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angle and its true position
- Thread starter pawek
- Start date
PeterStock
Mechanical
Position tolerance should be applied to the slot width and length, not a locating angle. If your "slot" has a angular dimension, I think a profile tolerance may be better, please post a sketch.
Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services
Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services
Please post a sketch and state which standard you're working to as I'm not sure I understand your questions.
Certainly position controls can be used with slots, but I'm not sure what you're trying to do with the angle.
Generally the position FCF's are based on the overall length and width of the slots, I'd think the angle would be basic.
Certainly position controls can be used with slots, but I'm not sure what you're trying to do with the angle.
Generally the position FCF's are based on the overall length and width of the slots, I'd think the angle would be basic.
Posting guidelines faq731-376 (probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484
What is Engineering anyway: faq1088-1484
- Thread starter
- #5
If you have a copy of the Y14.5 standard, look at Fig. 7-16 (or Fig. 6-14 of the 1994 edition). Is that a similar situation to what you are asking? That is applying a position tolerance to slots that also have an angle...
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
pmarc
Mechanical
- Sep 2, 2008
- 3,248
J-P,
I would not say 7-16 is similar situation to this case because walls for the slots on 7-16 are nominally parallel. This allows using positional tolerance.
For OP's case I would suggest applying profile of surface callout to whole outline of the shape (maybe with ALL AROUND symbol attached to the leader of FCF). IMO angled walls can not be considered as a feature of size and positional tolerance should not be applied here.
I am starting to worry that can of worms entitled 'Feature of size definition' has just been opened again
I would not say 7-16 is similar situation to this case because walls for the slots on 7-16 are nominally parallel. This allows using positional tolerance.
For OP's case I would suggest applying profile of surface callout to whole outline of the shape (maybe with ALL AROUND symbol attached to the leader of FCF). IMO angled walls can not be considered as a feature of size and positional tolerance should not be applied here.
I am starting to worry that can of worms entitled 'Feature of size definition' has just been opened again
SteveMartin
Mechanical
I don't think position is appropriate here. Maybe the whole slot could qualify, but it's not clear to me what a position tolerance attached to this dim would mean. Profile's out too, unless the angle dimension is made basic (no indication from OP whether that would make sense). Without more understanding of the other unshown elements of the drawing I'm inclined to just leave the angle dimension alone with no added gtol.
Belanger,
I don't have the current standard in front of me, but can you double-check that 6-14 is the figure you mean to reference for the 1994 version? It doesn't seem applicable to me, showing profile between two points.
Belanger,
I don't have the current standard in front of me, but can you double-check that 6-14 is the figure you mean to reference for the 1994 version? It doesn't seem applicable to me, showing profile between two points.
Check that -- it's Fig. 5-14 of the 1994 standard. (Thanks Steve!)
But yeah, if the OP is talking about a slot that has a varying width, I'd probably steer clear of using position.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
But yeah, if the OP is talking about a slot that has a varying width, I'd probably steer clear of using position.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
If any of us have dealt with a slot in a molded part, for instance, which will likely have draft on the walls of the slot & if we have applied a position tolerance under a "+DFT" or "-DFT" size dimension (see Y14.8-2009 sect 3.6.1 (pg 8) and figures 3-6 & 3-7) then we have really done the same thing pewex is asking about... Yes, the included angle of pewex's wedge appears to be much bigger than a draft angle and as the included angle gets larger and larger position is possibly less and less "attractive", but I think a lot of us dealing with drafted features have applied position to cones and wedges. I think the next edition of Y14.8 should clarify what such a position tolerance means for a drafted feature then maybe an extension to cones and wedges with greater included angles would be logical enough..?
A 1) wedge or 2) cone is now sanctioned by Y14.5-2009 as a datum feature, which would have a "wedgical" :^) or conical datum feature simulator, with the datum being 1) a line (the wedge's apex) on a plane (the wedge's center plane) or 2) a point (the cone's apex) on a line (the cone's axis)... If cones and wedges have axes and center planes when used as datum features then is stands to reason that those feature elements could have a position tolerance applied to control them.
Especially since center planes on even a normal slot are not so easy to find (cmm software programmers provided capabilities for cylindrical features pretty well, but not yet for slots, "slabs", cones or wedges), I agree with those that have said that a profile tolerance, with basic dimensions to define the center of the zone/true profile would probably be better in this case... At least until software is quite a bit better and standards advance a bit more.
Dean
A 1) wedge or 2) cone is now sanctioned by Y14.5-2009 as a datum feature, which would have a "wedgical" :^) or conical datum feature simulator, with the datum being 1) a line (the wedge's apex) on a plane (the wedge's center plane) or 2) a point (the cone's apex) on a line (the cone's axis)... If cones and wedges have axes and center planes when used as datum features then is stands to reason that those feature elements could have a position tolerance applied to control them.
Especially since center planes on even a normal slot are not so easy to find (cmm software programmers provided capabilities for cylindrical features pretty well, but not yet for slots, "slabs", cones or wedges), I agree with those that have said that a profile tolerance, with basic dimensions to define the center of the zone/true profile would probably be better in this case... At least until software is quite a bit better and standards advance a bit more.
Dean
pmarc
Mechanical
- Sep 2, 2008
- 3,248
Dean,
Do you know why there is not a single example in Y14.5 that would show position tolerance applied to an angle dimension?
Isn't position of conical / "wedgical" features common enough in reality to deserve showing on at least one figure in the standard?
I am asking not only by curiosity, but also because I have really no idea if such callouts are legal or not. Since there is nothing in Y14.5 (and as far as I see in Y14.8), I have nothing that would scatter my doubts. Is there any other document that could help?
Do you know why there is not a single example in Y14.5 that would show position tolerance applied to an angle dimension?
Isn't position of conical / "wedgical" features common enough in reality to deserve showing on at least one figure in the standard?
I am asking not only by curiosity, but also because I have really no idea if such callouts are legal or not. Since there is nothing in Y14.5 (and as far as I see in Y14.8), I have nothing that would scatter my doubts. Is there any other document that could help?
CheckerHater
Mechanical
pewex,
Could you get away using linear dimension instead of angle?
(The picture is intentionaly incomplete)
Could you get away using linear dimension instead of angle?
(The picture is intentionaly incomplete)
- Thread starter
- #14
CheckerHater,
IMO your proposition sounds good according to Y14.5
Anyway I decided to not use true position, but locate slots on parts perimeter by toleranced angles. Slots are defined by +/- angle like it is on my sketch and controled by +/- radius.
The question is still open. I didn't find the answer in any document I know.
Thank you all gentlemen for quick response and I look forward to hearing some good news from you.
IMO your proposition sounds good according to Y14.5
Anyway I decided to not use true position, but locate slots on parts perimeter by toleranced angles. Slots are defined by +/- angle like it is on my sketch and controled by +/- radius.
The question is still open. I didn't find the answer in any document I know.
Thank you all gentlemen for quick response and I look forward to hearing some good news from you.
pmarc,
You're quite right that Y14.5 and Y14.8 don't really provide direct support for a position tolerance for cones or wedges. I also don't know of any other standard that would help.
I think it's logical enough and could be done, but unless/until a new revision of either Y14.5 or Y14.8 supports it better, maybe with a flag note to explain that the tolerance applies to the cone's axis or wedge's center plane..?
pewex,
Toleranced angles don't mean much... I hope you might reconsider profile of a surface. I understand that we're all operating with suppliers that may not be comfortable with profile though.
Dean
You're quite right that Y14.5 and Y14.8 don't really provide direct support for a position tolerance for cones or wedges. I also don't know of any other standard that would help.
I think it's logical enough and could be done, but unless/until a new revision of either Y14.5 or Y14.8 supports it better, maybe with a flag note to explain that the tolerance applies to the cone's axis or wedge's center plane..?
pewex,
Toleranced angles don't mean much... I hope you might reconsider profile of a surface. I understand that we're all operating with suppliers that may not be comfortable with profile though.
Dean
powerhound
Mechanical
According to the 94 standard, it doesn't seem that you can position a cone because a conical shape does not meet the definition of a feature of size and only a feature of size can be positioned.
Of course, I've been wrong a lot lately so feel free to correct me while I wallow in my own inadequacy.
Powerhound, GDTP T-0419
Engineering Technician
Inventor 2010
Mastercam X5
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
Of course, I've been wrong a lot lately so feel free to correct me while I wallow in my own inadequacy.
Powerhound, GDTP T-0419
Engineering Technician
Inventor 2010
Mastercam X5
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
pmarc
Mechanical
- Sep 2, 2008
- 3,248
Dean,
Thanks for reply.
It seems I would have to wait another 10 years or more until proper examples appear in updated revisions of Y14.5 or 14.8 and clear my doubts.
powerhound,
I agree with you that feature of size definition in Y14.5M-1994 is not including conical features. IMO modified 2009 definition is not doing it as well, but this is another story.
Actually I believe whole confusion stems from inprecise FOS definition in the standard. I think such essential concept for GD&T should be supported by at least several graphical examples that would help in better understanding the intent of Y14.5 committee members.
Without this we have a situation that every GD&T user has its own interpretation of FOS definition and noone knows for sure what is really going on.
Thanks for reply.
It seems I would have to wait another 10 years or more until proper examples appear in updated revisions of Y14.5 or 14.8 and clear my doubts
.powerhound,
I agree with you that feature of size definition in Y14.5M-1994 is not including conical features. IMO modified 2009 definition is not doing it as well, but this is another story.
Actually I believe whole confusion stems from inprecise FOS definition in the standard. I think such essential concept for GD&T should be supported by at least several graphical examples that would help in better understanding the intent of Y14.5 committee members.
Without this we have a situation that every GD&T user has its own interpretation of FOS definition and noone knows for sure what is really going on.
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