Hi all, I need to reposition a lathe to another part of a workshop. The manufacturers have thoughtfully provided flanges at the base of each corner with holes that will accept M12 threaded studs. I've acquired four HD castors with M12 mounting studs for this purpose. At the price I got them it was cheaper than renting machinery skates. Now, the lathe weights 760Kg and the castors are rated at 200Kg max. each, so in theory no problem so far. However, it's just occurred to me that the weight distribution will be unequal. About two-thirds of the weight of this machine is at one end (gearbox, motor, chuck, headstock accounting for most of it) with the remaining third at the other end. Is this inequality going to queer the deal? I'm not too hot at figuring out this kind of thing, so thought I'd best check with you chaps first. Cheers. CD.

OK say your numbers are right, in round numbers you have 500 kgf at one end and 250 at the other, in each case spread over two castors. So 250 kg on a 200 kg rating castor at one end. There's likely to be a reasonable safety factor on the 200 so you might well get away with it. Two things are going to push up the loads. Firstly, your floor probably won't be flat and while the castor which "lifts" will probably be one at the light end, the weight at the heavy end won't be split evenly any more. The highest loads are likely to arise when you hit a bump / crack. To reduce the effect, try to move it as slowly as possible. Or do most of the move with something slightly compliant under the wheels, like hardoard? (I assume you are on concrete). The other thing in your favour is that the castors will presumably be rated for "continous operation", whereas you only need them to work once. You might find the axles bend slightly but you still get away with it.

Anyone for applied fizzicks?

Oct 31, 2013 23 Replies

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Cursitor Doom 12 years ago

Er, not sure that's correct. If one of the heavy end castors fails, that corner will instantly collapse to the floor where it will once again be firmly supported, albeit the machine will be listing over. The remaining heavy end castor may have to suffer a transient overload until the other corner hits the floor, but that doesn't mean it will necessarily fail.

Add to this fact that (as some kind soul suggested) I'll have attached/ slid suitable lengths of timber under both ends of the base to minimise the drop in the event of a castor failing to a centimeter or two, I think the risks of a failure such as you describe are pretty minimal.

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Cursitor Doom 12 years ago

Yes, I know we tend to lean down on things we're pushing, but I think you're still missing the finer point here. According to the parallelogram of forces, *even if I push the load in a perfectly horizontal plane* there will be more stress on the castors than if I

*pull* it in the same plane.

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newshound 12 years ago

You are wrong. Draw a diagram with *all* the forces.

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GB 12 years ago

Yes, that's one good reason for making the lathe's journey as smooth as possible. People have already suggested laying a hardboard track.

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