Machining tollerancing

[brooker2008uk]

I have a quick question regarding machining tollerancing. I have a 10mm diameter component want to go into a 10mm hole ideally. I have specd the tolerance at +- 0.2mm.

Can anyone recommend what sie the component and what size the hole should be to get a snug fit but still allow for for both + and - tolerances

 

[Shox Dr]

Push fit,or fit you don't want it to move bearing fit

 

[gordon stephenson]

The + or - 0.2mm covers arrange of of 0.016"(thou) which is quite a lot, For a decent fit the hole should be -0mm +0.05mm

 

[Shox Dr]

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

 

[daleyd]

http://www.green-oval.com/data/zeus.pdf

Edit, shoxdr beat me to it!

 

[ronan]

0.2mm is normally used as a general tolerance as its quite generous in most smaller assemblies. When the way two parts fit together matters , then a specific tolerance is called for, eg. 0.02mm. As the lads above have said Its the relationship between the parts and what you want them to do, that determines the tolerances and fits. If the hole is dead on 10.00mm and the shaft is 10.20mm, you'd have no hope really of getting the shaft in, short of heat shrinking the parts.

 

[scott0031]

Depends on what you want it to do. There are 3 types of fit, interference, transition and clearance and is is dependent on what you need.

Interference means the fit will interfere so it will be pressed in (the degree of interference depend on the tolerance) e.g. 10.00 hole 10.01 shaft
Transition means size for size e.g. 10mm hole 10mm shaft
clearance means one will clear the other e.g 10.00 hole 9.99 shaft


Again the degree of what you need only you can decide. Most reamers are up a bit to start with from new. But this does come down the the people doing the job and selecting either a new reamer or a worn one pending the fit required then altering the size of the shaft to suit the reamer they have.

The common practice is to use standard reamer as its a quick way to make a sized hole, then you tolerance the shaft to suit. So if you want this thing to go in and stay in, I would suggest a .015 -.02 interference. You can go a little more but it does not serve a whole lot of purpose unless there is a good reason why its required. If you start going closer to .05 interference then be warned it will be very tight for the sizes involved and may damage the hole permanently unless people know that they are doing. Like all Engineering practices there are variables like materials being used as some will have more give than others which can affect the tolerance selection.

If you need any more info please ask.


Kind regards,


Scott

 

[nick205]

As above you need to define the type of fit you need first. E.g interference fit, then work out your tolerances. Typically +0.xx/-0.00 for the hole and +0.00/-0.xx for the shaft.

 

[ronan]

Even as a fitter i never understood the transition fit. You either want something to rotate or be free in the hole, so a clearance or running fit. Or you want something to be held tightly in the hole, an interferance fit. The only example of a transition fit i could get out of the lecturers at tech was king pins in a lorry, you wanted the pins to turn , but not easily. if they turn easily by hand , they would be too loose in service. Any ideas ?

 

[scott0031]

Even as a fitter i never understood the transition fit. You either want something to rotate or be free in the hole, so a clearance or running fit. Or you want something to be held tightly in the hole, an interferance fit. The only example of a transition fit i could get out of the lecturers at tech was king pins in a lorry, you wanted the pins to turn , but not easily. if they turn easily by hand , they would be too loose in service. Any ideas ?

I agree with you totally its option that allows for a lot of confusion. If shaft is bigger than the hole even by .001 its still an interference, just not by much. I think it stems from years ago when more bushes and shafts were used for 'running fits' as apposed to the more common use of pre-made bearings these days.

Really its not something to be concerned with any more. The only real reason for a tolerance system is to give definite instruction to a 3rd party so parts can be made in different shops and fit. This is exactly why the tolerances system was derived and it came from one from one word wars and i think it was ww2 from memory (could be wrong) for most of us the sizes don't actually matter all that matters is the actual fit between the parts. I have to say I personally hate the limits and fits system we use it's a bit out of date and could be simplified a lot and it would save a lot of cock ups.



Kind regards,


Scott

 

[Rocketman]

I would go for a H7 on the hole because it's a the basic reamer size - so it will be just a drill and ream - unless they bore it but a decent reamer in most cases is fine if it's not worn.

Then select what tolerance you want on the shaft. g6 on the shaft will give a nice snug fit but allow movement.

To give you an idea of that fit it is the same as ejector pins on a injection mould tool. Enough clearance for the ejector pin to move up and down but not enough for the plastic to go down the reamed hole

 

[ronan]

To give you an idea of that fit it is the same as ejector pins on a injection mould tool. Enough clearance for the ejector pin to move up and down but not enough for the plastic to go down the reamed hole

Is that a transition fit you mean rocketman ?

 

[Rocketman]

Is that a transition fit you mean rocketman ?

It would be classed a tight sliding fit (in the clearance cat). This would give accurate location and would be able to move = you would have to push it wouldn't just drop out.

h6 would be even tighter but would still be able to be dissembled without a slide hammer.

Bit hard to know what the OP is after without further explanation.