[davtuner]

I use a 2.2kw chinese spindle with a hitachi x200 vfd. I was thinking recently about how keeping your bits cool can extend their life significantly, and noticed that during use the entire spindle and its coolant runs at a basically uniform temperature; after long runs the entire spindle is the same temperature, maybe 30 degrees C (the bit is cool to the touch though).

I have a computer coolant refrigerating unit that is being unused at the moment, and was wondering if this would be a good idea, since I could chill the entire spindle/bit to 40 degrees celcius below ambient easily. The only concerns I had were condensation on the inside of the spindle, which could short one of the windings, I don't know if this is a decent concern though, and I could use a coat of petroleum jelly around the possible entry areas for moisture to prevent this. My bits seem to be running for quite a while and keeping a very good edge (whiteside, freud bits) in plywood, I was just thinking in advance...

Thoughts, opinions?

I was also thinking about whether or not the cooling would cause the spindle's internal parts to deform, since I read in a colombo spindle maintenance article that it is good to warm up your spindle for a few minutes before cutting since it causes the bearings to assume their proper diameter when heated. I figure I could measure if this had an effect on spindle by measuring the static runout once chilled.

[keebler303]

30C is nothing, leave it as it is. Condensation is a true concern, I would worry more about corrosion than shorting but either way you want to avoid condensation.

Matt

[Christian Knüll]

Hello

cooling the spindle to a lower temperature than normal won't reduce the temperature of the bit (at least not significantly in the area where it is actually cutting and hottest).

If you like to cool the bit you can use compressed air - but usually this is not necessary if feed and rpm are chosen correctly.

Christian

[davtuner]

I suppose Occams razor wins on this one...

If you are milling metal though, what about cooling the workpiece

[keebler303]

Water cooled spindles are water cooled to protect the bearings from overheating and to maintain some degree of dimensional accuracy by holding the temperature constant. The tolerances and clearances inside a precision spindle are quite close and excessive expansion and contraction will reduce their accuracy and life. The cooling is not designed or intended to cool the tool or workpiece. Thats what through tool coolant and flood coolant are for!

Matt

[jsheerin]

Additionally, machinery like this is usually designed to run at a certain temperature which is usually above ambient. Everything expands slightly as it heats up, and at the designed running temperature all the designed tolerances are correct. So if you cool it to -40C, you're going to shrink everything and potentially cause more problems. What would probably be more beneficial to the performance and life of a spindle would be to know what the operating temperature was supposed to be (obviously we don't have this kind of info for the cheap Chinese spindles) and then control the temp of the coolant to maintain the spindle at that temperature.