Load on Bearings

[Cursitor Doom]

Hi gang,

I'm going to make up some skates to make it easier to move around my burgeoning collection of light industrial machinery. None of my machines weighs more than 1,000kg, so four skates with two rollers per skate equals 16 bearings (2 per roller, obviously) which will each have to cope with 62.5kg if the load is equally distributed and all wheels are in contact with the ground at all times. But the skates will be used on a slightly uneven concrete floor, throwing the above assumptions into the rubbish bin. Plucking a figure out of my arse, let's say I allow 100kg per bearing instead of 62.5, then, and hope for the best. Now, can I get away with plain bearings with this loading, or will it have to be some fancy and expensive ball/roller/pin arrangement?

cheers, cd

[John Williamson]

Depending on the size of the rollers relative to the bearings, you could get away with plain sleeved bearings.

Whether you could push the result along by hand is a different matter, and certainly if your time and effort have value, it'll be worth using a`pair of tapered roller bearings per roller.

[Cursitor Doom]

Why tapered? Is there some lateral loading involved I'm not aware of?

[meow2222]

Going from 62 to just 100 seems very optimistic. The uneven weight distribution of machinery alone would eat up that little margin.

NT

[newshound]

How uneven is uneven? How low do you want to make them? You could go for wheels with pneumatic or solid polymer tyres. The larger the wheel, the easier it is to push over changes of level. Pneumatic tyres are easier to push over roughness too. Also they "share" the load between them.

Assuming you want to change direction, you want at least some casters rather than fixed wheels. I think I would start by looking at off-the-shelf casters (e.g. from Machine Mart) rather than designing and making rollers on bearings.

Here is a list with loads

There are other suppliers, but MM have a good web site for looking at options.

[dennis]

Toolsatan do some 160 kg castors for less than £5

but they are 125 mm dia.

[Cursitor Doom]

Yeah, impressive stuff for the price. But as you say, a bit on the big side. I wonder if one can buy rubber sleeves to stick over steel rollers to increase their tolerance to uneven floors?

[Andrew Mawson]

I have two sets of commercial 'tank track' skates for machine moving, but I confess they usually don't get used. I find that a pair of lengths of 1" gas barrel far easier to use moving large machines single handed. Any really uneven bits of floor can be covered in a bit of thick steel sheet as you go over it. I have a hydraulic wedge in a car body repair set that I slip under one corner, jack up and slip the gas barrel under. It is then easy to push the machine to the balance point and kick the other roller under. The pipe has the advantage of a low lift compared to the skates so things are a bit more stable.

Last big move single handed was my Radial Arm Drill. Weighs about 2 1/2 tons, is top heavy and had to be manoeuvred up one bay, across where the height was sufficient, then back down the next bay , turning through 180 degrees in the process. All done by a 64 year old out of condition, old fart using two rollers and a bit of 4x2 as a pry bar.

Andrew

[newshound]

Do you mean tyres? Rubber hose? You won't get much tolerance from a solid sleeve.

I still think there are several factors you need to consider.

How *rough* is the floor, this will affect the rolling resistance for different types of wheel.

How *flat* is the floor, this affects the resistance you will meet each time you hit a ramp or a ledge, and also the extent to which load will be transferred between wheels as you move. The classic "builders barrow" wheel is the design that it is for a very good reason.

And related to the latter, how low do you need your skates to be? Low is good from the viewpoint of reducing the lift required to mount them, but bad from the viewpoint of how easy things will be to move.

And you need to decide whether you will include castors or not. There are omni-directional "ball" fittings but depending on the size, number, and condition of the concrete they might damage the concrete locally.

[John Williamson]

Easier to adjust, and unless you know you're never going to be pushing on anything other than a straight line on a perfectly smooth floor, there will be side loads.

[PeterC]

At work I had castors fitted to test chambers that weight about that. I spec'd castors (nylon wheels) of 1 ton each: load will be on 2 castors some of the time; shock loading possible. That was on a test floor in an electronics factory - your floor might be a bit rougher.

[Cursitor Doom]

I've never heard of "gas barrel" rollers and a search of the wiki shows up nothing. Can you elaborate? It sounds promising.

[Andrew Mawson]

Gas was conventionally plumbing in steel pipe known as 'gas barrel' up to the (I suppose) 1970's when copper replaced it. Far safer under floors and in walls as you can't knock nails or drive screws through it! End were threaded 1" BSP where the 1" refers to the bore of the pipe, so 1" gas barrel had an o/d of about 1.3".

So essentially for your purposes 1" gas barrel is just a heavy walled steel pipe. 30 or 35 mm solid bar would be just as effective.

Andrew

[cl]

Late to the fray but anyway....

My understanding is that 'plain' (as in basic bushed bearings) are better at carrying heavy loads than ball or roller bearings. Ball and roller bearings are lower friction though.

[Gazz]

Or scaffold tubes if you lift the machine a little higher to get it on them as they are a larger diamiter.

[ss]

Not quite the same but I am also older and weak back and currently having to move some 3 x 2 feet paving slabs around. I just crowbar one end up and use old wooden broom handles that are about 1 inch diameter slip under and push them around with ease. I am not suggesting broom handles but the principle works well.

[Vir Campestris]

I know nothing about bearings - but here's my 2p worth.

At some point the floor is going to put all the load on opposite corners of the machine. So you need to spec each skate for half the load.

Doubtless at the same moment the floor will also manage to put all the load on opposite corners of one of the skates. So 2 bearings carrying half the load. 250kg each. Plus some margin for shocks - if the thing could ever drop over a ledge you might want to allow 6G.

Are you scared yet? :)

Andy

[The Other Mike]

Instead of making skates to a dubious spec plucked out of thin air maybe you should ask yourself how often do you really need to move this kit? Not often I'd bet.

I've got access to some skates and a roller pry bar but steel scaffold pipe, preferably smaller diameter thick wall steel pipe, or even a bit of solid steel bar works just as well and often better in many cases and involves nothing more than a few minutes exercise with a hacksaw.

Break the kit down into manageable bits and a hired in engine crane with a polyester lifting sling will also do the job.