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alanganes
11-17-2016, 10:32 AM
So I have a set of gauge pins I bought on CL a wile back. The label on the set indicates that they are an "M1 -" set. It also specifies "Minus" on the label.

Does this indicate that the pins are on the "small side" of nominal or that the hole I try them in is smaller than pin nominal?

For example If i have a good .25" hole, will a
0.25 minus pin go into it or not?

I guess I sort of assumed that "minus " pins would be to the small side of nominal but then read this:

"A go gauge checks the minimum hole diameter. A no-go gauge checks the maximum hole diameter. If the go gauge enters the hole and the no-go gauge is unable to enter, the design specifications of the hole have been met."

This is from the McMaster Carr descriptions where it calls the minus pins "no-go"

Color me somewhat confused. Please educate me...



Sent from my iPhone using Tapatalk

George Bulliss
11-17-2016, 10:47 AM
Yep, you need a .250 minus pin to fit a perfect .250 hole. An on-size pin won't have any clearance. It will fit, but only with a hammer!

So, if you have a good, tight sliding fit with a .250 minus pin, it's a .250 hole.

EricM
11-17-2016, 11:16 AM
"Minus" pins (Class ZZ) are .0002" under the nominal size; "Plus" pins are .0002" over the nominal size. As George Bulliss said, you need a "minus" pin to verify a hole size.

alanganes
11-17-2016, 11:28 AM
Thanks guys. That makes perfect sense to me and is the intuitive answer. It was the Mcmaster reference to the no-go gauge being a "-" gauge that confused me. Must be a typo...

Thanks again, order has been restored to my world.

enl
11-17-2016, 11:52 AM
Not a typo. The minus is the no-go. A minus pin is never larger than the specified size (ZZ are no more than 0.0002" undersize). This if how you are sure the hole size is not too large. Imagine a min 0.2490", max 0.2500" hole. If the 0.2500" minus pin does not go in, the hole is at most 0.2498", which is below the max. If you use a plus pin, the pin could be 0.2502", and it would not go in even if the hole is 0.2501", which is oversize, but the minus pin would, showing you htat the hole *could* be oversize. The no-go is to insure that the hole is NOT oversize, so you want the tolerance to insure that.

The plus size is used for the GO pin, to insure that the hole is AT LEAST the minimum size in the tolerance range.

Paul Alciatore
11-17-2016, 02:02 PM
So a no-go gauge pin, which is 0.0002 undersized will have that 0.0002" extra range to ensure that any hole that it does not go into will definitely be UNDER the specified maximum size.

And within that 0.0002" range the pin will go into a few holes that are still within the specified hole size. But those few rejections are the price of doing business, I guess.

And likewise, a go pin would be just a bit over the specified minimum hole size.

It takes a minute to wrap your mind around it, but it makes sense.

I wonder what the tolerance range on the pins is. Must be at least down to the tens of millionths.

EricM
11-17-2016, 03:23 PM
So a no-go gauge pin, which is 0.0002 undersized will have that 0.0002" extra range to ensure that any hole that it does not go into will definitely be UNDER the specified maximum size.

And within that 0.0002" range the pin will go into a few holes that are still within the specified hole size. But those few rejections are the price of doing business, I guess.

And likewise, a go pin would be just a bit over the specified minimum hole size.

It takes a minute to wrap your mind around it, but it makes sense.

I wonder what the tolerance range on the pins is. Must be at least down to the tens of millionths.

The tolerance of gage pins depends on what class they are. "Normal" (shop floor gages) pins are typically Class "ZZ"; Deltronic gage pins are Class "X". This will break it down for you: http://www.meyergage.com/abcs-of-gages/differences-between-z-zz-classes-of-gages/

enl
11-17-2016, 03:27 PM
The tolerance on a minus pin, class ZZ, is -0.0002, +0.0000. On a plus pin, it is -0.0000, +0.0002. These pins are spec'd in all classes with the nominal size at one end of the tolerance range. Master pins have a symmetric tolerance (class zz would be -0.0001, +0.0001)

For the example I gave above ( a 0.0010" range for acceptance) the class ZZ pin would likely give excessive rejects of good parts, as the gauge pin tolerance (go and no-go combined) takes 40% of the tolerance range. 10% is common practice, so for the given hole, class X would make sense (0.00004" tolerance) or class Z (0.0001") might be ok for a lot of applications, given that the pins don't usually ride the limit of the tolerance.

A quick ref chart (first on google search) is www.gagesite.com/documents/Gage%20Makers%20Tolerance%20Chart%20PQI.PDF

alanganes
11-17-2016, 10:23 PM
Thanks for all of the insightful replies. It does indeed take, as Paul A. said, a minute to wrap your mind around it but it makes sense once it you do. The truly dumb thing I was overlooking is that the "go" and "no-go" pins are generally two different sizes (different pins) at either end of the range for the hole you are measuring. Not sure how I was forgetting that, but there ya go. I suppose it stems from how I generally use these, which is not for checking holes for tolerance (just a hobby guy doing non-critical stuff) but for finding out just how big some particular hole is. So when I have some part with a hole I want to measure, I can simply try successive pins in the hole until I find the one that won't go in. Last one that did is the size, so I can make a part to match or whatever.

It is interesting how something that is so seemingly straightforward as poking a calibrated pin in a hole can rapidly become complicated and confusing once you start considering all of the details. As is often the case there is much more than meets the eye.

Thanks for helping to set me straight.
-Al

alanganes
11-17-2016, 10:25 PM
Not a typo. The minus is the no-go. A minus pin is never larger than the specified size (ZZ are no more than 0.0002" undersize). This if how you are sure the hole size is not too large. Imagine a min 0.2490", max 0.2500" hole. If the 0.2500" minus pin does not go in, the hole is at most 0.2498", which is below the max. If you use a plus pin, the pin could be 0.2502", and it would not go in even if the hole is 0.2501", which is oversize, but the minus pin would, showing you htat the hole *could* be oversize. The no-go is to insure that the hole is NOT oversize, so you want the tolerance to insure that.

The plus size is used for the GO pin, to insure that the hole is AT LEAST the minimum size in the tolerance range.

Thanks for this. It took me a few times reading this through before it sunk in. I'm a bit sluggish at time. Much appreciated.

oldtiffie
11-19-2016, 09:53 PM
The assumption here seems to be that both the "hole" and the "shaft" ("pin") are straight and without taper within the limits set - but are they?

And that if one or both have a total of straightness that is "out" (ie "bent"??) by at last - in this case - 0.0002"?

How would you know?

MichaelP
11-20-2016, 02:10 AM
Tiffie,

You have a good point, but IMHO, this deserves a separate discussion. There is no reason to over complicate a basic explanation that was asked for and given here. A way too many threads on our forum go into an endless counting of angels on a pinhead that has very limited or no practical application.

Jaakko Fagerlund
11-20-2016, 03:27 AM
The assumption here seems to be that both the "hole" and the "shaft" ("pin") are straight and without taper within the limits set - but are they?

And that if one or both have a total of straightness that is "out" (ie "bent"??) by at last - in this case - 0.0002"?

How would you know?
The tolerance classes have a maximum geometry deviation as per standards, so yes it can have a taper and yes it can be out of round and out of cylindricity, but the significance of those is very minute compared to the readings you are doing with those pins.

If your hole is not staright or cylindrical, well, it ain't the pins fault.

JCHannum
11-20-2016, 09:19 AM
I am also confused with the go/no-go description. It is my understanding that, when using a go/no-go gage with the red and green ends, that the green go pin is under the desired size, the red no-go pin over. The hole is larger than the go pin and smaller than the no-go.

That is, if you want a 0.250" hole, a 0.249" pin should go, a 0.251" pin should not. If a plus pin will pass, the hole is over that size.

enl
11-20-2016, 11:50 AM
I am also confused with the go/no-go description. It is my understanding that, when using a go/no-go gage with the red and green ends, that the green go pin is under the desired size, the red no-go pin over. The hole is larger than the go pin and smaller than the no-go.

That is, if you want a 0.250" hole, a 0.249" pin should go, a 0.251" pin should not. If a plus pin will pass, the hole is over that size.

You understand correctly, sort of. The go/no-go method is used to confirm that a feature is within a specified range. Yes, if the plus pin will pass, the hole is over the nominal size of the pin.

This is why the minus pin is used for the no-go, and the plus for the go. The minus pin will not be larger than the designated size, so, if it does not go, you are certain that the hole is less than the max. If it DOES go, the hole may be less than the max (in tolerance) and there is a false rejection of the hole. The plus pin will be at least the minimum size, so if it does go, the hole is at least the minimum. If it does not, then the hole may actually be large enough, and there is a false rejection.

The intent is to insure that there are no false acceptances, at the expense of a small number of false rejections.

JCHannum
11-20-2016, 12:44 PM
Which begs the original question, why does MCM refer to the minus pin as no-go and the plus as go?

If the minus pin does not go, the plus pin is redundant and the hole is undersized.

enl
11-20-2016, 03:38 PM
Which begs the original question, why does MCM refer to the minus pin as no-go and the plus as go?

If the minus pin does not go, the plus pin is redundant and the hole is undersized.

The Go pin and the NO-GO pin are not the same nominal size. The GO is selected to test the minimum allowable size. The NO-GO to test the maximum. If the minus pin DOES go, the hole is oversized. The NO-GO pin should not go in. The plus pin (the GO pin) will be a smaller nominal size, and smaller then the minus pin used for NO-GO.
...


Another example. Imagine a hole that is specified as 0.900" minimum, 1.000" max (0.950+/- 0.050, or 0.900 +0.100,-0.000, or 1.000 +0.000, -0.100, or any other tolerance that gives the given bounds)

To insure that the hole is AT LEAST 0.900", you would use a pin that is as close to 0.900, but NOT SMALLER. This is a PLUS tolerance pin (0.9000, -0.0000, +0.00024" in class ZZ). If the pin were smaller than 0.9000, then the hole might be undersize and still allow the pin to enter. If this pin does not go in, then the hole is undersize. Hence, the plus pin (nominal to oversize, never undersize) is used.

To insure that the hole is AT MOST 1.000", you want a pin NO LARGER than 1.000, so you use the MINUS pin, whoch may be smaller than 1.000", but will never be larger. If it DOES go in, then the hole is oversize, and rejectable. Hence, the NO-GO pin, as it should not go in for the feature to be accepted.
...

In a home shop, this may not be much of a concern unless you are making parts to mate with existing parts you don't have in hand (and therefore can't check the fit), or parts where clearances are critical. In the manufacturing world, from mass production to one off jobs, and in the repair and maintenance world, where parts are routinely checked for in or out of tolerance, the use of these gauges is second nature. In the firearms world, GO/NO-GO gauges are used to insure that commodity ammo (and accessory and repair parts) will properly fit a weapon. In automotive, they are used to check such things as shaft fits for seals, proper clearance of valve stems in the guides, and so on.

JCHannum
11-20-2016, 04:50 PM
"To insure that the hole is AT LEAST 0.900", you would use a pin that is as close to 0.900, but NOT SMALLER. This is a PLUS tolerance pin (0.9000, -0.0000, +0.00024" in class ZZ). If the pin were smaller than 0.9000, then the hole might be undersize and still allow the pin to enter. If this pin does not go in, then the hole is undersize. Hence, the plus pin (nominal to oversize, never undersize) is used."

OK, that is the part I had not sorted out. It makes sense looking at it that way, it is a refinement I had not considered. Thanks for clarifying it for me.

alanganes
11-20-2016, 06:03 PM
The Go pin and the NO-GO pin are not the same nominal size. The GO is selected to test the minimum allowable size. The NO-GO to test the maximum. If the minus pin DOES go, the hole is oversized. The NO-GO pin should not go in. The plus pin (the GO pin) will be a smaller nominal size, and smaller then the minus pin used for NO-GO.

This is exactly the thing that had me confused at first: The fact the Go and No-Go pins are not the same nominal size, but rather two pins chosen to be at the extremes of the tolerance range. Makes perfect sense once someone points it out.

oldtiffie
11-20-2016, 06:51 PM
Originally Posted by oldtiffie

The assumption here seems to be that both the "hole" and the "shaft" ("pin") are straight and without taper within the limits set - but are they?

And that if one or both have a total of straightness that is "out" (ie "bent"??) by at last - in this case - 0.0002"?

How would you know?






The tolerance classes have a maximum geometry deviation as per standards, so yes it can have a taper and yes it can be out of round and out of cylindricity, but the significance of those is very minute compared to the readings you are doing with those pins.

If your hole is not staright or cylindrical, well, it ain't the pins fault.


Thanks JF - appreciated.

I agree with all the very good points you made.

But they do shift the discussion into high class metrology (including the required environment) from the norm here which is or seems to be the normal run of tools available to the OP and other members here.

oldtiffie
11-20-2016, 07:38 PM
The OP only needs a reasonable surface plate and a reasonable Test Dial Indicator to check the pin for straightness and get a reasonable result.

First using a reasonable spirit level - a good "Starrett" one/type is best but a good Carpenters level will suffice if necessary.

Set the surface plate as level as you reasonably can - as that is your reference horizontal plane.

Next, clean the pin and set it stationary on the surface plate. If it does not move or roll the pin is OK.

If it does roll, the speed at which it moves is an indication as well.

If the pin hesitates or stops it is "bent" but if the pin slows and stops it should be OK as well.

Other-wise tilt the plate slightly (use shim stock or "feelers") and repeat. If the pin continues to roll it is OK - as it will be if the pin eventually stops.

Use the dial indicator - roll the pin under the indicator at the "high point" of the "hump" due to bending and reads off the dial deflection to get a good indication of what the bend in the pin actually is - by measuring it.

alanganes
11-20-2016, 08:46 PM
Thanks for the additional thoughts, Tiffie.

I do have a granite surface plate ( a Starrett pink) that has not had any calibration check in years, but has not seen much use either. It is miles better than my needs dictate. Similarly the set of pins I have don't have much mileage on them, from the look of things, the guy I got them from used maybe 8 or 10 of them with any frequency. But I appreciate hearing these sort of techniques. Good to file away in the back of the brain for future reference.

In any case, I don't foresee much high-class metrology happening in my shop any time soon. But I do have find the whole science and technique of metrology very interesting. As I said above, it is quite interesting how such a seemingly simple test can involve so much nuance.

In this case, I needed to order replacements for three missing pins from my sets. The "go" and "no-go" descriptions sort of confused me. Thanks again for chiming in.