GR&R for Dowel Pin Holes Using Deltronics Pins

S

SPC_Newbie

#1
Given most of the total tolerances on dowell pin holes we do is .0005 inches, what do you use to measure them?

We're using deltronics pins (.0001 increments) which I'm pretty sure is what most people do.

Pactically, with these numbers am I dead before I even start? If we have any variation in measurement it is likley to be 1 pin or .0001 - that's already 20% of the spec before we start.

If this is the case, what is typically done? I'm guessing this would be one of those times you share results with the customer and come up with alternative solutions? I'm sure many of you in precision maching have already addressed this very typical scenario - please share your experiences!

I am interested in both keeping parts in spec and also process monitoring.

I did actually run this GR&R (see attached) but still thought the questions are fair ones to ask. Comments on my results appreciated too - still learning!! :)
 

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Stijloor

Staff member
Super Moderator
#2
Re: GR&R for Dowell Pin Holes Using Deltronics Pins

Given most of the total tolerances on dowel pin holes we do is .0005 inches, what do you use to measure them?

We're using Deltronics pins (.0001 increments) which I'm pretty sure is what most people do.

Practically, with these numbers am I dead before I even start? If we have any variation in measurement it is likely to be 1 pin or .0001 - that's already 20% of the spec before we start.

If this is the case, what is typically done? I'm guessing this would be one of those times you share results with the customer and come up with alternative solutions? I'm sure many of you in precision machining have already addressed this very typical scenario - please share your experiences!

I am interested in both keeping parts in spec and also process monitoring.

I did actually run this GR&R (see attached) but still thought the questions are fair ones to ask. Comments on my results appreciated too - still learning!! :)
Can someone provide some comments on the GR&R attachment?

Thank you very much for helping!!

Stijloor.
 

bobdoering

Stop X-bar/R Madness!!
Trusted Information Resource
#3
If you want to verify hole size, you can use a tenth set at 75% of the tolerance on the shop floor (which leaves you pretty much go/no go). Pins are MMC, so you do not detect any out of round. That may be just fine for dowel holes, its your call.

For SPC you must have more resolution, and one approach is to use an air gage. Remember, you are in millionths range, so you need to treat the measurement with kid gloves (clean gage, clean part, controlled temp, etc.) On top of that, you need to know what is the lobing in the hole - tri-lobal, bi-lobal, etc. - so that you can pick the correct air plug probe - 2 jet, 3 jet, etc.
 
S

SPC_Newbie

#4
OK - I've re-run the GR&R and I think we've done about the best we can do. In every case but one, when there was a 'range change' it was the same across the operators and thru the remainder of the study for that part. I suspect some sort of lag in the parts warming up in the shop (parts are 304 SS). I guess if there had been no (assumed) temperature effect we would have been almost perfect concerning EV?? :)

At any rate, attached is the data. The numbers seem good to me but the R Chart by Operator shows points as either Zero or Out of Control.

So, what should my take away be?

My SPC (or Study) results 'seem' better than my 'Product Spec' results! Not sure how this happens when I definitely have limited resolution.

All comments appreciated!!

(ps - still thinking about airgages longer term - we have a d2500 mahr/Federal - but MMC for dowel holes does make me think intuitively I may be ok with deltronics pins)
 

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S

SPC_Newbie

#5
Sorry to be a bother but is anyone available for a quick data review (above post)?

Thank you so much!!
 

Stijloor

Staff member
Super Moderator
#6
Sorry to be a bother but is anyone available for a quick data review (above post)?

Thank you so much!!
It's not a bother, but most of us have also a job to do, and we are not always available to respond. GR&R questions/issues are not easy stuff and we rely on a few Members who have the expertise to address the GR&R (MSA) questions.

Responses will come. Hang in there...

Stijloor, Forum Moderator.
 
S

SPC_Newbie

#7
Thanks for the update. In a certain way I guess I'm glad to hear that this stuff is not easy. I sometimes feel discouraged that I'm not able to put this stuff together yet but maybe that's not uncommon. Not that misery loves company or anything...:biglaugh:
 

Stijloor

Staff member
Super Moderator
#8
Given most of the total tolerances on dowel pin holes we do is .0005 inches, what do you use to measure them?

We're using Deltronics pins (.0001 increments) which I'm pretty sure is what most people do.

Practically, with these numbers am I dead before I even start? If we have any variation in measurement it is likely to be 1 pin or .0001 - that's already 20% of the spec before we start.

If this is the case, what is typically done? I'm guessing this would be one of those times you share results with the customer and come up with alternative solutions? I'm sure many of you in precision machining have already addressed this very typical scenario - please share your experiences!

I am interested in both keeping parts in spec and also process monitoring.

I did actually run this GR&R (see attached) but still thought the questions are fair ones to ask. Comments on my results appreciated too - still learning!! :)
Another quick bump!

Can someone help with this?

Please see file attached in Post#4. It contains the data.

Thank you very much!!

Stijloor.
 

Miner

Forum Moderator
Staff member
Admin
#9
I reviewed your data. The cause of your problem is the resolution of the Deltronic pins. This is apparent in the Range chart, which has a lot of zero values. The only non-zero values are out of limit. Since you have a lot of part variation, the spreadsheet says that the resolution is acceptable. However, compared to the tolerances, the resolution is inadequate. This has a ripple effect throughout the other calculations.

Was this study for a customer, or was it internal?
 
S

SPC_Newbie

#10
The study was conducted as a learning opportunity and gut-check for myself and as an example for a customer wanting us to be capable of doing GR&R. They requested we do studies on THEIR parts (unfortunately a limited selection of parts this time of year), even during this time of ramping our capabilities (I would prefer to hit as many gage families as possible across whichever parts we make that legitimately could benefit from GR&R). As such, they do wish to review these results. This is a key customer and one of several that really want us to develop our SPC program (and the main one for which I was hired to implement SPC in our precision machine shop).

I am still somewhat in the drivers seat as far as setting expectations but the further we progress the more locked in we'll be. In short, the more I know know, the more I can share up-front and steer expectations towards reality. Of course this means I need to have a good understanding of things as well. This forum has been GREAT in helping to get there - both GR&R and all kinds os SPC stuff.

The hardest part is I don't really have any peers to bounce things off of in just daily conversation to reinforce learnings. Often the first time the words come out of my mouth regarding a subject it turns out I am presenting to my company's owner! Funny how different things sound when you say them verus reading and writing about them :)

Thanks for listening to me ramble on ;)
 
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