Acme Thread Gage Tool Wear Measurement

J

Jane27

#1
I work in a machine shop that produces high precision parts for aerospace. The Acme thread gages are often used 100% to verify tapped holes, and we are looking for an in-house means to determine when the gage has become worn. Any suggestions would be appreciated.
Thanks
 
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T

t.PoN

#3
If you don't want to send it to calibration lab, you still can do visual check and you need to have thread wires to check the Gage diameter.

do you have reference for acceptable tolerances?
 

Wayne

Gage Crib Worldwide
#4
I work in a machine shop that produces high precision parts for aerospace. The Acme thread gages are often used 100% to verify tapped holes, and we are looking for an in-house means to determine when the gage has become worn. Any suggestions would be appreciated.
Thanks
Jane;

This depends on the type of thread gage you wish to validate: Plug Gage or Ring Gage.:yes:

Thread Plug Gages are tested by using the 3-wire method. The 3-wire method can be done with just the 3-wires of the correct size and a micrometer, but many people find that you need three hands to do this method well.:lmao: Alternately; it can be done with a simple fixture and holders for the thread wires.:agree1:

Thread Ring Gages must be tested with a Master Plug Gage, which is first validated by the 3-wire method.

I hope this helps.:popcorn:
 
M

MotorCityQuality

#5
Just to piggyback a little on Wayne's post:

I'm... familiar with your dilemma; the best way is to buy a set of corresponding thread master rings and periodically test your plugs to the rings. If they wiggle, you got wear.

Besides: How many plug gages are we talking about? From a cost perspective, if you only have 5-10 gages, you may just want to order new ones periodically. they're relatively inexpensive, and they'll be certified at manufacture.

The difficulty in measuring them yourself is twofold:

1) You can measure them directly as an over wires measurement, but that requires actually having the same size wires as is called out per the spec. Even if you do have those wires available, there is a correlation requirement for calibration purposes (I BELIEVE that they have to be within .000020" of the specified wire diameter, and all three must be within .000010" of each other... please correct me if I'm wrong). Plus, the wires must be calibrated per your calibration interval, whatever that may be. If you don't have those, you can use the Pitch Diameter, which is the calculated diameter of contact on your gage, and you can use whatever wire size you have, provided you know the math to derive the pitch. Incidentally, this is why most thread gage manufacturers will report the size as a Pitch, rather than the direct over wires measurement.

2) Even if you have all the above available to you, how do you define "acceptable wear"? Is that definition acceptable to your customers?

Again, if you only have a handful of plugs, you may just want to look at replacing them periodically. It'll save time, heartache, and probably money as well.
 

Wayne

Gage Crib Worldwide
#6
The best way is to buy a set of corresponding thread master rings and periodically test your plugs to the rings. If they wiggle, you got wear.
I respectfully but completely disagree with you. :(

:caution: The B1.5 ACME thread specification does not allow for testing a working plug gage with a master ring gage. :caution:

To what size would one make the master ring? A standard working ring gage will not work as it is much smaller than the working plug gage. Are you suggesting a solid design ring gage or an adjustable style ring gage? If adjustable you need to also purchase the master plug for the master ring because that is the only way to calibrate the ring gage. Depending on the size, even the solid ring needs a master plug.

How do you define "acceptable wear"?
This is the easiest part. The tolerance for the gage is established in the gage specification. This information is available from many sources: The B1.5 Gage specification itself; The Long Form Certification which comes with new gages; Thread engineering software like ThreadTech (if it is a one-time thing ThreadTech has a Free 30-Day Trial Version).

How many plug gages are we talking about? From a cost perspective, if you only have 5-10 gages, you may just want to order new ones periodically. They're relatively inexpensive, and they'll be certified at manufacture.... Again, if you only have a handful of plugs, you may just want to look at replacing them periodically. It'll save time, heartache, and probably money as well.
As a seller of thread measurement equipment I LIKE THIS IDEA! However; ACME work plug gages are a bit more expensive than the Standard UN-series or M-series work plugs. Developing an inspection method will be cost effective.

You can measure them directly as an over wires measurement, but that requires actually having the same size wires as is called out per the spec. Even if you do have those wires available, there is a correlation requirement for calibration purposes (I BELIEVE that they have to be within 0.000020" of the specified wire diameter, and all three must be within 0.000010" of each other... please correct me if I'm wrong). Plus, the wires must be calibrated per your calibration interval, whatever that may be. If you don't have those, you can use the Pitch Diameter, which is the calculated diameter of contact on your gage, and you can use whatever wire size you have, provided you know the math to derive the pitch. Incidentally, this is why most thread gage manufacturers will report the size as a Pitch, rather than the direct over wires measurement.
There is no difficulty in determining which wires are required. That information can be found on the web (here is one place); or by using thread engineering software. Basically all you need to do is to request ACME thread wires for [specify the threads per inch].

Using Thread wires is the most economical method of validating your working plug gages. They can be tested in-house with micrometers for a good shop calibration. The cost of thread wires may be around $100 with a 3 week lead-time. Compare that to the cost of a special master ring gage of $300 plus another $225 for the setting plug and with 4 to 8 week lead-time. And then you have the Solid Style Master Ring which runs about $600 and takes 6 to 10 weeks to make.

In a nutshell...
You can use thread wires to check your working plug gages :agree1: or...
You can use a master ring gage to check your working plugs. Your master ring gage needs to be calibrated with a master plug gage. The master plug gage needs to be tested, so send that to a calibration laboratory and they will test it with... yes... Thread Wires. :bonk:

I know, some of this stuff is clear as mud.
I hope I have helped in some small way to clear the murk. :bigwave:
 
M

MotorCityQuality

#7
*** Post truncated 'cause I apparently can't submit a post that has links in it, even if I'm replying with someone else's already posted links.

*** Also Edit: I prolly misspoke when I said "the best way". I should have said, "Another way to do this is..."

I respectfully but completely disagree with you.:(
You're a racist!

Just kidding. Don't you hate it when people can't disagree civilly? No worries, though. To be honest, in my experience, the above statement was probably the best I've ever been treated in a dissenting post. Thanks! :lol:

:caution: The ACME thread specification does not allow for testing a working plug gage with a master ring gage. :caution:

To what size would one make the master ring? A standard working ring gage will not work as it is much smaller than the working plug gage. Are you suggesting a solid design ring gage or an adjustable style ring gage? If adjustable you need to also purchase the master plug for the master ring because that is the only way to calibrate the ring gage. Depending on the size, even the solid ring needs a master plug.
I think I can clear this up a bit... the assumption I was making was that the originator of the thread asked for indications of thread wear, not how to qualify the thread. My response was geared toward a practical and easy solution, that wouldn't require additional measuring/records keeping duties, and one that a layman can understand without getting all technical and stuff. You can get a ring set to your specifications, if it fits, great, if it is sloppy, get a new (or rework the old) gage.

This is the easiest part.
The question probably could have been clearer... like, "What does your organization think is tolerable wear". It was meant as more of a metaphysical question. Kinda like, "Why is pizza good?" - the answer is left up to the observer.

Unfortunately, there is no hippy smiley for this statement.

As a seller of thread measurement equipment I LIKE THIS IDEA! However; ACME work plug gages are a bit more expensive than the Standard UN-series or M-series work plugs. Developing an inspection method will be cost effective.
I do too!

I will take your word on this, as my only experience is with UN/M plugs.

The thought was that in the grand scheme of gages, those aren't particularly expensive, and for a couple of hundred dollars every two years or so (of course, depending how how they're kept, how often they're used, how many you have, etc.) for a small number of gages, that would seem to be a cheaper alternative than having operators log many hours of measuring on a yearly basis. This solution goes out the window, however, if they have many gages. Then, I absolutely agree with you.

There is no difficulty in determining which wires are required. That information can be found on the web ; or by using thread engineering software. Basically all you need to do is to request ACME thread wires for [specify the threads per inch].
** Saving that link, btw. Thanks!

This is where I jump off. I have seen prints, primarily with large companies that you've heard of (and, being from Grand Rapids, probably service as well) that have weird cockamamie thread wire sizes called out. This probably stems from their own gage cribs having a specific set of wires in 1968 or whatever, so everything on the prints is geared towards their own measuring capability. In 1968 or whatever. Besides, most of those prints ask for certifications on both the over wires AND pitch diameter...

I've gone head to head with those people and argued for changing the prints, or at least getting them to accept, only a pitch diameter certified rather than the direct over wires measurement. Without getting into too much detail, the issue started with ISO17025 requirements, and our vendor not having the wires as specified by the customer, plus our vendor doesn't have over wires measurements as part of their scope. Of course, these are the same shops that use tapping fluid on their go thread gages because, "They are just too tight to fit in, tap fluid makes 'em go in easier".

:jawdrop:

To sum up, I have seen odd wire sizes called enough that I wanted to point out that this may not be as cut and dry as ordering some Mahr thread wires and calling it a day.

However, as I don't have as much experience with the standard and non-UN/M threads as you do, it may just be that easy. :notme:

Using Thread wires is the most economical method of validating your working plug gages. They can be tested in-house with micrometers for a good shop calibration. The cost of thread wires may be around $100 with a 3 week lead-time. Compare that to the cost of a special master ring gage of $300 plus another $225 for the setting plug and with 4 to 8 week lead-time. And then you have the Solid Style Master Ring which runs about $600 and takes 6 to 10 weeks to make.
Again, it's not just $100 for the thread wires: if you only have a small number of gages, there may be a cost advantage to simply purchasing new: in addition to the upfront cost of the hardware, you have setup time, operator time, soak time (if fancy enough to have a soak room), gage downtime, thread wire maintenance, cataloging and maintenance of the new database, etc.; all those things cost money as well. The advantage of purchasing new on a periodic basis is that these things are all "outsourced" to the gage manufacturer, for one low price.

If, on the other hand, they have a plethora of thread gages, then I completely agree with you. :agree:

In a nutshell...
You can use thread wires to check your working plug gages :agree1: or...
You can use a master ring gage to check your working plugs. Your master ring gage needs to be calibrated with a master plug gage. The master plug gage needs to be tested, so send that to a calibration laboratory and they will test it with... yes... Thread Wires. :bonk:

I know, some of this stuff is clear as mud.
I hope I have helped in some small way to clear the murk. :bigwave:
HOW DID YOU GET IN THAT NUTSHELL?

Anyway:

Again, yours is the proper method, and can be done by anyone with proper equipment. Just trying to offer more options.

Whee!
 

Wayne

Gage Crib Worldwide
#8
It is nice to have civil conversations. :argue: Thanks for your part.
I have seen odd wire sizes called enough that I wanted to point out that this may not be as cut and dry as ordering some Mahr thread wires and calling it a day.
Ordering wires is as easy as calling me and telling me what diameter you need, even if it is a full special. A full special set of thread wires at today's cost is around $130 for most sizes with a 3 week lead-time. The Long Form Certifications are extra; of course.

Again, it's not just $100 for the thread wires: if you only have a small number of gages, there may be a cost advantage to simply purchasing new: in addition to the upfront cost of the hardware, you have setup time, operator time, soak time (if fancy enough to have a soak room), gage downtime, thread wire maintenance, cataloging and maintenance of the new database, etc.; all those things cost money as well. The advantage of purchasing new on a periodic basis is that these things are all "outsourced" to the gage manufacturer, for one low price.
Keeping this easy for the small shop, or in this case the shop which requires 100% thread gage check on all parts. The check of the gages is a simple pass/fail test done outside of the calibration system and with no care for being a 68? room. Just have a basic set-up for the high wear thread plug and make the crib attendant check them on return from the shift's work. (The linked system is only about $500 including the micrometers.) Know that the uncertainty will be more so use a slightly smaller tolerance band and discard when the result nears the minimum gage material condition. Some good news is that most of the system can be repurposed for another size when the next job arises with a similar 100% requirement.

Well there is my :2cents:
 
H

HarishReddy

#9
Hi,

I have a similar query based on thread gauges. My Company is into cold forging.
For some components we roll the threads after forging.

Of late we are receiving complaints from customers regarding some components missing threads or having thread flats. Now I am under a lot of pressure from the customer to come up with some kind of in house Poka yoke gauge to stop this.

Any Suggestions??

Thanks!!

P.S: Now we are inspecting the components 100% with Ring gauges.
 

Wayne

Gage Crib Worldwide
#10
My Company is into cold forging. For some components we roll the threads after forging. Of late we are receiving complaints from customers regarding some components missing threads or having thread flats. Now I am under a lot of pressure from the customer to come up with some kind of in house Poka yoke gauge to stop this. Any Suggestions??
P.S: Now we are inspecting the components 100% with Ring gauges.
First I have more questions. :bigwave:
-What type of thread?
-What nominal major diameter?
-What pitch or TPI?
-What class-of-fit??

Second a general statement or two or three. :popcorn:
-Missing threads or flats may be an indication of a blank which is too small.
-Depending on the function of the thread, a missing part of a thread or flat should not cause serious problems.
-Voids are difficult to detect by any means other than visual.
 
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