It is 4 X 72 or you are dual dimensioning, implicitly on the tolerance.
Unless of course you are using basic & positional in which case 5X is correct, and which would be better.
It's amazing how angular tolerances tend to add up, especially as the radius increases.
If you have 5X 72 +-.5 then on the last 'segment' it's actually possible that you are speccing both 72+-.5 or 72+-2. As such not only are you dual dimensioning but the dual dimensions conflict.
Of course if you use 4X and dont give which direction then which segment is 72+-2 is open to variance.
Just use basic and positional if you care about the final location.
KENAT, probably the least qualified checker you'll ever meet...
You might also look at Fig 4-15, 4-16 and 4-17 of Y14.5 -1994. If you are using geo tolerancing, I think either method will work. If you are not using geo tolerancing, as shown in the attached drawing, both would be incorrect in that they do not locate the apex of the angle.
In answer to your original question, I believe you can have as many angles as you would like in a circle.
Very good question! I've often had this philosophical discussion, and I am in complete agreement with KENAT. 4X or 5X 72 if using basic dimensions (both return same result), 4X if using +/- tolerancing due to the tolerancing build up.
I have to caution anyone from following the illustrations in the standard for anything other than what they are trying to explain. Page 49 fig. 1-56 is intended to show feature control frame placement, and the angular dimension is not addressed in the text. On page 1, para 1.1.4 it is stated that "The figures in this standard are intended only as illustrations to aid the user in understanding the principles and methods of dimensioning and toleranceing described in the text."
I've heard arguments either way, but that's my opinion, and I'm sticking to it (until shown otherwise).
Believe it if you need it or leave it if you dare. - [small]Robert Hunter[/small]
I knew this might be a bit contentious. It always has been in my past.
ctopher: I'm asking the question, not providing my forgone conclusion. I can be swayed by the argument of folks with qualified opinions. In fact I've flip flopped on this several times. Mostly due to the all powerful reign of the checker I'm working with at the time.
PaulJackson: Can you find that specific ASME standard declaration? I'd love to be able to refer to something in writing.
Currently I'm on the side of "B". however, KENAT I haven't heard the argument of it depends on whether GD&T is involved or not. Yet another wrench in the monkey works. I'll have to ponder that one.
MintJulep: I think your analogy is what makes sense to me. There is always one less space than there are features in a pattern. And we are dimensioning spaces. Yet our standard makers seem to be conflicted in their examples Fig 1-55 is showing us 5 spaces in a 6 hole pattern while Fig 1-56 shows us 8 spaces in an 8 hole pattern. Fig 1-56 further confuses me as the space to the 1st hole is shown and not as a reference.
ringman: Your comments about location of angle apexes and centers seem to miss the topic. My examples were submitted to address a specific question, not as drawings with complete requirements. If you're suggesting that the apex isn't defined because the center lines do not cross, then Ok. Maybe that's another topic. At the risk of further derailment, your reference to figs 4-15, 4-16 and 4-17 don't extend the center lines either.
ewh: Thanks for the reminder of the caveat about the illustrations.
So, does the amount of spaces in any given pattern change whether it's circular, radial or linear? I've never given the dimension of the space back to the 1st hole of a linear pattern, why would I do it on a circular one? Would you dimension the leftover space in the radial pattern shown in Fig 1-55?
I'm usually bowing to the wisdom (or lack thereof) of the checkers and conventions of the employer I work for. I'm now in a small company and finding myself as the checker and referee in things of this nature.
The 5[×]72[°] callout makes perfect sense to me. It shows that the holes are equally spaced on the pitch circle. If I went 4[×]70[°], it is fairly clear that the spacing is not equal.
Yes, that does make sense, and 4X 70° is obviously not going to give you equal spacing, but 4X 72° will, though it may not be as obvious as 5x 72°.
It boils down to semantics, and I feel that both sides have merit. I eagerly await a definitive answer to this problem.
Until then, I suggest doing whatever the checker wants
Believe it if you need it or leave it if you dare. - [small]Robert Hunter[/small]
cwdaniel,
I don't know if you looked for answers at your work place or if you are a student. I was simply asking your thoughts what you think the answer should be. I didn't want to just give you an answer and send you off on your way without response from you, I didn't know.
Chris
SolidWorks/PDMWorks 08 3.1
AutoCAD 06/08 ctopher's home (updated Apr 30, 2008)
To get back on track, I believe that the figures 4-15, 4-16 and 4-17 Make the association by using the center hole as a related datum feature. Therefore the cl need not be shown. Does that help any.
And again without GD and T the examples you gave are 'ambiguous'.
Paragraph 1.9.5.2 of ASME 14.5M-1994 explains spacing...with and without the use of the "X" symbol. It refers to illustrations that are consistent in declaring the # of spaces between features... as are other illustrations throughout the standard...
So one may conclude from that that the 5X 72° trumphs 4X 72° however fundamental rule 1.4 (c) states, "Each necessary dimension of an end product shall be shown. No more dimensions than those necessary for complete definition shall be given..."
So I still think that it was a good question but I would go with the practice that is illustrated throughout the standard just to be consistent.
First off, let me say that where I work there isn't really and standard followed. We have "the way things have always been done," and "that's the way the shop likes to see it."
Therefore, I think that it would be produced the same regardless of which way it was dimensioned here.
However, without a standard I would interpret it as there should be 5 spaces at 72 deg. Additionally, I would think the dimensions being like basic, and the third hole should be (3*72) = 216 deg from vertical, +/- the angular tolerance. If the tolerance for all holes was +/-1 deg and the second hole was at 143 deg, I would not accept the third hole being at 214 degree, even though that is within the tolerance stack-up. However, without a standard I wouldn't really have a leg to stand on if it became a dispute anyways.
I guess I just feel that it is more likely to fit function if the basic positions of the holes are given, and the tolerance applied to those. It wouldn't make much sense to allow the tolerance to stackup in this case (I presume, without knowing the application). If the angular locations are taken as basic, I think 5X 72 makes more sense since it gives the complete circle. If the position is based on stacking up the tolerances from one hole to the next, this does over-define the last hole, but if they are taken as basic then it doesn't really matter.
Bravo, Paul, for listing that excerpt. Though, logically, it seems like double dimensioning to me, you are correct that it is indeed addressed and should be followed as stated in the standard. Isn't the first time I've had to do something in which I didn't agree with the logic, and won't be the last.
Believe it if you need it or leave it if you dare. - [small]Robert Hunter[/small]
I'm kind of late to the party, but I have always gone for total spaces, i.e. Example A for the reasons Paul J. cited as well as others.
Basic (for me) is the only way to go for holes, so forget ± tolerance.
There are those that would argue with me, but I have always wished that ¶ 2.1.1.1 of Y214.5M-1994 started out with "Manditorialy" rather than Preferably"--that is, Basic dimensions vs ±.
WhitmireGT sort of got picked on for citing Fig 3-25, and there was merit in the criticism, but it is still a good example. Morever, it is one of the few Y14.5 examples where the part is fully dimensioned, and that lends some credence to it.
Besides that, it agrees with way I see it
(Checker's preference sneaking in---EWH opened the door).
Uh oh, what'd I go and do...
My only difficulty grasping the concept is that I was taught to always avoid double dimensioning. If you have a circular hole pattern and the topmost hole is properly located and use the total no. of angular spaces, then the "extra" angular dimension is also locating that hole. All the holes are tied down without that extra angle, so what is its purpose?
Not quite string theory, but it bugs me.
I'll be good though and follow the standard.
Believe it if you need it or leave it if you dare. - [small]Robert Hunter[/small]
