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Bearings

Average life would depend on service and conditions. Scraping or clicking sounds coming from the headstock would be a clue of possible problems to come. Really excessive heat in the spindle / headstock would be a clue that you might have waited too long to address a problem. Shrieking metal and sparks flying out of the headstock would be a clue that you definitely waited too long.

If you have concerns, call Jet tech support to discuss it. They are very helpful.

Ed
 
Like the man said, but the first signs I'm familiar with are more often a rumbling or grinding sound that you can nearly duplicate with the motor disengaged. That's friction, which makes heat, which pair I would consider the signs that it's time to replace the bearings.

The MTBF - mean time between failure - of any component has both a low and a high end, so unless you're abusing the lathe with a steady diet of out-of-balance cantilevered pieces or sanding behind your turning, it's probably nothing you did which affected it.
 
When I was worried about noises, Redmond Machinery told me to just run the lathe for a few hours at a high speed and see what came of it. I spent a nice afternoon prepping blanks and cleaning/organizing my shop until the noise reached the point where there was no doubt!
Also check the temp of the headstock periodically as you do this.
 
Heat is not a good indicator. Double row angular contact bearings, such as used in many high end lathes, will run quite hot if the speed is high. As others mentioned, grinding noises are an indication. Sometimes you'll get a little tick, which means there's a spot on one of the balls/rollers. It will probably run forever this way. You'll know when they do go.

Often folks will attribute out of round pieces with bad bearings, but that's an operator problem.😀 The fact is bearings rarely go bad.

John
 
I did wear out a set of bearings on my PM3520A. I was sanding which I do at slow speeds because of my warped bowls. Mostly, it wouldn't run smooth at slow speeds, and when turning the spindle by hand, it felt rough. This was after 3 plus years of turning chainsawn blanks with no tailstock. The second set lasted a lot longer because of the purchase of a Laguna 16HD bandsaw. Much less roughing to do.
roob hippy
 
robo hippy said:
.............................................. This was after 3 plus years of turning chainsawn blanks with no tailstock. The second set lasted a lot longer because of the purchase of a Laguna 16HD bandsaw. Much less roughing to do.
roob hippy
Click to expand...

Just this week after roughing several large(for me) chain sawn cherry blanks, I would get a loud clunking every so often. Turned out to be the dreaded loose set screws on the spindle pulleys. If my hearing was up to snuff I probably would have heard the clicking long before I heard and felt the clunking. History repeats its self, my dad used to call my Model A Ford a clunker. I wonder what he would call my 3520-A.😛
 
Use a screwdriver stethoscope

Remove chuck, etc from headstock. Take a large, and long screwdriver. Put the blade of screwdriver against the housing in area of bearing. Press your little ear flap against end of screwdriver handle, closing flap in the process. Turn on lathe and listen. You can hear all the problems in the bearing. Good bearings will HUM, bad ones: clunk, scrape, squeal, knock, etc. Listen to a set of new bearings for comparison. Don't get your tie caught in the spindle! Be safe.
 
When in doubt, one could completely loosen/remove the belt and turn the spindle with fingertips. If there is a little bump, almost anything but completely smooth, that's probably a bad bearing. Found a bad bearing on my table saw arbor that way.
 
Routine maintenance on a lathe is a requirement that most turners overlook. Often noises that may seem to be bearing noises are simply loose set screws that should be checked periodically. Reading through the owner's manual will give a good idea of areas that need attention. Bearing wear can be spotted by first loostening the belt, then rotating the spindle by hand. With a bit of experience, you can feel a bad bearing...you don't even need to hear it.
 
If treated properly, bearings normally last a very long time. The way to very quickly ruin bearings is to apply large axial preloads or to subject then to sharp axial impulse loads. Most lathes do not use angled race ball or roller bearings that are designed to handle a certain amount of axial loading. Standard single or double row bearings that are typically found in lathes are only intended to carry pure radial loads ... in that respect, most lathes have not been properly designed since it is normal practice to apply some axial loading to the spindle via the tailstock. Also, even the forces exerted during normal turning will result in some significant axial vibration loads when doing aggressive hogging of wood. A couple things that your bearings will thank you for doing is not applying heavy tailstock pressure and never hammer anything on or off the spindle. If you find it necessary to pound a Morse taper insert to remove it from the spindle then your lathe already has a very serious problem with a damaged (most likely galled) mating surface.You can salvage a damaged taper bore if you do not wait too long to ream and hone it ... if you do wait too long, you can count of replacing the spindle at the same time that you replace the bearings. Bearings are relatively cheap ... a new spindle is definitely not cheap.
 
At least we don't have those grease cups up top any more. They grew dust trees no matter how well you THOUGHT you wiped them after lubing. Tapered roller bearings were certainly a good thing, but the present-day roller type seem more than good enough if you don't abuse them heavily.

Wondering if the right-hand rule for torque doesn't help balance the thrust toward the headstock a bit.
 
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