Simple runout question(s) but uncertain about measuring technique...clarification please

[brandnew1]

Hi All,

The first part of this question is very simple but i need guidance on this to make sure i understand the GD&T call-out.

Customer has a drawing in which they call out circular runout. Bare with me on the simplicity or stupidity of the questions but i want to make sure i'm on the correct path according to the drawing.

A) Circular runout of diameter 1.585/1.588 is to Datum A right?
B) How is circular runout defined? (Do i have the right definition: "Circular run out controls the cumulative variation of circularity (roundness) and coaxiality for features constructed around a datum axis and circular elements of a surface constructed an angle not parallel to the datum axis."

This is how i'm understanding the blueprint:
According to the blueprint section, Diameters 1.585/1.588 are to be rotated about Datum A (which mean's i need to consider location of diameter 1.585/1.588 in reference to Datum A as well as circularity)

Please correct me on this interpretation.

There is a pdf attached which the first two questions relate to the top image of pdf.
The bottom images are actually why i'm asking the question here about runout.
This is how i'm told customer measures runout on feature which i need understanding. Basically the part is placed on two v-blocks or similar on outer feature of part, it doesn't appear to be inner diameter (datum A). They place indicator with long tip reaching inside to datum A, do a TIR, from here they move the indicator to the featured diameters and do the same thing and then calculate their runout.

With this method i'm not seeing how this ties into Datum-A since the part is rotating on outside features, even though they start off measuring datum A. From there they move onto the diameters in question and based on direction indicator goes they either add to value found from Datum A TIR or deduct.

Can someone clarify why this works or why it's not accurate?

thank you

 

[3DDave]

Their method is flawed. They assume that A is perfectly circular. If it isn't, it will add or subtract randomly from the delta between it and the target surface. If you want a bad answer for runout use V-blocks. If you want a really bad answer use V-blocks on a third, unrelated surface.

They failed to establish an axis simulator for A from which to measure.

The drawing is also weird, having a straightness tolerance of .010 on a feature with a diametral size variation of .005, but then requests a runout of .001 to this distorted feature.

You need a collet and a lathe or something very similar to establish A. If it's hour-glass shaped you're in even more trouble as there are an unlimited number of candidate orientations.

 

[dgallup]

You need an expanding mandrel to pick up on Datum A. Datum A is also a bit short, preferably it would be longer than the diameter to be a good datum. This would work much better if the 2x 1.585/1.588 bores made a composite datum and you measured the run out of the 1.403/1.408 bore.

Alternately you could use something like a Taylor Hobson Tallyrond roundness gauge. These have the ability to chuck on the outside surface then shift the center and tilt of the part to align the machine axis to your datum A surface. Once the machine axis is aligned with Datum A then you can measure the roundness or run out of the two 1.585/1.588 bores. Not a very fast process but highly accurate.

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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.

 

[brandnew1]

Thanks for the response.

So when there is a circular runout callout, this is both a location and circularity?

3DDave - in regards to the datum A being perfectly circular, based on their method they following this method:

If datum FIM is .000 and controlled feature has FIM of .002 = circular runout is .002
If Datum FIM .001 and controlled feature has FIM of .002 in the same direction of Datum = circular runout is .001 (subtract FIM from FIM)
If Datum has FIM of .001 and the controlled feature has FIM of .001 in the opposite direction of the Datum = Circular Runout is .002 (add FIM to FIM)


So i'm not sure if this is their way of account of this potential lack of perfect circularity in Datum.