Bearings

Merry Christmas all.

I am changing the spindle bearings on my cj18a lathe and i have got some angular contact bearings but they are a bit open so i was wondering whether to pack them with grease or thick oil as you cant get to them to lubricate them regular.

Thanks

Henry

Have a search on the SKF site for grease volume in a bearing. Overfilling can be worse than under, causing overheating and early failure. Also the correct grade of grease should suit its purpose. I am sure if you do a little research, on the web and on this site you will find plenty to confuse you.

Pack the bearings and surrounding cavity inside the seals about half full of good quality wheel bearing grease and you should be right.

I was an engineer at Warner & Swasey, Cleveland, Ohio, in the 1980's as the change was made from oil-lubricated taper roller bearing Headstocks with selectable gear trains to grease lubricated Ball Bearings. This change came about due to the vastly improved Spindle drive motors coming onto the market. Many of the Lathes (8" to 12" Chuck) were sold with no Gearbox. Larger Lathes (16" to 24" Chuck) were sometimes fitted with a separate 2-speed Gearbox.

The Ball Bearings were typically sourced from FAG. We had a "clean room" in which the bearings would be packed with a German grease, Kluber if I remember correctly. The grease was weighed out for each bearing. It was stuffed in a large plastic syringe which had been previously weighed so the grease could be ejected till the final net weight was obtained. This remaining amount would be injected around the bearing. Typically we had 3 Ball Bearings and the head end and 2 at the tail end - all angular contact (15 to 20 degree).

One of the most important steps of the process was the running in of the Spindle. I seem to remember this run-in lasted 4 hours. Since these were all CNC machines, it was a matter of loading the run-in program, attaching a couple of thermocouples and hitting a button. The thermocouples were used "just in case" as the machine was run-in without supervision. The Spindle would run at 50 rpm for 15 minutes to start, then bump up to 100 rpm for a minute, back to 50 for 10 minutes, then up to 200 for a minute, back to 50, and so on. At the end the Spindle could run all day at its max design speed. We had a range of Spindle designs from 1,800 rpm to 4,500 rpm.

I remember one machine where the run-in was missed. As the machine was being prepared to do a customer's demonstration part, the Spindle locked-up and kicked out the Drive Motor. It was determined the run-in had been missed. The grease had not been "channeled around the Bearings". The ensuing churning of the grease generated enough heat to cause the Spindle to expand and lock the bearings. The Spindle was allowed a day to cool naturally, the run-in procedure was done, and no measurable problems could be detected in the bearings. That was a relief as those bearings cost in the neighborhood of $1,000 back then.

The long and short of it is - pack the bearing around half full, allow the grease to "channel" by running the lathe at a low speed for say 15 minutes.

Ok thanks everyone i did not know it could be so complex what with too much grease and running them in.

Henry,

Good idea to read this thread.

Ketan at ARC

BTW, the traditional way of getting grease into the bearing between the rollers or balls and the cage and race etc is to put a good wodge of grease in the palm of your hand and push the bearing into it while closing your hand a bit, so the grease is forced in between the rollers or balls. There's a bit of a knack to it but if you do it a few times you will see grease coming out the other side of the bearing so you know it's getting through the working parts.

Thanks.

i will get the first one on then clean it out to make sure there is no grit in there then grease it.