Water-cooling (active?) flow indicator

Quick survey for those of you who own a water-cooled spindle, do you have some kind of coolant flow indicator installed ? After I installed everything it hit me: the coolant pump that came with my spindle probably costs 20$, and its failure can probably kill my 200$+ spindle in a few minutes.

I see some of you use a visual indicator in the coolant line, I’ll go for that as a minimum:

but I have a dream about some kind of inline flow indicator that would embed a bit of self-powered electronics to either produce a beeping alarm when the flow stops, or better yet trigger a signal that I could then wire back into the VFD controls to do an automatic emergency stop.

Bonus points for Amazon links!



Both are basically a switch, so you could wire that back to the vfd as a stop signal on an input.


The spindle really takes a while to heat up. 10 or 15 minutes is not a big deal from what I can see. If I was milling steel and drawing high loads I’m sure it would be more critical.


Put a few small goldfish in the water, you’ll know if the pump stopped running if they’re swimming backwards :stuck_out_tongue_closed_eyes:

More seriously though, does anyone just use a chiller with their spindles? Like a fully closed loop system?




I have inadvertently ran my spindle for 5 mins or so (a couple of times!) without coolant. After I figured out what I was doing, I felt the spindle and it was warm, but just.

I have a cheap pump - probably $10 worth, and it was essentially quiet for the first few weeks - just a nice humming sound. Then it developed a really irritating noise - but still pumps the same. Anyways, I took to unplugging the pump when I wasn’t machining anything as the noise drove me batty. That’s why I forgot to start it a couple of times.

I’ve built a simple arduino based flow indicator that displays the flow rate and coolant temp. It will also start and stop the pump on a signal from the VFD (haven’t got that bit working yet - as I need to repackage the whole thing in a decent box first).

You can just start and stop the pump via the VFD - but I like to complicate things and have lots of readouts to look at - bells whistles and lights etc.


You had me at “Arduino” :slight_smile:
Would you mind sharing a description of what you came up with / schematics ?


@Luke uses a chiller made for computers on his system with 2 fans, if I remember correctly he has a closed system with a reservoir.

Goldfish would not work in this case because the color of the coolant is too close to that of a goldfish. :wink:


You are correct! It works really well to. Even on the hottest day of the of the century, and 2 hours of aluminium work it didn’t get part 31 degrees.

I think the setup only around about $40-50. I certainly would not blow $200 on a speciality chiller. I actually think it might be a bad idea and introduce condensation, although not something I can accurately comment on.

It turns on with the motors and is virtually silent, has a temp gauge and a visual flow meter


When I’m older, I’ll get myself an HDZ, Spindle and cooler just like @Luke. :wink:


Do NOT wait until you are older (like I did). You’ll cheat yourself of so much!


Luke’s setup was very slick, Axiom put a similar cooler on their CNCs, just a very compact PC cooling radiator, with 1 or 2 fans, a small pump and a reservoir.

As far as flowmeters and temp transmitters, search for parts for co2 laser engravers, they use them to monitor CO2 tube cooling systems

Here’s an example Here

1 Like

Judging from your picture, I would say we’re in the same bracket.

Wrong side of 70?..

Not crying, just wish I’d jumped into all this fun, say, 15 years earlier when the kids moved on.

Not quite but on my way… good picture!

Here’s what I did.



And I bet that even if you never put those fans on there and just recirculated the liquid from the tank into the spindle and back, it would work just fine since it’s a big jug of liquid and would take a lot of energy to heat it up that much.

Also, this is just bad for my CNC addiction. I realize now that I have a radiator at work that would work perfectly for this. @Griff really is going to have me buying a spindle sooner rather than later…



I’ll take some pictures on the weekend. I need to make a decent enclosure for it - at the moment there are just wires hanging out everywhere.

But it’s pretty simple, just a flow sensor very much like the one pictured earlier in the string, a temp sensor, an arduino nano, and a recycled Nokia LCD.

Like I was saying I want to integrate a relay so the pump can turn on/off via a signal from the VFD - but I haven’t gotten that far yet.

1 Like

Where did the container come from?

@HDRyder that’s a very tidy bench/setup, very nice!