tolerance analysis to ISO 8015 & 2768 part 1 (again!)

tolerance analysis to ISO 8015 & 2768 part 1 (again!)

PREFERRED FITS AND TOLERANCES CHARTS (ISO & ANSI METRIC STANDARDS) Preferred fits and tolerance table for hole and shaft basis systems which are given in ISO 286-1 (2010) and ANSI B4.2-1978 standards. The usage of these tolerances is advised for economic reasons. Supplement: Preferred fits advised by ISO and ANSI standards.

This is a follow on to thread1103-196260: Tolerance analysis ISO2768.
I sent a message out to the engineer copied to the manufacturing engineering manager and my boss saying I was still concerned about interchangeability but that if that Engineering department and Production didn't think it was worth the effort of verifying/ correcting it then it could be excused check.
No one seems to just want to say 'excuse it from check' but at the same time the engineer involved is now telling anyone who'll listen that I'm wrong, I don't know what I'm doing and that I haven't read the correspondence he had with the vendor. (He may have a point on the first 2 but I did read the correspondence.)
I've looked at ISO 2768-1 in detail and find nothing to suggest that 2 holes, independently located from a surface by their own separate dimensions (in one plane) with tolerances from iso2768 are in any way linked to each other such that the distance between them also has to be within the tolerance from the iso.
For instance (same example as before) I have part of a hole pattern, two threaded holes in line. The first is 36.66mm from the 0 ordinate. The second is 103.34mm from the 0 ordinate. Nominal spacing therefore is 66.68mm. From the extract of the ISO I found both 103.44 & 36.66 are +-.15mm. Therefore for interfacing purposes I assumed that the spacing is effectively 66.68 +- .3 (.012”). The vendor says this is wrong and that the spacing is 66.68+-.15.
I’ve also looked at ISO 8015, which is referenced by 2768, and find nothing to change my opinion.
The only ISO referenced on the drawing is 8015, it doesn’t invoke any others.
Another example from the drawing, they have a stepped female hole (like a large c’bore hole). They specify it as R35 & R42 from iso 2768 this gives them +-.15. I’m trying to do the calculation in B6 of ASME Y14.5M-1994 so need to convert to diameters. To do so I’m multiplying both the nominal radius and the tolerance by 2 to get 70+-.3 and 84+-.3 does this sound correct?
Given the addition of ISO 8015 does this change anyone’s opinion?
If anyone thinks the vendor is correct could they let me know which ISO gives this information, and if possible give me the paragraph number.
I am going to contact the vendor but it has got so political that I wanted to back it up with a post here.

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

General tolerance ISO 2768 does not specify where to use these tolerances. As per design requirements and manufacturing capability tolerance class is defined. For example : For sheet metal parts ISO 2768–mk is used. And for machined components ISO 2768–fh can be used. In the above example “m” and “k” has defined the tolerance class.

Critical dimensions tolerance is calculated using tolerance stackup analysis. You can also use a tolerance stack up calculator for this purpose.

It is not possible to define tolerance against each dimension. Therefore variation in dimension without tolerance are defined using general tolerance. ISO 2768 has defined general tolerance for:

• Linear Dimensions
  
• Angular Dimension
• External Radius and Chamfer height
• Geometric Tolerance such as straightness, flatness, perpendicularity, symmetry and runout.

Linear Dimensions
Nominal Length Range in mm	Tolerance Class
	f (fine)	m (Medium)	c (coarse)	v (very coarse)
0.5 up to 3	±0.05	±0.1	±0.2	–
3 up to 6	±0.05	±0.1	±0.3	±0.5
3 up to 30	±0.1	±0.2	±0.5	±1
30 up to 120	±0.15	±0.3	±0.8	±1.5
120 up to 400	±0.2	±0.5	±1.2	±2.5
400 up to 1000	±0.3	±0.8	±2.0	±4.0
1000 up to 2000	±0.5	±1.2	±3.0	±6.0
2000 up to 4000	–	±2.0	±4.0	±8.0

External Radius and Chamfer Heights
Nominal Length Range in mm	Tolerance Class
	f (fine)	m (Medium)	c (coarse)	v (very coarse)
0.5 up to 3	±0.2	±0.2	±0.4	±0.4
over 3 up to 6	±0.5	±0.5	±1.0	±1.0
over 6	±1.0	±1.0	±2.0	±2.0

Angular Dimensions
Nominal Length Range in mm	Tolerance Class
	f (fine)	m (Medium)	c (coarse)	v (very coarse)
up to 10	±1°	±1°	±1°30′	±3°
over 10 up to 50	±0°30′	±0°30′	±1°	±2°
over 50 up to 120	±0°20′	±0°20′	±0°30′	±1°
over 120 up to 400	±0°10′	±0°10′	±0°15′	±0°30′
over 400	±0°50′	±0°50′	±0°10′	±0°20′

Straightness and Flatness
Nominal Length Range in mm	Tolerance Class
	H	K	L
up to 10	0.02	0.05	0.1
over 10 up to 30	0.05	0.1	0.2
over 30 up to 100	0.1	0.2	0.4
over 100 up to 300	0.2	0.4	0.8
over 300 up to 1000	0.3	0.6	1.2
over 1000 up to 3000	0.4	0.8	1.6

Perpendicularity
Nominal Length Range in mm	Tolerance Class
	H	K	L
up to 100	0.2	0.4	0.6
over 100 up to 300	0.3	0.6	1
over 300 up to 1000	0.4	0.8	1.5
over 1000 up to 3000	0.5	0.8	2

Symmetry
Nominal Length Range in mm	Tolerance Class
	H	K	L
up to 100	0.5	0.6	0.6
over 100 up to 300	0.5	0.6	1
over 300 up to 1000	0.5	0.8	1.5
over 1000 up to 3000	0.5	1	2

Conclusion

To sum up, Engineering tolerance is a very important and critical part of product design. And ISO-2768 standard defines the values of general tolerance. It is always recommended to run tolerance stackup analysis before design finalization.

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