Thread Ring Gage won't go... Is it me or the gage?

[GBeaman]

I don't want to drag this on too far, but there is a lot of info here.
I have a brand new ring gauge from MSC. The rep just personally dropped it off here at my shop. I am cutting a male fitting with a 7/8-20 2b thread on the OD.

I am using Vardex 3/8 IC External full profile 20UN threading inserts on my Mori Seiki SL-2 Turn center. So I thread the normal way, start a little off the major diameter, thread and check that the thread has not been topped, then measure with thread mics. I double checked my anvils on the thread mics and they are in the 14-24tpi anvils. Thread to pitch diameter minus 2 thou. Now the thread has been topped. Should by all measures be in size. The ring gauge will not go. Take some more... starts but is tight. Finally hit the bottom of the tolerance .8368 PD my mics show around .8365 and finally the gauge will go!

Sounds exactly like the behavior of a properly sized no go gauge. But the gauge is clearly laser marked from the factory and says "go" PD .8412. Is it possible that MSC has issued an improperly labeled gauge? Should it be a no go that is labeled go? I don't have a way of measuring the ID PD of the gauge. I have a 2b male thread plug gauge. But even the go shouldn't go into the ring gage, and it doesn't. I could double check on a bolt if there was such a thing commercially made. Any ideas? The gauge says "GF" gage on it I believe it is made in China. I don't know how to qualify my parts. I have always used the gauge as bible. If I had a thou or so discrepancy between the gauge and thread mics I would ignore it and use the gauge. But this the whole tolerance of the thread!

The pitch looks good. The pitch meshes very well with the male plug gauge, and 20 pitch is just .050 so I don't see that being the problem. It would act differently if it was pitch too!

Thanks in advance.
-Greg

 

[screensnot]

Thread wires are dirt cheap and very accurate. You could use them to double-check your mic reading.

 

[GBeaman]

I double checked with thread wires and they agree nearly identical with the thread mics. I maybe should have mentioned that. Thanks for the thought. I am looking to see if I can find a commercially available fitting to compare to the gage.

 

[toolmaker96]

Check your ring gauge against a male go/no go gauge.

 

[Bobw]

Measuring threads sucks, too many things that can go wrong.

The mic and the wires, they are assuming a perfect thread form and lead, and that the part is actually round.

The gage, also assuming a perfect threadform and lead, but will only pick up the high spots on something not round.

You've got wires and a mic jiving with each other, that's a good thing.
I'd get that thread to an optical comparator and make sure your threadform is correct.

Also possible you have some weird tri-lobal thing going on.

Quite possible your thread gage is crap also. You've got a plug gage with a known diameter, you can check your wires and your thread mic on that.

If your insert or turning tool holder is a bit off, or has a chip under or next to it, you're threadform isn't going to be perfect, the wires may say its good,
the gage may not.

I'm no expert on threads, I hate the damn things, and I've run into your problem before. It was usually solved with a die or a tap.

 

[Guest]

Do you have a comparator to check the thread lead, or angle?

 

[rockfish]

In my opinion, a thread that checks good with a thread mic will always check bad with a thread ring. I've been down this road before, and what it boils down to is basically what is your customer going to check the thread with. I have used wires and thread mics for years and all of the parts that passed this inspection worked in their application and never came back. Then, I started doing government work which required a thread ring check and found that when my mics said the part was in spec, the rings won't go on. Only when the thread mics to the bottom of the tolerance will the rings screw on.



Frank

 

[Ox]

I think this is a common issue.

Guages usually won't go 'till the mics say that it is on low.


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I am Ox and I approve this h'yah post!

 

[SND]

I've always had that problem with them, it never goes on, whatever be the size, until I'm way at the bottom of the wire measurement. When you fit the part in a tapped hole it fits loose, sloppy, I hate it, but ring gage has to go on, or it gets rejected. And yes they are good and calibrated and all that fun stuff.
Best fun is when I made all the mating parts, and it still got rejected although everything fit perfectly, just cause of a damn ring gauge.

 

[rockfish]

To be honest.......... I hate this kind of work. What would pass inspection with rings is always a sloppy, horrible fit that would (or should) be unacceptable in most applications.


Frank

 

[Hertz]

When they make a ring gauge, don't they make it on the minimum purposely? I always thought they did so that if you ever get a female thread part on its minimum tolerance(like the gauge), it would still fit. A go-nogo gauge is different, or so I thought. And like rockfish said, it all boils down to how the customer will check it.

 

[screensnot]

When they make a ring gauge, don't they make it on the minimum purposely? I always thought they did so that if you ever get a female thread part on its minimum tolerance(like the gauge), it would still fit. A go-nogo gauge is different, or so I thought. And like rockfish said, it all boils down to how the customer will check it.

A Go-gage should be at the max PD. Every good thread should fit in it. Those that don't are too big.

The NoGo-gage should be at min PD. Threads that fit the Go-gage need to be checked in a NoGo-gage. The threads that fit a NoGo are too small.

 

[Toms Wheels]

Recently I had a case where the go ring would fit one way, but turned around would not fit. I now figure its because of 'Fuzz" on the threads, run a nut over the threads a few times and the gage goes fine. Here I thought it was only me.

 

[screensnot]

To expand a bit further, the gages for female threads are the opposite. Go is at min PD, and NoGo is at max PD.

The PD for a female thread is larger than the male thread. In fact, the min PD of a female thread is larger than the max PD of a male thread.

Even when the male is at max, and female is at min, there is clearance (that's what she said).

If you produce a male thread that is over max PD by 50% of the tolerance, you can probably grab a random nut, and it will spin right on. But you may find a batch that were made near the min PD, and have trouble getting some of them to go on.

 

[Mydrrin]

I sometimes have this issue with laydown style inserts and rubbing on the sides. If you don't have the right shim or something isn't aligned right it can cause this real easy. I would suggest trying it with a top notch insert as they have a 5 degrees of clearance, I have found them to be very reliable. If it is bad then talk to the maker of the gauge. If you have a chipped corner can also be a problem, sometimes buildup. I would go with the top notch and check it that way.

 

[GBeaman]

I am glad it isn't just me.

I went all over town looking for a carburetor plug or a compression fitting that might have a commercially made 7/8-20 thread. Not much luck.
I will email my customer, who is a larger shop, and see how they want me to verify it. To further muck things up, I ran these same parts a couple of weeks ago and thought just like Mydrrin said that the gage was bad. I told MSC so. That is why the rep brought me a new one. I have ring gaged a fair amount of threads and never had trouble like this.

I don't have an optical comparator. I would like to buy a used one and snipe a great deal on a used one, but have no idea what to even look for.

Since my options for checking the threads are limited, I may try the top notch insert in the morning and see if it could be insert geometry, and then I will have a discussion with the customer and see what they want. I don't understand why what is right, (2b standards) and the gage, and the micrometers wouldn't all be the same answer. Very frustrating. Thanks for the input, and responses. I won't go totally insane yet... give it another week.
-Greg

 

[racen857]

My guess is the ring gage is off. I have one that is the same way new. It never worked. When the mic says the thread is good the gage doesn't go on. Every other gage matches my thread mics numbers but this one. When running this part I always rely on the mic. No rejected parts. After a few times I cut a part to the pitch measurments that the gage should be. And readjusted the gage to fit the part. Last year when we sent it out for calibration I was waiting to see if they were going to tell me the gage was wrong. They did NOT, and it still works today. Meaning it was adjusted wrong from the factory.

All of our gages are certified every 2 years, to maintain accuracy.

Every new part is not perfect and I belive China is where the gage came from that I had problems with too.....

 

[Hertz]

A Go-gage should be at the max PD. Every good thread should fit in it. Those that don't are too big.

The NoGo-gage should be at min PD. Threads that fit the Go-gage need to be checked in a NoGo-gage. The threads that fit a NoGo are too small.

Ya exactly as I thought. So a ring gauge (not necessarily a go-nogo) may be cut on the minimum to prevent any low tolerance parts to get rejected.

 

[Ox]

And readjusted the gage to fit the part. Last year when we sent it out for calibration I was waiting to see if they were going to tell me the gage was wrong. They did NOT, and it still works today. Meaning it was adjusted wrong from the factory.

All of our gages are certified every 2 years, to maintain accuracy.

Every new part is not perfect and I belive China is where the gage came from that I had problems with too.....

I have zero faith in guage (re)certification places.
I had a customer give a set of rings for some odd thread that they needed post haste. We got a partial back out to them ratt away, and then I got the call saying that the threads were all bad.

???

Ran over there with guages in hand, only to find that the set that they were using on the floor on some other parts was adjusted no-where's near in compliance with this set! (I was told to go home and finish running the order as I was BTW)

These rings all had "cert" stickers on them...
If they were both wrong would be one thing, but both completely differ'nt?
I don't even think they check them... or something .... ????


If I want my rings checked - I'll buy a "setting plug" guage!


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I am Ox and I approve this h'yah post!

 

[PixMan]

I'd question the quality and calibration (including thread form) of the new gauge, especiallly considering the source. MSC isn't always known for seeking the highest quality. Highest margins, perhaps, but not always quality.

Do you have a local calibration house who can certify it? Does your customer have a gauge they can loan you for comparison purposes? Would you consider returning that MSC-sourced gauge for one from Vermont Gage, Swanson, or other reputable house?