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Cocentricity with short cylinders

Posted: Sun Feb 03, 2019 3:17 am
by Klinctegleda
Hi,

I have faced with interesting problem. I need to measure cocentricity betwen cylinder (datum) and circle. Problem is that my cylinder used as datum is very short (diameter 55mm lenght 2,5mm). How realistic the result will be?

I found information that if I measure cocentricity betwen circles CMM manager will use ref. frame axis instead my base circle so this option is not OK.

I was thinking....what if I measure two circles of diferent diameter on the front side of the item, create a center line through this two circles and then use this line as a datum to control cocentricity of circle on the back side of the item. Or if I make it short.....can I use line as a datum for cocentricity????

Regards

Gregor

Re: Cocentricity with short cylinders

Posted: Mon Feb 04, 2019 10:31 am
by CrashN8
Concentricity of Line for reported feature and Datum feature is allowed. Your idea is valid as long as you are okay evaluating the concentricity from end to end as circles as opposed to using complete cylinder data. As you say the very short cylinder may lead to fitting issues so I think you proposal is valid.

Re: Cocentricity with short cylinders

Posted: Wed Feb 06, 2019 5:18 am
by Klinctegleda
OK

what about option to use datum for cocentricity as a circle.....is this by the rules.

I think it's better to use circle as a datum and get realistic result....or am I wrong?

Regards

Gregor

Re: Cocentricity with short cylinders

Posted: Fri Feb 08, 2019 6:50 am
by Murguel
Klinctegleda wrote:
Wed Feb 06, 2019 5:18 am
what about option to use datum for cocentricity as a circle.....is this by the rules.
Bearing in mind, your probe diameter might be 3, 4 or 6 mm but your "cylindar" is merely 2.5, you have not enough space to measure an ideal cylindar anyway. So the drawing is actually nonsense. Engineers are humans and make sometimes mistakes.

You as CMM-Engineer have sometimes to recognize mistakes and suggest changes. And as you suggest, I would measure a simple circle because everything else sounds against logic. And to achieva a repeatability for future, your CAD-engineer may changes the drawing to show the "Cylindar" to be measured as Diameter.