Hi George,

The spindle motor itself is pretty quiet, aircooled or water cooled. The noise comes from the cooling system which is either a fan on the end of the shaft (20,000rpm) or a water cooling system to a proper radiator with a fan running at 2000rpm.

Hi Ecat,
Interesting project there! The ali/copper question is a good point, and is steering me back to the less efficient ali ones to be on the safe side.
Would prefer to use the internal cooling channels, and not mess about with extra cooling circuits, although its a nice idea.

I'm contemplating working out the flow resistance of the spindle cooling channel:
Cut the bottom off a plastic bottle, invert it, hang it out the 1st floor window
Run a pipe down to the spindle on the ground, with a pipe on the spindle outlet into a nearby bucket
By timing how long it takes to put say 10 litres into the bucket, whilst topping up the bottle to keep the same head, I can work out the flow rate and pressure characteristics.
Pressure is mass (of head of water) x gravity x head (of water), all of which are known and constant for this test.
Flow rate is the time is takes to fill 10 litres, converted back into some suitable units.

If I then repeat this test but without the spindle it would give me the flow characteristics of just the long pipe, and I'm guessing I could subtract that out.

If I then select a pump, look at the flow rate pump data at that pressure, it will tell me the flow rate through the spindle if I were to attach just that pump. I might then be able to plug this into the spreadsheet and see what would work in terms of radiator and fan spec.

I know water has a specific heat capacity value, the amount of energy required to heat a gram (or kilogram?) of water one degree. This might factor in somewhere, but it would be nice not to go down to first principles if possible.

I have read someone trying something similar but just holding the bottle at ceiling height, with the spindle on the machine on a desk (so head was about 1m). The water either did not flow out at all, or barely flowed, added to my suspicion that there is a lot of resistance in the cooling channels.

Whatever I end up do, I'm sold on the idea of using PC cooling bits, just a matter of getting something which works and is not too expensive.