Bearing/shaft interference

[ElevatorGov]

I'm no machinest by any means so I have a few questions. Currently working on an old Otis geared machine, (have attached a few pictures) one of the pedestal bearings went out and ruined the spider assembly. Long story short got a new one in place but the bearings that were sent Timken 643 measured at 2.746 but should have a measurement of 2.750 and the shaft is at 2.753. I've tried heating the bearings to 250F but had no luck getting it to go on. I have ordered a new set of bearings incase I got shipped a bad run. But any insight on bearing interference references would be much appreciated.

 

[guythatbrews]

Forgive me, but how are yiu measuring the cone? Are you confident of your number?

I'd contact Timken for their input. It may take a while to get a human to answer the phone, but I'll bet you can. If the cone is undersize, I'll bet they'd want to hear about it.

Also, Timken has some great online tools. This tool specs the cone seat at 2.7515/2.7525 for severe use. You're already out of their advice on the shaft.

Bearing Fitting Practice - Timken

See the suggested fitting practices for bearing inner and outer rings. Proper fitting practices can extend bearing life, minimize downtime and help ensure reliable operation for the life of the bearing.

engineering.timken.com

This tool shows cone bore should be 2.7500 +.0005/-.0000.

Bearing Tolerances - Timken

Locate standard tolerances and dimensions, such as inside diameter, outside diameter, width and runout of tapered roller bearings, spherical roller bearings, tapered thrust bearings and ball bearings.

engineering.timken.com

Heating to 250* will get you just over .003 growth so it's still a close fit with the numbers above. Everything has to be just right to prevent cocking.

 

[eKretz]

I'd be getting that bearing replaced. I would not, under any circumstances, be trying to put it on with .006" interference. Around .002" would be plenty.

 

[hvnlymachining]

For .003" (or.0025" as spec'd) interference fit on a 2-3/4 shaft you're going to need to heat the bearing AND cool the shaft to get the bearing to slide on. And by cool, I'm guessing at least -200°f , so dry ice or liquid nitrogen. My personal favorite is LN for the speed of cooling, (plus much colder!) dry ice is very slow at cooling. If you don't have ample clearance during assembly the bearing can suddenly seize before you get it where you want it. At that point it becomes a real mess!

 

[chipss]

Just a note: Be careful heating bearings. Ball and roller bearings are made from 52100 spherodized hardened to around 60-62 C.
Heating above 350F will start tempering the alloy back. At the 250 you're going to, no problem.

 

[mottrhed]

Are you sure you got the right class bearing? Cup/cone bearings come in many different tolerance classes, and the further you go away from the best, the wider the window gets for acceptable sizing and runout of the races, rollers and relative shaft/housing fits. Id venture to bet you have the right "size" bearing, but in the wrong class. Usually in a given size, there is a $70 version, a $300 one, and a $2500 one. There is a reason and they arent all the same or interchangeable.

Just a guess.

If I were you, Id double check that its the right size, then Id call around to bearing suppliers and have them look on their shelves for the one with the largest ID to compensate for the +.003 journal you have.

 

[Farmer Phil]

If that bearing is successfully installed on the shaft, or isn't going to last long.

.001 interference will be just fine for your application.

 

[4GSR]

That much interference will split the cone the moment a radial load is applied and rotated a few RPM's. If you're using dial calipers to measure the bore, throw them out the window and get some mics and telescoping gages to do your measuring with.

 

[ElevatorGov]

I am measuring the shaft with outside micrometers and telescoping gauge to measure the bearing cone

Forgive me, but how are yiu measuring the cone? Are you confident of your number?

I'd contact Timken for their input. It may take a while to get a human to answer the phone, but I'll bet you can. If the cone is undersize, I'll bet they'd want to hear about it.

Also, Timken has some great online tools. This tool specs the cone seat at 2.7515/2.7525 for severe use. You're already out of their advice on the shaft.

Bearing Fitting Practice - Timken

See the suggested fitting practices for bearing inner and outer rings. Proper fitting practices can extend bearing life, minimize downtime and help ensure reliable operation for the life of the bearing.

engineering.timken.com

This tool shows cone bore should be 2.7500 +.0005/-.0000.

Bearing Tolerances - Timken

Locate standard tolerances and dimensions, such as inside diameter, outside diameter, width and runout of tapered roller bearings, spherical roller bearings, tapered thrust bearings and ball bearings.

engineering.timken.com

Heating to 250* will get you just over .003 growth so it's still a close fit with the numbers above. Everything has to be just right to prevent cocking.

I've measured numerous times with micrometer and telescope gauge for both the shaft and current bearing. Currently waiting for new bearings to come

 

[4GSR]

I have a hard time understanding why Timken would let out a bearing with a way undersize bore, even if it's a automotive class bearing. I haven't looked it up, I would say holding a bore that size to within a couple of tents shouldn't be a problem. I know I can do that once in a while, holding my tongue just right.

 

[ElevatorGov]

I just got a new set of bearings in and they measured to 2.750..was able to get the new bearings installed easily with heating to 250F..thanks for the advice and education on this. Is there a book anyone would recommend for reference information?

 

[4GSR]

Go to Timken's website and look for a download of the Engineering manual as one reference. They have several references that I would recommend downloading and taking a look at. Most may not apply to your needs, but all good information to have when needed.

 

[John Garner]

There's a fair chance the bearing cone with the 2.746 inch ID is counterfeit. And if it is, the outer race that came with it is probably also counterfeit.

 

[gbent]

Just a note: Be careful heating bearings. Ball and roller bearings are made from 52100 spherodized hardened to around 60-62 C.
Heating above 350F will start tempering the alloy back. At the 250 you're going to, no problem.

OP is using tapered roller bearings, case hardened 8620, not 52100. I do not know the tempering temperature used.

 

[john.k]

Bearing makers specify 150C as the max for fitting ........go over that the service life of the bearing is much reduced.

 

[Richard King]

I'd be getting that bearing replaced. I would not, under any circumstances, be trying to put it on with .006" interference. Around .002" would be plenty.

Or less. I'd think .001 it to much. Timken will have an 800 # I ould bet. Your shaft looks worn. Do you know how to use an outside and inside micrometer? Don't use a veneer or tape measure...lol. just kidding on the tape measure. Even a telescope gage would work. Be sure to measure the very end of the shaft now as it may have got expanded /wedged if you tried to press it on cockeyed. I have a cone shaped bearing heater I made on my lathe out of a 5" diameter shaft of aluminum and in the bored hole in the end and I slid in a heat sink. I use an infrared thermometer.

 

[eKretz]

Or less. I'd think .001 it to much. Timken will have an 800 # I ould bet. Your shaft looks worn. Do you know how to use an outside and inside micrometer? Don't use a veneer or tape measure...lol. just kidding on the tape measure. Even a telescope gage would work. Be sure to measure the very end of the shaft now as it may have got expanded /wedged if you tried to press it on cockeyed. I have a cone shaped bearing heater I made on my lathe out of a 5" diameter shaft of aluminum and in the bored hole in the end and I slid in a heat sink. I use an infrared thermometer.

It sounds like this is for an elevator, so I wouldn't go *too* light on the interference. Probably under a decently heavy load at all times with a counterweight, etc. Too little interference will tend to wear things out faster in those kinds of circumstances due to slight relative movement and fretting. A lot of the steel mill equipment I used to repair and make new had pretty heavy interference fits for that reason also. It's a little different ballpark than the precision realm.

 

[jccaclimber]

In a passing comment I let my SKF guy know that we'd measured one of his bearings to be in spec, but in the upper 10% of the tolerance band for inner race ID. Purchased from an SKF dealer. His response was that they absolutely had not sent a bearing that far from median spec and if I was confident in my measurements that he wanted the part back, the packaging, and any other bearings from the same batch we had available because even kissing the edge of the specification would imply a failure of their internal processes.

Turned out he was right, our measurement was off by about 1.5 um and the bearing was just fine. Fortunately we figured that out before sending it back to them.

I've heard similar from other reputable bearing manufacturers and seen their process capability reports. I'm sure Timken would want it back, even if it turned out to be a counterfeit.

 

[Richard King]

It sounds like this is for an elevator, so I wouldn't go *too* light on the interference. Probably under a decently heavy load at all times with a counterweight, etc. Too little interference will tend to wear things out faster in those kinds of circumstances due to slight relative movement and fretting. A lot of the steel mill equipment I used to repair and make new had pretty heavy interference fits for that reason also. It's a little different ballpark than the precision realm.

I never saw that....I bet in the old Machinist handbook it would say.

 

[farmersamm]

I might be wrong, but in the case of ball bearings, increasing either housing, or shaft, interference beyond spec can lead to decreased life due to excessive preload.

Every bump up in interference, decreases the internal clearance in the bearing.

I would assume that there would be the same effect when dealing with tapered roller bearings.

Timken is very precise when it comes to ball bearing fits. Depending on whether the housing is stationary, or rotates, shaft size...........etc. I've seen the same with other manufacturers.

In my application(hay equipment), my main concern is overheating resulting in fire. It's not something to be trifled with. Although it's believed that loose bearings on the point of failure cause fires...............you have to consider how that bearing became loose. Lack of lube is one cause(sealed bearings are notorious for seal failure), fitment can be another.

Bearing quality is also an issue. The industry is apparently shifting from Timken OEM, to Peer OEM. Bearing failures are more common as a result. Some aftermarket bearings are even riskier.

I found it interesting that a lot of the bearings on these machines are "extra clearance" bearings. I assume this is due to the inherent alignment problems encountered on this type of equipment. The frames on most balers are not very robust, which leads to a lot of flexing.

And.................are you getting genuine bearings?? Who knows these days. Even genuine bearings, produced offshore, can't be assumed to be in tolerance. It's become a messy world out there.