Different profile tolerances on segements of profile 2

[TrailMaker004]

I have an application of profile tolerancing on a gage. There is a cavity in the gage where portions of the inside profile are very critical, and the remainder much less so. In the attached dwg, the portions designated y-z and w-x are the critical areas held to .0004 profile. The remainder is essentially clearance (held to .005 profile). The cavity features are constrained only to datum surface A, which is the plane perpendicular to this cavity. Rotation and location of the cavity are unimportant to the application.

My concern, and what is important to us is this: the (3) profile segments indicated by the w-x and y-z extents must be correctly related to each other (within the .0004 profile requirement) That is to say, they cannot just be correctly machined within their individual extents. I do not want to hold the remainder of the features to the .0004 requirement just to ensure that. Nor do I want to impose additional datums that would be unnecessary to the application because either of these would make this more difficult and expensive to mfgr.

The way I see this callout presently however, it would allow the (3) segements to "float" independently of each other in the X-Y plane both in location and rotation (at least from an inspection point of view). Am I incorrect in that?

 

[CheckerHater]

You can simply “draw” your tolerance zone on the drawing as you like it.
Check out ASME Y14.5-2009 Para. 8.3.2 together with Fig. 8-11.

 

[KENAT]

To my reading of it what you have works. I don't believe it allows the specified segments to float more than the .0004 specified.

You could perhaps argue it allows a small 'step' where the tighter and looser zones meet but if you've assigned your tolerances correctly then functionally that probably shouldn't matter.

(I'm dubious on the use of Y-Z twice though, I'd probably assign separate letters.)

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[CheckerHater]

KENAT,
I think you are right. Also Y and Z - good catch.
It looks like OP is concerned that drawing, when legal, may still confuse the people in the shop.
So my thinking was towards “enhancing” the presentation, so the shape of tolerance zone could be clear to everybody.

 

[axym]

TrailMaker004,

There is a default rule in the Y14.5 standard called Simultaneous Requirements. I can't remember the actual text, but here is the general idea. If more than one feature control frame references the same seqence of datum features, any translations/rotations of the datum reference frame must be the same for all of them. In other words, the tolerance zones for those FCF's form a "composite pattern" and cannot shift around relative to each other.

In your application, all of the Surface Profile FCF's reference only datum feature A and so would be linked by Simultaneous Requirements. So they cannot float independently of each other.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[TrailMaker004]

Thanks everyone for all your input. I had not been aware of the simultaneous requirement rule. Having just read it in section 4.19 Y14.5Y 2009, I am still not sure I have my head completely around it, but I can see where it applies in this application.

 

[dtmbiz]

Trail....

The profile control as presented is confusing as to intent. As it shows on the drawing there are 2 profile
tolerances which the smaller tolerance overrides the larger since the same datum reference frame applies to both. It states that the profile tolerance is .0004 with the .005 pretty much meaningless.
Add to that the combination of two “between points” under the .0004 frame; and add to that “two” points with the same name Y and Z; well that is certainly a setup for misinterpretation.

The profile control arrow is important as to where it actually lies on the geometry. It is not the sequence of the letters but the position of the arrowhead that indicates where the tolerance applies.

As presented the W-X which should “not be a dash” but the “between symbol” with arrowheads, would apply from the X point all around the profile counter clockwise to W; applied to the top portion.

The Y-Z is really trouble because there are two sets of points. No telling what that applies to other than it is going to apply to bottom portion of the profile.

To clear this up, 2 profile FCF’s should be used to indicate where the .005 and where the .0004 apply.
Only one set of “between” points below each FCF; use the correct “between symbol”; and make sure the profile FCF leader arrowhead is located on the profile to the correct side of the between points.

Simultaneous requirement means that those features that meet the standards definition; same DRF with same material conditions; boundary conditions; and related with basic dimensions must pass inspection at the same time without moving the features around in the inspection setup; or that attribute gage(s) must verify those features at the same time; unless drawing notation would override the requirement. (SEP REQT)

Caution though; if the profile where made to be a composite control; then the simultaneous requirement does NOT apply, unless drawing notation would apply the requirement. (SIM REQT)

Keep it simple with: two FCF’s; FCF leader arrowhead position pointing to the intended side of the point for which the profile tolerance is intended; NO two points designated the same letter.

~dtm~

 

[Belanger]

There's also the matter of whether all the "between" stuff applies to both feature control frames. I se it as applying only to the bottom FCF. Thus, the top one only covers the simple curve on the right-hand side, unless you use the "all around" symbol to impose the top FCF on the entire perimeter. (The lower FCF will still trump the "all around" in the designated portions, however.)

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

http://www.gdtseminars.com

 

[dtmbiz]

I agree with your post JP as far as how to interpret the dwg as is. IMO the "shortcut" to use only one FCF where with only one leader creates the problem. As I read it with one leader pointing to one curve.... smallest tolerance wins.

I understand that certain softwares make a "talking point" figure / dwg difficult to delineate exactly, however the delineation is important in regard to the profile control leader.

I have never seen an attempt to use 2 between symbols with a single FCF. That doesnt make practical sense to me.

Anyway, as much as I have seen; it certainly is small compared to what there is to see

 

[TrailMaker004]

OK, thank you. Please help me clarify:

1) Ok, I got the part about using a different letter set for each specified area, and that "between" arrows must be used (not dashes - our bad). As I stated in the OP, only the profile areas designated are critical to the application,and that all else is clearance. To define for sake of this conversation, those critical areas would be the R.0075 (2 plcs) in the areas currently called Y-Z, the R.050 (2x), R Dim C (2x) and R Dim B in the segment currently called W-X. I am thinking the the order specified (Y-Z & W-X) would correctly dsignate those areas - moving clockwise for the Y-Z, and CCW for the W-X.

My original thinking was that the .005 profile requirement was to include the entire perimeter (maybe the all around symbol should have beem used?) superceded however in the 3 critical zones (only) with the .0004 requirement.

2) Regarding the use of the "and" for including the W-X and Y-Z segments in the .0004 requirement, are you saying that if I have multiple portions of a larger profile, each held to the same tighter tolerance, I have to have individual FCF's for each? Seems redundant, especially since we have another design coming through up where there will be 4 separate segments of a larger profile necessarily held to the same tighter tolerance.

 

[Belanger]

Regarding #2 -- you may use "and" for the W-X and Y-Z segments; no need for separate FCFs.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

http://www.gdtseminars.com

 

[dtmbiz]

Trail...

Not sure you are picking up on a key point. That is that the arrowhead as shown for the lower segment is from the X point and then "counter clockwise" to W. It is really not a matter of clockwise or counter clockwise or sequence of w to x or x to w.
It is from one point to the other indicated by the arrowhead placement.

The dwg shows two slightly separated FCFs with one leader from the top FCF. If this is not a composite FCF then each FCF should have its own leader(s). If it is a composite FCF then the simultaneous requirement does NOT apply unless you add notation.

If it is a composite FCF then both FCF's should be sharing a horizontal line for each. (the lower horizonal of the top FCF and the top horizontal of the lower box)

Whether or not composite FCF, the dwg shows one leader shared by both.

X to W in the counter clockwise direction "includes both sets of Y and Z points" (this is very confusing). Interpretation can be that from X to W (which does NOT include the curves between X to W on the lower portion of the drawing because of arrowhead placement) would be a .0004 profile control from X to W; with only the curve the leader points to as .005 tolerance which is overridden by the .0004.

To place a couple more FCF's with the leaders directed to the correct surfaces would clear things up. Really... you aren't hand drawing these FCF's so why is it a problem?

The redunancy comment makes me think you are trying to take a "shortcut". It will be a great benefit to all who interpret the drawing if you would just add the needed FCF's for clear understanding of which tolerance applies where.

JP
I have a little difficulty agreeing with you that "and" can be used because there is only one leader being used. If additional leaders were added to clear up where the Y to Z applies then it would clear up some questions, but not all questions as to what tolerances are being applied where.

 

[TrailMaker004]

dtmbiz:
Thanks for your feeedback. The reason I questioned having to repeat the FCF for each segment was not corner cutting but because the dwg you are seeing attached here is a blow up of a blow up detail . This view on a std 8 x 11 1/2 (typically size sent for quoting)is quite small even in the blow up detail view. Adding 2 more FCF's with leader lines included along with all the basic dim's would crowd an already very crowded dwg, perhaps making it even more difficult to understand. Also,we had already released several product dwgs utilzing the "and" approach where there were multiple areas within a profile held to tighter tolerances. I was just borrowing a concept I had already seen used sucessfully for more than a year with no complaints or repercussions. I am not saying now that it was necessarily correct, but that's why I'm putting this out there. Y14.5 is very brief in describing limited segment of profile (8.3.1.5), gives few examples, and those examples are fairly elementary. Additionally I have another gage dwg coming down the pike that will have several more profile segments than this one. Adding inidividual FCF's for those will make it really crowded, so the "and" approach was particularly appealing there.

 

[dtmbiz]

Trail...

Understood...

If you use the "and" method; hope you use more than one leader.
One leader at least to the surface(s) for each set of between points would be the minimal IMO. Two sets of between points=2 leaders.

Good luck [Smile]

 

[MechNorth]

Use two leaders; one with an all-around symbol for the .005 control, and the second for the .0004 control with the arrowhead in the intended segment. "and" is fine, or stack them W-X, then Y-Z below it. As indicated above, graphically show on the drawing how you want the tolerance zones to transition.

There are other things to be fixed too; quantities in reference brackets mean "ignore this"; TYP isn't allowed; what is the datum symbol base doing on the top of the page with the 7 in a triangle? Quantities generally precede rather than follow.

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

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[TrailMaker004]

MechNorth:
Just to clarify: are you saying use mulitple leaders for the .0004 requirement? That could get to be an awfully busy looking print.

Also, by qty's in brackets, you mean the 2X next to the R.0075, remove the parentethes? And by "..qty's generally precede.." you mean the 2X should be to the left rather than to the right?

The 7 in the triangle is a dwg note indicator that means see that note for further definition. The datum symbol indicator is poiniting to the .0002 parallel requirement.

 

[MechNorth]

TM4,
Maybe so, but it is clear then. Otherwise there are two routes for each of the "between" zones, and you could end up with the wrong ones selected ... your choice of clarity or quick drafting.
Yes, quantities generally precede the item.
Round brackets ( ) mean "reference" which means that it can be ignored; if it can be ignored, then it can be removed from the print without impacting the end product. Is that the case here?
Why do you have a datum feature symbol without a datum feature indicated? Something amiss there.

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

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com