TIR on rolls
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Posted by: strataballer02 ®

07/19/2006, 20:48:25

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I am trying to wrap my head around this TIR problem. Picture a roll sitting on a pedestal. One support is at 3 o'clock, the other at six o'clock. Now check the TIR with a dial indicator at 12 o'clock. Let's say you get .002" or .004" or anything you can make up. Now put the indicator at 9 o'clock, it reads zero runout. How does this occur?







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Re: TIR on rolls
Re: TIR on rolls -- strataballer02 Post Reply Top of thread Forum
Posted by: randykimball ®
Barney
07/19/2006, 22:58:46

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Let's play with our mind eyes for a second...

In your mind place the supports at 5 o'clock and 7 o'clock. Now place the indicator at 12 o'clock. Now look for the TIR.
If your roll has been squeezed in a three jaw chuck you need to also check it for roundness with the supports at about 4:00 and 8:00 with the indicator at 12:00. A part that has been squeezed in a three jaw chuck can read round checking between 6:00 and 12:00, although it is not and is somewhat triangaular in shape. With the supports at 4:00 and 8:00 you will find it in a heart beat. A micrometer will not check this. In this case moving the indicator to different clock positions will get totally different readings. This could be playing a part in what you are discribing.

Also, placing the shaft on a support and indicating the roll should show roundness IF the shaft is straight and round.

As I understand in your example the support at 3 o'clock is only there to keep the roll centered under the indicator. I asume you are placing the indicator on a shaft at the end of the roll or in a bore... or have the shaft on supports and are checking the top of the roll, ...this would be the TIR of the two diameters (shaft to roll diameter).

You should check for roundness.

I prefer the 5 o'clock and 7 o'clock positions.. notice that a shaft balancer uses aprox 5:30 and 6:30.

Geeze.. is that muddy enough? There are several factors at play here.





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Modified by randykimball at Wed, Jul 19, 2006, 23:59:49


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