Clocking cylindrical parts with datum feature
Clocking cylindrical parts with datum feature
(OP)
When positioning features on a round part, like a flat disk, should one of the features be made a tertiary datum C to clock the location of the rest of the features?
Do not all features orient to the X and Y plane that establish the datum axis, eliminating the need for a tertiary datum to “clock” other features with?
Reference drawing attached.
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RE: Clocking cylindrical parts with datum feature
It is certainly not "wrong" to add a clocking feature.
RE: Clocking cylindrical parts with datum feature
Also, there is slightly different view on it between ASME and ISO.
So, if you are in ASME world, technically, yes, you can do without clocking datum. But adding one to be safe and better understood, is not entirely wrong.
RE: Clocking cylindrical parts with datum feature
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Clocking cylindrical parts with datum feature
We use a tertiary/clocking datum (we're still under 1994), and feel that it is necessary, to the point of many times adding construction holes just for that purpose. However, if there is a way to get out of using it, I'm eager to hear about it.
Thanks
RE: Clocking cylindrical parts with datum feature
Start here:
http://www.tec-ease.com/gdt-tips-view.php?q=161
http://www.tec-ease.com/gdt-tips-view.php?q=126
RE: Clocking cylindrical parts with datum feature
To be clear, I am not a fan of simultaeneous or envelope.
Frank
RE: Clocking cylindrical parts with datum feature
When you make one feature a datum and control another feature wrt the first, you somehow imply that functionally first feature is more important than the second one.
Why not use it where it makes sense?
Typical sim req example shows shaft with two keyways – fine with me.
But if one of them is really somehow “primary” to the other, why not use a datum?
RE: Clocking cylindrical parts with datum feature
I am all for functional requirements. I am not sure you can easily say which has a precedence with two keys or two round dowel pins.
Frank
RE: Clocking cylindrical parts with datum feature
RE: Clocking cylindrical parts with datum feature
Good point to make, we should not leave the impression they are completely equivalent! If a datum feature of size or pattern of features of size is referenced MMB, I thought that the datum virtual condition rule (rule #5) makes it the same, though, true or not?
Frank
RE: Clocking cylindrical parts with datum feature
RE: Clocking cylindrical parts with datum feature
Sorry, we are still at 1982, I believe it is the same statement as section 2.11 in 1994. I am not sure in 2009.
RE: Clocking cylindrical parts with datum feature
I do not think that MMB concept changes anything. There will still be a difference between "simultaneous requirements" and "one of features as clocking datum feature".
RE: Clocking cylindrical parts with datum feature
It sounds like the correct answer is it could go both ways…?
lightweight, cheap, strong... pick 2
RE: Clocking cylindrical parts with datum feature
John Acosta, GDTP S-0731
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