Angular contact bearing question

[Rube]

I'm doing an X3 conversion and have a question on angular contact bearings. I got the bearing pictured below (INA 3200 series). this is a double row angular contact that is is to absorb axial loads in BOTH directions. Now, I must be having a bad day, because I'm confused as to how to pre-load this. If I was using two single row units back to back, I could see pre-loading it by squeezing the two inner races (would need a small space between them) then capture the outer race in the bore. In fact some of the larger double row units I've seen have two separate inner races. So does that mean these do not need to be pre-loaded? I've searched the manufacturers web site for tech info, but couldn't find it. These were "cheap" at $27 each, and I got them thinking I would only need one on one end of the screw. But I think I'd be better off with two single row units, one on each end of the screw, so I could completely remove any slop in the bearings.

Rubes

so thats how I end up with so much stuff...always doing things twice!!!

[HuFlungDung]

I believe you don't add any external preload to these. Whatever axial play these have is what you've got to settle for.

[Rube]

Yeah...thats what I thought (I should learn how to think BEFORE opening my wallet...ha...ha).
I think I'm gonna look for some single units with a steeper angle than these 25* also. Since in this application most of the force will be axial.

[NC Cams]

Double row bearings (pictured in post 1) can NOT, NOT, NOT be preloaded.

IF you want/need preload, you'll need the two single row bearing idea that you already envisioned. With two single bearings, you can shim the outer or inner races or some such similar method to preload as needed.

[rexstep]

Double row angular contact bearings DO come preloaded but I don't know if they come non-preloaded. I have some and they are certainly preloaded.

You can easily tell: try to axially move the inner race to and fro while holding to outer race. If the inner race will wiggle, it's non-preloaded. If not, you're good.

BTW, you can get preloaded ones at www.vxb.com

Rick L.

[Rube]

Thanx Rick...these certainly feel tight now, but for the price I paid for them they are most likely not precision pieces. Besides, they are only 15* contact angle, and in this application most of the force is axial, so I got some single row 40* pieces from VBX last week. They too were extremely inexpensive, but at least this way, I can readjust later if I have too. I'm sure those first ones I got would be fine, but I just like the added adjust ability of the two singles.

[NC Cams]

Having worked in the ball bearing industry for a number of years, I have to take exception to the contention that double row A/C's like that pictured are "preloaded".

The industry typically makes these bearings for taking a combination of axial and radial thrust. As precise as the industry is, they have NOT found/figured out a way to "preload" a double row bearing. THis is why they are sold with clearance codes (IE "normal", CE, C2, C3, C4 etc) as these are radial clearance specs - if you have radial clearance in a bearing, you pretty much HAVE to have axial clearance as well.

When I say preload, I mean to literally run NEGATIVE axial clearance. The reason why you preload a bearing has to do with the load/deflection that takes place until you FIRST remove all the axial clearance that SECOND tke out the initial "spring" or compliance that occurs as load rises. This is readily discernable by making PRECISE load/deflection studies of the bearings.

"Feeling" or 'shaking' the bearing is an irrelevant inspection method. You can have no perceptible play in a bearing but the rings will axially deflect quite substantially when you load them. Recall that bearing clearance/deflection is in terms of MICRONS (0.001 mm). What "feels" like no clearance can actually be a lot. For this reason, preloading is NOT an inconsequential force.

This can be as low as 1%-2% of the radial load and go as high as severl HUNDRED pounds negative preload. It is pretty much impossible to put such preload into a double row, especially when you know/see how they load and space the balls - it simply doesn't happen.

Unless something has changed drastically, I'd think twice about using a double row in place of a true and properly preloaded A/C or better yet a true ball screw bearing.

Before you take my or anyone else's word regarding double row bearings and preload, call any bearing maker's engineering dept (IE SKF, Koyo, NSK, etc) Ask them for a "preloaded double row" and see what they tell you about the availability of same.

In the mean time, caveat emptor.

[Rube]

NC, thanx for your input. As in anything else once you think through all this stuff, it becomes somewhat clearer. I thought I had seen some double row units (they were large ones though) that had a split inner race which I assumed was for applying pre-load.

In any case, I decided that two single row units are the answer for me in this application. I'm trying to get the best precision I can, and I dont want to have to wonder if ANY of it is coming from those bearings. An added benefit (although I already spent the money on both) is that two singles are cheaper than one double. Thanx again for your input.

[NC Cams]

A double row UNSPLIT outer ring with a set of SPLIT ROW inner rings could very well be preloaded - it depends what sort of "preload" is applied if/when the inner rings are shoved together until tight.

The bearing pictured in post 1 is definitely a traditional, non-preloaded double row with, typically a combination of radial and axial clearance.

[Robin Hewitt]

Axial race at either end and a die spring trying to stretch the ballscrew, that way you never have to compensate for wear. Things will move around a bit when everything goes horribly wrong but even so, might save overloading your nut

[project5k]

Originally Posted by Robin Hewitt might save overloading your nut

insert crude joke here....

[rexstep]

Hi NC Cams,

I readily admit that I am not a bearing expert but I know that Universal Thread Grinding Company, makers of a very high-end preloaded leadscrew product, offer their assemblies with just such a preloaded double row assembly.

Moreover, I called VXB several months ago with this same question and was assured that their double row angulars were preloaded. To my understanding, no play detectable to the fingers indicates at least a light preload, but I remain open to learning.

Rick L.