@Rene_Jurack Look on ebay for 40mm cpu watercooling. Been using these for more than a year, and they work great.
You can strap them to the side or back of your stepper.
@Cristian_Nicola yes, fins would work, but take a lot of space.
Peltier elements are a pain in the behind, you need to actively cool the hot side with a fan to get results. Apart from that, they use a lot of power.
Watercooling is the best option for 3d printers.
We really need someone to manufacture steppers made for watercooling where the water flow is integrated in the housing for the motor
@Adam_Steinmark I think the patent is 2021. Forget which expiration rule applies in this case. 2004 patent grant with I think 1999 priority date.
I was thinking about whether you could cut a water port within one of the stepper endcaps, but I don’t think there’s enough meat. Our volume is basically nothing for a stepper fab shop, so I don’t think you’d get it done at the factory. Replacing an entire endcap with an aftermarket part would require REALLY precise fab tolerances… the rotor bearing pocket is like a 1um precision type thing because rotor concentricity with the stator is so critical.
Maybe if you took out two of the housings screws and stuck a 3mm copper tube in there? Eh. Probably not worth it.
Brazing a cooling block to the existing endcap is probably the most realistic high-conductivity option I think.
make your own with a cheap chinese desktop 6040 cnc 
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@Daryl_Bond very interesting. I have a 3040. Did you have to do 2 sided milling? Is that how you got the tubes made? Did you have to separately drill the tubes after?
@raykholo Yes, I had to put it on the side for the tube holes. That can be done with a drill-press, or even a hand drill, as long as you design to allow for some tolerance in postioning the holes. The 3040 may even be better, possibly more rigid = less chatter. These chinese mills are very flexible…
I actually was thinking mill 1 side and then turn it 180 degrees to mill out the other exterior half of the tube. Otherwise you’d have a half dome half square tube.
Those tubes are some 4mm OD pipe that I then glue in place, no milling required! Unless I’m missing your point?
Oh I see. I thought the tubes were part of it and the whole thing was a single milled piece.