[Pharkas]

Hi,

I'm in the process of setting our shop up with a few go no-go gages.

I did a bit of research and learnt a few things and I have a few questions which someone here could certanly help with.

So, I learnt that....

A GO age should have a + tolerance while a NO-GO should have a - tolerance.

If I need te measure a 1.000 + 0.001/-0 hole, the GO member should be 1.0002 and the NO-GO should be at 1.0998, right ?

I trying to figure out why it would not be the reverse ?

If my hole is at the minimum of 1.000, then my GO gage would not work right ? Same with the opposite, if my hole is at the max, then the NO-GO might still fit.

If it would be the opposite, the GO being at 0.9998 and the NO-GO at 1.1002, wouldn't it, in theory, work better ?

If my hole is at the min of 1.000, then my GO would pass. Never tried but I would assume that passing a 0.9998 gage in a 1.000 hole would not be an easy thing to do which is why I say in thery..

Can someone help me out with this and explain ?

Thanks !

Pharkas

[TarHeelTom]

Generally speaking, (personally) I think of a Go/NoGo gage as being something I try to fit a part into, say to check the diameter of a shaft. So the Go gage should be slightly larger than the shaft, and the No Go gage should be slightly smaller than the shaft.

I've never seen (in my limited experience) a Go/NoGo being used for checking hole sizes, but don't see why it couldn't be used. You would, of course, need a bit of a taper to ease entry into the hole. And of course, in this case, the Go gage would have to be slightly smaller than the desired size, and the NoGo gage slightly larger then the desired size. Hence the confusion.

Tom

[christinandavid]

There are good reasons to reduce your tolerance slightly when checking with go/nogo gauges of any type. The first reason is that your go gauge will wear (regardless of what material it's made of). The second is that pedantic inspectors will try to force the nogo gauge in and tell you that the job is wrong.

I prefer the single-ended double-diameter style gauge, as once the go portion has slid into the hole the gauge is then squared up perfectly to test the nogo portion. The benefit of a double-ender is that you can chop off the worn part of either end.

I would only chamfer the gauge if it was a homemade one that wasn't hardened. The chamfer would then offer some protection if the gauge was dropped.

DP

[techrat]

I think that what the OP is talking about has more to do with the gauge maker's tolerance for the plug gauge than the target size of the gauge pin. Some discussion of the various classes/tolerances of gauge pins can be found here: Plug Gages, Pin Gages, Trilock & Taperlock Gages - Meyer Gage Co.

What it all boils down to is that cylindrical plug gauge manufacturers must have a tolerance for their work. If I need plug gauges for a 1.000 +/- .001 hole, the Go plug gauge would be .999 diameter however a tolerance must be applied.

If the plug gauge tolerance was a minus tolerance, any deviation from the target dimension on the plug gauge would result in the plug gauge being smaller than the target dimension which in theory would allow the inspector to accept under-size parts.

The same applies for the no-go. The target size for the No-Go plug gauge would be 1.001. If the gauge makers tolerance was a plus tolerance, the no-go could potentially be larger than the maximum hole size allowable which in turn could allow an inspector to accept parts that are over-size.

The link at the start of this post goes into more detail but in general there are several tolerance classes for plug gauges. When selecting go and no-go plug gauges, it is good practice to use the class where the total amount of plug gauge tolerance is no more than 10% of the hole tolerance being measured.

Also of importance is that cylindrical plug gauges have 3 tolerance types; Go, No-Go and bilateral. A Go tolerance plug gauge has the tolerance applied to the plus side of the target dimension only. A no-to tolerance plug gauge has the tolerance applied to only the minus side of the target dimension. Finally the bilateral has the tolerance applied evenly to the plus and minus side of the target dimension.

Hopefully this helps to clarify some things.

[Pharkas]

Techrat,

Thanks for the link, I had found that company during my research as well.

Back to your 1.000 +/- .001 hole and using a go gauge of 0.999 with + tolerance of 0.0002.

- If my hole is 0.999 and the GO plug gauge is 0.9992, it won't fit.
- If my hole is 0.9991 and the GO plug gauge is 0.9992, it won't fit.
- If my hole is 0.9992 and the GO plug gauge is 0.9992, it won't fit.
- If my hole is 0.9993 and the plug gauge is 0.9992, it possibly won't fit
...

and the same goes for the no-go.

However, if the go had a negative tolerance...

- If my hole is 0.999 and the GO plug gauge is 0.9988, it will possibly fit.
- If my hole is 0.9991 and the GO plug gauge is 0.9988, it will fit.
- If my hole is 0.9992 and the GO plug gauge is 0.9988, it will fit.
- If my hole is 0.9993 and the plug gauge is 0.9988, it will fit

I guess I'm being a bit picky but I'm just trying to make sense of it. I'll be ordering several go /no-go plug guages and a few ring guages shortly and I want to make sure I get it right !

Thanks for the help and feedback.

[techrat]

Pharkas,

In standard practice, it comes down to uncertainty of the system and guaranteeing that the gauging system cannot accept out of tolerance parts. I will try and expand on this using your last examples:

Back to your 1.000 +/- .001 hole and using a go gauge of 0.999 with + tolerance of 0.0002.

- If my hole is 0.999 and the GO plug gauge is 0.9992, it won't fit.

"good" part rejected due to uncertainty of the gauge system

- If my hole is 0.9991 and the GO plug gauge is 0.9992, it won't fit.

"good" part rejected due to uncertainty of the gauge system

- If my hole is 0.9992 and the GO plug gauge is 0.9992, it won't fit.

in this case the gauge may fit and accept a good part although due to form error, the gauge may not fit. i.e. it is uncertain whether or not the gauge will fit

- If my hole is 0.9993 and the plug gauge is 0.9992, it possibly won't fit

In this case, with good form on the hole, the gauge absolutely will fit but that is OK because the hole is in tolerance

In none of the above cases will a part that is out of tolerance under size ever, under any circumstances be allowed to be accepted.

and the same goes for the no-go.

However, if the go had a negative tolerance...

- If my hole is 0.999 and the GO plug gauge is 0.9988, it will possibly fit.

This would be fine

- If my hole is 0.9991 and the GO plug gauge is 0.9988, it will fit.

This is also fine

- If my hole is 0.9992 and the GO plug gauge is 0.9988, it will fit.

This is also fine

- If my hole is 0.9993 and the plug gauge is 0.9988, it will fit

This is also fine

The case that you did not mention that is the reason for the way industry approaches the tolerance the way it does is as follows:

Hole= .9989 Plug Gauge is .9988 ---- The plug gauge in some circumstances WILL fit. In this case, the plug gauge would allow a non-conforming, out of tolerance part to pass through the gauge system as conforming.

Again, standard practice requires that the uncertainty in the gauge system will always reduce the tolerance in the favor on never possibly accepting out of tolerance product.

One last thought...using a tighter class tolerance (X instead of Z or XX or XXX and so on) of gauge pin reduces the amount of tolerance that is taken away due to gauge system uncertainty.
I hope this clarifies the issue.

[Pharkas]

Ok, I understand.

A GO with + tolerance may reject good parts close to the minimum but would never accept bad parts.

A GO with - tolerance might accept bad parts close to the minimum.

Thanks for the help.

Go + , no go -.

Fred

[dertsap]

go no go gages should be made to the exact tolerance sizes , if they wear out then turf em and make new gages , if there is a concern that good parts will be rejected because of miss measuring then proper measuring equipment should be used instead

[techrat]

Just to be clear, the discussion relates to the way that the gauge maker's tolerance is applied not the nominal or target dimension of the gauge itself. Simply put, a go cylindrical plug gauge will have the gauge maker's tolerance applied to the plus side of the nominal or target dimension. A No Go cylindrical plug gauge will have the gauge maker's tolerance applied to the minus side of the nominal or target dimension.

When ordering the gauges, you will order to the exact tolerance limits specified for the part (hole) but must indicate whether the gauge is to be a GO or NO GO gauge as well the tolerance class of the gauge. Indicating whether or not the gauge is a GO or NO GO will dictate whether the gauge maker's tolerance is a plus or minus tolerance. The gauge class specifies the amount of deviation from the nominal that is allowed in the manufacturing process for the gauge.

[Pharkas]

Techrat,

One of the gauges I am interested in purchasing is for the following hole in a milled aluminum part, made with an end mill :

1.1250 + 0.0005 / -0

We normally measure these with a bore mic but recently had issues which is why I want to order gauges. This is for a press-fit bearing. Our client does not actually measure the part so a few tenth "under" is still ok.

I want to order a go no-go gauge, XX class.

Because of the 5 tenth tolerance, I am wondering if the gauge will actually fit. I can't really tell if the hole is 100% round and don't know if the gauge will actually help.

Based on your experience, what would you think ?

Thanks,

Pharkas

[donuts]

use a bore gage to check size and roundness, buy a pin gage .0001 below your low limit. the pin should go snug if hole is at low limit. pin gages are good checks for function. buy Deltronic pin gages. there tol is exact for what u need.
vincent.

[Pharkas]

I've never used a plug gauge to measure a 0.0005 tolerance.

I am just wondering if it's going to work or if the possible ovalness of the hole will make it hard to measure.

This gauges aren't cheap so I just want to know your experience on this before going out and spending the $.

Thanks.

[donuts]

then dont worry about the plug gages, if u check all around with a bore gage you can have readings from high to low and have a good part to print. if roundness is an issue then try finish boring for a true round hole.
vincent.

[M250cnc]

Interesting arguments, the wiki says you make the gauge to the actual dimensions.

Go/no go gauge - Wikipedia, the free encyclopedia

Phil

[christinandavid]

I can't really tell if the hole is 100% round and don't know if the gauge will actually help.

If you are milling the hole I would be amazed if it is round within half a thou. A milled hole can even appear "round" with a bore gauge because its more than likely S shaped than oval. Not to mention tapered. Follow donuts advice and bore/ream it.

You can't tell how much the hole is out of round with a plug gauge - but you try one on a milled hole and a bored hole and you can certainly feel the difference.

DP

[dertsap]

a plug gage will be a pita for that size of hole that has that tight of a tolerance
if you need to use pin gages instead of proper measuring instruments , then your easiest and most precise approach would be to use 2 pins .
for short winded eg , if you use a .5 and .625 pin together then you will for one know the fit but you will also be able to tell if the hole is out of round
your best bet on tight tolerance stuff is to buy the proper gauging and use pins for reference only
my opinion about this whole idea of gage tolerances is the same as what I stated previously and that is the simple fact that a gage tolerance should be non existent

[techrat]

My suggestion would be to use a XX GO and NOGO plug gauge to the exact size limits of the hole as a functional check. For a bore this tight, I highly recommend putting a slight radius on the end of the plug gauge.

A split ball bore gauge can be used to monitor the output of the process so that you can understand what is happening with the form of the hole i.e. out of round, taper, bellmouth etc.

If this is a high production part, you may consider using an air gauge which is very accurate and can be less fickle to use than a split ball bore gauge.

Technically, if you have form error that does not allow the go gauge to go into the part, it is not to size.

As an aside, you need to determine for yourself what will ensure that your customer is happy with the part as well as what will protect you from the possibility of future rejections. For example, using a plug gauge a couple of tenths under the min spec may be totally functional and even agreeable to your customer but if you don't coordinate with your customer on this, are you setting yourself up for future rejects? This is something that only an agreement between you and your customer can definitively answer.