2" -0.003/-0.007 allowed in asme y14.5?

[Bouing]

I had a badly fabricated pin where on the drawing it was indicated 2" -.003/-0.007 and they machined it at 2" exactly (+/-0.0005). I've been in the code asme y14.5 1994 but it is not clear.

Code just claim we can put fit tolerance (where we have -/-) for metric fit. Other examples are just with (+/-)

On the drawing it was the stacked version but still with 2 minus signs.

Do you think it can be misleading as a quote or it is obvious for whomever should be working with drawing?

 

[DesignerGuy16]

Y14.5M-1982 shows some examples of +0/-X unilateral tolerances and +X/-X or +/-X Bilateral tolerances. The text itself states:

They also have a recommended metric tolerancing setup:
_______________
29.980
29.959 (30 f7)
____________________

30 f7 (29.980)
(29.959)
____________________
30 f7

James Spisich
Design Engineer, CSWP

 

[DesignerGuy16]

Sorry I cut off the text halfway through writing it after just copying the examples for the fit tolerances. Forgive them not lining up. Doesn't work so well in a little text box.

James Spisich
Design Engineer, CSWP

 

[KENAT]

What version of 14.5? A quick look at ASME Y14.5M-1994 section 2 doesn't explicitly address the issue. It too mentions metric limits & fits.

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[DesignerGuy16]

ANSI Y14.5M-1982 Section 2.2.1.1

It has a figure with the above example as a recommendation when a system is introduced by an organization.

James Spisich
Design Engineer, CSWP

 

[DesignerGuy16]

My opinion though is it should be changed to a base number +x/-x or +0/-x just as easily as what they left it, without the confusion of having double negative tolerancing.

I've seen it before, but I don't like it for the reason you're posting.

James Spisich
Design Engineer, CSWP

 

[KENAT]

For people who've worked metric limits & fits or other systems where similar is used it's not really a problem.

For people that haven't worked in such systems though it can be confusing, they may assume the upper value should be +ive. Of course, if not sure they should ask whoever they got the drawing from and so on back to the designer/custodian, but that doesn't always happen.

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[DesignerGuy16]

Like the example though, usually you'd have a nominal dimension calling out the metric fit tolerance right next to it. That's the way I've always seen it personally.

James Spisich
Design Engineer, CSWP

 

[ewh]

While I have seen it used, I have also seen parts made under the incorrect assumption that the tolerance was ± almost as often.

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[KENAT]

Not sure about usually, at least your usual may not match mine.

I think I've seen it with rivet holes, the hole size is given as the nominal rivit dia. The tolerances are then +/+ these weren't to any metric shaft fit basis or whatever. They were in good old fashioned inch, based on the tolerance in the rivit spec.

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[KENAT]

rivet, not rivit.

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