Hot Spindle Bearings

All info relating to the Denford Novamill CNC Milling machines

Moderators: Martin, Steve, Mr Magoo

Post Reply
Deck36
Posts: 3
Joined: Sat 06 Mar , 2021 22:25 pm

Hot Spindle Bearings

Post by Deck36 » Wed 10 Mar , 2021 10:46 am

Hoping someone can give me some advice.

I have a Mach3 converted Novamill, which after some very minor use started making some horrible sounds from the spindle bearings.
So I got the specs and installed new bearings (correct specs) packed with spindle grease (not the Denford specified grease)
I did a gentle run in starting at low rpm building by 100 rpm steps up to 3500, but noticed that the headstock was really hot, almost too hot to touch, so probably 65-70 degrees.
Checked the drive belt and it was properly aligned and not over tight.

Is this just down to me not using the right grease or is there something else I'm missing?

My temptation is to get the most expensive bearings I can, the Denford specified grease, and start all over again.

Appreciate your help.

DavidB
CNC Expert
CNC Expert
Posts: 173
Joined: Tue 19 Oct , 2010 16:06 pm
Hardware/Software: Triac, Orac

Re: Hot Spindle Bearings

Post by DavidB » Wed 10 Mar , 2021 22:59 pm

As no one else has replied yet do you have any information from Denford about how to set-up the bearings when replaced and what level of heating is to be expected. From looking at the Novamill assembly drawings the heating could be the result of doing the lock nut up too tight which holds the pulley assembly in place and bears on the upper angular contact bearing creating too little or no internal clearance in the bearings so maybe back the nut off slightly and re-test. It could also be the result of over packing with grease.

moray
CNC Apprentice
CNC Apprentice
Posts: 97
Joined: Thu 12 Sep , 2013 20:02 pm
Hardware/Software: Triac VMC

Re: Hot Spindle Bearings

Post by moray » Wed 10 Mar , 2021 23:34 pm

Sounds like you've overtightened the bearings.
How long did you run the spindle for between speed increments?

Try slackening the retaining nut slightly (probably 1/8th turn would do to start with), and running again.
If the spindle is warming up after 30 minutes of running, you'll have it about right. If it's still stone cold after 30 minutes, you'll probably want to add a bit more preload.

Deck36
Posts: 3
Joined: Sat 06 Mar , 2021 22:25 pm

Re: Hot Spindle Bearings

Post by Deck36 » Fri 12 Mar , 2021 10:34 am

I was really careful not to over tighten the lock nut. I only went as far as removing any play and no further (I thought anyway) so probably almost no preload on the bearings.

On startup I waited a couple of minutes between raising spindle speeds so that I didn't stress the parts too much, but it got hot much faster than I would expect. The headstock is always going to get warm I know, but it was almost too hot to touch within 5 minutes.
I did pack the grease in though, so maybe this might be the problem? Should I clean it all out and try the correct amount of the properly specified grease?

moray
CNC Apprentice
CNC Apprentice
Posts: 97
Joined: Thu 12 Sep , 2013 20:02 pm
Hardware/Software: Triac VMC

Re: Hot Spindle Bearings

Post by moray » Fri 12 Mar , 2021 18:09 pm

Too much grease can be worse than too little grease, but excess grease should work it's way out.

It sounds like you've possibly ran the spindle up too fast. I'd normally increase spindle speed in 500rpm increments every 15minutes, ensuring there's no significant heat generated before each increment.

Deck36
Posts: 3
Joined: Sat 06 Mar , 2021 22:25 pm

Re: Hot Spindle Bearings

Post by Deck36 » Sun 14 Mar , 2021 19:29 pm

What kind of temperature would be considered normal?

I also found a good instructional video about spindle bearings

https://www.youtube.com/watch?v=grUdsTTRGl4&t=3244s

Post Reply