Slewing bearings (Cheaper alternatives?)

[Zathras]

Hi all,

I have a need for a slewing bearing (not necessarily for machining application) and after searching high and low I came across the IGUS Iglidu PRT.
here's the link;
http://www.igus.co.uk/wpck/default.a...b-en&Version=1
Checkout the vid of one being put together at the bottom of the page.
It's just a sandwich of anodized aluminium rings and a polymer sleeve material.
Looks interesting to me.
I'd love to know the axial and radial runout of these things however they do not have much in the way of specs. It would seem this (basically) sleeve type arrangement may be a viable alternative to the giga-buck Kaydon, FAG, etc ball & roller type.

What do you guys think? Could one be fashioned with some sleeve bearings to give reasonable performance? 2x Flanged sleeves + 2 alu rings.??

What about building one like the FAG radial-axial cylindrical roller bearings;
http://www.fag.com/content/en/branch...ined_loads.jsp

2x needle thrust + 1 cylindrical roller bearing. Has anyone tried this before?

Interested to get some ideas and suggestions going.

[fkaCarel]

It all depends what you want to do with it. If you want to make something with the precision off a rotary table, I would stay away from the Igus design. Apart from that the video proves it can be assembled, it also showed that it spins freely, so there is play. I would look into the AXK series from INA for the thrust bearings. These consist of two runner plates and a needle cage. For the radial load you could look at needle bearings. With these parts you can determinate the backlash or preload yourself. I used these, but for another application.

http://medias.ina.de/medias/en!hp.ec.br/AXK

Carel

[NC Cams]

It is all a function of package size, cost and performance.

The most cost effective approach would be a single duplexed pair of angular contact ABEC 7 ball bearing, appropriately size, mounted DB or DF would give superb axial and radial runout performance. You could build a inner and outer housing to hold the bearing and transmit any external loads to it.

The use of an L, M or H preload would give correspondingly higher stiffnesses and rotating torques.

The 7900 series bearings would give you the smallest package size.

A single row deep groove ball bearing MIGHT be used but that gets into too many qualifiers for a DIY'er to get involved with.

Ultimately, the commercial package may have the better cost/benefit/availability/ease of use ratio.

[Zathras]

Wow, I left this topic a while ago. Sorry
Thanks guys for you input.

I have certainly taken your comments on board and will look at those 7900 series a/c bearings.
I'm also considering a double row tapered roller, 4-point contact bearings and a recent discovery for me; combined needle roller bearings (from Nadella) that have thrust load capacity in both directions. (Thinking around 50-60mm bore for these types.)

My problem remains; I need deflection for applied moment load data. Apart from the 4-point contact type, it's not supplied in any data sheets I have seen for other types. I suppose it's not possible to do this due to many factors like obviously preload and arrangment of the bearings right? How can one calculate this without a reasonably sophisticated model? Is there software available for this type of modeling?
The moment loads experienced will be on the order of 100Nm-150Nm (around 1,000 in.lb) and I need to have deflection to arcmin order of magnitude or better. This seem quite realistic with say a 6" bore Kaydon Reali-Slim acording to their data but I need a cheaper alternative.
Working volume I have to work with is up to 11" or so dia with around 2" of axial room to play with.

(Still) waiting on some pricing for some bearings. Seems like they won't bother getting back to me though. Just an idea of the relative costs would be usefull.

Thanks guys.

[NC Cams]

NOTHING 11" in diameter is going to be inexpensive - those are essentially custom made bearings.

Generally, slewing ring bearings are custom made bearings and pricey.

4 point contact bearings are often LBNS - listed but not stocked. See prior sentence

Some bearing mfrs applications engineering depts can give you design assistance with moment stiffness but it can be hard to get thru to someone who knows what and how to do.

A/C's get pricey, especially in 50mm sizes due to the economies of scale involved.

A simple deep groove ball bearing can serve as a slewing ring bearing. However, if you apply a moment to it, stiffness is pretty much non-existant.

There is a book written by Harris (I believe) that goes into the mathematics of calc'ing pretty much all the stuff you discuss about bearings.

Keep this simple axiom in mind - you need a heavy preload to make a bearing stiff. A high net contact angle (60 deg for example in a ball screw bearing) with a bunch of preload will give the most axial stiffness. Add to this that moment stiffness is further enhanced by an INCREASE of the ball pitch and a ball bearing will roll easier than a tapered roller.

Simple case of packaging, economics and geometry.

[Zathras]

Well, to give an idea to anyone else who may be looking, I got a price for Kaydon metric series slewing bearings. I thought they might be around $800AUS for the smaller and around $1500AUS for the larger size (120mm bore) but I was in for a little shock.

50mm bore: $1,995AUS
120mm bore: $2,500AUS

This was totaly out of the questions since I need both so the search continues.
I've ask for some thin section 4point with a range of bore diameters to get an idea of the price. At least I will know the price range I will be looking at. I was not suggesting that I would be after 11" bearings just stating what I had to work with. Yes it's probably not going to be cheap as it turns out no matter what bearings I choose to get the stiffness I want.

As for the book, I think this is the one you're referring to?
Author: Tedric A. Harris
Format: Hardcover
Published: December 2000
Edition: 4th
ISBN: 0471354570
List Price: $200.00

I'd be most interested to have a look at it. (Not afraid of a little math) Thanks NC cams.

Thanks again for the advice.

[NC Cams]

That's it.

Every bearing spreadsheet I ever used as a bearing engineer had their origin(s) from the math contained in that book.

Look at multiply mounted deep groove ball bearings. Depending on the amount of preload, they'll be stiff and rotate fairly smoothly.

HOWEVER, as you use a deep groove ball (IE 6010 for 50mm bore) for axial thrust, you force the ball out of the "crotch" of the raceway and up the side. They don't roll as well or as consistantly AND the stiffness is NOT as good.

See prior post about high contact angles v stiffness v friction. If you buy the Harris book, you should be able to figure out what you want IF you can get info about the ball complements and raceway radii out of the bearing maker - my former employer didn't give out that info readily....