Safe Spindle Temperature?

[RJS100]

I recently upgraded the spindle motor on my PM833TV. The max stated spindles speed of the OEM mill was 3200 rpm. It never actually ran over 2900. I always thought the spindle ran a bit hot because you could barely handle a tool after running at 2900rpm for 20+ minutes. Precision Matthews could not give me an actual spindle temperature but said it can run "Hot". They suggested I loosen the pre-load a bit. I did this, but it made no difference.

I read a number of posts of other users complaining about the same. Some suggested replacing the oil seal with one with a larger diameter, and others said they replaced it, but were not sure if it actually helped. They all agreed, this seal is hard to remove.

The mill uses tapered roller bearings. SKF bearings of the same size are rated for 9000 rpm max. Most other brands I researched were rated for around 5000+. I do not know what exact brand were used by the OEM.

WIth the new spindle motor installed, and the ability to hit around 6000 rpm, I ran it today for a short time at 3600 rpm and the bearings were running warmer than usual. I would like to know what is considered as a safe temperature. There are a number of articles by Timken, SKF etc. that I read suggesting a break in period that looks like:

Starting at 10% of the max speed, running for 30 minutes, increase 10%, run for 30 minutes, and keep going to max speed. If the temp exceeds 140F at any point, stop, cool to room temp, go back to the previous temp range and start again.

I recognize that I cannot measure the actual bearing temperature, but it is surrounded by the quil (#6) and the spindle sticks out right below the oil seal (#2). Since the quil is polished and shiny an infrared temp gun will not work well. My plan is to put electrical tape with a known emissivity on the quil to measure the temperature and run the break in procedure above and see where the temps fall.

Does this mean the max safe temperature is 140F. Does this approach make any sense?

Thanks... Richard

[suntravel]

Depends on the bearing grease, I use Isoflex NBU 15, thats good from -40 to 130C

My spindle is reaching 45-50C fast and stays there even if I run jobs with 6000 rpm 16h a day.

If your spindle temp keeps rising and will nor equal out at some point, I would stop at 80C, dismantle, clean and fill with NBU 15 max 30% of the space in the bearings.

Too much grease and too much preload are main reasons for a too high temp.

Uwe

[RJS100]

Thanks for the guidance. Exactly what I was looking for.

Best... Richard

[RJS100]

I did some additional testing and confirmed that at 3000 rpm, the temperature measured on the surface of the quill was 140+F after 30 minutes. I think my first step will be to replace the oil seal with a slightly larger one. There are a few posts regarding the fact that OEM seal is too tight. There were also comments that this seal is extremely difficult to remove. Some folks screwed a sheet metal screw into it and pulled it off. Looking for a better method.

If this doesn't help, I will replace the grease with Isoflex NBU 15 since I have no idea what the factory used for grease. I think I can do this without removing the bearings.

Best... Richard

[suntravel]

If you mean leaving the bearings on the spindle and in the head, ok. But you must remove the spindle to wash out all old grease.

I doubt it will be the seal, but also NBU15 will lubricate the seal better than cheap grease.

Uwe

[RJS100]

Yes. We are on the same page. I will be removing the spindle. Is there an easy way to wash out the old grease without removing the bearings?

[suntravel]

Without special equipment, brake cleaner spray and compressed air.

Will make a funny mess

Uwe

[RJS100]

Got those... All set for a big mess. Since the bearings are pretty much new... I don't see any reason to replace them.

I spoke with a company that rebuilds spindles today. He thinks the seal is either too tight, or pressed in too far so that it is touching the bearings. He suggested replacing the seal and making sure it is coated with the Isoflex NBU 15. He also said these seals are really not designed to run over 3600 rpms, so a slightly larger size may work well.

Next steps for now, clean & regrease bearings and replace seal.... Fingers crossed.

[suntravel]

Maybe you can find a labyrinth ring seal in the right size, they could take more rpm with less friction.

Uwe

[Nigelo]

How about researching if Ceramic Bearings could be an option assuming they are available in your size. My air cooled Router spindle uses this up to 24K rpm but does need 10 minute warm up before use. However, I don't know the suitability for a Mill