Spindle Speed Controller Question

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Its a question of choice

Exactly. ...and one choice is not necessarily worse or better than the other. It seems that not everyone understands the meaning of this simple word called "choice".

Water cooled spindle :
1 Does not care about wood or metal dust , so will not clog, and dust there is , believe me on that. Even a vacuum shoe could not cover all typical scenarios.

I don't know if that clogging spindle is really such a problem in reality. Yes, dust is an issue, especially with wood, but even with water cooled, one should still have dust extraction. I can't for my life understand people milling wood on CNCs day in and day out and not installing any dust shoe, regardless if they use water cooled or air cooled spindles. If nothing else, they should think about their own health.

2. Will make negligible noise, which will not matter as usually cutter makes more noise. But not so with small cutters on plastic or metal. There its virtually silent

Like I said to the OP... compared to air cooled 400W DC motor, or any other air cooled spindles, like the pretty popular Kress, the brush less air cooled motors are pretty quiet and DEFINITELY not noisier that the those compared with at the same speed. I never said water cooled are not quieter that air cooled brush less motors. On the other hand, in my case I have used an air cooled 400W DC motor for one year, and the noise of the motor is definitely not a lot at maximum speed (12k RPM). I compared it with my air cooled brushless spindle and that is DEFINITELY even quieter. Once milling starts the motor noise is totally gone, overtaken by the cutting noise even though I basically only cut plastics. That cutter noise would be EXACTLY the same regardless if I used a water cooled spindle or air cooled one. Comparing the spindle at 24k RPM with the DC motor at 12k RPM is pointless, of course that the spindle is noisier in that case, just like if I drive at 100 kmh and then accelerate to 200kmh, engine noise will increase even in the best car. So the noise argument for my part is just nonsense. But, never the less, of course, I understand that by eliminating the fan and closing in the motor, like it is in a water cooled one, that motor generates less no load noise that one with a fan inside and holes right through. Also, as I said, if I'd run my CNC for many hours a day and 5-6 days a week I would not hesitate installing a water cooled spindle, but I don't, so for me life is easier with an air cooled one.

3. In fact there is no need for pump at all. Connect to water using garden hose connector and transparent cheap tubing and let it run. it will wast how much? 5 $ for one year

It is wasting water never the less. Very anti-environmental, considering the majority of earth does not even have access to potable water for their survival. Never the less, yes, that's an option if one is keen on saving a few bucks or have his CNC near enough to water. Again, I just described MY needs and MY choice. I know there are many other alternatives and many options to how water cooling can be done, but using air cooled spindle is one such option if there is no need for water cooled one.

4. A good proper spindle pump is 35$, an italian brand garden small pump is like 20 euro here. from a second hand market 1 euro and will run forever. yes even a 3$ one. The pump inside have no elements that could fail. Ceramic rotor and plastic fins. Water is the cooling and bearing.

Yes, I am aware of those prices and 35$ is more reasonable than the previously mentioned £3. I would not even touch a pump that cheap. Never the less, I don't know why people bring up costs as an issue. Why does everyone assume that cost savings was something I consider against water cooled spindles? On the other hand, if I'd go for a water cooled spindle I'd buy quality parts because it is indeed a critical part of the spindle. After all, if the pump fails your spindle will send smoke signals after a few minutes...

Actually, pumps can fail, they have indeed elements that can fail, but they don't rotate as fast as a fan in the spindle. Anyway, I have so far not heard of fan failure in these spindles. It can happen, I know that, but in really... anything can break, even a water cooled spindle or a pump.

When i bought my first spindle nobody had run it more than 5 months or disassembled it. Spindle bearings were a sacred subject. Water cooling was sth from science fiction. All were using Kress or Dewalt , etc. routers. Now all we know water cooled spindles are good for years to run. bearings are cheap. Most come with front ceramic bearings. So i don't see why the doubt.

I don't doubt at all that there are advantages of water cooled spindles. Where did you get such an idea? All I try to say that it is not needed, nor necessary for everyone and that not everyone wants one. You said it yourself, "Its a question of choice". It is not necessary to have one SINGLE choice for all, that's not choice...