Thread: Hot Spindle Bearings

I've been fooling around with a pair of high speed drive pulleys on my little 9" Hercus. Because of a small difference between the diameters of the counter shaft V pulley and the headstock V cone pulley on the standard lathe (mine) and the high speed version, my lathe runs at slightly higher speeds. The one exception is the top speed, mine runs 70 rpm slower than the stated 2600 rpm. Why, I don't know.

At top speed, the spindle roller bearings become hot, enough for the headstock casting around the bearings, to be uncomfortable to touch.

The preload on the Timken tapered roller spindle bearings is 2 inch pounds as per the manufacturer' s recommendation. This is the preload suggested for the standard lathe, with a maximum spindle speed of 700 rpm ( 1050 with a 2 speed motor ) and the beautiful Craftsman lathe with it's maximum of 1840 rpm. I'm wondering if preload is contributing to the heating. Obviously, a bearing is going to generate more heat running at high speed than if it is idling along at 700rpm.

The simplest way of avoiding the heat would be to not run it flat out but I need to know how hot's too hot. Any suggestions?

Bob.

Are the bearings grease or oil lubed.... If they have too much lube or the wrong type of lube they can get hot... But 2600rpm is not a fast RPM for a small bearing

I have never heard anyone give a figure for preload in all my research about bearings.
I would say you have to much preload on them and as it gets hotter it gets worse because tolerances tighten up even more with everything expanding with the heat.

Getting bearing preload is tricky between being to tight and getting hot or having movement in the spindle, it is something you have to play with. The bearing place told me that wheel bearing grease is fine for something you can have your hand on, after that you need a HT bearing grease.

Dave

Oil R.C.

Mobil DTE Heavy Medium circulating oil, ISO 68.

The Mobil oil recommended for the old 9 inch and newer 260 Hercus lathe was Vactra Oil Heavy. DTE Heavy Medium is it's modern day replacement, according to Mobil's technical department.

On Hercus roller bearing equipped 9" lathes, there are oil cups at each bearing location. Oil enters the bearing from the cup then drains out through a hole in the bottom of the bearing cap. There is no ponding of oil in the bearing, the only pond being the one in the chip tray.

Bob.

Here you go Dave.

Page nine of Peter's book.

I have seen that way of testing torque before but I was thinking you where meaning tightening torque on the nut.
What I did with my mill spindle which has tapered bearings as well, was to tighten it up just until there was not side ways movement with a dial indicator resting on the side of it. Then monitor the spindle by the heat and it should run warm but not hot. If it is running cold after 15 minutes it needs nipping up a bit and if it is too hot give loosen it slightly and give the end of the spindle a bump with a soft hammer to release the preload.

Dave

With your oilers do they have some felt or something in them to release the oil over time? If not, when it's running a these higher speeds I would be putting a drop in every 5 - 10 minutes of running.

Dave

Dave,

There is no felt and given that I have 20 litres of DTE, I'm liberal with the oiling.

I will check the preload I have tomorrow.

Bob.

It would not take long for the bearing to push the oil out a high speed.
If you find you are using these higher speeds a lot, it might be worth while getting some drip oilers to save the hassle and time of having to oil the lathe through the job.
I have seen some really nice brass and glass/plastic oilers around.
Here are a few I have seen
RDG Tools - Online Engineering Tools Drip Feed Oilers

Dave

Originally Posted by Dave J

I have seen that way of testing torque before but I was thinking you where meaning tightening torque on the nut.
What I did with my mill spindle which has tapered bearings as well, was to tighten it up just until there was not side ways movement with a dial indicator resting on the side of it. Then monitor the spindle by the heat and it should run warm but not hot. If it is running cold after 15 minutes it needs nipping up a bit and if it is too hot give loosen it slightly and give the end of the spindle a bump with a soft hammer to release the preload.

Dave

Hi Dave,

What would you think is too hot in your view?

You'll remember I did the same tapered bearing mods that you did on your mill.

Anyway, I've been running my mill for longish periods today, (cutting a new idler gear for the lathe) and the spindle bearings are fairly warm to touch, probably 40-50 degrees C. My question is, how hot is too hot? I notice the belts and pulleys are probably about the same temperature.

Regards
Ray

Hi Ray,
That sounds about spot on after running for a while. The bearings will cope with the heat it's the grease that fails.

Dave

I reduced the preload on the bearings yesterday to about 1 1/2 pounds. At 2530 rpm they are still running hot after a couple of minutes. I checked the preload with the hot bearings and it was about 2 pounds.

I'm using a spring balance that could very well be an inaccurate POS. Something made to puff up a fisherman's ego.

I'll contact Steve Durden at Hercus and see what he reckons.

Bob.

I'm going to look for the reference I have, but I am sure that I have read 65º C is an acceptable temperature for a roller bearing with grease lube, higher with oil.

Greg

I did a bit more experimenting tonight. The most sensitive indicator that I own measures in 1um increments. As per Dave's suggestion, I loosened the nut on the spindle to the point that there was play then carefully adjusted the nut to remove the play. At that point the bearings still ran hot at 2500 rpm but nowhere near as hot as yesterday. The fish scale may have been more of a hindrance than a help.

I'm interested to read Greg's findings on bearing running temperatures.

I need to buy a cheapish non contact infra red thermometer. There is an abundance of cheap ones on Ebay. Any suggestions?

Bob.

Bob, I just checked my source books to find the following:

Industrial Machine Maintenance quotes 150º C

SKF Bearing Catalogue only mentions plastic cages, and states 120ºC continuous, 140ºC part time and 180ºC peak

I guess with oil lube you are limited by your paint job and spindle growth with temperature.

FWIW my 4000 rpm lathe has grease lube, and the books recommend grease change after 3000+ hours of continuous use.

I think my 65ºC figure came from the maximum safe touch temperature, which could be lower depending on time of exposure...as low as 50ºC for continuous contact.

Greg