Is anyone inspecting Runout on sheaves?

[inspector212]

We have sheaves that we inspect from suppliers from time to time and we are in a debate about whether we are using the best method to check them.

We have a fixture, that is quite old, that holds the sheave on a zero spindle with an expanding mandrel and then has two dial indicators with balls on them that we move in to check wobble and hop. The problem is that the error in the fixture is pretty close to the tolerance available. We need to update the fixture and don't know if we should just check them on the CMM, which method do we use, or do we invest in a Runout machine.

I was hoping that someone in this forum has experience in checking sheaves and could lend me a hand.

[Paul Sarrach]

Invest in a runout Machine. There are some awesome video scanners out there.

[bboyd]

Repeat after me,
I _____ will not use my CMM for checking any runout dimensions unless I have a scanning head that never looses contact with my part.

[Paul Sarrach]

Repeat after me,
I _____ will not use my CMM for checking any runout dimensions unless I have a scanning head that never looses contact with my part.

Funny, but true. I quess I should of stated that. Never, ever try to check out run out if you can't keep your head on/or in the surface

[craiger_ny]

What bboyd said. Put a piece of tape on your monitor where the runout button is if you have to. Better yet put a Mr. Yuckface sticker on it.

Craig

[inspector212]

OK, please forgive for asking. But, Why?

[Wes Cisco]

Runout is deviation of form from an axis of rotation. You will not be spinning the part as you measure it on the cmm, which is the easiest way take care of the axis of rotation part. You will be measuring a finite number of points. Even if you take a lot of them, you know nothing aobut the surface between your hits. Also, once you have the raw hit data you will be relying upon a mathmatical algorythem to construct a circle from your points. This means the center, (axis of rotation) and the circumference are generated from this formula and the discreet points you collected, NOT the actual center or circumference of the part. The differences may be very small most of the time, but Mr. Murphy is always looking for an opportunity. HTH

[inspector212]

OK, fair enough, that makes sense.