Difference between IT6 and H6 when applying to parts? 3

[David R]

It’s a bit of a nooby question, but I was asked to put tolerances on a part and I was asked to use IT6 as the tolerance. I understand that IT is a class and 6 is the grade of tolerance, and H6 is a fit tolerance with no deviation (from what I’ve seen).

My question is in the drawing/part why would I use just the IT6 tolerance and not give an H6 or h6 tolerance for shaft/hole?

If I am supposed to give an IT6 tolerance do I just take it from the table and use a bilateral/symmetrical tolerance? Otherwise I feel as if I should just use the H6 or h6 tolerances.

 

[pmarc]

6 defines only the amount of tolerance, i.e. how wide the tolerance zone bandwidth is.

The letter preceding the number, e.g. H, h, g, p, N, defines "location" of the bandwidth relative to the nominal dimension.

Therefore, the whole tolerance specification must contain both, the letter and the number, to avoid ambiguity.

 

[CheckerHater]

You might be mentioning IT in general tolerances, like "DIMENSION WITHOUT TOLERANCES +/-IT11/2", but this usually implies wide open tolerances,like IT10 ... IT14.

You may want to double-check with your superior, exactly what kind of fit you are trying to achieve.

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[hatsegal]

Consider also if the tolerance of IT6 is per the "hole basis" or "shaft basis" as that also impacts the tolerancing.

Cheers, hatsegal
"Think first"

 

[juergenwt]

They want you to apply IT6 tolerance to a part which determines how this part - hole or shaft - is manufactured. You are required to put the IT6 tol. in the right position. Depending on the part requirements. Could be a standard hole (preferred method) with a H6 tol. combined with a shaft tol. of h6 for a sliding fit or any other combination with the tol. of IT6. A lot depends on the dia. or shape of the part.
So when they require IT6 it means you must find the manufacturing method - grinding, honing etc. - to produce the part within within IT6.
That is your job. It is up to you to put that tol. in the right position by adding the letter depending on the type of fit you desire.
I would advise you to attend some classes on ISO Tolerance or at least read up on how to use the system. Looks like you are going in the right direction.
You must understand that by asking you to stay with IT6 requires a production process capable of producing that quality (cost??).
Again - study the ISO System of Tolerances. Start with ISO/DIN 286.
To better understand the system also find a table giving you manufacturing methods to produce a certain quality (Google is your friend).
Good luck!