Dimension tolerances
Dimension tolerances
(OP)
Folks
I always had trouble interpreting a cut vs protrusion. In Figure 1, the step feature has a dimension 0.296 -0.005". Wouldn't this cut read 0.296+0.005". The same for Figure 2. It boils down how is machined. Does anyone have a references to read? any tips.

I always had trouble interpreting a cut vs protrusion. In Figure 1, the step feature has a dimension 0.296 -0.005". Wouldn't this cut read 0.296+0.005". The same for Figure 2. It boils down how is machined. Does anyone have a references to read? any tips.






RE: Dimension tolerances
Regardless, no, 0.296 +0/-.005 would absolutely never be read as 0.296 +.005/0 because that's a completely different set of acceptable values.
It doesn't matter if it's cast, forged, welded, bored, milled, punched, or spun and finger-shaped from clay by the ghost of Patrick Swayze.
The acceptable values for that dimension are between the 0.296 maximum, and 0.291 minimum.
Assigning the tolerances on those dimensions has only to do with the design, assembly, or functional requirements which can not be certain to me from what is presented.
RE: Dimension tolerances
RE: Dimension tolerances
That's just not how this works.
At all.
RE: Dimension tolerances
My interpretation is that the designer wants the depth to be from .291 to .296". There are no rules for which direction tolerances should go. The machinist's job is to hit the dimensions, as specified.
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JHG
RE: Dimension tolerances
John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
RE: Dimension tolerances
It's not a requirement of any standard, just a local preference.
External features would be nominal +0/- tolerance; internal ones nominal +tolerance/-0.
Processes such as EDM will want the kerf of the process to be taken into account.
None of these need to be taken into account on the engineering drawing but should be considered for manufacturing process drawings.
RE: Dimension tolerances
Would you please at least hint to what's new for stacked tolerances order?
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: Dimension tolerances
I've heard similar before, and also heard opposite, and also heard that they should always be bilateral +/- tolerances so there's no mistaking where to 'hit it in the middle'.
No one is more correct than another. It's all illogical crap to suit someone's particular flavor. It's not something particular to a process; it's a request specific only to a /person/ and so I don't really respect it at all as any form of legitimate practice.
My personal experience is that ideas like that are typically to make up for lazy or incompetent machinists or simple bad practices in programming or tool settings.
ETA: And yes, I have programmed, set up, and ran machines from various drawings.
RE: Dimension tolerances
JNieman - that's why I prefer to use +/+ tolerances or -/- tolerances. 2 +12.03/+11.97, for example. Makes them think.
RE: Dimension tolerances
When you say that it isn't a requirement of any standard do you mean that since Y14.5 is a voluntary standard that nothing in it is a requirement? If so then I agree, but if you're saying that the order that stacked limit dimensions should appear isn't addressed, then I refer you to 2.2(a) of the 2009 standard.
CH,
It currently places the plus value above the minus value and in the case of one of them being a nil value, the nil value will have the opposite sign of the non-zero value for inch tolerancing. All the illustrations show the plus value above the minus value and the nil value with the opposite sign of the non-zero value but no verbage locks it in that way. Of course since this is still in draft, it could change but I hope not.
John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
RE: Dimension tolerances
RE: Dimension tolerances
But I like the 2 +12.03/+11.97. I might do that on the print I whip up for someone that wants a quick jig laid out, just to screw with them :)
RE: Dimension tolerances
John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
RE: Dimension tolerances
I still don't know why or how 'limits' dims ever entered the convo.
RE: Dimension tolerances
John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
RE: Dimension tolerances
Given that machine shops want my CAD model or a DXF of my drawing, I would prefer that the dimension shows the actual as-modelled size of the feature.
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JHG
RE: Dimension tolerances
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Dimension tolerances
RE: Dimension tolerances
I think it would be weird to see a dimension origin symbol starting at the bottom of the hole. Maybe it is just me. I find the OPs drawings to be completely interpretable.
In general, when I dimension features like this, I use the top as the origin. The tolerances, as shown, do not support that scheme. The distance from the bottom of the hole to the feature, seems to be critical. If I saw the design, I might disagree with the drawing. My first assumption has to be that the designer/drafter thought this through, and that they know what they are doing.
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JHG