Cheap and expensive Stainless bearings

[yadnom1973]

I’m building a little device I designed and am shopping for the bearings. They will carry about 50KG per bearing max and around 800rpm max. It’s intermittent use but could be outside and could be abused a bit so I’m going to use Stainless steel bearings. The ones I’ve settled on for now are 15x28x7.

I’ve found bearings which seem almost identical, dynamic load around 3.5kN, static load around 2kN, sealed 400 something stainless steel standard deep groove bearings that range from over £30 per bearing from SKF and the like all the way down to £3 per bearing and everything in between.

Now as far as I can tell I’m well below the load specifications and speeds for these bearings. It’s a camera dolly so they do need to be as smooth as possible and with as little friction as possible but I’m looking at these £3 bearings and trying to understand how they can make them so cheap, it’s not like you can make them fly by night. Surely once the industry is in place to mass produce bearings they are going to be of a certain standard?

Anyone know what’s going on, will the cheap bearings have egg shaped balls inside? Will they rattle and fail, do they use some terribly cheap pot steel that will pit and dent? Anyone had any awful experiences? Or do you need to run both bearings at 5000 rpm under heavy load for a few months before you get you clip board and statistics out to find the difference?

 

[purpleknif]

Used to get Boca bearings in small sizes foe $1 each for r/c racing. Never had a problem even after taking the seals out .

 

[yadnom1973]

Well that's one for the cheepies then I guess. I want to believe they are all the same but £3 to £30, it's such a difference. Most of the bearing shops hear list the named brands at around £30, The they have a high quality budget section at £15 odd, mostly made in the EU. Then the better Chinese ones for around £10, then there's Budget Budget at £5ish. Why such a price spread? There must be some difference in them.

 

[bazmak]

The precision and finish and of course the NAME determine the price
I have always used the cheaper bearings and for your application
wont notice the difference.If i wanted them for a car or plane or hydro-electric system then i would plump for the more expensive one

 

[Herbiev]

In my experience with bearings, you get what you pay for. The cheaper ones tend to wear out a lot sooner

 

[Walsheng]

Check the ABEC rating of the bearings:

The ABEC rating system includes grades 1,3,5,7, and 9. The higher the ABEC rating, the tighter the tolerances are, making the bearing a more precision part. High precision and small tolerances are required for bearings to function at very high RPM, in products like high speed routers that must spin at 20 to 30,000 RPM.

John

 

[Cogsy]

ABEC numbers are routinely faked by cheap suppliers and mean little unless attached to a reputable brand. Also, interestingly, when I worked for SKF skate bearings (608's) were beginning to be in high demand by the skate/inline crowd, and they wanted high ABEC numbers for high speed, not realising in these applications the higher drag created by tighter clearances and tolerances.

As far as your dilemma, I have found ID and OD tolerances to be quite variable for cheaper bearings, even from the same packet. I.E. one bearing is a slip fit on an 8mm shaft and the next is a press fit on the same 8mm shaft. I imagine the same variances exists within the bearing itself, with variable clearances having an adverse effect on bearing life and usability. When the SKF 'Explorer' series was released, they claimed such tolerance perfection and surface finish that if one of their rollers was enlarged to the height of the Eiffel Tower, the largest 'peak' or 'valley' on the surface would be less than 2mm. Another really critical difference is likely to be the bearing cage which can range from non-existent (just junk - think $2 fidget spinners) to pressed steel (very bad) to 'proper' cages such as phenolyic, fibre or machined steel (other too).

I'd say you would likely be fine with the mid-range bearings but the cheepos can be more hassle than they're worth.

 

[XD351]

If you want to see what you can get cheap then take a look at doubleboost channel on youtube , look for the truing roller he made ( just a bearing on the and of some round bar ) all was going well until he found he could machine the bearing as easily as mild steel !
Turned me off cheap bearings for life ! Timken , nsk , nachi or fag for me thanks ! I'm led to believe koyo are ok as well and there are probably a few more .

 

[Cogsy]

SKF is a premium brand although NSK is the industry leader for deep groove ball bearings. Just an FYI, Timken tapered roller bearings are case hardened rather than through hardened like all the japanese brands are. This means they have a slightly higher hardness than the japanese ones, and subsequently will last a little longer in service before they start making noise. However, once they start making noise they have worn through the hard layer and into the soft metal underneath and will fail very quickly. Through hardened tapered rollers will last for hundreds of thousands, or millions, of revolutions after they begin making noise. For this reason I always use quality japanese tapered rollers just for peace of mind in case I'm half way across the country and my wheel bearings start to make noise - jap ones will get me home, Timken probably won't.

 

[yadnom1973]

Well that’s a lot of interesting responses, thanks everyone for chipping in. Variation is size is disconcerting. All the 20 odd bearings are sitting in counter bores and I’m still weighing up whether to go for an interference fit or a rougher fit and just a bit of loc tight to hold them in place. Most of them are well below 700 rpm but there are two of them at up to 5000 rpm, I might fork out the extra cash for the named brand ones here though buy the same logic all the other bearings are load bearing and the two high rpm ones are not.

£3 is so cheap, there has got to be some big compromises going on, they are stainless steel too.

SKF at over £30 would increase the cost of the build by 40% and at my loads and speed I’m thinking that it’s over kill.

There are a couple of reliable bearing suppliers in the UK that offer a “Quality Budget” range. I’m presuming they have looked into them and stand by their stock. I’m going to buy some of these I think and have a look at variations in sizes and such.

 

[Wizard69]

Better manufactures do make a difference in bearing performance. The question is do you need that performance. As mentioned above some to the import bearings are worthless as bad bearings. They will have gone through little to no heat treat.

Of outside Stainless may or may not be worth it. Often what kills bearings in outdoors use is water getting into the bearing and washing out the lube. You then end up with dry bearings grinding themselves down. Shields will not keep water out and seals have a limited ability.