Profile tolerance for an array of slots 3

[kkeenn]

I have an array of slots that are defined by basic dimensions (Radius, length) and a profile tolerance. I would like to dimension and tolerance the pattern but am not sure how.

If it was a hole pattern I could write 300X .25+-.004 with the attached positional tolerances and basic dimensions identifying the pattern. How do I add a profile tolerance to multiple features?

 

[pmarc]

You fully dimension one slot using basic dimensions and place nX prefix in front of profile FCF. In the attachment you can find example from Y14.5-2009 standard (forget about composite profile FCF if you are not interested in refining orientation of the slot relative to a datum).
If the slots are of regular shape (so that the center is easily identifiable, just like in case of elongated holes), spacing within the pattern of the slots may be defined by basic center-to-center dimensions.

http://files.engineering.com/getfil...f44-6d811b711ef4&file=fig_8-21_Y14_5_2009.png

 

[CheckerHater]

So, if I call out 300X [PROF|.010|A|B|C], will it control profile of any single slot 300 times, or combined profile of all 300 slots simultaneously?

 

[fsincox]

That is the idea

 

[MechNorth]

Simultaneously, as they are a pattern based on the quantity callout.

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[dingy2]

Don't know why anyone would want to apply a profile (line or surface) on a pattern of slots. At least if you use positional at MMC, one can develop a checking fixture and truly check them simultaneously. Why profile rather than positional??

Dave D.

http://www.qmsi.ca

 

[MechNorth]

From a design perspective, Dave, slots are generally clearance features (i.e. the center of the slot isn't the critical aspect). So, controlling the surfaces (as with a Surface Profile) makes more sense. Position at MMC gives you a single goundary for the slots, but profile will give you both the inner and outer boundaries. Just thinking quickly here, but why couldn't you hard gage the inner & outer boundaries for a profile control?

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[pmarc]

Jim,
Thinking quickly too, I would say you could only hard gage inner profile boundaries for slots and outer profile boundaries for pins (that is boundaries that lie outside of material of a feature). The other boundaries are not verifiable by hard gages.

 

[flash3780]

You can combine a profile tolerance with a positional tolerance like so:

http://www.tec-ease.com/gdt-tips-view.php?q=129

Using that technique, I think you can tolerance a pattern of slots just as you would a pattern of holes.

 

[pmarc]

This is another (third) option, Frank.

 

[pmarc]

Ah, my apologies flash3780, I thought it was fsincox who posted the reply with link to Tec-Ease's tip. Or maybe you are Frank too ?

 

[MechNorth]

Pmarc,
I'm fuzzy minded lately from helping kids with high school exams ... seemed a lot easier when I did the material first time around! IF you had a no-go gauge for the outer boundary of a profile control, wouldn't that work? I.e. the gage element cannot fit in the slot or else the slot is too big. Of course, the outer boundary gauge may have to be in segments to check each portion of the slot. Perhaps it is that most people tend to think of just the MMC boundary as hard-gaugeable, but G/NG gages have been around for a while; are they not also hard gauges? Perhaps I am mistakenly including them under the banner of hard gauges?

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[CheckerHater]

If you think of your functional gage as GO gage, and separate pin as NO GO gage, the inspection is do-able, but is it in line with any GD&T call-out?
Or, better yet, which GD&T call-out will better describe this inspection procedure?

 

[pmarc]

Jim,
Let's say for simplicity that we have only one hole defined by basic diameter 10 and equal bilateral profile tolerance of 0.1 wrt typical DRF A|B|C| and we want to verify by no-go hard gage pin of diameter 10.1 that surface of the hole does not fall outside of outer boundary, ok?. So imagine two cases:

1. The hole's surface is everywhere within profile tolerance zone. The part will not fit onto your no-go gage, so it is OK. Right?

2. The hole's surface is everywhere within profile tolerance zone, except one small area where it falls outside of OB. The part does not meet print requirements, but will it fit onto gage? No. In other words gage check gives the same result for good part and bad part. That is why the method cannot work.

I made one mistake in my previous comment though. I implied that inner boundary for external feature (e.g. pin) is not verifiable by hard-gage. This is wrong. It can be verified by no-go gage. The only boundary that cannot be fully checked by any hard gage is the outer boundary of internal feature (hole, slot, etc.).

 

[MechNorth]

Pmarc,
I understand your example, and again it is a good one. I like that you challenge me because it makes me rethink things and improve my communication. I was never taught to use a no-go gauge as a blind tool though; part of hard-gauging is still the visual aspect, so if any gap extends beyond the no-go gauge, the part would fail. One of the problems with hard-gauging of any kind is that it is always a subjective and skill-based process. Of course, a good inspection protocol document would establish the proper how-to for any gauge ... not that many people develop them though.

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[dingy2]

Jim:

I agree that slots are clearance and the word "boundary" should apply when using positional. The virtual condition boundary will give us inner boundary shape, location and orientation. Love to see those profile hard gauges for a pattern of holes but I certainly can make a positional gauge at MMC (boundary).

Dave D.

http://www.qmsi.ca

 

[bxbzq]

pmarc,
I'd say IB of external feature can not be verified by no-go gage either. Imagine a similar case as you depicted but with a pin, some areas of the pin's surface is out of profile tolerance zone (smaller than low limit) and other areas is within profile tolerance zone. The part does not meet spec but it is a "no-go".

 

[pmarc]

You are right, bxbzq.

As usually, the first thought is the best. I incorrectly assumed that a different concept can be transferred to this one, thus my additional unnecessary comment.

 

[fsincox]

The requirement to state "BOUNDRY" has been dropped and is an option now in 2009.
Frank

 

[GordyRC]

As you all can see there are multiple ways of controlling size and location of a pattern of slots.
First of all, I see no mention of the functional engineering requirements of the pattern of slots.
So, I would ask, what are the requirements?????
1) Does the pattern of slots interface with an equal nummber of "male" features?
If "YES" then I ask;
1a) Are the male features similar in shape, as in, elongated?

If "elongated", then the entire perimeter of the slot is considered to be a mating
surface. In this application either profile of a surface or positional tolerance is
applicable. Either control will define an inner boundary (virtual condition) which can be
checked with a functional gage. The outer boundary can not be verified with a functional
gage.

2a) Are the male features cylindrical pins?

If "cylindrical" such as a pin, then it is likely that the width inner boundary is more
critical than the slot length inner boundary. Applying a profile tolerance would apply a
constant width tolerance zone around the perimeter of the slot(s). While this is not
technically incorrect, it is likely overly restrictive based on the functional
requirements. What I mean is that the slot can likely tolerate more boundary tolerance
in its length than it's width, but the profile control is not capable of a variable
tolerance zone length vs. width. Positional tolerancing (boundary concept) is capable and
also benefits from the additional tolerance based on slot size departing from MMC(bonus
tolerance).

If "NO".......the slots do not have mating male features then there is not a functional interface to consider. The slots might be weight reduction, or they might be ventilation slots.

2c) If there is no mating condition for the slots and they are weight reduction or
ventilation then the engineering requirements are much different from the scenario above in
2a and 2b. If "venting" for example the size may be of more importance to generate the
combined minimum air flow. The location of the slots is secondary. In this scenario I would
suggest controlling size with a size dim and related size tol, and use positional tol to
control location. As in above, a functional gage could check the inner boundary of the
slot regardless if profile or position is used.

While this only covers some of the possible engineering scenarios, I hope it sheds light on the importance of considering the engineering/functional requirements before applying geometric controls.

Regards,
Gordy