Spindle bearings on a bridgeport type machine

[zoeper]

I have a Avon 3000 CNC Mill based on the bridgeport design, but i suspect the spindle bearings might be ready to retire.
When the machine is run at 3000RPM or more the spindle generates a lot of heat, to the point where the spindle expands due to heat and have trouble retracting. Is there a way to lubricate these bearings without stripping, or how do i know when the time has come for replacements?
The sliding surface of the spindle is well lubricated and operates fine when run at moderate speeds.
Any sugestions welcome.
Pieter

[NC Cams]

THe typical Bridgeport spindle is built with essentially special versions of 6206 bearings. They "specialize" them by offset grinding the inner rings so that the raceways are preloaded when all is clamped together at assembly.

Bearings that heat up are/can be quite normal, it all depends on how much "heating up" is going on. "Hot to touch" is quie meaningleass as some folks tolearate "hot" better than others. THus, when you say something is warm, that may not be the same TRUE state of temp rise to me, to my touch anyway.

First try to quantify the amount of temp rise via the use of a thermoeter or temp probe. THis will be more helpful than the by touch method you're probably using.

Next, the temp rise of your machine may be normal. Reason: it depends on the amount of preload in the original spindle bearings. And, it depends if the bearings used to make up those in your spindle.

IF you spindle has high prelaod bearings, it will be a gigid spindle, at least more so than a spindle built with light or medium preload. bearings. LIkewise, the lowere the preload, the lower the "normal" temp that will/should be encoungered.

Seal type or presence will also affect temp rise. We made up some spindles that had NON CONTACTING seals. They ran much cooler than the OEM seals which were CONTACTING SEALS - they rubbed against the sides of grooves in the inner ring - this is why sealed bearings typically have a LOWER max speed rating potential in the catalogs - friction heating due to seal friction.

Too much lube can cause bearnigs to heat up. A bearing that will see repeated high speed operation should se less grease lube than than the exact same bearing that will chug along at low speed. The bearing has to push its way thru the grease and the more this goes on the more temp rise tjat camwo;; gp on. It is simply natural.

The point is, a rapid change in apparent bearing temp MAY indicate that something is going awry. However, it may also be that you are running the spindle at a speed HIGHER than it was originally designed to run at. Althought it may be capable of running at that speed, higher operating temps should NOT be a surprise. Nor should it be a surprise that higher speeds will result in LOWER grease life in the bearing. Higher speed equates to more energy being put into the grease which means shorter life.

WHen bearing people say "lubed for life", they are really saying "for the life of the bearing, or the life of the grease, whichever occurs first".

Now, to what is probably the meat of your question, you can't diagnose a bearing problem without doing an inspection of hte bearnigs - so get prepared to crack into the spindle. It is not unusual to get diverging opinions when it comes to how a spindle "sounds" or "Feels". Some fo the above comments may even seem to be in conflict with what you've been told or heard. However, after having spend a decent amount of time doing spindle bearings for a noted bearing supplier, I assure you that my comments are "factory based" and quite valid.

NOw that you've had the basics of "temp rise" explained, you can plug on in relative piec, do some more precise temp measurements or run it until it smokes. If you do really care about the machine, maybe it is simply time to put some bearings into it - just don't go pulling apart the spindle, reading the generic numbars on the bearings and buying just ANYTHING that has the same number on it. Spindle bearings are a bit more sophisticated than that. . .

[HimyKabibble]

Originally Posted by zoeper I have a Avon 3000 CNC Mill based on the bridgeport design, but i suspect the spindle bearings might be ready to retire. When the machine is run at 3000RPM or more the spindle generates a lot of heat, to the point where the spindle expands due to heat and have trouble retracting. Is there a way to lubricate these bearings without stripping, or how do i know when the time has come for replacements? The sliding surface of the spindle is well lubricated and operates fine when run at moderate speeds. Any sugestions welcome. Pieter

Pieter,

I have to wonder if perhaps you're mis-diagnosing the problem. I don't think the spindle bearings would have any impact at all on the spindle retraction. What will, however, is a lack of lubrication on the splines. Power is transmitted from the motor to the spindle by a splined shaft. The splined shaft slides within the spindle when the spindle moves up and down. When the spindle is under load, the pressure on these splines will make the spindle harder to move up and down. My guess is the grease on that splined shaft is dried up, which is a far simpler repair. I'd bet your actual spindle bearings are just fine.

Regards,
Ray L.

[zoeper]

I will try to plot the temperature rise and post here for your scrutiny.
As far as the splines and their lubrication goes, the lubrication could definately be depleted as i can see no way to reach the splines to top it up. On the lubrication plate it specifies that you should pour 6 drops of oil down the drawbar, but since the power drawbar is fitted, the hole the manual refers to cannot be accessed.

Looking at the drawings of the head, you can see that both spindle bearings are located quite close to the bottom end of the quill. My theory is that when you are working with the quill extended, both these bearings are outside the sleeve and the localized heat buildup makes the quill expand. since the bearings and bottom part of the quill are outside the sleeve, the sleeve does not heat up (and expand) at the same rate and therefore the quill can not be easily retracted into the sleeve.

Would it be wise to remove the bearings and to clean, re lube and replace them? The machine is a +-1992 model and i do not know if the lubrication was ever checked during that time.

What would me a good lubrication/ maintenance scedule for the spindle and head assembly this type of machine?

[NC Cams]

A "normal" temp for a 'lubed for life" bearing would easily be 150-212 deg F. For each 10 deg above 212 that you runt he temp, you cut the grease live IN HALF. Thus if it got to 222. the grease life would be half of what it was at 212. Grease life is affected by temp, contamination, simple expiration of time plus other things that happen as part of the normal vicissitudes of life. Grease doesn't last forever.

Imagine looking at spindle lube as it were a car engine. Would you expect the same lube that was in your 1992 car to be still working as well today if you hadn't changed the lube since 1992? I do think not.

By all means, the 16 year old grease, if it is still there, and still contamination free and still capable of lubricating, should be cleaned out and replaced. DOn't go hog wild with refilling the bearings. You only need to use enough grease to fill the cavity about 30 percent full.

Don't just smoosh it in either. Use an industrial syringe and PLACE the lube 'tween the balls and raceways. Do it evenly and precise like.

When you restart the bearings, run them in slow so as to channel the grease effectively. Oh and use a product like "CRC BrakeClean" to clean the bearings prior to lube - dont' spin the hell out of the bearings with air as this can screw up cages and/or cause ball skidding - it is oh so fun to do but oh so wrong. YOu can use generic solvent to clean out the old crud but use CRC to do the pre grease cleaning.

Bridgeport used Andok C grease in their spindle bearings. You don't need to get real fancy with grease as in real expensive high speed stuff ala Kluber. Most mill work is well within the range of use for non synthetic, mineral based greases. Rykon 2 would work as would most other NLGI 2 viscosity "wheel bearing" greases. Stay away from the "green" Exxon Mobil SRI greases - great for water pumps, can be REAL Noisey in electric motors and spindles due to how the thickening agents recongeal at cool down, especially in preloaded bearings.

For the splines, I'd used something like Lubriplate MoLith #2. ANother would be valvoline "black" moly grease for wheel bearings. Similar properties, one is easier to get at local auto parts stores than the other.

Take a look at the ball paths in the raceways with a good lighted magnifier. If the balls and/or pathes are "frosted" this means that they are worn and probably debris dented. If true debris dents are visible, replace the bearings. Regreasing will buy time but won't EVER fix what are essentially irrepairably damaged bearings.

Changing the oil in a car with trashed bearing never fixes them and neither does regreasing old, tired ball bearings.

You got 16 years of life out of the bearings and probably never did ANY service to/on them. How much service do you expect to get when you subject the bearings to that much duress????

If you do change the spindle bearings, DO NOT expect the spindle to cut the same unless you have the spindle taper reground when the spindle is fully reassembled. Spindle bearing replacement is NOT a mindless effort of knocking off the old and pressing in the new. WHen done properly, you will have a like new spindle - do a kluge job and the spindle will surely disappoint you.

If you do a "birdgeport spindle bearing" or spindle bearing replacement" thread search, I've previously explained how to fully and properly replace spindle bearings. The explanation is too long to retype for me anymore - I can't see or type as well as I used to....

[NC Cams]

BUMP.

I always wonder what happens on threads like this. Don't you???

[TOTALLYRC]

Originally Posted by NC Cams BUMP. I always wonder what happens on threads like this. Don't you???

You did such a good job of explaining why it will not be easy to do what needs to be done to do it right that I think you may have scared him off.

Mike

[zoeper]

More determined than ever, just realized i would have to wait a while longer before i will have the time (and $) to do it right! BIG job apeared out of nowhere and big jobs funds downtime and spares.
P

[TOTALLYRC]

Keep us posted.

Mike

[mikeyg]

Originally Posted by NC Cams A "normal" temp for a 'lubed for life" bearing would easily be 150-212 deg F. For each 10 deg above 212 that you runt he temp, you cut the grease live IN HALF. Thus if it got to 222. the grease life would be half of what it was at 212. Grease life is affected by temp, contamination, simple expiration of time plus other things that happen as part of the normal vicissitudes of life. Grease doesn't last forever. Imagine looking at spindle lube as it were a car engine. Would you expect the same lube that was in your 1992 car to be still working as well today if you hadn't changed the lube since 1992? I do think not. By all means, the 16 year old grease, if it is still there, and still contamination free and still capable of lubricating, should be cleaned out and replaced. DOn't go hog wild with refilling the bearings. You only need to use enough grease to fill the cavity about 30 percent full. Don't just smoosh it in either. Use an industrial syringe and PLACE the lube 'tween the balls and raceways. Do it evenly and precise like. When you restart the bearings, run them in slow so as to channel the grease effectively. Oh and use a product like "CRC BrakeClean" to clean the bearings prior to lube - dont' spin the hell out of the bearings with air as this can screw up cages and/or cause ball skidding - it is oh so fun to do but oh so wrong. YOu can use generic solvent to clean out the old crud but use CRC to do the pre grease cleaning. Bridgeport used Andok C grease in their spindle bearings. You don't need to get real fancy with grease as in real expensive high speed stuff ala Kluber. Most mill work is well within the range of use for non synthetic, mineral based greases. Rykon 2 would work as would most other NLGI 2 viscosity "wheel bearing" greases. Stay away from the "green" Exxon Mobil SRI greases - great for water pumps, can be REAL Noisey in electric motors and spindles due to how the thickening agents recongeal at cool down, especially in preloaded bearings. For the splines, I'd used something like Lubriplate MoLith #2. ANother would be valvoline "black" moly grease for wheel bearings. Similar properties, one is easier to get at local auto parts stores than the other. Take a look at the ball paths in the raceways with a good lighted magnifier. If the balls and/or pathes are "frosted" this means that they are worn and probably debris dented. If true debris dents are visible, replace the bearings. Regreasing will buy time but won't EVER fix what are essentially irrepairably damaged bearings. Changing the oil in a car with trashed bearing never fixes them and neither does regreasing old, tired ball bearings. You got 16 years of life out of the bearings and probably never did ANY service to/on them. How much service do you expect to get when you subject the bearings to that much duress???? If you do change the spindle bearings, DO NOT expect the spindle to cut the same unless you have the spindle taper reground when the spindle is fully reassembled. Spindle bearing replacement is NOT a mindless effort of knocking off the old and pressing in the new. WHen done properly, you will have a like new spindle - do a kluge job and the spindle will surely disappoint you. If you do a "birdgeport spindle bearing" or spindle bearing replacement" thread search, I've previously explained how to fully and properly replace spindle bearings. The explanation is too long to retype for me anymore - I can't see or type as well as I used to....

I agree that after 16 years (where lube is not changed) ismore than one should expect. We sell a variety of various "bridgeport bearings". These range from 6207, deep groove to 7207 angular contacts. They can be pairs or quad sets. We use Kluber NBU15 w/excellent results.
mikeyg