Gage R&R on plating thickness - What do I use as the total tolerance?

B

billsfan

Hi guys!
I need to do a Gage R&R on plating thickness. The spec calls for .00035 min.
My question is, what do I use as the total tolerance?????
Thanks in advance for the help!!!
P.S. GO SABRES!!!!(Are you out there Batman?)
 
B

Brian Dowsett

Billsfan,
Why not do the study in the normal way and express measurement system variation as a proportion of total study variation (or use your process variation (6sigma)if it's known).

Regards

Brian
 
J

Jim Biz

Wouldn't want to point you in the wrong direction - but I can tell ou how we view it in our place...

All our plating specs seem to be print identified on a similar basis 3um or 5um MIN only- no max - how we approach that is to determinte what the final "fitup" dimension after plating is supposed to be and view that as our upper limit.

Hope this helps, What's a SABER anyway <grin>
 
J

Jim Biz

Oh now I know what a Saber is *GRIN* was going to ask ya why you were trying to gage the plating thickness on one - HA

As far as "Fitup" quite often when we see a print with a "Min" plating spec it is accompanied with a "Max" diameter after plate call out That gives us an idea of what can be used as a high/low for reading purposes .. But sounds like you have a good handle on where you want the readings to be.
 
B

billsfan

Brian & Jim,
Thanks for your help.
First, I should explain that this is not our process, it is one of our suppliers. I needed a gage R&R for PPAP requirement and our supplier called to ask what total tolerance to use on the Gage R&R form. This supplier did a small (30 pieces) capability study.

Brian, should I use 6 sigma of this small study? X bar chart from 30 piece study yielded a mean =.00044, sigma = .0000189 and range=.000031.

Jim, I'm not sure what you mean by;
"determining what the "fitup" dimension after plating is". The part in question is cylindrical and parts are added to both the inside and outside. I ended up using the spec itself (.00035) and ended up with a Gage R&R of 9.15%. I think that I'll use this and argue the merits at a later date!
And Jim, to answer your question: "What's a Sabre?" I'm refering to the Buffalo Sabres a National Hockey League team on the cusp of missing the playoffs!

Again all, thanks for your help!
Peace......out!
 
B

Batman

The only qualification I would add to Jim's post is that sometimes plating thickness has little to do with the feature tolerance. For example the plating may be .00035 min, and the feature tolerance is +/- .010. You won't have that much plating ever.

For billsfan, perhaps as an alternative to his mini capability, I would question the supplier and determine the absolute maximum plating expected from his process. The mini capability is for that batch only. He should be able to calculate this either from his current / time / mass values or maybe from long term data and determine a +3s. This could be established as an upper tolerance.

AND, I waited until today to answer this:
Who won in 13 seconds in overtime last night??? IN BUFFALO??? GO PENS!!!
 
D

Dawn

Don't forget-the Gage R & R is on your gage-not your parts. The gage hasn't been mentioned here so I'm a bit confused......
 
B

Brian Dowsett

If you know your historical process capability this could be used in the calculations. In this case just carry out calculations as per the QS9000(AIAG)book and you will get a figure for total gauge variation and one for part to part variation.
Plotting the results will hopefully give you tight control limits on the X chart, with lots of points out of control.

Brian
 
B

Batman

Yes Dawn, the R&R is on the gage. But you usually report a R&r as a percent of tolerance, and this is what billsfan was asking - what is the tolerance. Typical plating specs state some minimum, and no real maximum. In the case billsfan is speaking, theoretically electroplate could go forever, but there are some process settings that determine that you get at least a .00035 thickness, but with those settings what is the expected maximum plating thickness in the batch / process? This was one way to get some form of a tolerance to which one could compare the actual R&R.
 
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