Thursday, November 28, 2019

Living in the world of sub-micron

Run-out is an inaccuracy of a rotating mechanical system; specifically when the tool does not rotate in line with the main axis of the spindle. For example, when drilling, the run-out will result in a larger hole than the drill's diameter due to the drill being rotated eccentrically.

The first law of machining: the run-out is dynamic and cannot be compensated for.

The second law: the run-out is complex with the run-out error being compound. It is a result of a number of factors such as imperfect bearings in the spindle, worn bearings, imperfect chuck, collets or an imperfect tool itself.

And here is the final postulate of machining: "Absolute alignment is impossible, a degree of error will always be present."

This is a scary thought, you invest in a machinery tool holding the best tools money can buy, and you know upfront that no matter what, there'll always be some run-out.
Of course, if you're to drill a 6mm hole in the wall with a $99 cordless hand drill using a $5 drill bit from bunnings, then a run-out is not going to be important at all. But if you're trying to drill a 50 micron hole then even a 1 micron run-out of your entire system is way too much. This is the kind of challenge that we face in watchmaking. In particular, the weakest point in our system is not the spindle of the German CNC mill nor the 'Swiss drill bit', it is the chuck (the clamping system) that connects the two. To machine a watch main plate alone, it takes 12 tools which are rapidly exchanged, each one held in its own chuck. Most of those chucks have a run-out under 1 micron. But recently, we have acquired Japanese high precision tool holders by BIG Daishowa. These are sub micron run-out tool holders and the difference in price between the standard and ultra precision model is over $1,000 AUD per holder.

Here is the link to Instagram video showing the measured run-out of our milling system:

This information is in the public domain and we are proud to share advanced manufacturing capabilities that we all, as Australians, can be proud of.

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