How many angles are in a circular pattern? 6

[cwdaniel]

See attached drawing.

Is fig. A or B correct?

 

[btrueblood]

I don't buy that 5X is double dimensioning, for +/- tolerancing. The gap between the top hole and the hole to left or right are seperate physical dimensions, and are only linked by implication that they are equally spaced about a full circle. If you only measure 4 locations, then the tolerance stack applies, and the gap will vary somewhere, and the question is, where does the gap not apply (which way do you start clocking the index table)? If you specify 5X locations, then the closure rule of land surveying applies, and the error between any two holes must be within the tolerance. In GDT, you are SUPPOSED (well, okay, strongly urged? Recommended? Asked politely?) to use the 5X example. Case closed.

Unless, could you just write the note "5 holes, equally spaced"? Oh wait, we already beat that horse to death, didn't we?

 

[DraftingMan]

Sorry guys, you are all over analyzing this issue!!

Here are my two cents:

1. A note that says 5 holes equally spaced.

2. A dimension, as shown, if the holes are not equally spaced.

To btrueblood,

This is not land surveying but machine parts.



John H. Dunten, CD
Certified Drafter

 

[btrueblood]

DraftingMan, you are correct, drafters are too dumb to be surveyors.

Usually I wouldn't say artillery-baiting stuff like that, but it's nearly the 4th over here, and we kinda like loud noises for that...

 

[wallyd999]

it'a TYPO get it fixed by the designer.

 

[KimBellingrath]

I have to respond to MechEng2005 especially on this: You don't count the MOVES that it takes to create a 5-hole pattern; you coubt the SPACES. There are 5 spaces between 5 holes and they ALL matter in your dimensioning. That's how you keep accumulation limited. If all of the 5 spaces have a tolerance, it becomes a good limiter. If you only tolerance the 4 MOVES to make 5 holes, the last space can be way off. Don't make the mistake of thinking like the machinist and counting the 4 moves - there are 5 angular dimensions in a 5 hole bolt pattern.
Made the mistake before but never again.
Kim

 

[wallyd999]

Kim - thanks now I understand what was meant!

 

[cwdaniel]

Ok, I've been watching this long enough to see some "consensus" leaning toward the fig A example. As I said I can be swayed either way. So I shall follow the convention until I may be forced to do otherwise at some other job. Hopefully none too soon.

Now, along the same lines (no pun intended), have a look at another possibility I've run into. See attached dwg.

Does having the holes connected by a common center line negate the requirement of specifying the number of angles?

 

[ringman]

Are we talking apples (GD and T) or oranges, (non-GD and T)?

Once this is detrrmined, we can come to a solution, perhaps.

 

[CheckerRon]

I've seen this one before, and it circumvents, or as KENAT likes to say, contravenes the 5 space callout we have been talking about. I you are still subjent to whatever tolerance is assigned to untoleranced angles.
I have seen hexagon features dimensioned this way also and I think it is poor substitute for BASIC and an FCF for the features. In the case of hexagon dimensioning I think it is wrong.

 

[cwdaniel]

I guess I need both apples and oranges in my fruit salad.

 

[ringman]

In which case the ans to the orig question is Neither.

 

[drawoh]

cwdaniel,

If you use GD&T style positional tolerances on your holes, most angle dimensioning schemes are perfectly functional. Your drawing is unambiguous, although it is not explicitly shown that your angles all are equally spaced. I might use your dimensioning scheme if my two angles were, say, 57.5[°].

If you apply [±] tolerances to your drawing, you need to work out the effect of your allowed error. This may be weird. The linear displacement due to your angular error is affected by the pitch circle. This all is an excellent argument for GD&T positional tolerances.

JHG

 

[CheckerRon]

To elaborate, I personally don't like the two angle concept and would never use it. The underlying thread in this thread seems to be "why go through all these gyrations just to avoid GD&T dimensioning?" Just use GD&T and all these problems and senarios go away.

 

[MintJulep]

There are 5 spaces between 5 holes and they ALL matter in your dimensioning. That's how you keep accumulation limited.

No it's not. You keep accumulation limited by applying a dimensioning scheme that doesn't allow accumulation.

If you dimension as "5 x 72" then the angular tolerance applies to 5 individual dimensions. This leads to the possibility that 5 individually conforming features result in a non-conforming part. Over-constrained, ambiguous, whatever you want to call it, it's wrong.

If you only tolerance the 4 MOVES to make 5 holes, the last space can be way off.

Dimensioning as "4 x 72" eliminates the over-constraint and ambiguity - although it may not yield "conforming" parts that work.

Yes, the last hole may be "way off" from where it really needs to be. This arises from the poor decision to use chained dimensions.

there are 5 angular dimensions in a 5 hole bolt pattern

Yes there are. They are: 0, 72, 144, 216, and 288 degrees. If those angles are where you want your holes, then those angles should be dimensioned. Or specify 72 as basic, and use GT&T to control the location.

 

[ctopher]

Fig B does not exist. You show 5 spaces, but dim "4X 72" ??
Would you draw 4 tires on a car, but show 3 on the BOM?
Fig A is the correct drawing. They are shown eq sp, but not indicated...and should be.
72 x 4 = 288
72 x 5 = 360

Chris
SolidWorks/PDMWorks 08 3.1
AutoCAD 06/08
ctopher's home (updated Jul 02, 2008)

 

[KENAT]

Wow, I put my post on the first day of my forced vacation (plant shutdown at short notice for financial reasons) and didn't look again while off, this one has legs.

Re 1.9.5.2 of ASME 14.5M-1994 & figure 1-56, it can't be used to fully answer this question because it doesn't address tolerance and as 1.1.4 is in force can't be readily extrapolated from the figure.

Fig 3-25 on page 49 is clearly using Basic, in this case I agree with X being the total number of spaces and = the number of holes, no tol stack up.

It's quite possible that the theoretical 'complete drawing' that 1-56 is taken from has the old "UNTOLERANCED DIMENSIONS LOCATING TRUE POSITION ARE BASIC" note somewhere we can't see or something.

I'm apparently disagreeing with several posters that are far more qualified than I, which I'm usually loathed to do but in this case, if not using basic then I can't see how 5X72 with +- tolerancing can be correct when you take tolerances into account.

As to over analyzing, no I'd say that considering the tolerance aspect is adequate analyzing. It's ignoring the tolerance aspect that is under analyzing the situation.

Given that virtually all the examples in the standard use basic/position on this type of hole pattern I disagree with the "use 5 X 72 because that's how it's always shown in the standard" argument.

5 X 72 without using basic or some other custom note/requirement leads to having two different allowable tolerances on one of the dimensions, I believe this contravenes the standard but can't quote chapter & verse. 1.4 (c) sort of addresses dual dimensioning but not explicitly. 1.7.7 is kind of relevant

Where an overall dimension is specified, one intermediate dimension is omitted or identified as a reference dimension. See Fig 1-17.

So if you consider that showing the holes in a circle implies 360° then you should leave one angular dim out, but it's perhaps a stretch.


It's not the explicit dimension scheme that is so much the concern as its implications on tolerance.

However if we're happy to ignore that then use whichever floats your boat.


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

 

[ewh]

I still agree with KENAT. One question, are the holes located and can the part be made using 4X 72°? If not, why not?
As I have stated before, I will use 5X 72° when the dimensions are basic, per the standard - no tolerance stackup involved. I still need convincing in regard to +/- tolerancing. MintJulep makes a valid point that "the last hole may be "way off" from where it really needs to be. This arises from the poor decision to use chained dimensions".

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

 

[vc66]

I agree with MintJulep. You need to dimension so that the machinist can make the part. Any more than that over-constraining. The machinist won't make the five holes, and then re-drill the first hole to hit the 5th angle. It doesn't make any sense.

It's like saying you have 5 steps on a shaft, and you chain dimension all 5 steps, and then dimension the entire length of the shaft. It's over-dimensioning. The only difference is that the "entire angular length" of the circle is implicitly 360 degrees.

V

 

[ajack1]

I totally agree with drawoh and CheckerRon, why would anyone in their right mind not use G,T&D in this case?

 

[KimBellingrath]

KENAT,ewh,
Remember, you are measuring a part as it exists in it's final configuration, NOT writing an operation sheet for a machinist. The 5th dimension exists even if the machinist does not have to make the move. 4 x 72 allows accumulation where as 5 x 72 actually limits the fifth space as well. The "equals 360" is understood because of the vert/horiz divider rule in angular dimensioning. 'If you start on the vert and go all the way around 360 is apparent, no?'
Your standard tolerances control the first 4 'moves' and the vertical start line is also the end which can't move so the dimension from the 4th hole to it becomes your limit on accumulation. You guys can analyze this to death but for as many years as I have been doing this, I have always counted ALL of the gaps in a pattern like this not how many 'moves' it takes to make the part. As a former machinist, I can tell you that nobody ever drills the first hole twice!