View Full Version : Mill spindle heat

loose nut
07-07-2008, 10:32 PM
On my new zx45 mill I have been milling some brass bar, the proper RPM's for the end mill I was using is way too fast for this mill but I ran it in the second highest speed and it cut the metal very well with a very good finish. The only thing that I found is that the lower spindle heats up after 15 min. or so and will get to a point that it can be uncomfortable to hold onto but seems to work just fine. My old belt drive mill didn't heat up like this (this is a gear head mill). Is this a problem or is it normal for this type of machine. I'm assuming this is the bearings heating up, but they don't seem to be in distress IE. making noise or vibrating. At the lower RPM"s it heats up only a little bit.

Any ideas.

07-07-2008, 11:09 PM
High temp can mean bearing problems like too much preload. Get an infrared thermometer and start checking.

07-08-2008, 03:24 AM
The bearings are good to around 150 F before they start to have trouble. That is just into the "too hot to touch" range whereas "uncomfortable to touch" is around 130 to 140 F. Those are very reliable indicators and nearly everyone responds in the same way to the same temperatures.

I have the standard R-8 mini mill spindle head on my machine that I built but early on I replaced the stock bearings with good quality brand name bearings. The originals didn't last long at 6000 rpm which is the highest speed I run it at. Someday soon I am going to replace those bearings with some angular contact bearings which are available in the same form factor as the deep groove ball bearings.

07-08-2008, 04:39 PM
A RongFu X45 likely has reasonably good bearings.
A RongFu knockoff, very plentiful, may or may not.
Short of a dissassembly of the spindle, a process not
as complicated as it sounds but requiring some willingness
to proceed despite initial hesitations, a lightening up of
the preload is the next step. Should be a castle nut
up there under the pulley, look at the exploded drawings
to see where. Back it off one notch and try again.
Quantify the temp rise with an infrared thermometer
if available (sold for $60-100). Repeat until the spindle
loosens up or temp drops. You need some preload so going
to the point of loose spindle is overshoot. Redo of the lube might
help as OEM lube can be stiffer than necessary to
survive a container ride from east asia, but a disassembly
is needed to get to the bottom bearing. A friend went through
this on his HF x45 clone with a bearing change out as part of the
process (name brand bearings are ~$20 or so) and had a noticeable
drop in the mill head temp after an evening of milling.

07-08-2008, 05:11 PM
Lube is a good starting point. A friend told me about the poor quality of Chinese lubricants. I opened up a little 4 1/2" grinder gear box and was faced with something that looked like ear wax. I washed/ picked that stuff out of the bevel gears and replaced it with good ole USA high temp bearing grease and she ran like a clock....and still does.

07-08-2008, 06:47 PM
Scishopguy and Even are right on. lube is #1, do what it takes to make sure its lubed good. 150F is about right as far as temps.

I used to rebuild machine spindles all the time on muti spindle screw machines that ran 24/7/365.

I dont care if a spindle is oil fed or not I always use grease when I put them together, that way if the lube takes time to get working the bearings are never dry. I had a shop forman tell me dont grease a spindle once "he said its oil fed dont grease it". I told him he was an idiot. sure as hell the spindle ran 2 minutes and seized a 25 horse power machine. the bearing was melted down and purple.

I would rather see a spindle full of grease and pooping out grease from the labyrinth seal then run dry.