How many angles are in a circular pattern? 6

[cwdaniel]

See attached drawing.

Is fig. A or B correct?

 

[vc66]

Sorry--figure on the right is considering double dimensioning, and the figure on the LEFT is not.

V

 

[ewh]

After all we've been through, I'm not sure I want to go there, but...
I've had this "discussion" before with customers. My take on it is that if the holes are on the same centerline and that centerline goes through the center of the hole pattern, then one angular dimension is sufficient to define that centerline. Just don't ask me to back it up .

Believe it if you need it or leave it if you dare. - [small]Robert Hunter[/small]

 

[KimBellingrath]

Thanks for your support, bTrueblood. Dimensioning bolt circles IS a different animal, no? I don't have a good answer for vc66 but I know that adding the 360 dimension to a round thing is not required. Yet, it IS assumed which make's it overconstrained in the linear world, but done often in the circular.
I have used this dimensioning scheme on stepped parts or hole patterns as follows:
5 X 5.00
= 25.00
quite often without question or complaint as it gives you each increment plus a total which all have to be within the general tolerance.

 

[ewh]

I have used the same method, but made it either "5X .50 (= 25.00)" or "(5x 5.00 =) 25.00". That old double dimensioning monster...

Believe it if you need it or leave it if you dare. - [small]Robert Hunter[/small]

 

[KENAT]

cwdaniel , your second sketch wasn't ignored, a couple of people responded. I'm pretty much in agreement with CheckerRons (7 Jul 08 13:29 & 7 Jul 08 13:49 ) take on it (However, I wouldn't have used contravenes this time Ron as it wouldn't make sense;-)). Use positional/basic and the ambiguity goes away.

As to the "grand posturing, slander, and condescension", well it's not my fault if many of the other posters can't admit I'm right;-).

VC66, 1.7.7 says that the right hand view is wrong. I think (hope) we can all agree to that. I would tend to extrapolate 1.7.7 to the circular case even if the 360 isn't shown, Kim and others disagree & choose not too. I think I'm right but can't be sure based on what is in the standard as far as I know it. Although, you've now got me thinking what happens if all the dimensions on the right hand view were basic, since the standard does show 5X72 when using basic, hmm.

Just invoke 1.4D

Dimensions shall be selected and arranged to suit the function and mating relationshp of a part and shall not be subject to more than one interpretation.

I think the 5X72 is open to more than one interpretation when tolerances are taken into consideration, Kim & btrue disagree.

George Washington smarter than I, given what he achieved/was part of I can probably live with that.

KENAT, probably the least qualified checker you'll ever meet...

 

[ringman]

I believe:

If your company is large enough to write and maintain a standard for documentation definition, great, and you should adhere to the standard. If you are in compliance with Y14.5 or ISO or any other recognized standard,you should abide by their guidelines. Short of this you are pretty much on your own as is indicated here by the various interpretations placed on the sketches provided.

And the drawing should indicate the standard to which it has been prpared, if any.

 

[drawoh]

KimBellingrath,

If you hold all five spaces to your tolerance, you limit the accumulation, but you do not eliminate it.

If your fifth hole is allowed to shift four times the angle tolerance, it can shift four times the angle tolerance.

Your method uses the first hole as nominal, and it controls the second and fifth holes to the angle tolerance. The third and fourth holes are controlled to twice the angle tolerance. This is better than the above case, but the caution about combined tolerances still applies.

5[×]72[°] is an non-English and minimal typing way of saying the holes are equally spaced.

JHG

 

[vc66]

Oh no, are we gonna start the EQLSP thread again? lol

V

 

[KENAT]

You mean EQUISPACED ;-)

Out of interest, or maybe lack there of in continuing this thread as is, is there a reason for you not to use GD&T, basic + positional, as shown by pretty much all the examples in 14.5?

KENAT, probably the least qualified checker you'll ever meet...

 

[btrueblood]

"I think the 5X72 is open to more than one interpretation when tolerances are taken into consideration, Kim & btrue disagree."

How can there be more than one interpretation? You can measure the 5 independent angles, and determine if they are +/- 1 degree from the indicated value. Yes, the part is perhaps "over-constrained" (to borrow terminology from 3Dcad software), but it is not over-dimensioned, nor un-buildable with the tolerancing scheme shown in vc66's left-hand sketch (ignoring the ambiguous 0-degree or 360-degree measurement). If the values for each dimension can be independently measured it is not over-dimensioned. Whether it is against "para 1.4(c) No more dimensions than those necessary for complete definition shall be given." is open to intrepretation - if the designer wants the constraint given by the dimensioning scheme shown, he dimensions it as shown, or alternatively uses GD&T to constrain the tolerances to a more rational system.

By the same token, I do not think that vc66's right hand sketch is truly over-dimensioned for all cases, since again, each dimension can be independently measured (the fact that one of the dimensions may not vary independently without possibly affecting other dimensions is immaterial, we don't specify how it's made, just how it is to be inspected, right); it may or may not be over-dimensioned, depending upon how the designer wanted the tolerances to accumulate (or not accumulate), thus the vagueness of "para 1.4(c) "No more dimensions than those necessary for complete definition shall be given." It IS over-constrained, again to borrow terminology used in the 3D-Cad world, and I would agree that both sketches, IF he had placed basic tolerances boxes around the dimensions, would/could be construed as over-dimensioned, but then the spec. requires you to put the 5X in the circular pattern for GD&T (or does it?).

But there are times when that right-hand sketch may be required by a designer (who is essentially saying, I need 5 steps within some tolerance, and the whole part has to fit within this gap). Yes, it requires a machinist to do some thinking, and is more complicated to make than a stepped shaft, but if the part requires those tolerances, it's his job to stop whining and figure out how to build it.

...and, all kidding in front (the opposite of all kidding aside), Kenat and ewh and et. al. on this forum should know that my comments re that rebel George are done with tongue firmly, rigidly in cheek ... plus or minus 1/2 cheek.

 

[KENAT]

btrue, so you're saying you disagree with 1.7.7 in y14.5?

KENAT, probably the least qualified checker you'll ever meet...

 

[MintJulep]

No more dimensions than those necessary for complete definition shall be given.

There you go.

The btrueblood/kimbellingrath interpretation that each hole must simultaniously conform to the angle from its adjacent two holes violates that provision of the standard.

The angular location of each hole can be fully defined with one and only one angular dimension.

As I wrote earlier, if you want holes located at 0, 72, 144, 216, and 288 degrees, then those angles should be dimensioned. Or specify 72 as basic, and use GT&T to control the location.

 

[ewh]

... which brings me back to my question of 8 JUL 08 09:20, "are the holes located and can the part be made using 4X 72°?" The answer is yes. They may not end up where you need them (the tolerancing issue), but their positions ARE fully defined. If this is insufficient due to tolerance accumulation, don't use chain dimensioning. Any additional dimensions are superfluous, and result in double dimensioning.
OK, I've had enough. I guess it's time to agree to disagree.


Believe it if you need it or leave it if you dare. - [small]Robert Hunter[/small]

 

[ajack1]

What a good job this is only a very basic part with 5 holes in it, what chance would we have of agreeing on anything slightly complicated?

 

[btrueblood]

Mint: "No more dimensions than those necessary for complete definition shall be given."

And yet the same spec. shows "5X 72 degrees".

Kenat: "btrue, so you're saying you disagree with 1.7.7 in y14.5? "

Kenat, you should know by now that there is a LOT of things in the holy Y14.5M that I disagree with. But, in this case, vc66's sketches never invoke Y14.5M, and (I thought) we are talking more generally about +/- tolerancing and double-dimensioning. I maintain that the right-hand sketch has a solution, and can be manufactured, even though its tolerancing scheme is confounded. If Y14.5M were to be invoked on the drawing, then the author would deserve several dope slaps for not using 5.0 as basic dimensions, setting one end or face as a datum, and controlling profile or flatness or parallelism of the surfaces to within whatever tolerance is required.

Also, although the spec. is next door, I will bet you a pint that 1.7.7 has the word "should" not "shall", so maybe I really don't disagree.

But, no, I'm playing devil's advocate here for the most part, and agree (wholeheartedly) that GD&T is the way to go, as there is/will be LESS disagreement on what is 'the design intent' using the spec. than there is without it.

All of my drawings go out with Y14.5M invoked by general note. But, yes, I can, do, and will still, "violate" Y14.5M whenever I please feel that it is necessary to achieve a design purpose. And add explanatory notes describing what is required. And expect to hear from inspectors, etc. So, I try NOT to do it very often, and am trying to update hundreds of older drawings with dimensioning schemes much more nefarious than the one in vc66's sketches, often behind the back of the authors (my seniors).

As far as using 5x72 degrees or its equivalent, in BASIC dimensions, as part of a GD&T position tolerancing scheme, I also see no problems with it either way. Because both 4x72 and 5x72 will produce the same hole pattern, since basic dimensions are exact and thus there is no ambiguity, you will achieve the same result. Whether or not it is "over dimensioned" becomes something of a moot point, and affects drawing clutter or "style" more than whether or not work can proceed.

 

[btrueblood]

wups, no. "Also, although the spec. is next door, I will bet you a pint that 1.7.7 has the word "should" not "shall", so maybe I really don't disagree."

At least, in the copy of the '82 spec. I was able to lay hands on quickly, it's pretty clearly spelled out as a "DON'T".

Your pint awaits you in the pub, Kenat.

 

[KENAT]

1.7.7 Overal Dimensions. Where an overall dimension is specified, one intermediate dimension is omitted or identified as a reference dimension.

No shoulds about it, although as VC66 doesn't explicitly reference 14.5 on his sketch or in his post then I doubt you oweing me a pint is enforcable in a court of law;-).

Rules, laws or in this case standards are for the obedience of fools and the guidance of wise men, or something like that. I'm pretty sure I don't fall in the wise category and the more I get to know the standards the more reluctant I am to contravene them, however maybe you're wiser than I;-).

Enough of this though, it looks like both sides are entrenched in their positions, and it sounds like the OP thinks he has his answer so I should just let it go like I tried to do before.

KENAT, probably the least qualified checker you'll ever meet...

 

[ewh]

Right you are, btrueblood. The 1994 standard started wimping out, replacing many shalls with shoulds.

Believe it if you need it or leave it if you dare. - [small]Robert Hunter[/small]

 

[KENAT]

But not in this case.

Doh, I wasn't going to post again.

KENAT, probably the least qualified checker you'll ever meet...

 

[MintJulep]

Mint: "No more dimensions than those necessary for complete definition shall be given."

And yet the same spec. shows "5X 72 degrees".

Imagine that! A standard with internally conflicting requirements.

As is my prerogative as an obstinate cuss, I choose to pay attention only to the requirements that support my view of the world, and ignore those that don't.