Bearing Life and Scheduled Equipment Maintenance

Replacing worn-out bearings is a non-routine task, but routine maintenance can keep you from having to do it often — or ever. Here's a detailed discussion of maintenance planning and bearing repair. May 15, 2012

About halfway through a job yesterday, I had to shut down my shaper. The vibration had just gotten to be too much. I knew I should have looked into it a couple weeks ago, but never found the time. So as I'm in the process of changing out the bearings, it has me wondering about a couple other machines that are getting up there in miles.

I'm wondering how other shops handle maintenance? Do you change bearings automatically after so many years? Or do you just wait until the signs start to show? I've always waited, but the problem is they never go at an opportune time. It's always when something has to get out the door. Of course some are much easier and cheaper to replace than others… tablesaw versus planer, for instance.

Forum Responses
(Solid Wood Machining Forum)
From David Rankin, forum technical advisor:
Maintenance is important. I maintain my machines every 150 hours of operation. As for bearing repair, most sealed bearings will run for 5-7 years without much concern. This is true if the tools are balanced. Bearings that have grease fittings should be greased every 150 hours or so. Bearings that have oil lines to them should have oil available at all times.

From the original questioner:
Thanks David. My concern is that I've heard several different numbers for lifespans on sealed bearings. Some of them indicate that I'm going to have a lot of bearings to replace over the next several years.

I have a couple machines I've owned for more than a decade without having replaced bearings, but they sound fine and are not daily machines, so I'm not too concerned yet. Alternatively most of the machines in my shop have been purchased used and as such I have no idea as to the age of the bearings. The biggest hurdle being that on old machines, it's not easy/possible to find out what bearings are needed until you break the machine down.

I think it's time to finally start a maintenance log. I want to be able to keep track of when I lube, what bearings are needed as I find out, and what belts are needed. I'm at a point where there are more machines than my memory can keep track of, so maybe this will help.

From contributor T:
Bearings are hard to predict. But good maintenance is an awesome thing to have a log book of. Even if it just means arming your guys with grease guns and a checklist for an hour twice a month.

From contributor H:
I work on many types of equipment and have worked for many companies producing products. It really varies across the board. I have seen shops that only repair the equipment when it breaks and no pm. Then you also have ones that constantly are on top of the pm's. Being on top of pm's is a good thing, but it doesn't prevent down time. You never know when a part will fail even with the best pm.

Performing basic lubing, etc. is better and will help you keep running longer. I would not skip this. You can also sometimes notice other problems when you do this.

In regard to bearings, you also get what you pay for. But you don't have to pay high dollar for a bearing either.

If a machine is going to sit awhile, I would apply some grease and run it for a few minutes. Let the grease get worked in and prevent rust and other problems from happening while idle. Belts dry out due to dry rot. Bearings will also dry out if they sit too long.

From contributor M:
Spend some time and create a maintenance schedule for each machine. What we have found works best is to have a daily, weekly, monthly, quarterly/annual checklist. The operator or person responsible for maintenance performs the daily checklist before they run the machine every time. Then on Monday morning, add the weekly items. Put the monthly, quarterly items on the calendar and do them. If you need help creating the checklist, see the manufacturer's manuals, talk to suppliers, etc. Stuff will still break down sometimes, but you will be way ahead with a lot less downtime.

From David Rankin, forum technical advisor:
A PM log is a good thing. I agree that breakdowns occur, and these can be reduced by a good PM program. Buying used machines can be even more unpredictable. On used machines, I do not replace all of the bearings unless I do a complete rebuild. I have used machines that have run for several years with no problem. On the other hand I have brand new machines that have lost bearings in under a year. The quality of the bearing is important to try to reduce the risk of failure.

One important thing to remember: on precision bearings, only half pack them with grease. Over lubrication is one of the main causes of premature bearing failure.

From the original questioner:
Thanks - a lot of good advice here. I'm going to set up a system for keeping track of all my bigger equipment over the next few weeks.

Dave, I have several machines that are in the 30 - 40 year old range bought used several years ago and are still running great. The shaper that went down was a 2-3 year old Powermatic 27 bought new. Of course I don't think they designed these machines to be running 6" corrugated knife heads, so maybe I was asking a bit too much.

Anyway, bearings are changed and she's back in action. More importantly her replacement, a 42 year old Martin, is proceeding along and will hopefully be operational by the middle of next month.

From contributor B:
When we buy a new machine, we log all the recommended maintenance procedures into a scheduling software and make sure to do them. The recommended maintenance is usually far above and beyond what most people will actually do, and that's a good thing. For example: if the manual says to replace the bearing at 12,000 hours, we order it at 11,000. We then decide what the time frame to replace it is when it goes out. If it takes 5 minutes to replace the thing, we just wait until it goes out (and we might get another year out of it, who knows), even if we're in the middle of a run. If the thing is going to take 4 hours, and we've got important jobs on the floor for the next month, we replace it!

From contributor C:
We use Sherpa displays for a lot of setup info for machines. This is a good place for a maintenance log or just attached to the machine itself. It's out there and visible, so easier to remember when maintenance needs done.

My worry is with computers and electronics now that some of those machines are approaching 10 years old. I want to learn how to troubleshoot and repair these without complete (expensive) parts replacement. The techs tell me it's not that complicated once you learn the basics, but it's still overwhelming for me.

Click here for higher quality, full size image

From the original questioner:
I know what you mean… That's why I'm buying 40 year old shapers for my shop ;>)

I have an 80's era Italian CNC drilling machine that is a huge time saver in my shop. However, if it ever has a problem it's essentially going to be a very heavy pile of scrap iron, as there's no support whatsoever for it. It has a floppy drive for saving programs. Anyone remember floppy discs? I haven't been able to get it to work right, so I'm limited to the 100 programs stored in it. Currently trying to get one of the pneumatic cylinders rebuilt and even that's been a failure so far. Replacement parts… I'd have better luck with a 120 year old planer!

From contributor J:

I work on machines for a living, and most of the machines are maintained (in theory), but bearings are not something that you normally replace as a maintenance item. Lubing yes, replacement no. So when it comes to replacing them, the lifespan varies significantly.

This can have many factors, so let's assume that all of the tooling is correct and that no damage has been done to the spindle. Bearings come in different classes. The more precise the bearing, the better the lifespan, and the more difficult to install.

You cannot just buy the cheapest bearing, beat it in with a hammer, and run. The bearing life will be shortened. Instead, you need to determine the class of bearing. A good bearing house will help you with this. I use Motion Industries and Applied Industrial Technologies.

Also, you will need to determine the type of protection for the bearing (open, shielded, or sealed; single or double sided, or combo).

This is all pretty straightforward. Installation is where it gets tricky. There basically are two ways to install a bearing. Press and heat/shrink.

When pressing a bearing in place, you literally force the bearing to fit. The pressing action must be done on the race that is being pressed and not the counter race. Damage to the races and/or element can result.

When heat/shrinking a bearing in place, you will either heat or freeze the bearing to make it expand and contract. This movement will allow it to be slip fit into place. Sometimes it is necessary to do the opposite process to the bearing's mating component (i.e. heat a bearing, freeze a shaft).

Either way, you create stresses in the bearings and their alignment. To remove these stresses you must break in the bearings. To do this, first spin the arbor by hand to confirm it spins free. Then, using a motor of some kind, spin the arbor for a few minutes. Depending on the arbor, sometimes I can do this on my bench with a drill. Other times, I do this directly at the machine.

Rotating the arbor will cause the bearings to warm and heat up. The slower the rotation, the longer it will take, but do not exceed the unit's rated speed. Once the unit heats up, turn it off and allow it to cool. Then repeat.

This constant heating and cooling will cause the bearings to shift and move, helping to eliminate the stress of being installed. I use the following schedule on most class B and C bearings. Class A, I extend the schedule. Class AA, I do not. Too precise for my capability. This takes about 3 hours. 6 sessions of 30 min each. It is important for the unit to cool as close to ambient as possible. It may be necessary to extend the pause time.

1) on 5 min. off 25 min.
2) on 10 min. off 20 min.
3) on 15 min. off 15 min.
4) on 20 min. off 10 min.
5) on 25 min. off 5 min.
6) on 30 min. Then ready for production.

Keep in mind that when the bearing warms, it should not get more than around 100 to 130 degrees F. Temperatures exceeding this can damage the lubricants and the machine/arbor. Unless it is a motor bearing. The motor tag will usually state its nominal temperature.

From the original questioner:
Thanks - that's some good information. Although I've been using machines for a long time, I haven't done too many bearing replacements yet, so I take each one pretty slow.

I have read about freezing the shaft/arbor before and it seems like a common practice. However I've also read bearing companies don't recommend it, as the cold shaft coming up to room temperature could cause condensation to form between the bearing and shaft. They recommend instead carefully heating the bearing.

Like I said I'm still fairly inexperienced with installing bearings so just relating what I've read. As such I'll probably stick with the heating method for now. Luckily the bearings I've done so far (Unisaw/27 shaper) had small enough shafts they could be pressed slowly on a patternmakers vise. The Martin shaper bearings coming up next will not be so easy. Probably going to pick up a cheap Harbor Freight shop press for those.

From contributor J:
The condensation is a good point. I wipe the unit down well before reassembly. Like I said, I don't do real high class bearings. This is one of the reasons. One of my colleagues made a bearing heater out of a 100w flood light and a BBQ grid rack covered in foil. Worked great. I prefer a double boiler. Either way, the idea is not to overheat the bearing.

From the original questioner:
I like the idea of using a light bulb. Like you say, you don't want to overheat it. Do you lubricate the shaft before installation when heating them? Or just press them onto a dry shaft? Just wondering how that would work?

I'm not sure how the letter classes translate to ABEC numbers? I'm planning on a 7 for the top bearing, and pending price I may try to save a few bucks on the slightly less important bottom bearing by using a ABEC 5. They'll both be open bearings and certainly the most expensive bearings I've ever done. Believe me there'll be no hammers used in this install.

From contributor J:
Sometimes I lube the shaft. Depends on the application. I wouldn't do it for a motor. Either way, I always use a cleaner to degrease the shaft and race before assembly. The microscopic metal residue will freeze a bearing to a shaft or housing, or worse, scour the surface. Then, lube with a thin layer of lightweight oil.

From David Rankin, forum technical advisor:
When I install bearings, I use a hot plate to heat up the inner race of the bad bearing. After it is hot, I place the new bearing's inner onto the hot one and wait 30-45 seconds. This heats up the bearing so that it slides onto the shaft. This does not work well if you are installing the bearing onto the shaft and into a housing at the same time. I bought a hotplate a few months ago for $15 new at Target.

From contributor N:
I used the hot plate on our coffeemaker in the break room once. It worked great.

From contributor V:
I have created a maintenance schedule very similar to contributor M, and I think you will find that if it is simple, it is more likely to get done. I also created a calendar of weekly, biweekly, monthly, bi annual and annual. I put a calendar in a binder with the entire year. I then made a copy of the picture of the machine from the maintenance manual and put it in the rear of the binder. I used a colored pencil and colored the weekly fittings red, the biweeklies green, and so on for all the grease points. Then when I made the calendar, I put a red banner on the top of Monday and filled in the fitting to be greased in red text. Tuesdays were green, Wednesdays were blue, and so on. Then the operator could just flip to the picture in the rear of the binder and see exactly where the corresponding colored fitting was located on the machine. After greasing the scheduled fitting, he would sign or initial that day indicating he had serviced those particular fittings.

It is also important to let your guys see you check the binder once in a while, and not just a week or two, but spot check it six months from now so they know it is not only important but mandatory. Have them turn them in monthly.

You can then document any repairs or tooling changes on that calendar and keep it on file. For example, we write down when we change out our straight line blade what blade came off and what blade went on, to keep a good rotation and evaluate our tooling vendor's performance. In addition, document when you changed a bearing, or belt, sharpen planer knives, etc. It has worked great and the maintenance is getting done as it should.

Find a good bearing house that you trust and use a screwdriver to check for possible problem bearings by putting the handle against your ear and the other end on or close to the bearing housing. You will be able to hear a growl in its infancy and prevent possible downtime or a missed ship date.