Sanity check -- spindle temperature after running at 3000 RPM

[ichudov]

I ran my mill for 16 minutes at 3,000 RPM (I get email when my CNC
jobs complete). It was machining a mold prototype for a kids toy. We
will need to cast 18 of them that in wax, and the mold will be made
from Aluminum. But I digress.

After I finished running for 16 minutes, I measured a few temps:

*) Inside the shop - 86 degrees
*) On the variable speed transmission on top -- 105 degrees
*) On the low part of spindle (at the QC-30 collar) 115 degrees. I am
not sure if I fully believe this last measurement. The bottom of the
spindle feels warm to the touch, I can hold it indefinitely, but it is
not comfortable.

Would you consider this temp rise to be excessive?

[Davo J]

In my opinion it sounds about right to me.

Dave

[polaraligned]

Sounds fine.
Try running it at 5000 rpm for 16 minutes then you will know what a hot quill is.

[ichudov]

Guys, are there any guidelines on how much temperature rise is permissible?

If the outside temp rise of the spindle is X degrees, what happens inside the bearings? 2X?

i

[Bubba]

While this does not exactly apply to your situation, I found the following in reference to the taper rollers for my mill drill. It might give you some guidance.

"The ideal equilibrium operating temperature is 95 to 115 degrees F. Maximum temperatures should not exceed 170 degrees F. Timken's published specs for tapered roller bearings, including bearing life specs, assume an operating temperature of 130 degrees F."

I am in the process of doing a break in of the bearings now and find the housing temperature seems to lag the bearing temp by about 8-10°F as measured by my non contact thermometer.

Hope this helps.

[machintek]

When things are not going your way with spindle bearings, typically 3 things happen. A lot of heat, a lot of noise, and a poor finish.
For years I have been sending Bridgeport spindles to C and M precision spindles in Oregon.
Their number is 1-503-691-0955. They can give you a good answer.

George

[ichudov]

Thanks, Bubba and Machintek. I will call C&M on Monday.

The "poor finish" angle is worth pursuing. I could try side milling a piece of steel, using a new endmill, a light cut, lots of lubricating coolant etc, and see how good is the finish.

[johnhb]

According to my catalogs max. suggested temperature for SAE 52100 bearings is 250 deg. F. Lower is better, but there should be no problem with the temperatures you are measuring.



john

[Rich Carlstedt]

John
You are completely correct
We worked with Timkens in High Heat conditions in the machines we built, and they told us that 270 F was max, and we kept a temp probe on them . These were $ 5,000 bearings and we tried to stay under 250 if possible. Some of our customers even put water tubes around the housing to cool it.
The point is not how close to 250 you get, but Spindle Growth and Lubrication.
If you want to run very high speeds, you have to stay on the light side of lube "volume".
The heat is coming from your grease.
to control "growth I would put a fan, or a heat transfer plate on the spindle housing and run my flood coolant first through the plate to help cool it off

[ichudov]

So, Rich, you also think that "uncomfortable to touch for more than 5 seconds" on the outside of the spindle is okay?

i

[Rich Carlstedt]

Yes, as far as the bearing being able to survive.
You will not anneal the steel
What you do get is thermal expansion. That "may" increase the preload.
Increased preload, like higher speeds, and/or greatly loads, all have an effect on Bearing life.
Without seeing the Bearing layout, its difficult to determine if the load increases or decreases ??
I would noy be afraid of the temperature alone

[ichudov]

Originally Posted by Rich Carlstedt Yes, as far as the bearing being able to survive. You will not anneal the steel What you do get is thermal expansion. That "may" increase the preload. Increased preload, like higher speeds, and/or greatly loads, all have an effect on Bearing life. Without seeing the Bearing layout, its difficult to determine if the load increases or decreases ?? I would noy be afraid of the temperature alone

Rich, thank you!