Roller steady - bearing type / surface geometry

gregormarwick · Oct 18, 2019

We have a big steady that uses INA NUTR3580-A track roller bearings.

These have a crowned (extremely slight, hard to tell it's not cylindrical even with a straight edge) outer surface, rather than being completely cylindrical.

However, they are also available in plain cylindrical shell.

The crowned ones we use have a fairly short life before the outer shell gets a bit scarred up in the centre where it contacts the workpiece, and then they get noisy.

Are these the correct bearings? Is there a reason to use crowned rather than cylindrical in a steady? Should we be using cylindrical shell ones instead?

Milland · Oct 18, 2019

If the support arms for the bearings are true to the Z axis, then use cylindrical OD bearings. If there's an axis twist in the arms, then you might get a slight axial force along Z while rotating, but it should be small.

At worst, try them and see what the results are.

jhruska · Oct 18, 2019

gregormarwick said:
We have a big steady that uses INA NUTR3580-A track roller bearings.

These have a crowned (extremely slight, hard to tell it's not cylindrical even with a straight edge) outer surface, rather than being completely cylindrical.

However, they are also available in plain cylindrical shell.

The crowned ones we use have a fairly short life before the outer shell gets a bit scarred up in the centre where it contacts the workpiece, and then they get noisy.

Are these the correct bearings? Is there a reason to use crowned rather than cylindrical in a steady? Should we be using cylindrical shell ones instead?

The plain cylindrical bearing will leave an edge imprint, score on the diameter.
The heavier the part the deeper the the score.
Torrington YCRC or YCRCS if you want seals, will chrome plate the outer running diameter .....on request.
Light oil on the running diameter for the rollers helps.
John

gregormarwick · Oct 18, 2019

jhruska said:
The plain cylindrical bearing will leave an edge imprint, score on the diameter.
The heavier the part the deeper the the score.
Torrington YCRC or YCRCS if you want seals, will chrome plate the outer running diameter .....on request.
Light oil on the running diameter for the rollers helps.
John

We have this already with the crowned bearing, except it's a single score in the centre.

Score isn't really the right word as it's not a depression - but it leaves a mark. No biggie as it gets turned off in the next op.

Surface speed is probably a contributing factor, 16" OD at 400 rpm for upwards of an hour cycle time. It's not spinning that fast the whole time of course, but still.

Vancbiker · Oct 18, 2019

I've only ever used lightly crowned rollers. Some jobs, we would put little "brush guards" mounted to the support arms to prevent chips getting caught between part and roller. That helped with part quality and roller life. They were made from some brush material we got from Mcmaster-Carr and folded into a little shape to enclose the roller and rub the part.

Gobo · Oct 18, 2019

Our LNS steady rest has crowned rollers. Must be a good reason.

gregormarwick · Oct 18, 2019

Vancbiker said:
I've only ever used lightly crowned rollers. Some jobs, we would put little "brush guards" mounted to the support arms to prevent chips getting caught between part and roller. That helped with part quality and roller life. They were made from some brush material we got from Mcmaster-Carr and folded into a little shape to enclose the roller and rub the part.

I actually did something very similar during this last run, very rough and very quick, but it definitely helped.

Need to do a proper job of it...

CarbideBob · Oct 18, 2019

It is just side of impossible to align multiple bearings true to each other.
So you end up with contact on one's shoulder or the other and that corner rad is smaller and thereby high pressure per area.
Since it is not a perfect world you use crowned.
Dirt, contaminated coolant, too little or too high pressure, plus fast start and stops will all cause scaring.
Bob

gregormarwick · Oct 18, 2019

CarbideBob said:
It is just side of impossible to align multiple bearings true to each other.
So you end up with contact on one's shoulder or the other and that corner rad is smaller and thereby high pressure per area.
Since it is not a perfect world you use crowned.
Dirt, contaminated coolant, too little or too high pressure, plus fast start and stops will all cause scaring.
Bob

Makes perfect sense, thanks.

jhruska · Oct 18, 2019

gregormarwick said:
We have this already with the crowned bearing, except it's a single score in the centre.

Score isn't really the right word as it's not a depression - but it leaves a mark. No biggie as it gets turned off in the next op.

Surface speed is probably a contributing factor, 16" OD at 400 rpm for upwards of an hour cycle time. It's not spinning that fast the whole time of course, but still.

Brinelling or fretting is the term for the mark. Not surprised after an hour or so. Good housekeeping and try some oil. The shoulder of a cylindrical bearing will score-indent the work as CarbideBob described. Another reason why rollers are not run on finished journals or seal lands.
John

HuFlungDung · Oct 18, 2019

I have 4 roller steadies and they all use flat bearings. One set of bearings has a large corner radius but is nonetheless flat for about 1/4" of width.

A full crown almost has to have extreme pressure on the contact point and will cold work the material a little bit. I think that if your steady is reasonably accurately built then the rollers are pretty well aligned with the spindle axis. And the outer race is able to float a little bit due to its internal manufactured clearance, and so the race can tilt slightly as all the looseness shifts to the unloaded side.

I always lube the track that the rollers run on to decrease fretting.

specfab · Oct 18, 2019

Just a note "in case":
I set up a steady rest for my 12" Clausing lathe a couple of years back (converted a 6900 model to a 5900 bed interface), and put ball-bearing support fingers on it. I realized as I was selecting the bearings that for a larger workpiece, the bearings would be spinning much faster than the part at a given RPM, and had to do some figgerin' to make sure the bearings were rated for their ultimate speed, and whether I needed to limit spindle RPM to accomodate resultant speeds on small bearings. In any case, good to check out the possibilities.
The bearings I used were standard square edge units.

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