Expressing dimensions, tolerance, clearance... ??

[skanskan]

Hi


Imagine I have designed a part that fits inside another one.
For example a block with a 1cm diameter hole, and a 1cm diam cylinder piece that fits in that hole.

How do I express their dimensions/tolerance/gap/clearance in such a way that this cylinder can be introduced in the hole? As tight as possible but being able to move.

I guess that just writing that both have 1cm diameter would be wrong because their surfaces would overlap.
and saying 1.00+-0.01cm for both pieces could imply that the inner piece could be bigger than the outer one.
Do I need to say 1.00cm, 1.00-gap cm for the other one? being gap >=2*tolerance

I mean what's the proper way that could be understood by a manufacturer.

 

[IRstuff]

Depends on how many you're building and what percentage of them you want to fail.

This really isn't that complicated, if the maximum dimension of the cylinder is less than minimum dimension of the hole, then there will be no interference.

TTFN
faq731-376

 

[skanskan]

Yes, but how should I express it?

 

[IRstuff]

??? You find out from your suppliers what their tolerances are, and you state your dimensions so that the tolerances don't overlap, which means that the cylinder's nominal dimension MUST be twice the allowable tolerances smaller than the hole.

TTFN
faq731-376

 

[IRstuff]

Perhaps you should read up on tolerancing in ASME Y14.5M, or get an actual ME to do the design.

TTFN
faq731-376

 

[Brad1979]

You really haven't given enough information. "As tight as possible but being able to move" could mean different things to different people. It could just mean really tight tolerances or it could mean you'd want a straightness or runout GD&T on the parts or it could mean you'll need to specify a surface finish, etc. It depends on the material and method of making the parts (plastic or aluminum?, cast part or machined part?).

I mean even an interference fit will still move if you apply enough force.

 

[skanskan]

OK, I've being reading a little bit about tolerancig
Imagine I want to say that my pieces measure 10mm and I want a clearence fit RC3 (precision running fit) and a tolerance of 0.1mm.
How and where should I write all this?

 

[MiketheEngineer]

Call your machinist - he can help A LOT!!

 

[KENAT]

This information usually needs to go on the engineering drawing.

Typically these drawings should be created in accordance with an industry drawing standard.

These vary some by location & industry but the primary one in the US is ASME Y14.5.

Most of the rest of the world use ISO, or their local variations.

Are these production parts or some kind of captive tooling/test fixture or similar? In the latter case you can sometimes get away with more 'so long as the parts work'.

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[KENAT]

Oh and this isn't really the appropriate forum, the drafting standard forum may be better but you'll need to be able to fully articulate your question to get a good answer.

Posting guidelines faq731-376

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(probably not aimed specifically at you)
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[skanskan]

Thank you all.
I'm reading the ASME and ISO standards.