8 April 2019
8 April 2019,

Ultra precision machining requires an ultra precision arbor. Why? Because you can’t get precision without taming TIR (total indicated runout). Its the difference between being close and close enough for hand grenades. And you don’t machine with hand grenades, do you?

The TIR Concept

Things that spin don’t spin perfectly. In a perfect world, they would. But, it’s not a perfect world. That’s because the axes on which they spin are not absolutely straight. Static TIR is the result of the way the tool, collet, and spindle come together.

Measurements of TIR usually involve a combination of angular and radial runout. Radial runout happens when there is a lateral offset between the rotational axis of the tool and the central axis of the collet/spindle setup. Look to your tool mounting as the most common source of this problem. Angular runout happens when the rotational axis of the tool and the spindle/collet are off. The cause can be something as simple as a set screw or as complex as a worn spindle taper.

TIR is the difference between the maximum and minimum values measured across an entire rotating surface. In geometric dimensioning and tolerancing language, you identify the datum points and tolerances.  It looks like this:

Taming TIR

So, the way to tame TIR is to start with your tool holding. And start your tool holding with an arbor made for precision. The ultra precision arbor isn’t like a general reach arbor. It is made for tight tolerances because it is designed to control runout. Remember radial runout? That can be blamed on the wrong tool holder. So, to tame TIR you’ve got to use the right tool holder. The right one has a deep cap that absorbs vibration. That vibration is a problem. With more support from a deep cap, you have more rigidity. More rigidity reduces your TIR.

ultra precision arbor

Ultra Precision Arbor

Taming TIR takes an ultra precision arbor. An ultra precision arbor is just what Sierra American Multi-Systems manufactures.

The unique Vibra-Core design reduces runout. It is perfect for carbide blades. Feel free to run at high speeds, Sierra American has you covered. Don’t worry about TIR. The gold series of arbors is heat treated and ground to .0004″  concentricity and square. Buy one or buy a set.

If your tool supplier doesn’t carry Sierra American, tell them to order it for you. Get the best and get Sierra American.

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