Z Datum Average of 2 Points callout

[SDETERS]

We are working on a casting part, in which we have an X datum as three datum target areas and Y datum Axis which is specified as a small portion of the taper.
Now the Z datum point, we want to use two sides of a drafted surface, and average these two points to create the Z datum point. Centering type datum.

When this part gets machined we use a 30 deg tapered pin to locate off the slot in the machine fixture. This pin will hit off of the edge fillets.

What would be the best way to specify this Z datum setup on a print? I have attached an example print for clarification.

 

[jassco]

I would use a "V" block to control 6th DOF ("clocking").

Best regards,

Alex

 

[3DDave]

The print is fine for the "Z" clocking; I am uncertain about the clarity of the "Y" because it looks like it is a cylindrical datum feature on a tapered surface. A basic diameter and no area marking would be more applicable. Alternatively I would propose using a precision sphere as the datum feature as that will conform to the taper along a line but not gouge into the taper.

 

[SDETERS]

Thank you both for the feedback. I appreciate it. We will look into the Y Datum a little bit further.

 

[mfgenggear]

OP
What is the goal, and purpose.
Are to trying to understand how to measure the
Taper. And dimensions?

 

[SDETERS]

The goal is to determine the best way to set up the part for inspection to get reproducible, and repeatable results. In the Machine fixture we have 3 datum pads for X, for Y we have a spring-loaded tapered pin that hits off the taper top radius, and for the Z Datum, we have a spring-loaded tapered pin that clocks that part. We want to figure out if a "VBlock" type setup is possible in a CMM setup vs using datum points?

Also, what is the proper way to callout the "average" of points on a drawing per the standard? Or is it better to hit off one side vs a centering type of averaging of points.

 

[mfgenggear]

OP
I would throw a ball calculated to fit in the Tapered hole. A calculation can determine the dimension from top of the ball to the datum , or chosen surface.
The casting foe tooling should be machined flat and parallel. Then the dim to the ball will be accurate
A CMM can inspect random points on the surface. To average dimention.

 

[3DDave]

"Average" is fundamental for pairs of things, such as the two sides of a width measurement or two targets for the same datum feature.

An actual v-block has millions of points of comparison - every atom of both surfaces take part. A CMM cannot duplicate that and will only be sort of close.

 

[mfgenggear]

Cm can be programed to measure radon points then a logarithms will calculate the results. Worked with CMM inspectors. It depends on the sophistication of the software and hardwsre.