Thread: Cooling down a mini-mill motor

I have a mini-mill with the classic motor (smooth, un-ribbed sides).


When I mill a big cut it eventually get hot. I have to stop perodically to let the motor cool down. Same with my lathe.


I have been thinking to add a fast running (computer type) fan on top to force suck air through the motor at high speed. This may assist the motor to take more time before I have to take a break.


The ordinary 100mm (4 inch) fan is too big as the fans blades are extruding to past the holes in the top and the dead, solid area of the fan blocking the motor's holes. A 75/80mm (3 inch) will have a smaller inner area, causing the blades to be exactly over the breathing holes of the motor.


I have read an article on Andyf's Warco WM180 lathe page about adding a computer fan to the motor to cool it down and this inspired me in this direction of thinking.


Any ideas or references?

80 mm computer heatsink cooler fans are quite common and may do what you want. However I have a similar mill with a motor as you describe. It has a variable speed controller and has a thermal cutout built into the motor. I've not yet managed to trip this due to over heating though. Looking at mine I think it would be difficult to get any appreciable air flow through the motor. Blowing air from the side would be quite easy. How effective that would be I don't know.

Hi Jors,

A few people have done a similar thing with their DC motor conversions. If you are having trouble finding a fan to fit or match your motor end, then perhaps making a shroud or some ducting will allow you to place the fan in another location and give you more variety in fan size/type.

Cheers,

Simon

Even these low cost DC motors (made inhouse by Sieg in Shanghai) do have a simple inbuilt fan. It works by moving the air inside the motor housing. The heat is then dissipated through the outside surface of the motor housing. Adding some surface area to the outside of the motor, like a ribbed sleeve, would be a passive method to improve cooling. Adding a box fan to blow air over the outside surface of the motor is an active method to improve cooling.

But consider this: If you run your motor with variable speed at low speeds and load it, it generates heat, mainly in the rotating armature. But at low speed the inbuilt fan is ineffective and insufficient to transport this heat from the armature to the outside surface. Therefore, just adding ribs or a fan to the outside may still see your armature overheat and burn out.

You could use a larger motor that is designed for continuous duty (the Sieg motor is not).

Or you could avoid using the existing motor at low speeds under high loading and for prolonged time.

Or you could use a motor with an open frame for internal cooling. But a brushed DC motor with an open frame on a machine tools has some unwanted risks: metal chips can enter the motor and cause a short on the commutator, instantly ruining the motor / steel and iron chips and dust can collect on the permanent magnets and may be hard to remove / sparks from the commutator may be blown outside the motor enclosure and ignite solvent based coolants (like WD40 spray often used to cut Aluminium). These sparks may be especially dangerous when you run the motor in reverse and thus there is extra strong sparking because of the commutator advance now being a retard, and running in reverse now the airflow is towards the commutator and directly outside the motor. So you have to incorporate a filter/ safety mesh etc. I feel it is much easier and "cleaner" either buying a larger good quality DC motor designed for continuous duty, or converting to 3-phase VFD. Chris

I have done the mod because I was itching.
The result can be seen here:
Cool down a mini-mill motor. | Model Engineer
It works like a dream.

have you considered putting an air filter on the air intake side of the explair

reason....dust etc will be forced into the motor which will have the effect of making the motor run hot due to airflow restriction and thermal insulation on the windings etc