< > [Motion](../) > Turbines
## Turbines
#### High Speed Spindles
---
#### Big fans of big RPMs
Electronic Spindles have a reasonable upper limit of ~40k RPM. This is related to motor inductance: at high speeds it becomes very difficult to switch coil currents fast enough to commutate the motor effectively.
As a tool's diameter decreases, the RPM required to maintain a reasonable surface speed increases radically. You can experiment with this variable with [this calculator](https://pub.pages.cba.mit.edu/feed_speeds/).
It's desireable to use very small endmills for PCB milling, or in Tool and Die manufacture, where something like an injection mold needs to have very fine surface finish.
<iframe width="960" height="680" src="https://www.youtube.com/embed/4Uygm2VToCc?rel=0" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen></iframe>
While they're fast, they have limited total power. Although that hardly matters with such small endmills!
Air turbines are something of a rare tool, available from [Air Turbine Tools](http://www.airturbinetools.com/) and [Bryan Machine Services](http://bryanmachine.com/spindles/), among others.
However, they should be relatively easy to manufacture. There is one example of a very simple 3D Printed Turbine Spindle [here](https://www.youtube.com/watch?v=Fj1gir4tJbU). These could be very easily made quite small, using compressed to drive the turbine, for a micro-machining or pcb machining center.
]]>