Low friction rolloer bearing help.

[CADInventor09]

I’m looking for a low friction bearing for a slow rpm balancing kinetic art project. The bearing needs to be an easy startup type. I plan on removing the grease and using light oil. I was considering the Bones Ceramic Skateboard bearings but another thread here mentioned that these bearings were just OK for this type of application.

Any recommendations on brands I should look at or specific bearing types would be appreciated.

Thanks,
Bill J.

 

[MikeHalloran]

Start by estimating the bearng loads, then size the bearings for that.
Skateboard bearings are probably not the best you can do.
Ceramic is not magic.
The bearing catalogs, at least the thicker ones, can tell you what the ABEC-n numbers mean.


Mike Halloran
Pembroke Pines, FL, USA

 

[Tmoose]

If the bearing arrangement will include 2 bearings per shaft then the shaft and housing machining accuracy (cylindricity, co-axiality , axial clearance accomadation, etc) needs to be excellent to prevent binding. Some bearing types are self aligning internally or externally, and are the best/practical/only good choice sometimes.
Would a bicycle wheel turn freely enough for your application?

 

[CADInventor09]

Thanks for the responses. Every point made here and on thread821-269031 is exactly the same as when talking with a bearing engineer. I hope it’s OK but I’m not an engineer but have a passion for 3D cad design. I use Autodesk Inventor and have a habit of designing things that are expensive no matter how simple.

Yes, my cad design currently has two bearings per shaft and the load is 3 pounds. The bearings will be fitted into a cam roller v-groove wheel. Unfortunately the bearings that come installed in a cam roller do not meet the low startup torque requirement. I did find a bearing that seems to be an excellent choice but your point regarding alignment of two bearings on one shaft is something I will consider.

I hope the following bearing information will be useful to others. The bearing I have my eye on is the SKF-E2.

Here is a video demonstration.

http://www.youtube.com/watch?v=ixcJRsutVhw

I spoke with SKF engineer Steven Soetjiandi and he confirmed several details for me and I believe that this bearing will have a lower startup torque than the Bones bearing and are more precise. The Bones website makes it clear that their bearings are specifically designed and excel at skateboarding and therefore use a “skateboard rating” compared to the standard ABEC scale.
I found it interesting that motorcycle race teams will use the SKF-E2 bearing due to the low friction quality and then replace them after the race. If you ever have an application question Steven said you can contact SKF engineers directly at 888-753-2000.

The following bearing is too small for my purpose but it may be worth a look for very small scale low startup friction designs.

http://www.vxb.com/page/bearings/PROD/Kit7630

I mention this because of this double pendulum demonstration.

http://www.youtube.com/watch?v=y7dvAViIg64

I’m still open to any input but the SKF-E2 does look like a good choice for my gizmos.

Thanks,
Bill J.

 

[geesamand]

Here's a thought - we have an application where our driving machine is mounted on a pair of roller bearings so that we can directly measure the torque it's outputting. In this application we started with open bearings and found that regular levels of dust totally ruined the low-starting-torque properties. Now we're using shielded grease bearings and this helps keep the dust out. Definitely much less friction than a sealed bearing.

With low RPM I think that a low viscosity grease is the better choice. Light oil would need to be regularly maintained and it would probably prove impossible to re-oil without driving more dust into it.

 

[CADInventor09]

That’s a way cool experiment, thanks for sharing it. I was definitely tempted to take the shields off but you backed up what I’ve seen others mention including your point regarding rubber seals vs. metal shields.

I had no idea that dust would be a real factor in an average environment. With that said, I’m always surprised on how much dirt I find inside of my computer. It would be a shame to use high quality low startup bearings and then allow dust to slowly destroy the low startup performance.

As far as using oil goes, I now understand that if oil is used it needs to be the correct type. It was mentioned in a video that even 3-In-One oil is too thick and WD-40 is definitely a bad choice. It was said that “Electronic Oil” that comes in a small tube with a needle tip or “Sewing Machine Oil” may be a good choice if you don't have a specific bearing oil. The bearing I’ve chosen uses light grease and I’ll stay with that especially since it’s designed as a low startup torque bearing.

Thanks,
Bill J.

 

[geesamand]

When it comes to friction, at low RPMs there is much less difference than at high RPMs. You haven't mentioned a max rpm so we have no idea what oil really makes sense.

IMO, if the RPM is under 500, just start with greased/shielded bearings and see if that's good enough. The bearings will be extremely cheap and easiest option to maintain. Only use a more complicated solution when you prove it's necessary.

David

 

[CADInventor09]

Hi David,

A rough guess is 50 RPM with a 3 pound load. I included friction in the cad simulations but the parameters used are the program defaults for the most part. I have not included heat build-up and I’m sure the parameters could use adjusting. I will follow your advice and only experiment with oil as a last resort. Thanks for the input.

I’m about ready to send the drawings to my local machinist. I’ll post the results here and hopefully have a video demonstration of what at this point is only a cad drawing. Even if the experiment is a failure the low friction bearing information is going to be a big help to me.

A Tip For CAD Users; The McMaster Carr web site allows you to download cad models of all types of fasteners and bring them into your models.

Thanks,
Bill

 

[Tmoose]

Your drawing tolerances for bearing journals and seats on the shaft and in the housing should look like page 20 here.

http://www.ntn-snr.com/industry/fr/...g_retention_and_clearances.pdf?contentID=4676

Actually for low drag the shoulder runouts and seat concentiricities may be kind of high.
I'd consult SKF and FAG websites to check the tolerances in the NTN link.

 

[geesamand]

SKF and NTN also have very good CAD download resources of their bearings, and I have found that the 3d geometry forms a solid without error more consistently than the McMaster-Carr parts.

 

[CADInventor09]

Hi Tmoose,

The information on page 20 is interesting. I had asked SKF about housing clearance but I decided to check it one more time and sure enough I found a mistake that made the housing bore outside of the range suggested. I decided to confirm my shaft diameter was correct and it turned out that for my purpose I have that right.

Thank You,
Bill J.

 

[CADInventor09]

Hi geesamand,

Good to know not expect tight accuracy with the McMaster-Carr cad models. I admit I did think that. Fortunately I only used cad models for fasteners from there. I did download the exact bearing from SKF and I was pleasantly surprised that the model was the complete bearing assembly.

Recently I ran across

http://grabcad.com/home

which I find to be a neat download site along with

http://www.3dcontentcentral.com/default.aspx

They both are free but require sign up. I also recently found

http://www.traceparts.com/users/TracePartsOnline/index.asp#A

I initially downloaded a huge data base that took some 7 hours! and then deleted it because of the large size. Ha! Then I received a CD in the mail and an email with a code for restricted use. I haven’t tried the CD but I’m sure it will be real helpful with my cad experiments. It looks like they have had a partnership with the big cad companies for years.

This is off the bearing subject but I sometimes search for mechanical movements and this engineer from Hanoi is building a large selection of interesting mechanical simulations on his YouTube channel.

http://www.youtube.com/user/thang010146

Thanks,
Bill