Thread depth - Starting point for measuring FULL THREAD

Proud Liberal

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#1
Where on the thread geometry is the starting point for measuring FULL THREAD? I know to check the depth of a gage member when threaded into a hole to check the depth but am unsure on what to take off for the lead on the gage. I haven't been able to find the definition in Y14.5M. Should I be looking in another standard? If so, could someone post the definition citing standard, section, and paragraph?
 
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Wes Bucey

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#2
Proud Liberal said:
Where on the thread geometry is the starting point for measuring FULL THREAD? I know to check the depth of a gage member when threaded into a hole to check the depth but am unsure on what to take off for the lead on the gage. I haven't been able to find the definition in Y14.5M. Should I be looking in another standard? If so, could someone post the definition citing standard, section, and paragraph?
The simple answer is take off nothing; gage manufacturers make those allowances when they create the gage. Check with the manufacturer of your gage to see which Standard he conformed to.

Thread Standards are ANSI/ASME (google for the numbers)
Machinery's Handbook contains much of this information.
In any case, you ought to have data for thread style and tolerance Standard.

I'm curious why you need this information.
  1. Are you designing a product? (you ought to cite the Standard to which you expect the manufacturer to conform.)
  2. Inspecting a product? (The Standard should be called out somewhere in the drawing or Associated Documents. The gage manufacturer can answer all your questions about usage, technique, etc.)
  3. Just idly curious? (It will be more informative if you do the search yourself rather than have the info handed to you.)
 

Proud Liberal

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#3
It is a customer requirement. I have done extensive research on my own using Google to find the definitions on-line. The customer's published drafting standard doesn't cover the topic and they expect ± .005" tolerance on thread depths. I looking to head-off any problems in the future.

As the new guy here, I hesitate to change an inspection procedure that has been used for a long time. But, as our customer is constantly bringing in new inspectors, I would like to be able to quote chapter and verse of what the definition actually says. Additionally, if our methods (which is using a visual system and picking out the end of the last FULL thread by eye) perform the task, I prefer to leave the status quo alone. But if they are inadequate, I need to improve them immediately.

I also don't want to purchase a standard simply to search through it and not find the answer.
 

Wes Bucey

Quite Involved in Discussions
#4
Proud Liberal said:
It is a customer requirement. I have done extensive research on my own using Google to find the definitions on-line. The customer's published drafting standard doesn't cover the topic and they expect ± .005" tolerance on thread depths. I looking to head-off any problems in the future.

As the new guy here, I hesitate to change an inspection procedure that has been used for a long time. But, as our customer is constantly bringing in new inspectors, I would like to be able to quote chapter and verse of what the definition actually says. Additionally, if our methods (which is using a visual system and picking out the end of the last FULL thread by eye) perform the task, I prefer to leave the status quo alone. But if they are inadequate, I need to improve them immediately.

I also don't want to purchase a standard simply to search through it and not find the answer.
Methods of reading thread plug gages depend on the type of thread. I have a hunch from your description you are talking about a tapered dry seal pipe thread. If I am correct, your easiest source is the manufacturer of your gage. Even with all my experience on internal and external threads, I would hesitate to come and give you a tutorial.

Some manufacturers can follow the Standard for a tapered thread and come up with anything from zero-step to six-step internal and external thread gages. You ought to confer with your customer on his method and instrumentation for checking and try to replicate it as closely as possible.

When I was in the position you seem to be in, I went so far as to purchase customer's and my gages from the same manufacturer, built to the same master gage. Depending on the product and the application, this [thread gaging] can be a zero concern or a major concern. The customer is ALWAYS the driving force on the magnitude of the concern.

Ultimately, on some applications, even resorting to independent testing labs may not be "politically" feasible - you must reach agreement on method and instrumentation with customer to avoid a "he said - she said" scenario.
 

The Taz!

Quite Involved in Discussions
#5
Proud Liberal said:
Where on the thread geometry is the starting point for measuring FULL THREAD? I know to check the depth of a gage member when threaded into a hole to check the depth but am unsure on what to take off for the lead on the gage. I haven't been able to find the definition in Y14.5M. Should I be looking in another standard? If so, could someone post the definition citing standard, section, and paragraph?
Look into the ANSI B1 series of standards. Are you trying to measure the First Full thread from the tip of the thread or the length of Full thread? There are a few methods.
 

Proud Liberal

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#6
The print asks for a dimension from the top of the part to end of the last "FULL THREAD". The thread plug gage has a lead on it. I don't know how to measure the lead on the gage to be able to subtract it from the overall length of the gage member. Once I have that, I can use a drop indicator to measure from the top of the part to the top of the gage member and just subtract the lead.

At previous companies, the tolerances were loose enough that we simply counted the number of turns on the gage. But at ± .005", I'm don't think that would be accurate enough. Contacting the customer would only make me look bad and would raise question about everything we make.

BTW, these are straight Unified threads.

I checked out the ASNI standards website. Searching for threads, there were over 1,050 standards available.
 

The Taz!

Quite Involved in Discussions
#8
First of all. . . +/- .005" on a full thread depth is rediculous. . The tolerance of the Pitch diameter alone will not allow consistency as the tool wears. What size thread are you dealing with?

I also have to ask. . . +/- .005" at the Pitch Diameter? You have three elements to deal with. . .Minor, Pitch, and Major diameters.

If it is stated to the Pitch Diameter, a ground plug will not suffice.

I think I would ask the customer to verify that the depth actually has a +/- .005" tol. Did that tolerance come from a standard drawing tolerance block? Was it stated at the dimension? I think you will need to ask your customer HOW they want that dimension checked IF it is actually +/- .005" tol.

Usually thread depths are stated as a minimum unless the design could create an interference if the tapped hole is too deep. JMHO
 
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