Machining tolerances

[BelgiqueB]

This kicked off an unintended but very informative discussion, the shaft will be machined by a professional shop, so how they achieve the accuracy is their problem .

The reason of this topic is mainly to understand the ISO way of giving tolerances, in the Mechanical and metal trades handbook I found the following tables, but it's unclear where the combination of letters and number come from. I get that capital letters are for hole designations but where do the numbers come from, there must be some kind of logic behind the combination of the letters and the numbers, but I'm not getting it

 

[BelgiqueB]

If its just a shaft going into a standard ball or roller bearing, then don't over think it. What is the actual job ?

The question was more about how the ISO tolerance system works than actually achieving the tolerance on a lathe, guess I worded my question wrong :-). The discussion however was very informative though!

 

[ronan]

Get a Zeus book, they have charts much easier to understand than either of the two you posted. As a Fitter its the good book that everyone had in their toolbox.

 

[mike os]

Get a Zeus book, they have charts much easier to understand than either of the two you posted. As a Fitter its the good book that everyone had in their toolbox.

Still, have at least 3 and on phone and laptop

 

[AndersK]

guess I worded my question wrong :-).

No you didn't.

Was clear to me but then both you and me aren't native in english

The link you received in the first answer is easier to read than the other tables if you just want the tolerance range. The ones you posted are more for chosing mating part tolerance grade depending on what fit you want to achieve.

 

[Agroshield]

The reason of this topic is mainly to understand the ISO way of giving tolerances...

Put ISO286-1 and ISO286-2 into Google and within the first ten hits for both terms, you will find pdf copies of the standards. The graphical tables at the back of part 2 are interesting as you see how the various letters and numbers work - your m6, for instance, is quite a narrow range and all of it over nominal. Other letters in the standard have a much wider range, some centred on nominal, some under nominal.

 

[knighty]

that bearing has a tapered bore, you get a tapered collar which slides inside it... the end going in first is threaded, so it sticks out the back of the bearing where a ring screws onto it... which pulls the taper of the collar and the taper of the bearing against each other locking it into place

tolerances are pretty lose on the shaft, and you can get different collars to suit if there's a problem



oddly enough... I have a 70mms shaft running the same kind of spherical roller bearings at work

mine shaft only spins at 40rpm, but it has 20hp behind it, and there's a good ton bouncing around inside a drum about 300mm off the end of the shaft, so about 500mm away from the closest bearing..... that's a lot of bouncing/thrashing /leverage on the bearing... and they take it no bother :-)

 

[bricol]

that bearing has a tapered bore, you get a tapered collar which slides inside it... the end going in first is threaded, so it sticks out the back of the bearing where a ring screws onto it... which pulls the taper of the collar and the taper of the bearing against each other locking it into place

tolerances are pretty lose on the shaft, and you can get different collars to suit if there's a problem

Would need suffix "k" or "k30" to get the tapered bore - and while I could quote you the FAG adaptor sleeve number, I've no idea of the SKF number - but they do make locating on a shaft quite easy as you say.

 

[knighty]

oops you're right, I miss read the spec

https://www.skf.com/uk/products/rol...s/spherical-roller-bearings/productid-22214 E

 

[Munkul]

Get a Zeus book, they have charts much easier to understand than either of the two you posted. As a Fitter its the good book that everyone had in their toolbox.

It doesn't have an "m6" tolerance in the chart, though