Collet Runout?

[cdhknives]

I broke down and bought some cheap collets to use just to get a feel for them...so I can make a better informed decision on investing in either a 5C or ER set later.

I was trying to test the accuracy of what I got here:

Is this a fair test? Does measuring that far away from the collet tell me anything?

 

[RJSakowski]

Is this a fair test? Does measuring that far away from the collet tell me anything?

Your test is a valid way to test the TIR. However, you are actually measuring runout of your test fixture, the collet, and the reamer blank. When I test in this fashion, I make a mark on the test fixture, the pin, and the collet. Measure the TIR up close, and at about two inches out and note the values and orientation of the pin and collet. Now rotate the pin in the collet and fixture 90 degrees and repeat. Do the same for 180 and 270 degrees. If the runout follows the pin, the pin is the problem. If the runout stays in the same position relative to the collet and fixture, the problem is with one or both of them. In a similar fashion, you can isolate the runout in the fixture and in the collet. More than likely, you will find runout in all three components.

Runout at the face of the collet is primarily radial in nature. When you measure at a distance out , it is a combination of radial plus angular runout. It is an important measurement because much of our use of a collet is fairly well removed from the collet, whether workholding or toolholding. Ideally, bothe measurements will be close to zero TIR. Usually the measurement at a distance is greater because the effect increases with distance from the collet.