Hi!
On Friday, I thought it was time to clean my mill. As I already had an headache, I thought I could have a look into the coolant sump (or is it swamp?). A thick layer of brown jelly stared at me and was crying something like "no light!". Well, I pulled it out with my hands and decided to finally build an skimmer.
Looked around and found a PU belt (round cross-section). Only thing missing was a small geared motor. So on Saturday I went to buy one. 14.99 for a
12V, 8mA, 25 RPM motor. With that, next I turned two pulleys (20mm diam), welded some crap together to hold the motor and the second pulley. That thing was now a vertical bar with one pulley on an axle on the lower end and the motor with the second pulley on the top. The wiper (to wipe off the schmutz on the belt) was made of some brass milled, drilled, soldered, hammered and sawn and a bit of an old bicycle-tube with a 3mm hole punched into and a slit so the rubber could be slipped over the belt.The lower pulley went into the sump. The belt attracts oil more than water. So when the belt is moving upwards, it is elevating the oil upwards, over the top pulley and then through the wiper that is holding the mess back and collects it in some can.
Let it run over night and the next day my sump was clean like on the mill's first day in 1946. It really pulled all the oil (but not the solubeable(SP?) oil in the coolant, before you ask) out of the farest corner.
If you want to build your own, the belt's speed should be at least 1.5m / minute or maybe up to 5m / min. PU seems to work good enough. An oil-resistant rubber should work OK too.
The skimmer looks as bad as it works good.
Nick