cylindricity check 2

[waqasmalik]

Hi all,
I am confused about how to verify cylindricity? i have the concept that cylindricity does not require any datum reference and in order to check it you need to isolate the feature from rest of part. But in the figure( Attached) which i found in the book cylindricity has been checked in the same way as total run out. If this method of checking cylindricity is right then Wat will be the method of checking total run out?

Thanku

 

[CheckerHater]

Yes, you will rotate the part and touch it with the probe.

It's just equipment used and underlying math will be more complicated than for measuring runout:

http://cfnewsads.thomasnet.com/images/large/019/19472.jpg

For more information see ASME B89.3.1-1972 (R2003)

 

[axym]

wagasmalik,

Both of these characteristics can be checked with a rotating spindle and probe. The difference lies in how the part is constrained to the spindle's axis of rotation.

As you indicated, the Cylindricity characteristic never includes a datum feature reference. This means that if a spindle and probe are used to check the part, there is no requirement to use a particular axis of rotation. In other words, the part can be adjusted relative to the spindle in order to get the best (smallest) reading. Cylindricity checking machines and roundness testers have a floating spindle to accomplish this. If a fixed spindle is used, the part's centering and angle can be adjusted with a trial-and-error process until the optimal reading is found.

The Total Runout characteristic always include a datum feature reference, to define a datum axis. If a spindle and probe are used to check the part, the part must be aligned to the spindle using the datum features, so that the axis of rotation is the proper datum axis. There is no adjustment allowed and a floating spindle is not needed or appropriate.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[dgallup]

If you are serious about measuring cylindricity, you are going to be using a very specialized piece of equipment like a Mahr Formtester or equivalent. It can adjust the center and tilt of the work piece so that you can find the axis of the cylinder itself rather than the center of a datum or chuck. The image that CheckerHater linked shows the various micrometers sticking out normal to the machine axis used to dial in the workpiece. So while the probing of the surface is similar to total runout, the fixturing of the piece is much more complicated.

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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.

 

[waqasmalik]

axym
what i understand from your answer is that
1) To verify cylindricity part must always be made centered to the chuck so that our dial indicator reading could not be affected by eccentric error (if any).Cylindricity does not control coaxiality. It is a composite control of circularity,straightness and taper.
2) For total run out centring is not done.All which has to do is that just clamp datum feature of required length in chuck hence forming the axis of rotation then rotate the part and transverse the dial indicator so that you can study combined errors of cylindricity, straightness,taper and coaxiality.
3)There is no limitation on which end of the cylindrical part we clamp in chuck? No limitation on how much leghth will be clamped in chuck?

Am i right?
Thanku

 

[waqasmalik]

check hater, dgallup
Lets suppose we have a cylinder of 80mm length with a diameter of 50 plus minus 0.2 mm. I have made it in such a way like shown in figure.Part is round every where.If i clamp it in the chuck and rotate it while transversing the dial indicator along the longitudinal elements then surely part will not qualify cylindricity but it will be because of eccentric machining.What do u think?

 

[CheckerHater]

You are correct.
Your part will qualify circularity though.
Circularity will apply to horizontal "slices" of the part individually, while cylindricity to the entire part.

 

[waqasmalik]

so can i say that cylindricity is affected by coaxiality error?

 

[gabimo]

You got already your answer on linkedin. Right?

Mark Foster

Owner, Applied Geometrics, Inc.

Waqas,
The inspection scenario that you described is a runout type of inspection. Cylindricity does not control runout, although runout (total runout) will control Cylindricity. If you checked your part in the way that you described, and the resulting indicator movement you observed was within your Cylindricity specification of 0.2, then the part is definitely within a 0.2 Cylindricity. If, however, your measurement result was greater than 0.2, you might not be able to reject the part as being non-conforming to the Cylindricity of 0.2 specification since you don't know if the apparent error that you are seeing in your indication is due to form or offset. Of course, if the indication is extremely large, then you could certainly surmise that the part is also not very cylindrical, but you would not be able to report an "actual value" of Cylindricity using that measurement methodology.

 

[dgallup]

Cylindricity is NOT affected by coaxial error.
Cylindricity has no datum.
Cylindricity is just the form of the cylinder, not it's position.
When you measure cylindricity you correct the center and the tilt of the chuck to match the axis of the workpiece.

As said above, if you measure total runout and the measurement is less than your cylindricity allowance, the part is good. But if the total runout measurement is higher than your cylindircity allowance the part may still be good, you can't tell.

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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.

 

[waqasmalik]

dgallup
"When you measure cylindricity you correct the center and the tilt of the chuck to match the axis of the workpiece."

which axis? i have two axis as i have attached in my last figure.If i tilt the chuck to match the axis 1 of workpiece then other axis 2( Axis of portion which i have made by offset machining) will not be matched.

 

[CheckerHater]

We are talking derived common axis of both cylindrical bodies, forming one feature, that you are trying to check for cylindricity.

 

[CheckerHater]

Something like this:

 

[waqasmalik]

checkhater
Thanx checkhater, But one more question.
This common axis is the axis of actual mating envelope AME?Smallest perfect cylinder circumscribed to touch the high points of workpiece?

 

[CheckerHater]

Not exactly.
Generally, you will try to find an axis that will result in smallest possible distance between inscribed and circumscribed cylinders.
That distance will be your “out-of-cylindricity” measurement.