limit and fit tolerances 1

[naah]

Hi
I am designing a fixture with steel material. I have a shaft with a diameter 6 m5. I need to have a clearance tolerance between the shaft and hole. Than I choosed hole diameter 6 mm with F8 as tolerance.
Since I am not good enough in fit, limit tolerance, I want to ask you if I have choosed correct value for hole tolerance?

Thanks in advance
Regards
Nak

 

[TudorM]

Hi ,
You will have a clearence fit with a maximum clearence of 24 microns and minimum 1 .

Best regards

 

[naah]

Thank you for your replying. In this case I will have a sliding between shaft and hole withoute any extern force? Do am I right?
Regards
NAK

 

[Tmoose]

"maximum clearance of 24 microns and minimum 1 ."

What materials? Some Stainless steels gall and weld at surprisingly very low contact pressure.

1 micron / .000,04" .
With .00004" diametral clearance I'd anticipate assembly difficulties even if the cylindricity and surface finishes are magnificent.
If I needed a reliable "sliding fit" even with a 6 mm Ø pin, I'd be shooting for nearly .0005 "/ 12 µmm.

 

[drawoh]

naah,

Here is a description of ANSI fits on Engineer's Edge. Search around a bit, and find the tolerance tables. The actual tolerances are based on the ISO fits you are using. There are Limits and Fits tables in the Machinery's Handbook. I don't know how available this is were you are.

 

[Carlloss]

Naah,

As Tmoose pointed, not all steel behave in same way. Without application ifo. it's hard to determinate if selected fit will be best for you but I would say it will not, as shape geometry will play a role when it comes to sliding. Try to Google ISO fits (ISO 286) which should bring you more information about standardized fits and select something with more clearance if possible.

Karol

 

[juergenwt]

Looking at your post I am sure you are trying to use the IDO 286 System of tolerances. Unless you are for some reason tied to using 6m6 for a shaft tolerance I would recommend that as a first step you decide wich one of the two systems under ISO 286 you want to use. There are two systems. Standard shaft and Standard bore. Most common is "standard bore"
In that system the bore has a min hole size equal to the nominal size - the lowest dim is the nominal size -000.
Sample in your case could be 6H7 for hole size. The desired fit is achieved by adjusting the tolerance of the shaft. In your case it could be 6f7. that would give you a clearance from anywhere between +10 and +34.
Of course you can use any other combination, but by staying within the "standard bore" (hole) recommended sizes you
take advantage of the ISO system allowing you to use a standard 6H7 reamer and change your shaft size. This will
be a lot cheaper to manufacture. One micrometer will do all the measuring on the shaft. H7 Reamers are readily available anywhere.
If you decide to go with an 6F8 hole you will have to buy a 6F8 reamer. Just a heads up: If you have a reamer custom
made be sure to go to someone who knows reamers. Reamer tolerance (6F8) differs from the tolerance listed for
the dim tolerance 6F8.
Study DIN/ISO 286.