yet more ISO tolerancing 3

[MarineGreg]

I know the ISO tolerancing thing has been discussed to great lengths here but......

I have a 120n6 mm shaft and a 120H7 mm bore.

The website below describes the tolerancing a little differently than what I have read before. Here is how they describe it.

120n6 shows as +45 and +23 in micrometres.
First limit is 120+0.045 = 120.045mm
Second limit is 120+(0.045 + 0.023) = 120.068mm
So the limits are 120.045 and 120.068.

120H7 shows as +35 and +0 in micrometers.
First limit is 120+0.0 = 120.0mm
Second limit is 120+ (0.035 + 0) = 120.035mm
So the limits are 120.0 and 120.035.

Is this correct?

http://www.roymech.co.uk/Useful_Tables/ISO_Tolerances/ISO_LIMITS.htm

Thanks.

 

[dimjim]

no,
the shaft has a double plus tolerance and are not additive
meaning 120.045 to 120.023 120 plus .045 and 120 plus .023
bore is 120.000 to 120.035
ie may be a pressed fit at max material conditions.

 

[gearguru]

Check this web page:

http://www.tecnologix.net/en/tools/passungsrechner/passungsrechner_v05.html

click on "Fit Calculator" and enter your ISO tolerances.

Dimjim is right, your tolerances should look like this:

120n6 shows as +45 and +23 in micrometres.
First limit is 120+0.045 = 120.045mm
Second limit is 120+0.023 = 120.023mm
So the limits are 120.045 and 120.023

120H7 shows as +35 and +0 in micrometers.
First limit is 120+0.0 = 120.0mm
Second limit is 120+0.035 = 120.035mm
So the limits are 120.0 and 120.035

 

[dimjim]

Gearguru,
Thanks for the url for the fit calculator.

 

[prohammy]

Nice fit calculator (* for u)

Kevin Hammond

Mechanical Design Engineer
Derbyshire, UK

 

[mrainey]

How is it that a shaft 80h7 can enter a bore 80H7 with what is described as a "loose fit"? Can't they theoretically be the same size - 80.000mm - with zero clearance?

Software For Metalworking

http://mrainey.freeservers.com

 

[gearguru]

Yes, they can. But statistically how often it happens?
To control the loose fit it is better to select one of the parts H (h) and the other g, f, e... (G,F,E...)
The "farther" from H (h) toward A (a) is the second parts tolerance, the more guaranteed clearance the fit has; and the opposite is valid also - the closer toward Z (z), the more interference in the fit. The number in the ISO tolerance description (like 8 in the H8 tolerance) controls the total tolerance, the letter the location of that tolerance relative to the nominal size.

 

[xnicke]

I use this ISO-tolerance calc. Nice to have on your desktop (excel-sheet). In Swedish though, but you will figure it out (haven't had the energy to translate it).

http://www.megaupload.com/?d=WEQV0MOC