On threaded features checked with a GO / NO GO thread gage for conformance:
Is it aceptable for the NO GO side of the gage to start into the threaded hole?
Is there a specification / standard that addresses this?
The rule of thumb here has been two turns maximum is all-right.
If the threaded feature is half an inch deep I can see this as not being a problem. But when the threaded feature is going through a wall thickness that allows for only a limited number of threads this seems contradictory.
Thanks in advance for helping to enlighten me.

A Go/No Go gage is made as a quick check for dimensions. The "Go" side is small enough to fit, but the "No Go" side is supposed to be beyond the tolerance.

If a threaded part of a No Go gage fits part way, there could be two different causes: the gage is warn down to nearly the size of the Go gage, or the part is large enough on the end for the gage to fit in a little.

The organization and its customer sets acceptance standards for if, and how much of this part-way fit allowed.

So there is no specification or standard that can be sited?

The rule of thumb here has been two turns maximum is all-right.


In my experience - it should be nor more than 3 turns, unless it is sheet metal - then you only have 1.5 turns.

If you will look in the machinery handbook it will give you the standards for the gages read the section for calibration and gage maker tolerances.

Threads are notoriously interpreted differently by various locations. You might find an interpretation in a particular source, but you will find a different one in another source. Taper threads are treated differently that straight. Worse yet, from my experience, is that the customer will have their own interpretation - not only for turns to fail, but pressure to apply, etc. (Since they write the checks, it is good to know what they want.) Some want a go gage to spin on with virtually no torque, and others will crank the daylights out of a no go gage and say you fail. To be fair - whatever you do for the go gage (as far as torque) it needs to be the same for no go or you are artificially tightening the spec.

Planergal

The GO plug must enter and pass through the full length of the product freely and the NOT-GO plug must not exceed three full turns.

The applicable standards are

ASME/ANSI B1.2-1983 Gauges And Gauging For Unified Inch Screw Threads
ASME/ANSI B1.3M-1992 Screw Thread Gauging Systems Dimensional Acceptability Inch Metric Screw Threads
MIL-STD-120-1950 Gage Inspection

Bobdoering

Nothing notorious about understanding thread inspection when knowledge is applied based on a national/international standard.

Planergal

The GO plug must enter and pass through the full length of the product freely and the NOT-GO plug must not exceed three full turns.

The applicable standards are

ASME/ANSI B1.2-1983 Gauges And Gauging For Unified Inch Screw Threads
ASME/ANSI B1.3M-1992 Screw Thread Gauging Systems Dimensional Acceptability Inch Metric Screw Threads
MIL-STD-120-1950 Gage Inspection

Bobdoering


Nothing notorious about understanding thread inspection when knowledge is applied based on a national/international standard.

This information may be useful to the OP, but international (or any other standards) have no standing unless unless they are agreed upon by customer and supplier.

While it may be true that different people will want the threads to be a certian way does not mean the engineer who drew the blueprint meant for them to stray from the ansi standards. Please look at your tolerance box on the print does it not say ansi standards apply. Unless you have a specific tolerance on the print you are bound by ansi standard. Some inspectors simply just do not know how to use a thread gage. And if done correctly giving your customer a little guidance is never a bad thing.

While it may be true that different people will want the threads to be a certian way does not mean the engineer who drew the blueprint meant for them to stray from the ansi standards. Please look at your tolerance box on the print does it not say ansi standards apply. Unless you have a specific tolerance on the print you are bound by ansi standard. Some inspectors simply just do not know how to use a thread gage. And if done correctly giving your customer a little guidance is never a bad thing.

If a drawing just says that ANSI standards apply, you don't have enough information. There are thousands of ANSI standards. As far as threads are concerned, unless a specific standard is explicitly called out, there is no standard other than what the customer expects.

If a drawing just says that ANSI standards apply, you don't have enough information. There are thousands of ANSI standards. As far as threads are concerned, unless a specific standard is explicitly called out, there is no standard other than what the customer expects.


And if I recall correctly, the torque applied to the gage is never really accurately specified by the standards - and requires lab to lab coordination to ensure you are really on the same page with the customer.

when the print states ansi standard applies, yes you have enough information. you need to find the standard that applies. However, the "generic" ansi "inspection" standard refered to on the blue print is found in the machinery handbook. When it comes to go / no-go thread gages the norm is usually two to three turns to allow for wear this is stated in the gage makers toleranceing/calibration, however, gage corelation with the customer is done at the ppap stage of the process.

when the print states ansi standard applies, yes you have enough information. you need to find the standard that applies. However, the "generic" ansi "inspection" standard refered to on the blue print is found in the machinery handbook. When it comes to go / no-go thread gages the norm is usually two to three turns to allow for wear this is stated in the gage makers toleranceing/calibration, however, gage corelation with the customer is done at the ppap stage of the process.

It is not enough information, and the supplier shouldn't be expected to search through all of the standards and find the appropriate one. If the customer/designer has specific standards in mind, they should be explicitly called out on the drawing or in the contract. There was no reference to PPAP in the OP, and even if there were (assuming AIAG standards) there is no requirement for "gage correlation."

If you're not sure about the requirements, ask the customer!

On threaded features checked with a GO / NO GO thread gage for conformance:
Is it aceptable for the NO GO side of the gage to start into the threaded hole?

Personally, if I had and used a GO and No-Go thread gage and either the GO was tight (even if I could screw it into or onto the thread) or the No-Go could enter by even half a turn I'd measure the pitch diameter of the thread.

Tight threads cause unnecessary wear on the Go gage and too "loose" unnecessary wear on the No-Go gage. Unless the threads are being mde usind a tap etc. then the machine that manufactures the thread has not been set to the middle of the tolerance or is too unprecise to make the thread.

Thread pitch diameter measurement is alway preferable to gage control/inspection when setting up and performing SPC. Gages should be used to determine cutting tool wear (ful profile and pitch). Thread pitch diameter inserts cost less than most gages plus, if pitch diameter is measured, then only Go gages are required.

If anyone wants more details they'll have to contact me with a PM.

Thread gages have existed many years (and will continue for many more) but thread measurement inserts for external and internal threads are relatively new. I'm including an enclosure with advantages and disadvantages of various thread inspection and measurement possibilities.
Any and all comments and suggestions are welcome.

I have delete a few photos on the enclosure as the document was too large.

Some of the smaller companies just do not have the resorces to purchase the more expensive thread measuring equipment. I have requested quotes for various types, and ring gages are the least expensive. But, if you question the gage pitch there are pitch gages (the ones that look like radius gages), there is the hand held optical and many other less expensive ways to verify the pitch.:thanx: I'm not saying your way is not a good idea, I would love it if my company could afford the type of measuring equipment you are talking about. I've asked, they said no :nope::thanx:

Some of the smaller companies just do not have the resources to purchase the more expensive thread measuring equipment. I have requested quotes for various types, and ring gages are the least expensive.

These gages are good functional go/no go gages, but provide no process control or setting data (tap and die or cutting tool wear, even cnc setup or adjustment) - which does require variable data.

But, if you question the gage pitch there are pitch gages (the ones that look like radius gages), there is the hand held optical and many other less expensive ways to verify the pitch.:thanx: I'm not saying your way is not a good idea, I would love it if my company could afford the type of measuring equipment you are talking about. I've asked, they said no :nope::thanx:

Thread pitch evaluation should be a part of thread qualification, whether through sectioning and optical comparator, tri-roll thread gages, or similar. Other thread conditions (flat threads, burr rollover, etc.) might fool go/no go but kill a production lot.

I would love it if my company could afford the type of measuring equipment you are talking about. I've asked, they said no :nope::thanx:

Your gage R&R should be a good judge of what equipment is adequate, as long as you can sufficiently verify the thread form. I have used variable thread gages, optical comparator templates, profilometers, etc., depending on the nature, and uniqueness of the thread. You can not get ring gages for all threads - some are too custom (such as a 4 start high helix thread used for brake adjusters).

Hmmm, I don't know if "can't" is the proper word maybe it would be more costly and time consuming to have one made. I've worked with several types of threds but then, not all so, I don't know all. But then again, alot of the smaller companies do not manufacture the more complicated threads.:cool:

I'm not saying your way is not a good idea, I would love it if my company could afford the type of measuring equipment you are talking about. I've asked, they said no :nope::thanx:

To avoid any misunderstandings I'm talking about pitch diameter measurement and NOT pitch measurement.

I'm walking on a tightrope here but the type of PITCH DIAMETER MEASUREMENT thread inserts I mean aren't expensive.

I'll give an example:
a pair of thread pitch diameter inserts that can measure all external threads with a flank angle of between 50 and 80 degrees and all pitches from 1 - 2 mm / 24 - 13 TPI cost approximately USD 100 and similar internal thread pitch diameter inserts costs approximately USD 105. Internal measurement inserts can measure from 1/4 inch.

Thread pitch diameter measurement accuracy? - better than 0.0008 inches. The pitch diameter tolerance on a standard 1/4-20 UNC external thread is almost 0.0037 inches and on an internal thread 0.0049 inches. The larger the diameter and the courser the pitch, the greater the pitch diameter tolerance.

With 4 standard pairs of either external or internal thread measurement inserts all threads with a flank angle between 50 and 80 degrees with pitches from 05 - 8 mm / 48 - 3 TPI can be measured.

I'm already misusing Cove etiquette by writing what I already have and that is why I suggested contacting me by PM for more information. Either that or look at the information on my personal details by clicking on my name. I can easilly send reading material.

If anyone doesn't believe what I write, who'd have believed computers and mobile phones just a few years ago? :D

I understand what you are measuring. I have been in the quality business for 35 years. Like I said I have measured many types of threads. Looking at the file attachment. I have requested quotes for these types of gages and yes they are expensive. To measure pitch diameter we use pitch mics or wires. If in doubt we have the quality lab that calibrates our gages certify that they are correct. But we not only check the pitch diameter, we check the lead also. I would so like to know where these lesser expensive thread checkers can be purchased because I would like to present the quote to my company. My company does not have a lot of money so we have to work with what resources are available to us. Usually we use customer supplied gages. So we measure with what the customer wants us to measure with. Please if you would not mind giving me the name of the company that sells the less expensive thread checkers that would be great.

I understand what you are measuring.

I have sent you a PM :)

Go/No Go gage is a quick check for dimensions. Go gage mean the lower limit and No Go gause mean the upper limit. So go gage must go and No Go gage shall not go. That's the concept

And if I recall correctly, the torque applied to the gage is never really accurately specified by the standards - and requires lab to lab coordination to ensure you are really on the same page with the customer.

Hi all!

The torque can really be a sensitive issue, as sometimes using A LOT of it can make GO gage go all the way (like if there is burr from plating in the thread or smaller dents from transporti), but this is still a fail.

When we use GO gauges, we have a rule that gage must pass using only 2-3 fingers to run it throgh, if you need to use all fingers and use force, this is fail.

AFAIK, Fiat company had regulated exact torque that is allowed to use for this, others just use common sence using gages without any force.

Also, we had cases of return of screws with claim "doesn't pass GO gage", when their gages were old and worn out.

One more thing: gages are used for quick check, and only correct measurement can judge thread.

In mentioned case, we could measure complete thread under microscope and found it perfect, so we suspected customers gages.

:bigwave:

When we use GO gauges, we have a rule that gage must pass using only 2-3 fingers to run it throgh, if you need to use all fingers and use force, this is fail.

AFAIK, Fiat company had regulated exact torque that is allowed to use for this, others just use common sence using gages without any force.

Also, we had cases of return of screws with claim "doesn't pass GO gage", when their gages were old and worn out.

One more thing: gages are used for quick check, and only correct measurement can judge thread.

:bigwave:

When machining a thread, if the pitch diameter was measured to ensure set-up and start-up being close to the average pitch diameter, then thread gages should only be used to check profile and possible barbs etc. They would also last much longer due to lack of wear by "forcing". I've never met the machine operator yet that doesn't try a little "squeeze" to see if it can just get by. Thread pitch diameter tolerances are child's play for all CNC machines, when the machine is set-up correctly

If you want an example of "appplied inventivenes" you should see how some operators get stuck gages out of threaded holes or ring gages off external threads :lmao:

When machining a thread, if the pitch diameter was measured to ensure set-up and start-up being close to the average pitch diameter, then thread gages should only be used to check profile and possible barbs etc. They would also last much longer due to lack of wear by "forcing". I've never met the machine operator yet that doesn't try a little "squeeze" to see if it can just get by. Thread pitch diameter tolerances are child's play for all CNC machines, when the machine is set-up correctly

If you want an example of "appplied inventivenes" you should see how some operators get stuck gages out of threaded holes or ring gages off external threads :lmao:

I can imagine... like body builders on contest, using all body muscles to force pure GO gauge on, but with smile on their faces and appearant ease :lol: