Need help with thread plug gauge

[VFM3]

So the story goes as I am temporarily filling in for QC. I am inspecting some small pins with 1 - 72 UNF-2B threads and I grab out our plug gage.

The go enters the threads smoothly completely down to the proper depth. The No-go starts about three threads and I inform my supervisor about that.

My supervisor states that it is acceptable for the thread gauges to start no more than three complete threads. I was a very surprised to hear this as I was always under the impression that the no-go shouldn't start more than one thread (to account for the machining phase + if there is chamfer).

So this leads to my question on how many threads can a no-go start on a class 2 thread and still be acceptable to you?

 

[LKeithR]

I'm certainly no expert on this stuff but it seems to me that if you're getting a penetration depth of 3 full turns on the no-go your hole is too big--at least that's the way most inspection standards would view it...

 

[Eric M]

Scroll to the bottom of this page to find your answer: No Go Thread Ring Gages Per ANSI/ASME B1.2-1983

If you can'tt access it, here's what I think you're looking for:
No Go ( HI ) Thread Plug Gage


The NoGo (HI) thread plug gage inspects the NoGo (HI) functional diameter limit of product internal threads. The NoGo (HI) thread plug gage represents the NoGo (HI) functional diameter limit of the product internal thread.

Thread plug gages when applied to the product internal thread may engage only the end threads (which may not be representative of the complete thread). Entering threads on product are incomplete and permit gages to start. Starting threads on NoGo (HI) plugs are subject to greater wear than the remaining threads. As Stated in ANSI/ASME B1.2-1983, the “NoGo (Hi) functional diameter is acceptable when the NoGo (Hi) thread plug gage applied to the product internal thread does not pass over the thread more than three complete turns.” The gage should not be forced. Special consideration such as exceptionally thin or ductile material, small number of threads, etc., may require modification of accepting up to 3 turns of the gage. It is highly recommended that a manufacturer not allow a maximum of 3 turns during thread fabrication as every thread plug gage may gauge differently due the actual size and gage maker tolerances allowed.

 

[SeymourDumore]

I'm certainly no expert on this stuff but it seems to me that if you're getting a penetration depth of 3 full turns on the no-go your hole is too big--at least that's the way most inspection standards would view it...

From the way I see it, the No-Go element of any thread gage ( internal or external ) does not - by design - check for neither minor or major diameter
of the thread. It's sole intended purpose is to check the "max" pitch diameter and nothing else.
It is purposely truncated at the crest and is ground sharp at the root, just to make sure that the only contact it will have is on the flanks of the thread.
IOW, your hole can be extremely oversize, but as long as it's somewhat below the thread pitch diameter, your No-Go gage wouldn't know it.

Perfect proof of this would be an example ( which I'm sure we've all fallen into once or twice ) of that if you single point a thread with a broken or truncated tip, your Go element
would not fit, yet the No-Go will quite happily turn all the way in.
That is because it's the job of the Go element to check for the "min" portion of the major or minor, as well as the pitch diameter.
Neither element will check the "max" of the minor/major diameters, nor will they check true thread form. ( we're talking internal threads here, external would be the opposite )

So yes, the 3 turns is the max acceptable engagement and all of my customers hold me to 2.5 or less.

 

[AARONT]

It is something that should be addressed. But yes, like Eric and Seymour said, 3 turns is max.

 

[VFM3]

Wow thanks guys! I reviewed the link and have come to the conclusion that the parts are passed as my boss was correct.

 

[Gordon B. Clarke]

This is where the calibration result on the gauge is good to know as both the Go and No/Go have tolerances.

What you are finding out by 3 turns is that the max pitch diameter is very close to the max and if inspected by another gauge may well be able to be turned more than 3 turns.

If making more than one piece adjust and avoid the problem.

 

[Gordon B. Clarke]

So the story goes as I am temporarily filling in for QC. I am inspecting some small pins with 1 - 72 UNF-2B threads and I grab out our plug gage.

Not part of the thread but the thread denomination is wrong. A 1-UNF has 12 TPI. Hit the wrong "button"?

1-12-UNF-2B has a pitch diameter tolerance of 0.0076". With a tolerance that size there should be no problem keeping it well within tolerance.

 

[Mike1974]

Not part of the thread but the thread denomination is wrong. A 1-UNF has 12 TPI. Hit the wrong "button"?

1-12-UNF-2B has a pitch diameter tolerance of 0.0076". With a tolerance that size there should be no problem keeping it well within tolerance.

I think he means a #1 thread (like 2-56, 4-40, etc), not 1" thread...

 

[Mike1974]

I would like to add that for STI threads, the hole should be gaged, not the actual installed helicoil per their data. Also, the Helicoil 'booklet' (manual, pdf, relevant drill sizes and such) states a "HI limit (no-go) gage may enter provided there is a definite drag on or before the 3rd turn."

Ref. FED-STD-H28,
Screw thread Standards for Federal
Services.

 

[Gordon B. Clarke]

I think he means a #1 thread (like 2-56, 4-40, etc), not 1" thread...

And on reflection I'm certain you're right That makes the PD tolerance for 2B just 0.0025".

Now there I'm definitely in favour of metric threads as the real diameter can be seen immediately

 

[The real Leigh]

Not part of the thread but the thread denomination is wrong. A 1-UNF has 12 TPI. Hit the wrong "button"?

#1-72 is a very standard size, with a pitch diameter of .0640".

- Leigh

 

[Gordon B. Clarke]

#1-72 is a very standard size, with a pitch diameter of .0640".

- Leigh

Sigh. How many outside the USA know that? In fact how many Americans know what the pitch diameter is as an internal thread thread that size can't be measured?

With a thread that size the only two things I'd want to know are the OD on an external thread and the ID on an internal one.

BTW didn't you read my post #11?

 

[The real Leigh]

Sigh. How many outside the USA know that?

Who cares?

The question was posed by a member in the US, seeking replies from other members in the US.

If you're unable to contribute to the discussion... DON'T POST.

- Leigh

 

[Gordon B. Clarke]

Who cares?

The question was posed by a member in the US, seeking replies from other members in the US.

If you're unable to contribute to the discussion... DON'T POST.

- Leigh

You obviously don't. I posted what I thought was a relevant comment and apologized when a member helped me see the light. You, on the other hand, just can't resist the personal remarks. Try acting like a moderator and not The Supreme Emperor. I now know I won't get fair treatment from you so this is my last post in your sub human forum until there comes an unbiased moderator and replaces you.

It was a question posed to PM members. Only you regard it as being only for US members.

 

[kid5084]

A 1-72 is a very fine thread. I won't accept more than 2 turns on any plug gage. Remember that thread gage does not measure hole size. For that you must use pin gages. Understand that 55% to 68% is acceptable. In soft material you must slow down spindle RPM to reduce inertia.

 

[triumph406]

You obviously don't. I posted what I thought was a relevant comment and apologized when a member helped me see the light. You, on the other hand, just can't resist the personal remarks. Try acting like a moderator and not The Supreme Emperor. I now know I won't get fair treatment from you so this is my last post in your sub human forum until there comes an unbiased moderator and replaces you.

It was a question posed to PM members. Only you regard it as being only for US members.

Ignore the 'The Real Leigh' I'd like to see him tap a 1-72 thread, or any other thread for that matter, he's a pretend machinist as far as I can tell.

 

[yanshi]

your supervisor is correct, yes, no more than 3 turns,the best condition is the NOGO stop during 1-2 turns.

 

[The real Leigh]

Ignore the 'The Real Leigh' I'd like to see him tap a 1-72 thread, or any other thread for that matter, he's a pretend machinist as far as I can tell.

You're probably right, since I don't use #1 hardware.

Will #0-80 do? All 12 holes are tapped, and the 12 on the other end also.

- Leigh