I have piece that has a groove cut into the ID in order to take a snap ring to retain the guts of the assembly.

The spec for the groove ID is 0.330"+/- .001"
thickness of the groove is a ref dimension of .019"

in your opinion what is the best tool for this job?

I'm leaving it wide open by not telling how we have been doing it.
Suffice to say I don't believe our current method is up to the tolerance.


TIA

I have piece that has a groove cut into the ID in order to take a snap ring to retain the guts of the assembly.

I'm not seeing this. This groove is internal to what? How do you get the snap ring in there?

The spec for the groove ID is 0.330"+/- .001"
thickness of the groove is a ref dimension of .019"

I think this is what's confusing me. How can a groove have an ID? And a thickness? Do you mean just diameter and width?

There are things like this (http://www.swissmann.com/Model%20Q-40.htm) for measuring internal grooves, but I've never found them to be very repeatable, certainly not with a +/- .001 tolerance.

A 0.0508mm tolerance witdh for a snap ring groove? That sounds a bit tight, but anyway: If you can fit it into the groove I would go for a three point micrometer... or why not a CMM. Both of those would also catch a deviation in roundness.

I share the confusion Jim mentioned, though: Could you provide us with a drawing?

/Claes

I agree with Jim,
I have used (tried) alot of gages for the exact same type of measurement
(snap ring groove down inside a bore) and most will not give enough repeatability to hold a +/- .001.

I have have tried metrology puddy and measured grooves on a comparator,
(based off an accurate measurement of the ID)
not bad if your groove is being cut by the same tooling as the ID.

Section and use a comparator and/or height gage is another option,
again based of an accurate ID measurement.

The groove thickness is too small for most CMM probes , it also depends on how far down the groove is in the bore.

I'm going back a couple of years, if anything else comes to mind... I let you know.:confused:

Ed

hmmm... I guess I'm calling things out in this company's somewhat odd nomenclature.

Can't do a drawing. only the CAD guy can change drawings, so I can't remove secret secret info.

try to picture this:

you have a cylinder with a bore down the length. The bore is .291" - .293" in diameter.
.063" down from one end, a groove is cut into that ID.
The diameter of that groove must be .311" - .313".
The width (height?) of that groove is .019".
This groove is accept an internal snap ring.

Does that make more sense?

Why it's +/- .001"? Because it was overdesigned but now we're stuck with it.

Why it's +/- .001"? Because it was overdesigned but now we're stuck with it.

I hate to say it, but I don't think there's a reliable way to measure it. If this is for an outside customer, it might be helpful to find out how they measure it. If it's an internal thing, you need to get a design engineer to tell you how it should be measured or change the drawing to something more realistic.

I hate to say it, but I don't think there's a reliable way to measure it. If this is for an outside customer, it might be helpful to find out how they measure it. If it's an internal thing, you need to get a design engineer to tell you how it should be measured or change the drawing to something more realistic.

I was afraid of that.
Our customer knows that the tolerances are crazy, and on more than this one dimension, but they won't allow us to change. Too much cost for them to revalidate the finished assembly.

We're in in the process of designing a new part to replace this one and we're making the tolerances a lot more reasonable. But that's going to take a while.

Ederie mentioned sectioning and measuring on a comparator. Actually that's how we do first article. But we're trying to avoid that for in-process.

May I suggest you contact the engineers at Truarc Retaining Ring http://www.truarc.com/contactus.php and ask.

This is the successor company to Waldes Kohinoor, originally based in Long Island City. Waldes created the retaining ring industry during WWII.

I am aware Truarc used to sell an offset tool for cutting internal ring grooves. It would seem to make sense they know how to measure the groove.

May I suggest you contact the engineers at Truarc Retaining Ring http://www.truarc.com/contactus.php and ask.

This is the successor company to Waldes Kohinoor, originally based in Long Island City. Waldes created the retaining ring industry during WWII.

I am aware Truarc used to sell an offset tool for cutting internal ring grooves. It would seem to make sense they know how to measure the groove.

Done.
Thanks Wes.

The groove thickness is too small for most CMM probesYes, for most probes, but not all. I've had a few probes custom made over the years... Including one that could handle this task. See the enclosed picture

/Claes

Hi Discordian,

If you could get an accurate measurement of the ID (using deltronic pins), then lay the part on it's side.

Use a height gage with with an indicator (graduation .00005") find the low spot on the ID, zero the height gage/indicator, and then lower the indicator tip into the ring groove finding the low spot, multiply the difference by 2 and add to the ID diameter.

I checked our indicator tip and the diameter was aprox .039". Since the width of your groove is a reference dimension of .019" it would not hurt to widen this by .001" or so, for the tip to fit in.

I would then use Ederie suggestion of metrology puddy to verify that that the width of the groove is consistant, so I am not hitting a high or low spot, inside the groove, with the indicator tip.

You also mentioned cutting the part for a first article. If the ID is manufactured with the same tool as the groove. Could you not use the first article dimension on the ID dimension (with deltronic pins again) to determine the exact offsets you need to adjust the groove to stay in tolerance? Then you could base your groove ID off of the ID and adjust accordingly to the ID.

Brad

Done.
Thanks Wes.Were the folks at Truarc of any use?

Were the folks at Truarc of any use?

send a message via their web site - no response yet. But we do buy a few parts from them so if I don't get anything back I'll drag our purchasing guy into the action.
I'm going to try the same with our other supplier of these.

Just trying to keep this simple....


IMHO Will the customer allow you to (after machining the groove) to peform a type of fit form function verification by just inserting the correct size mating ring into the groove and check for proper seating?

In other words will your customer allow you to write this into your procedures as the verification of the groove dimensions?

Just trying to keep this simple....


IMHO Will the customer allow you to (after machining the groove) to peform a type of fit form function verification by just inserting the correct size mating ring into the groove and check for proper seating?

In other words will your customer allow you to write this into your procedures as the verification of the groove dimensions?

We could probably do that.
But I'd really like to be able to measure so I can help show to the chief engineer whether or not our process is capable of +/- .001" on that dim.

We could probably do that.
But I'd really like to be able to measure so I can help show to the chief engineer whether or not our process is capable of +/- .001" on that dim.
What did you learn so far?

What did you learn so far?

...that the customer's statistician is on our side because he convinced the project manager that it is a pointless dimension to measure on anything beyond first article.

...that the customer's statistician is on our side because he convinced the project manager that it is a pointless dimension to measure on anything beyond first article.I'm disappointed. I was really curious about an efficient method or tool to do the job Once you raised the topic, it was like one of those "worm tunes" you just can't get out of your head.

I'm disappointed. I was really curious about an efficient method or tool to do the job Once you raised the topic, it was like one of those "worm tunes" you just can't get out of your head.

I've faced this situation many times, and I'm pretty sure that trying to measure an internal groove such as the one in question, to the precision specified, isn't practically possible. While Discordian says that the customer is willing to forgo all but first-article inspection of the feature, if you can inspect it once, you can inspect it twice. As we've often said here, the best way to deal with this sort of thing is at the front door, and not when an inspector, probably faced with time constraints, is scratching his head and trying to figure out a way to defy the laws of physics.

Our last thought before it was determined not to measure in process was to modify a bore gauge by grinding down the the three "fingers" so they would fit into the groove.

Does the snap ring protrude into the bore after assembly?
If so, scribe a line across it, and document the Id to OD dim., pop it in the part and measure the ID. add the the two ring wall thickness (Id to OD dims) and that should be your snap groove dia. You could also have a functional gage made to do the same thing that could be checked with a CMM or even plug gages for in-process.

Does the snap ring protrude into the bore after assembly?
If so, scribe a line across it, and document the Id to OD dim., pop it in the part and measure the ID. add the the two ring wall thickness (Id to OD dims) and that should be your snap groove dia. You could also have a functional gage made to do the same thing that could be checked with a CMM or even plug gages for in-process.

There might be any number of ways to measure the feature; the problem is the tolerance.