Multiple Angle Dimensions (Equally Spaced)
Multiple Angle Dimensions (Equally Spaced)
(OP)
We have a customer that dimensions gussets welded to circular plates on a regular basis and we have come to an argument on their dimensioning scheme.
I have attached an example and am wondering if the 6X 60 Deg dimension for the 6 gussets is an accepted practice as the stack up doesn't make sense.
If a welder welded all of the gussets going around the plate at 60.5 Deg apart, he would be way out of tolerance when he welds the final gusset on. The dimension would be 57.5 Deg between the last gusset and the first.
-or-
Does this mean that the welder has to find all of the angles theoretically perfectly and he has +/- 30' off that?
I have attached an example and am wondering if the 6X 60 Deg dimension for the 6 gussets is an accepted practice as the stack up doesn't make sense.
If a welder welded all of the gussets going around the plate at 60.5 Deg apart, he would be way out of tolerance when he welds the final gusset on. The dimension would be 57.5 Deg between the last gusset and the first.
-or-
Does this mean that the welder has to find all of the angles theoretically perfectly and he has +/- 30' off that?





RE: Multiple Angle Dimensions (Equally Spaced)
Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: Multiple Angle Dimensions (Equally Spaced)
Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services
www.infotechpr.net
RE: Multiple Angle Dimensions (Equally Spaced)
"Good to know you got shoes to wear when you find the floor." - Robert Hunter
RE: Multiple Angle Dimensions (Equally Spaced)
I have seen 6X used too; that doesn't make it okay. It is incorrect to use it in this situation but like a lot of drawings that are illegally specified, the part can still be made and could possibly still work. Again, that doesn't mean the drawing is correct, because a second maufacturing run will likely yield a different result -but still be compliant to the print- and that may NOT work. Using EQUALLY SPACED is also incorrect because they will NOT be equally spaced, every gussett spacing will vary, the question is how much can they vary and still work. How can you justify both 5X and 6X being okay? One is incorrect and one is not. When you start getting into the "they know what we mean" mentality, you are setting yourself up for a big disappointment eventually.
Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: Multiple Angle Dimensions (Equally Spaced)
I agree that the 60° angle tolerances are cumulative, however, there are six of them. If the specification was 5X60°, the last angle could be out 2.5°. The "6X" means that all six angles must be within specification.
My point is a pendantic one, and I agree that basic dimensions and geometric position controls would make for a better drawing.
RE: Multiple Angle Dimensions (Equally Spaced)
thread1103-220265: How many angles are in a circular pattern?
KENAT,
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RE: Multiple Angle Dimensions (Equally Spaced)
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RE: Multiple Angle Dimensions (Equally Spaced)
Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group
RE: Multiple Angle Dimensions (Equally Spaced)
However, I argued this strongly last time and don't think I convinced anyone.
KENAT,
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What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Multiple Angle Dimensions (Equally Spaced)
"Good to know you got shoes to wear when you find the floor." - Robert Hunter
RE: Multiple Angle Dimensions (Equally Spaced)
I was just reading through the discussion that KENAT linked to. I must have taken some time on my responses there.
While cumulative tolerances do not affect the last hole in your series, they do affect holes in the middle. Adding two or three tolerances is not as bad as adding five or six tolerances, but you still are adding them.
For a given linear accuracy, angle tolerances to each of your features must get more accurate as the pitch circle increases. This gets very accurate very fast, even if all your tolerances are from the same reference point. This is the best reason to use GD&T positional or profile tolerances.
RE: Multiple Angle Dimensions (Equally Spaced)
RE: Multiple Angle Dimensions (Equally Spaced)
Why not box the 6X 60 degree angles to make them basic, attach some datums, and use a feature control frame to tolerize location in the tangential direction? That way, your gussets will be controlled for both location and orientation. No stack up at all!
RE: Multiple Angle Dimensions (Equally Spaced)
Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group
RE: Multiple Angle Dimensions (Equally Spaced)
Second thoughts forget it, we did this to death on the previous thread. To me if you have a circular pattern where you dimension all the angles with +- dimensions you end up with conflicting/ambiguous requirements.
KENAT,
Have you reminded yourself of FAQ731-376: Eng-Tips.com Forum Policies recently, or taken a look at posting policies: http://eng-tips.com/market.cfm?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Multiple Angle Dimensions (Equally Spaced)
I've done tons of drawings for a fabrication (weld) shop. True, there are AISC standards that leave drawing interpretation "loose". This is a matter of philosophy, and there is no "right" and "wrong" answer.
I would rather err on the side of being specific. Just because tolerances are loose, it's better to say just how loose. If it's rough, put a locational tolerance of .25 inch or so. Or .50. Then if there are problems, everyone is clear about what the standards for success are.
RE: Multiple Angle Dimensions (Equally Spaced)
Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group
RE: Multiple Angle Dimensions (Equally Spaced)
A linear array does not wrap around the way a pitch circle does. If I show six holes positioned around a pitch circle by 6X the angle, the final dimension value may be redundant, but not the tolerance.
RE: Multiple Angle Dimensions (Equally Spaced)
Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group
RE: Multiple Angle Dimensions (Equally Spaced)
This is sort of like discussing what sort of hammer to hit ourselves over the head with. We can have all sorts of opinions on the subject, but really, we shouldn't hit ourselves over our heads with hammers.
RE: Multiple Angle Dimensions (Equally Spaced)
"Good to know you got shoes to wear when you find the floor." - Robert Hunter
RE: Multiple Angle Dimensions (Equally Spaced)
- Dimension it with GD&T: Six dimensions, all basic, e.g. [6X 60°] with some geometric tolerance on the holes.
- Dimension it with a conventional tolerance, 6 angles: Six dimensions, e.g. 6X 60.0°±.5°
- Dimension it with a conventional tolerance, 5 angles: Five dimensions, e.g. 5X 60.0°±.5°, and one undimensioned gap
With the first method, nothing weird happens. Each hole is located according to the tolerance zone specified by the geometric tolerance.With the second method, because you've specified six angles, you have to measure six angles—you can't assume that if five are good, the part is good. For example, with actual angles of 60.1°, 60.1°, 60.1°, 60.1°, 60.1° & 59.5°, every angle conforms to the ±.5 tolerance and the part passes. But with 60.2°, 60.2°, 60.2°, 60.2°, 60.2° & 59.0°, only five of the six angles are valid, and the sixth is invalid. In effect, by calling out ±.5°, you're saying that you'll accept that deviation on any given angle, so long as the entire system is still self-consistent. Therefore, on average, an angle's actual deviation from nominal will be much less than .5° in a conforming part.
With the third method, five angles are specified, so you don't care what the sixth is (for purposes of inspection). As long as they all pass, the part passes. This means that 60.5°, 60.5°, 60.5°, 60.5° & 60.5° is valid, but if you measure the remaining angle, it's 57.5°. If that situation is unacceptable for your application, don't use this dimensioning method!
It looks like your drawing follows method 2, so that implies that the welder should definitely avoid placing the gussets at 60.5° from the previous one, because he'll quickly discover that he can't make all of the tolerances work. The assumption that because the tolerance is ±.5°, he could err by .5° on each dimension, is faulty. He can err by .5°, but only if he makes up for it in the other dimensions.
No. If he does that, he might put the first at -0.5° and the second at 60.5° (relative to the origin). The angle between them is 61.0° > 60.5° (out of tolerance).
So, the bottom line is that any of the three methods are potentially valid, but they're not equivalent. In particular, method 2 isn't overdimensioned, but it may be confusing (because the six dimensions cannot simultaneously and individually take advantage of a full .5° in tolerance).
With regard to the notation "EQUALLY SPACED", I think that would be unclear. How do the tolerances apply? Does that imply method 1, method 2, or EidenC's example (where you determine the theoretical lines 60° apart and apply tolerance from those points)? Or worse, does it override the tolerances (only perfect 60° angles are allowed, within the ability of the inspection gauges)?
RE: Multiple Angle Dimensions (Equally Spaced)
Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services
www.infotechpr.net
RE: Multiple Angle Dimensions (Equally Spaced)
Put another way: You can't properly control part geometry with only a ruler (or in this case a protractor).
Doing it right is simple. Box the angles to make them basic, and put a feature control frame on the drawing that describes the gusset tolerance zone. If a quarter inch is OK, then quarter inch it is.
Leave off proper geometric controls, and all you have is a down payment on a dispute about what the drawing really means -- after the part is made.
RE: Multiple Angle Dimensions (Equally Spaced)
Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group
RE: Multiple Angle Dimensions (Equally Spaced)
As if this poor equine carcass didn't get beaten enough then now it's been resurrected and the stench is terrible.
KENAT,
Have you reminded yourself of FAQ731-376: Eng-Tips.com Forum Policies recently, or taken a look at posting policies: http://eng-tips.com/market.cfm?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Multiple Angle Dimensions (Equally Spaced)
I'm ok with the angle dim followed with an equally spaced note.
The "17.99" is OK.
Chris
SolidWorks 09, CATIA V5
ctopher's home
SolidWorks Legion
RE: Multiple Angle Dimensions (Equally Spaced)
"Good to know you got shoes to wear when you find the floor." - Robert Hunter
RE: Multiple Angle Dimensions (Equally Spaced)
Chris
SolidWorks 09, CATIA V5
ctopher's home
SolidWorks Legion