Help - a bit of a heated debate going on here today

Can additional allowances be applied to a GO NO GO plug gage?

For example an "allowance for slip fit"

Yes or No would be great, but can you please also point me to an authoritative reference document one way or the other.

Thanks

Help - a bit of a heated debate going on here today

Can additional allowances be applied to a GO NO GO plug gage?

For example an "allowance for slip fit"

Yes or No would be great, but can you please also point me to an authoritative reference document one way or the other.

Thanks

What's the application? What's meant by "slip fit"? In general, it's expected that a go or no-go member will either fit or not fit, and it sounds like someone's trying to add some sort of fudge factor.

Is your heated debate about designing the Go/NoGo plug dimensions or using it?

If it is the first (design), it depends on the final application and your customer requirements. I recall a shaft OD and a bearing ID having a 5 micron difference between maximum shaft OD and minimum Bearing ID, for example.

If it is the second (use), Jim is correct.

What's the application? What's meant by "slip fit"? In general, it's expected that a go or no-go member will either fit or not fit, and it sounds like someone's trying to add some sort of fudge factor.

It has been years... I have not been involved in gage design since college... So, please feel free to correct me if my memory is deteriorated.

In England, there are three classes of fit:
1- Running or slip fit.
2- Interference fit
3- Press fit.

The allowance we used to add.... was "wear allowance" which was added to maximum material condition.

Maybe what I see is the old way of ordering gages for plug and ring.
Tolerance as stated at end
xx- precision lapped ( Plugs or Male Masters.
x - Precision lapped ring and plugs
Y - Lapped plug or ring
z - ground and polished
zz - Grounded only
This can range between 0.00002 to 0.0008 for tolerance due to size.

Is your heated debate about designing the Go/NoGo plug dimensions or using it?If it is the first (design), it depends on the final application and your customer requirements. I recall a shaft OD and a bearing ID having a 5 micron difference between maximum shaft OD and minimum Bearing ID, for example.If it is the second (use), Jim is correct.

The customer print calls out a size and a tolerance. We happen to know (or at least we think we know) that the shaft that our hole fits over is much smaller. But this is not shown on our print.

It seems the arguement is that if we get really close to the gage size it gets stuck, so some people wish to apply a slip fit allowance. But then what will happen when we get close to that size?

The debate seems to have settled down for now. We're going to do "a study".

The only place I ever found a description of how to size a plug gage was in the Machinery Handbook, but I don't have a copy right now.

Has anyone got any links?

The customer print calls out a size and a tolerance. We happen to know (or at least we think we know) that the shaft that our hole fits over is much smaller. But this is not shown on our print.

It seems the arguement is that if we get really close to the gage size it gets stuck, so some people wish to apply a slip fit allowance. But then what will happen when we get close to that size?

The debate seems to have settled down for now. We're going to do "a study".

The only place I ever found a description of how to size a plug gage was in the Machinery Handbook, but I don't have a copy right now.

Has anyone got any links?


Hello Caster,

Machinery's Handbook (http://books.google.com/books?hl=en&id=31eWvgTgD7oC&dq=machinery's+handbook&printsec=frontcover&source=web&ots=d1a5M2Bo5f&sig=Wd89s678aPY7JFbD_XnFBfSndhE#PPP1,M1). You can even search in this book.

Hope this helps.

Stijloor.

The only place I ever found a description of how to size a plug gage was in the Machinery Handbook, but I don't have a copy right now. Has anyone got any links?

OK, I found this helpful link, posted here for anyone else with this situation

http://www.vermontgage.com/tech/archive/rules.pdf

Page 4 tells all...including the always mysterious X, XX, Y, ZZ class defined so I can understand it!

Thanks to Vermont Gage!

Help - a bit of a heated debate going on here today

Can additional allowances be applied to a GO NO GO plug gage?

For example an "allowance for slip fit"

Yes or No would be great, but can you please also point me to an authoritative reference document one way or the other.

Thanks

IMO the title is not correctly worded,since Slip Fit (and for that matter,press fit/shrink fit/force fit etc.) is not applicable for GO/NOGO plug gages.

/Umang :cool:

OK, I found this helpful link.
Page 4 tells all...including the always mysterious X, XX, Y, ZZ class defined so I can understand it!Here is a link to an on-line calculator (http://www.ring-plug-thread-gages.com/ti-Gage-Makers-Tol-Calculator.htm) that will apply the 10% tolerance rule for you.

I still have yet to see any “authoritative reference” as to how much allowance must be given for the fit since a true 1.0000” pin will not go into a true 1.0000” hole. My gut tells me the allowance should not be fixed (i.e. “always allow .0002”) but rather should be some percentage of the hole size (i.e. the pin must be .05% smaller than the hole size), but the function may not even be linear.

Generally, I think using gage pins for tight tolerance jobs is very poor practice. We had a vendor doing final acceptance testing on a part with a hole (~ .5” deep) that was supposed to be .6500”-.6503” with gage pins. My contention was that his method was unacceptable as it did not meet our required minimum four-to-one gage accuracy requirement. I cannot point to any “authoritative reference” to support that, but he admitted he could not tell me for sure how much smaller a gage pin had to be than the hole size for the pin to go in.

And, how much force is acceptable to be applied to the pin to get it to “go”? Any authoritative references on that? :confused:

The customer print calls out a size and a tolerance. We happen to know (or at least we think we know) that the shaft that our hole fits over is much smaller. But this is not shown on our print.

It seems the argument is that if we get really close to the gage size it gets stuck, so some people wish to apply a slip fit allowance. But then what will happen when we get close to that size?

The debate seems to have settled down for now. We're going to do "a study".

The only place I ever found a description of how to size a plug gage was in the Machinery Handbook, but I don't have a copy right now.


It is true, a line to line fit is a press fit - and you will not get the gage off. If you compare a fit gage (pins or rings) to a touch gage (CMM), they will not match. Good news is, if it fits in a fit gage, you are good no matter what.

Your customer's mating part likely has fit designed into its size, so that it will slip fit. Using up that tolerance with your part will risk hard assembly, and then you get to go through all this fussing with the customer...even less of a joy.

It is nice to know all this, but the best idea is to control the dimension so it is not even an issue. That is easy enough to do, and far less overhead than all the fussing you are into now. A 'study' sounds like a waste of time to me.

Let me tell you a simple back yard way to prevent this problem. Get gages for production that are 75% of the tolerance. Only use gages that are 100% of the tolerance for final inspection. Better yet, use correct SPC on the dimension. My guess is if you are having these discussions, however, SPC is not going to be an option.

...a true 1.0000” pin will not go into a true 1.0000” hole....Mike, the first thing to know is that there is no such thing as a TRUE 1.0000" anything. Everything has tolerance applied.My gut tells me the allowance should not be fixed (i.e. “always allow .0002”) but rather should be some percentage of the hole size (i.e. the pin must be .05% smaller than the hole size), but the function may not even be linear.This is the reasoning behind the 10% tolerance rule. Math behind the rule (http://www.vermontgage.com/tech/archive/rules.pdf). On-line calculator for the rule (http://www.ring-plug-thread-gages.com/ti-Gage-Makers-Tol-Calculator.htm).I still have yet to see any “authoritative reference” as to how much allowance must be given for the fit.... My gut tells me the allowance should not be fixed (i.e. “always allow .0002”) but rather should be some percentage of the hole size (i.e. the pin must be .05% smaller than the hole size), but the function may not even be linear.In the below listed specifications you will find the “authoritative reference” you were seeking:read:. The standards discuss various methods of gage tolerancing available to use given specific product application parameters. You should pick-up a copies of:
ANSI/ASME B89.7.3.1:2001: GUIDELINES FOR DECISION RULES: CONSIDERING MEASUREMENT UNCERTAINTY IN DETERMINING CONFORMANCE TO SPECIFICATIONS
ANSI/ASME Y14.43:2003: DIMENSIONING AND TOLERANCING PRINCIPALS FOR GAGES AND FIXTURES and
ANSI/ASME Y14.5M:1994: DIMENSIONING AND TOLERANCING

And, how much force is acceptable to be applied to the pin to get it to “go”? Any authoritative references on that?I again point you to the appendix of: ANSI/ASME Y14.43:2003: DIMENSIONING AND TOLERANCING PRINCIPALS FOR GAGES AND FIXTURES.

I hope this has been helpful.:bigwave:

I appreciate the reply but I think you are missing my question.

The on-line calculator tells you what gage pins to buy in different instances, but it does not answer my basic question: how much smaller than the hole must a gage pin be to pass into the hole? The answer is not 5% or 10% of the hole tolerance. If the ANSI references you listed just speak on the issue of what tolerances of pins you should buy in various gaging situations, they, too, do not answer my question.

If you have a whole set of xxx grade gage pins, and you have to measure quantitatively what size the hole is, or even qualitatively if the hole is good, on a hole that is (supposed to be) between .6500" and .6503" can you do it? I say no. Required gage accuracy is four to one or at least 1/4 of .0003" or .000075"!!!!

Let me tell you a simple back yard way to prevent this problem. Get gages for production that are 75% of the tolerance. Only use gages that are 100% of the tolerance for final inspection. Better yet, use correct SPC on the dimension. My guess is if you are having these discussions, however, SPC is not going to be an option.

We started with SPC, but it died when it was felt by some that "unnecessary adjustments" were being done (after all - we were not out of spec).

Then we went to 75% gages, but once people found out QC had "better" gages, anything went.

Now we are beginning another cycle of SPC training.

The circle of life in Quality!

I appreciate the reply but I think you are missing my ... basic question: how much smaller than the hole must a gage pin be to pass into the hole?The basic question is at fault here.:frust: The current gage practice (in USA and EU) is: The GO plug gage is made at the low limit of the product tolerance with the gage tolerance all in the plus direction. The NOGO plug gage is made at the high limit of the product tolerance with the gage tolerance all in the minus direction. There is not an allowance between the gage and the product. If you start applying an allowance then you will get the same situation as Caster reports.Then we went to 75% gages, but once people found out QC had "better" gages, anything went.Related to the referenced standards...If the ANSI references you listed just speak on the issue of what tolerances of pins you should buy in various gaging situations, they, too, do not answer my question.The standards are the authoritative reference and will answer your question. The ANSI/ASME standards discuss the relationship of product tolerances to gage design. The standards present multiple gage design scenarios, one of them being the 10% rule. You may not like the answer:mad: because there is not a clear-cut one-way-fits-all answer, but these guidelines have been discussed to death by quality and manufacturing engineers in the field of measurement before they are published. The ANSI/ASME standards listed also discuss your question of how much pressure is to be used to insert a gage in a hole. There is much additional information in the standards like gage tolerances and gage measurement procedures, so you may have to wade through some information that is not pertinent to your question,:read: but the answer to your question is there.:agree1:

:sarcasm:The good part is that after you have read the standards you will be able to say to your boss, or to anybody else questioning your policy, that it is supported by [insert standard number with paragraph number here]. That will usually shut them up and you can go on your way. If not, you can ask them to show you in a standard where you are wrong. That is usually too much work and they will give up. If all else fails, you can let them read your copy (it is copyrighted so you can not give them a copy). The standard is wordy enough to deter them from lengthy on-the-spot perusal and the language will usually put the to sleep so they may not argue too much after that.:sarcasm:

We started with SPC, but it died when it was felt by some that "unnecessary adjustments" were being done (after all - we were not out of spec).


They were likely half correct, if you were doing X-bar-R charts, you probably were overcontrolling. But, "being out of spec" has nothing to do with out of control. that point needs to be made clearly, right off the bat. I can bet there were three things that happened, wrong chart, no production support, no management support. Most of that could have been resolved with correct charting, the remainder with management support of the control.

Then we went to 75% gages, but once people found out QC had "better" gages, anything went.

Again, for "control" (and not simple product verification which the standards relate to) 75% gages are extremely effective. Any time anyone does not follow the procedures, you really can not blame the procedures or the gages, it is a management problem. Who, with the authority to manage the people that used the wrong gages, let them.

Now we are beginning another cycle of SPC training.


I pray it is not X-bar -R...or you are heading down the same path. And...that management issue needs to be resolved or you are teaching a pig to sing. :cool:

The basic question is at fault? Oooookay. Well, despite what I’ve often been told, I guess there really is such a thing as a dumb question. :bonk:

Only thing is, other than promises that the question is indeed answered in at least one of several “wordy” standards, no one has been able to actually answer it. And why would such an august group of quality and manufacturing engineers address such a faulty question?

I guess I’m just as faulty as my question.:bonk:

Only thing is, other than promises that the question is indeed answered in at least one of several “wordy” standards, no one has been able to actually answer it.


If you want an answer more boiled down than the standards, here it is:

"It depends."

For more information, see the standards.

You are right, the tolerance changes depending on the size of the hole or shaft. So, refer to standard for correct tolerance for that size.

For ball park fit information, see http://www.engineersedge.com/general_tolerances.htm

To avoid the standard, control the process so that you do not have to even worry about getting so close you need to consult the standard. That is the simplest answer, the one I use when in that situation. :cool:

You are right, the tolerance changes depending on the size of the hole or shaft. So, refer to standard for correct tolerance for that size.



I don't think "correct tolerance" is really the appropriate term for what I am after. I'm not picking pins for a typical inspection task. It's more like "actual" -- how much smaller than the hole must a gage pin be to pass into the hole?

I think this can perhaps be best determined experimentally -- precisely measure the hole size and the gage pin size of many close-to-size gage pins, agree on a force limit for pushing the pin into the hole, and do the test.

It's more like "actual" -- how much smaller than the hole must a gage pin be to pass into the hole?


Check the link above. Pick the fit that best describes what you are shooting for.

Your problem is going to be trying to describe the force accurately that relates to the specific size you are trying to stuff in. Between that and the fact you are looking at MMC, what would be your gold standard measurement system to get your "actual" size? CMM?

Again, unless you were doing a critical sort at a customer, trying to get the absolute most good parts to avoid a huge PPM, I think you may be spending a lot of time trying to avoid spending less time just controlling the dimension. Inspecting in quality. But, to each their own.

You can lead a horse to water... :cool:

Check the link above. Pick the fit that best describes what you are shooting for.

Your problem is going to be trying to describe the force accurately that relates to the specific size you are trying to stuff in. Between that and the fact you are looking at MMC, what would be your gold standard measurement system to get your "actual" size? CMM?

Again, unless you were doing a critical sort at a customer, trying to get the absolute most good parts to avoid a huge PPM, I think you may be spending a lot of time trying to avoid spending less time just controlling the dimension. Inspecting in quality. But, to each their own.

You can lead a horse to water... :cool:

Sometimes you can't lead the horse to water. :( Why do you assume I am inspecting, sorting, or whatever? I don't need to be lectured on "inspecting in quality" vs having a good process. Step away from your pre-conceived ideas.

I am not trying to sort or approve parts. I am asking a question, something I am curious about and have been curious about for years. I know how to select gage pins or whatever other suitable method for measuring various IDs, and several folks have contributed nice links to places that aid that process. But not every question comes from "approving parts" perspective or a misguided soul focusing on blaming the measurement for bad parts!

And since you asked, as to what "gold standard measurement" I'd use in my little experiment, probably a P&W laser, accurate to +/- 2 millionths.

And since you asked, as to what "gold standard measurement" I'd use in my little experiment, probably a P&W laser, accurate to +/- 2 millionths.

You are right, it was not clear you were working through an academic curiosity. Between the links and the laser, sounds like you have everything you need. Congrats. :agree1:

Hi Wayne,

The current gage practice (in USA and EU) is: The GO plug gage is made at the low limit of the product tolerance with the gage tolerance all in the plus direction. The NOGO plug gage is made at the high limit of the product tolerance with the gage tolerance all in the minus direction.

ISO Gage practice has some differences, see the example in the picture.
The GO plug gage is made not at the low limit of the product tolerance, and tolerances for GO and NOGO plug gages are bilateral.

Hi Stefangh;
I hate it when I am in error.:o
My statement:The current gage practice (in USA and EU)...should have been: The current gage practice (in USA and UK)...ISO Gage practice has some differences,... The GO plug gage is made not at the low limit of the product tolerance, and tolerances for GO and NOGO plug gages are bilateral.Take another look at your screen shots. Based on them the GO plug gage is made based on the low limit of the product tolerance with a plus tolerance, and tolerance for the NOGO plug gage is bilateral.

Now for boring data spewing.
There are two ways to view the gages: 1) New (as made), and 2) Maximum wear condition.

The GO plug gage new condition...
Per ISO/R 1938; DIN 7150-2; BS 969:
The GO plug gage is made at the low limit of the hole with a +/+ tolerance so that it is larger than the hole in the new condition (i.e.: 1.0+0.025+0.050 = new gage tolerance range of 1.025 to 1.050).
Per ANSI B89.1.5:
The GO plug gage is made at the low limit of the hole with a + tolerance so that it is larger than the hole in the new condition (i.e.: 1.0+0.050 = new gage tolerance range of 1.000 to 1.050).
Considering the GO plug gage wear allowance...
Per ISO/R 1938; DIN 7150-2:
The GO plug gage is allowed to wear undersize by a prescribed amount. When the GO gage is near the allowed wear allowance low limit the gage could actually be passing parts that are out of tolerance.
BS 969; ANSI B89.1.5:
The GO plug gage is allowed to wear to the product low limit.

The new NOGO plug gage condition...
Per ISO/R 1938; DIN 7150-2:
The NOGO plug gage is made at the high limit of the hole with a +/- tolerance in the new condition (i.e.: 1.0+0.025/-0.025 = new gage tolerance range of 0.975 to 1.025). When the NOGO gage is near the maximum size the plug gage could actually be passing parts that are out of tolerance.
Per BS 969; ANSI B89.1.5:
The NOGO plug gage is made at the high limit of the hole with a - tolerance in the new condition (i.e.: 1.0+0/-0.025 = new gage tolerance range of 1.000 to 0.975).
Considering the NOGO plug gage wear allowance...
Per ISO/R 1938; DIN 7150-2:
The NOGO plug gage is allowed to wear undersize by a prescribed amount which is slightly smaller than the new condition low limit.
BS 969; ANSI B89.1.5:
The NOGO plug gage is allowed to wear to the new condition low limit.

Conclusion: Should there be an allowance made on the plug gages so that the gages will measure right up to the product limit? According to the four standards referenced above the answer is: NO.

I am not trying to sort or approve parts. I am asking a question, something I am curious about and have been curious about for years. I know how to select gage pins or whatever other suitable method for measuring various IDs, and several folks have contributed nice links to places that aid that process. But not every question comes from "approving parts" perspective or a misguided soul focusing on blaming the measurement for bad parts!Mike;
I apologize if I did not get the jist of your question earlier. My comment on your question is, as you are aware, it is impossible to fit a 1.0 plug gage into a 1.0 hole (without the use or a 10-ton ram:lmao:).

To answer your question, I would take it back to making an assembly, and to that end I like the link supplied by bobdoering back on 12/10/2008 which states that there is a minimum of 0.0001" to 0.0002" clearance required to have the closest fit that can be assembled by hand (Class IV Fit). :caution:Please remember that I am speaking academically, and not advocating for any deviation from the published gage standards.:caution:


Mike;
I apologize if I did not get the jist of your question earlier. My comment on your question is, as you are aware, it is impossible to fit a 1.0 plug gage into a 1.0 hole (without the use or a 10-ton ram:lmao:).

To answer your question, I would take it back to making an assembly, and to that end I like the link supplied by bobdoering back on 12/10/2008 which states that there is a minimum of 0.0001" to 0.0002" clearance required to have the closest fit that can be assembled by hand (Class IV Fit). :caution:Please remember that I am speaking academically, and not advocating for any deviation from the published gage standards.:caution:

Hi Wayne,

Speaking entirely academically, do you think the .0001" - .0002" clearance would be fixed regardless of pin/hole size? My hypothesis is that while .0001" - .0002" clearance might work for a 1" pin/hole, it wouldn't work for a 5" pin/hole, which might need .0005" - .001" clearance. Just a guess on my part, though.

Speaking entirely academically, do you think the .0001" - .0002" clearance would be fixed regardless of pin/hole size?Please review the link to the data (http://www.engineersedge.com/class_iv.htm). The amount of clearance does depends on diameter. I was just generalizing, assuming that you had reviewed the base information.