 

Wayne

Gage Crib Worldwide
#6
Re: (Acme) 29deg stub thread 9TPI - Thread dimensions & tolerancing and root dimensio

We have an 'American 29deg stub [ACME] thread 9TPI' and are in dispute with our supplier regarding thread dimensions & tolerance, particularly the root dimension. Can anyone please advise tolerances/dimensions….
Peterh;
Yes as normal I am late to the forum and late to reply, :eek: but...

:caution: I find that many engineers mess-around with the design parameters of ACME threads to meet their specific product limitations, thus checking the part drawing is critical when working on ACME threads to see if modifications from the standard have been added the thread requirements.

Once it is verified that no modifications to the thread form have been implemented on the part drawing, then ANSI/ASME B1.8 kicks in. :read: The standard may also point to ANSI/ASME B1.5 for some pieces of data. The standard has some tabulated sizes, but also gives the formula to calculate special sizes.

:caution: Another thing to watch out for with Stub ACME threads is the authorized modified forms listed in the standard. There is a Modified Form 1 (M1) and a Modified Form 2 (M2). These modified forms affect the major and minor diameters.

The easy way to get data on the thread parameters is to use the ThreadTech software. :magic: After answering a few menu-prompted questions the ThreadTech Software will give you the full thread parameters. The software is a purchase item, but there is a Free 30-Day Trial Version available which should be sufficient to calculate this one thread.

:2cents: When you are in a dispute with a customer, of course the customer is always right, but it would be helpful if he fully specified the requirements before the product is manufactured. :bonk: If ‘American 29deg stub thread 9TPI' is his print call-out he is obviously not well educated on the correct product parameters because the description is not in accordance with ANSI/ASME B1.8.

I hope you find this information helpful. :cool:
 
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Dean Frederickson

#8
Re: (Acme) 29deg stub thread 9TPI - Thread dimensions & tolerancing and root dimensio

Hello all I am back and I have a question. I have a customer print that is calling out "2/7 Pitch x 2/7 Lead left handed thread 29 degree acme thread" can anyone tell me what this means. Thanks in advance. Dean
 

Wayne

Gage Crib Worldwide
#9
Re: (Acme) 29deg stub thread 9TPI - Thread dimensions & tolerancing and root dimensio

Hello all I am back and I have a question. I have a customer print that is calling out "2/7 Pitch x 2/7 Lead left handed thread 29 degree acme thread" can anyone tell me what this means. Thanks in advance. Dean
Dean;
There are several parts of this, and it also appears that some parts of the thread designation are missing. :nope:

ACME threads are defined in ANSI/ASME B1.5 with STUB ACME defined in ANSI/ASME B1.8. :read: The specifications encourage ACME threads to be designated in inches and threads-per-inch. The specification defines specific classes-of-fit for best operation of the ACME thread.

:agree1: The normal thread designation for an ACME thread includes:
[nominal major diameter]"-[threads-per-inch] ACME-[class-of-fit][other optional modifiers].

Where the customer's print states: "29 degree acme"; it is being redundant. In the world of thread designation ACME = 29? included angle. The preferred designation would be just ACME except many engineers make-up their own ACME thread parameters even changing the 29? included angle. :mad: This adds to the confusion, which is why many people designate the 29? on the drawing with the word ACME. So, in this case, we know for sure that they intend to use the standard ACME form. :yes:

The customer print statement "2/7 Pitch x 2/7 Lead" is very odd :bonk: and seems at best poorly stated, but you need to get more data from your customer.
First and again; the print is being redundant because when pitch = lead only pitch is stated.
Second; the pitch is usually stated in threads-per-inch (TPI). Many times on European drawings TPI is stated as pitch in mathematical formula. Example 10-TPI would be stated 1/10. If you do the math on 1/10 (one divided by 10) you get 0.1" pitch which = 10-TPI. (A side note; some people may say it is: "10 pitch". While this is functional for communication, it is poor practice and should be avoided).
Third; taking the drawing at face value the 2/7 = 0.2857 pitch = 3.5-TPI. This is a common-ish TPI.
Fourth; Because the customer was so specific to include the 2/7 twice and the use of the '2' instead of a '1' leads me to believe that the customer may have intended this to be a 2-start (double lead) thread, but just does not understand the correct screw thread engineering nomenclature. :nope:

Where the customer's print states: "Left Handed Thread" I am sure he means what he says. :agree1: ACME screw threads are often Left Handed. Normally this is just designated as LH following the class-of-fit.

:confused: Things which are missing in this designation are the nominal major diameter (which I expect is dimensioned elsewhere on the drawing), and the class-of-fit which determines the location and tolerances for the Major Diameter; Pitch Diameter; and Minor Diameter.

You need to go back to your customer for clarification on his requirements :whip: because there are too many ways to interpret this designation, and it is very incorrect per B1.5.

Here is a link to a tool which may help with the thread parameters once you have gained answers from your customer: ThreadTech Free 30-Day Trial.

Other links which may be helpful:
The World of ACME Screw Threads
General Purpose ACME Screw Threads
 
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