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Standard for conectricity used in machining?

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var10

var10

Mechanical
Apr 4, 2013
188
Hi everyone,

what is the standard concentricity tolerance in machining T6 grade aluminium alloys?

Thanks,

V.
 
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There is no such standard.

You have to specify what you will tolerate on your drawing.



Mike Halloran
Pembroke Pines, FL, USA
 
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So I assume you're actually interested in 'typical' process capability?

Specified tolerance should arguably be based on primarily functional considerations, then verified that it can be achieved cost effectively.

Do you really mean concentricity or more generic coaxiality which might be run-out or even position tolerance?

What machining process are you interested in?

Posting guidelines faq731-376 (probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​
 
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Thanks guys, runout tolerances will not be relevant to my case (semi circle with holes). I see your point, I will request my supplier what they can achieve. Its CNC machined

 
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CNC lathe, CNC mill, CNC EDM, CNC water jet, CNC plasma...

CNC is not a manufacturing process, it's a way of controlling machines for many processes.

Posting guidelines faq731-376 (probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​
 
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Understood it is just the way we speak here, by default we mean mill here. My bad should have clarified.
 
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Hang on -- to the point made by Kenat (in his third line): What standard are you using? ASME or ISO?

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
 
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Tolerances are determined by functional requirements then manufacturing processes are selected to cost effectively achieve those tolerances. Even if you already know that you are going to CNC mill something because it's the only machine available today there is no point in specifying tolerances that are smaller the the part needs to function. Unnecessarily tight tolerances increase costs in many ways including additional tool changes, extra inspection, scrapping perfectly good parts, etc.

Just because something is CNC milled does not mean you can always achieve the same positional accuracy. If there are surfaces machined in one chucking with the same tool the result will be much better than if multiple tools are used and the part has to be flipped over and re-chucked.

----------------------------------------

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
 
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var10,

Centreing in a lathe depends to some extent on whether or not the machinist needs to re-chuck your part. If two features have to be centred, you should design them to be machinable on one setup.

I strongly agree with dgallup, above. Your tolerances should be based on functional requirements. You do need to be aware of what your fabricators can do.

--
JHG
 
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Yes, I agree. Belanger - We work with ISO standards.
 
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OK, just checking. Those of us who mostly work with ASME will see that use of concentricity as identical to a position symbol, then.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
 
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