Tapered roller bearings preload question

[sendkeys]

Does anyone know at full heat what a 1 to 1.5 in.(ID) tapered roller bearing should be preloaded too(how many pounds)? I can't find it on any bearing website. only the basic directions like you use on a car.

What i was hoping to do is preload them with a spring washer, to so many pounds with a little slack. so low rpm dont have any play and high rpm doesnt overheat. bytheway im going to be pushing them right around there max rpm(5k+-). I would have went with angular contact bearing but didnt have the room. so my only opinion was highend tappers.

I would like to use the highest preload i could but also dont want to overheat. Also if no really knows opinions on a starting point for testing would be nice too

Thanks for the help.

[HuFlungDung]

I'm doubtful of the success you'll have running tapered roller bearings at high speed for very long. I find it strange that you could not find angular contact bearings that were more compact than tapered roller bearings.

Are you running your two bearings back to back, or how far apart are they?

The preload is quite delicate to set for high speed. It should almost be zero.

If we could see a sketch of how you have the bearings laid out, we might be able to give you some ideas. Ideally, you'd have the bearings back to back or something, to prevent having to deal with heat growth of the spindle. Then, at the other end, you'd have a simple ball bearing steady, which is a slide fit in the housing bore. This one would be the one that deals with the heat expansion of the spindle.

[sendkeys]

It's one bearing on the shaft far apart on each end like a 9x12 lathe or benchtop mills.

well problem with the angualar bearings is i would need 4 of them 2 top 2 bottom (left right in this case) but only had room for 1 on each end. I'm hoping to be able to seal the bearings in and use a oil bath. not in crapy sketch but there are two caps that go over each end that i think i can fit with seals.

It just sounded better to me if i loaded it with say 100 pounds of springwashers with 1/4 turn back that i could have it all :P low rpm with no play and high rpm with less heat :P

[marx911]

well normally tapered bearings are set with an internal precision spacer that holds the 2 bearings apart at some predetermined amount of endplay... after you set the endplay you would run the spindle up to speed is steps while measuring the temp on the bearing housing.... what you would want is to see is the bearing heat up then stabilize, if it never heats up then your endplay is too much and you would make the spacer smaller..If it never stabilizes and keeps getting hotter then you have too little endplay and you need a bigger spacer ... these are just general guidelines and I agree with HuFlungDung "The preload is quite delicate to set for high speed. It should almost be zero”.... the problem with using a spring washer as I see it is that as things heat up and start to grow things are going to get tighter which is going to create more heat which is going to make it grow and you will end up with thermal runaway
The other thought is that if you are using a spring in a spindle you will have a springy spindle it might tend to move around under load
Just my thoughts
Mark

[HuFlungDung]

Originally Posted by sendkeys It's one bearing on the shaft far apart on each end like a 9x12 lathe or benchtop mills. well problem with the angualar bearings is i would need 4 of them 2 top 2 bottom (left right in this case) but only had room for 1 on each end. I'm hoping to be able to seal the bearings in and use a oil bath. not in crapy sketch but there are two caps that go over each end that i think i can fit with seals. It just sounded better to me if i loaded it with say 100 pounds of springwashers with 1/4 turn back that i could have it all :P low rpm with no play and high rpm with less heat :P

Sendkeys,
If you are building this spindle housing yourself, its still not too late
You said you needed 4 angular contact bearings: the reason being that you would run them in adjacent pairs. True, but the preload method is the same, whether using tapered roller or angular contact styles, so you could also run pairs of tapered roller bearings back to back. One pair at the front end of the spindle would be best, and then a plain ball bearing at the rear end to steady the spindle and allow heat growth would also be best. It must not be captive, but must be able to float endwise in the housing.

I'm looking in my FAG bearing catalogue (can I say FAG in here? ), and it says the limiting speed is about 5000 rpm in grease, and maybe 6500 with oil.

Be aware that your shaft seals are going to cause a significant rise in temp just from doing what seals do best: rubbing on the spindle. A bearing running in oil is not necessarily better cooled, either. If the oil bath is captive, the bearing actually generates heat from stirring the oil. Some kind of a stream of oil is the most superior method of applying the oil to the bearing. But that requires the added complexity of an oil pump.

If your duty cycle with this machine is short, say 10 minutes on, and 10 minutes rest, you might not have to worry about overheating. But, the long distance between your bearings is going to give you grief when you run at high speed, IMO. It will just be difficult to make it right at both low and high temperatures. That's why I recommend you change your construction plan before its too late

[sendkeys]

this is for a old horizontal mill that im sure im asking to much out of it hehe. main reason i need 4 angular bearings was 2 didnt have the load rating i needed. But that could have worked guess if this doesnt work i might end up doing that way ,anyway.
By the way duty time is around 4 hours on, 1 off.

ok well thank you both very much for the help, Guess the idea wasnt really a good one. Seeing i already have the bearings i will give a it a shot doing it the normal way. if it doesnt work will have to try somthing else or live with slower rpm,or lower load rating.

Thanks again

[IndHobby]

If posible assemble the spindle hot, a pinch hotter than it will see in normal operation. This way expansion (preload change) will already be handled in the process and you don't need to worry about changes quite so much.

[TPPJR]

[QUOTE=HuFlungDung]Sendkeys,
If you are building this spindle housing yourself, its still not too late
You said you needed 4 angular contact bearings: the reason being that you would run them in adjacent pairs. True, but the preload method is the same, whether using tapered roller or angular contact styles, so you could also run pairs of tapered roller bearings back to back. One pair at the front end of the spindle would be best, and then a plain ball bearing at the rear end to steady the spindle and allow heat growth would also be best. It must not be captive, but must be able to float endwise in the housing.


Is it possible to convert a taper bearing spindle to angular contact? I have a RF-45 benchtop that I am running at 3k rpm with tapered bearings. I have been fighting an heating problem with the gearbox and noticed the lower bearing was hot. Upon removing the spindle both bearings had been pretty hot burning the grease I was using. Going to go with high speed grease this time to see if it helps but angular bearings caught my attention.

Thomas

[wizard]

Interesting comments but I'm troubled by one. Spring loading of spindle bearings is done to prevent losening of the preload as the spindle heats up when mounted as you describe. At least that is the way it has always been explained to me. This seems rational as the spindle itself will elongate with teperature rise, a rise that should happen faster than the surrounding bearing housing.

To be honest the few spindles I've torn apart with spring loading have been high speed units with angular contact type spindle bearings. Almost all of the machines I've seen with roller bearings had the preload set with an adjustable nut. As far as the precision spacers, as described above, those are almost always in spindles using angular contact spindle bearings. Of course you have to realize that the vast majority of my spindle work was done 25 some odd years ago on machinery that was old at the time. I don't think the technology has changed that much since then.

HuFlungDung seems to be on the right track here with bearing arraingements. The issue is do you have the room to do such a retro fit on that old machine. I can't answer that but it might pay to consult with a bearing manufacture for non standard product that might do the trick. As to load rating you are likely to loose some on the taper rollers at high speed so maybe angular contacts are not all that bad.

By the way what are you expecting to do with the machine anyways?

Thanks
dave

[NC Cams]

Tapered rollers are designed to run with 0.000 to 0.005" endplay.

The "preload" deal is a quick-a$$ way to try to obtain this figure with a quick-a$$ one shot tightening approach. If you literally run the tapers with preload, you run the risk of having problems as the edges of the rollers start to rub the flanges of the raceway and overheating and/or flange/roller scuffing develops.

The above clearance achieved by shoving the shaft in one direction while rotating with a dial indicator on the end of shaft until it quits moving axially, Then continue rotating while you shove it axially in the other direction. Keep tightening the bearing end clearance until you get above clearance.

The longer the shaft/ergo span between the bearings, the more you have to compensate for thermal growth of shaft and housing.

If you're doing a lathe spindle, you can consider tapers. If you're doing a mill spindle, stick with A/C's.

Wave washers are good to load the end support bearing opposite the workend of the spindle. On the work end, you want a postion preloaded A/C bearing.

Example: if you use a 206 size bearing on work end, use a 7206CTYDULP4 or DUM or DUH. Use either a 6205 ot 6206 with 1%-2% preload washer on drive end.

You can't maintain bearing rigidity if you spread the bearings out like you're suggesting with a mill spindle. Lathe spindle (due to preominant radial load application) will work OK with tapers, providing you get machine tool grade.

Generic "automotive tapers"or the like typically won't have the tighter runout needed for M/T used.

[WhiteTiger]

A lot of the problem with tapered rollers goes away if you get away from static lube (grease). If you go to oil seals and a central sump between your bearings you can avoid the pump question the way you have your bearings illustrated. As long as your oil level is up high enough to feed the open small end of the bearings and you have an oil return channel, the bearings themselves will sling the oil to the larger diameter and suck new in from the sump.

Some old babbit bearing precision spindles used just that sort of arrangement, with slinger discs on the spindle shaft running in the sump to auto circulate the oil.

Has the benefit of conducting the heat away from the running surfaces and into the housing. Down side is you have to design for seals, and ideally you would have a closed sump on each end to supply the bearings independently, which means 4 seals and seal surfaces.

Just a side note: when I was doing a lot of high speed, small diameter work on my lathe I had a bit of heat problem despite sump type oil lubrication. I drained all the oil, stuck slick 50 in and let the thing idle at high speed long enough to heat up, then ran it a few minutes on lowest speed to give the ptfe time to start to cure on the race and roller surfaces without building up. Cured the heat problem, and it's something I re-did periodically all the years I actively used the lathe.


Tiger

[Stevie]

I use FAG tapered roller brgs in my small lathe (actually the big one too)

I have no problems with setting perload and running the spindle at 3600 all day; course you need to cool the head if it's Alum like mine or expansion creates more preload and so on and so on