IT# as a tolerance on feature control frame 1

[SeasonLee]

Please look at the IT# on Runout (and parallelism) callout, if I am not wrong, the IT# should be International Tolerance Grades, can we just specify the IT# as a tolerance on a FCF? It’s an ISO print.

Thanks for all comments

SeasonLee

 

[SeasonLee]

Thanks for all of your comments, attached is ISO 286-1-2010 for anyone who is interested to go through.

For the parallelism callout IT5 wrt datum B, I think the basic reference dimension should be the max thickness 3.1mm; but for the runout callout IT6 wrt datum A, is datum A (M8) the basic reference dimension or the max Ø16.1?

SeasonLee

 

[pmarc]

That's a great question, SeasonLee.
And some more food to eat: why do you think that 3.1 mm should be used as a reference for parallelism tolerance value? Table 1 in ISO 286-1 defines tolerance grades depending on nominal dimensions, not the max values. Now my question: what is the nominal for 2.9 - 3.1 dimension? Are you clearly able to answer without any assumption? Is it 2.9? 3.0? 3.1? Depending on the nominal value chosen the dimension may fall in different range of dimensions: less than 3 or 3-6, and the allowable tolerance value may change.

 

[CheckerHater]

Allow me to introduce use of IT grade in geometrical tolerance done by no one else but ISO itself.

Which basically proves my point that IT grade is better left for general note.
If you have catalog or standard listing 3000 bearings, it is better just mention IT9 once, than take 3000 chances to make a typo.

So, to pmarc: there are no apples and pears, just fruits. To MechNorht: allowed, but really hard to find. To fsincox: thank you for your support. To SeasonLee: I’d rather put actual values into FCF. As you can see using IT next to dimension that already has tolerance may be confusing.

 

[MechNorth]

Agreed, CH. Don't like 'em.

Jim Sykes, P.Eng, GDTP-S
Profile Services

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[TheTick]

Simple choice: a) tell the manufacturer, inspector, etc. exactly what you want, or b) hope that they understand, have the right up-to-date sources, and don't grab the wrong values from a chart.

 

[pmarc]

I have just one more observation to share, which is not going to be an argument against what CH showed, but gives some idea of my standpoint.

At the end of ISO 286-1:2010 and ISO 286-2:2010 there is a GPS matrix model which shows a position of both standards in the matrix, or in other words, which chains of the matrix are influenced by the standards (see link). Only "Size" chain is influenced in chain links 1 and 2. No impact on Orientation, Location, Runout controls, etc. That really does not surprise me...

http://files.engineering.com/getfil...2f68d524aed3&file=ISO286_GPS_matrix_model.JPG

 

[CheckerHater]

There is no need to be in an argument. We found that the technique was OK before, that many places still do it now; it’s possible that it will change tomorrow.
The changes ISO went thru during 2010, 2011, 2012 so far look like they just started the snowball rolling. I won’t be surprised if in the future several standards will be edited to harmonize with the whole “matrix” model. So, whoever will see something, please let us know