Two Upper Limits on Diameter Tolerance

[rbemben]

I believe I knew the answer to this a while ago but it has come up again.

I am looking at a through hole with a diameter of 6.0. The upper tolerance is +0.10 and the lower tolerance is +0.05.

A 6 mm shaft goes through the hole.

I attached a picture of the call out.

What is the meaning of this tolerance?

 

[JNieman]

MMC/MMB = 6.05
LMC/LMB = 6.10

6.0, though it is the nominal dimension, is not an acceptable size. Such annotation is typically used to clarify that the relationship between mating parts revolves around a 6mm piece of hardware (dowel, shaft, whatever) but the acceptable hole must be oversized to allow for proper fitment.

Edit-to-add: If you check out the typical "Limits/Fits" in ANSI B4.1, you'll see examples more thoroughly described. Charts with common sizes are typically found in Machinery's Handbook, Engineer's Blackbook, and other reference manuals like that.

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NX8.0, Solidworks 2014, AutoCAD, Enovia V5

 

[drawoh]

rbemben,

The tolerance is Ø6.10/6.05. I have no problems showing the nominal dimension and +/+[ ]tolerances. If your fabricator intends to use your CAD file to program his CNC, he needs to know the as-modeled dimension.

I am not so sure about the surface finish specification. 6.3[μ]m is equivalent to 250[μ]in. It is a very rough finish. You may want to look at a surface comparator. This is a do-not-exceed value. I would expect a Ø6.1/6.05 hole to be way within that specification. There is nothing in my Machinery's Handbook explaining the letter "Z".

--
JHG

 

[looslib]

As a side note, metric dimensions do NOT use trailing zeros per ASME Y14.5M-1994 section 1.6.1.
I first looked at your drawing and thought it was a 6 inch diameter hole because of the trailing zero!!


"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

 

[juergenwt]

Looks like somebody not familiar with DIN/ISO 286. He could have specified 6G5 (+9+4) or 6G6 (+12+4) or a reaming fit 6G7 (+16+4}.
Looks like a print (must be in metric but thinking in inches) made without knowing and understanding the System of Fits and Tolerances as per DIN/ISO 286.
6+10+5 is a proper designation but if sent outside the US it will most likely cause some head shaking.

 

[FMTim]

Everyone has interpreted the tolerance correctly here, and hopefully one of them makes sense to you.
The way I see it, different tolerances have their place to show design intent. +x/+y, +0/-x, +x/-0 and +x/-x all tell you very different things about design intent of that part or fit.
That being said, most machinists I have worked with loose their minds over anything but +x/-y. They want a number to go to and how many tries they need to take to get close enough.
So, from a design standpoint I think that tolerance is great, from a shop standpoint it can cause a lot of problems.

 

[TheTick]

It's like travelling to another state where the laws allow you to marry a close relative. Legal, but not advisable.

 

[3DDave]

Plus-plus tolerancing is quite valuable because the nominal can quickly be seen as matching across all the related parts - for example, a pin, the hole it is pressed into, and the bearing that rides on it will have a common nominal size and the tolerance displayed makes calculation of the clearance or interference an exercise that doesn't require a calculator.

The English side has used this for a long time: check the tolerances on screw threads. One doesn't call for a .2488 thread screw with a .2502 nut (I did not look up actual mid-tolerance values.) They have a nominal and fit class number. Makes things simple.

 

[JNieman]

@TheTick

Considering how prevalent and absolutely normal it is to see asymmetric and sometimes +/- and -/- dimensions, why would it not be advisable? On top of that, I've rarely encountered a machinist that didn't like it. The machinists I work with currently are all quite happy with it and pleased to see it. They prefer to know what it is they are making, what it does, etc, in order to make the best parts they can - especially if we'll be doing the assembly here. It makes "the next guy"s job easier.

Just take a skim through Carr-Lane and/or McMaster-Carr drawings for common hardware and tally up how many times critical features use symmetric tolerance versus -/- or +/+

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NX8.0, Solidworks 2014, AutoCAD, Enovia V5