Anyone for applied fizzicks?

[Cursitor Doom]

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.

[newshound]

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.

[Cursitor Doom]

Some good points here. I also dimly recall that one should endeavour to PULL such a setup into its new position rather than PUSH it, since the 'parallelogram of forces' (I think it's called) results in additional unwanted downforce on the castors when you push as opposed to when you pull.... Since we're agreed this is a bit borderline, I need everything going for me. I just wonder if one should ideally do the pulling from the heavy end or the light end to minimise the downforce? Anyone know?

[Cursitor Doom]

I did consider this, but really need the maximum manoeverability that only castors can provide...

[The Natural Philosopher]

bewarer.

As stidents we bopigh some rope and tackle from a yacht shop.

The blocks were rated at 1 ton breaking strain.

Adfequte we felt for ;iting a morris 1500 engine out...

it ws treicky and we nearly had thje front of the car off the ground. No the block did not break, but it was bent beyond use therefater.

[Dave Liquorice]

And tie the bits of wood up to the lathe so it's that 1/4" clear of the floor and moves with the lathe. No faffing about repositioning them all the time.

I'm wondering how the OP intends to lift the lathe to get the castors under it and fixed to the flanges in the first place.

[Vir Campestris]

1 ton breaking,or 1 ton SWL?

Those seem quite lightweight blocks to be holding any rope thick enough to hold properly.

ANdy

[Cursitor Doom]

Nifty! Cheers for that.

It's already on blocks 'cos I don't possess a toe jack or any other means of lowering it totally to floor level! I have found a Landrover Freelander jack with its 1 tonne capacity is close to ideal for raising and lowering the machine, one end at a time, within a range of 5 to 12 inches.

[Sam Plusnet]

1. Lever up one end of the lathe to put the castors in, then lift the other end - this puts lots more stress onto that first set of castors at an angle (i.e. not vertical) - hope they stand up to it.
2. Is this a sturdy smooth concrete floor?

1. Is the floor entirely level - you're about to find out.

[Richard]

Almost resembles English. That "infinite number of monkeys bashing an infinite number of keyboards" seems to be progressing though. ;)

[Cursitor Doom]

This won't be necessary; the whole thing is already on wooden blocks with sufficient clearance to insert the castors from below.

Sturdy yes, smooth pretty much. Standard garage type 'finish.'

Indeed I shall!

[Scott M]

Couple of thoughts based on my little Drummond (about 250kg) where the feet have good spread front to back (as it were) but are inboard of the edges at the head and tailstock ends. With this in mind, I'd be very loathe to pull at the headstock end for fear of the whole thing toppling towards me with the castors resolutely failing to turn being (literally) stuck in a rut.

Similarly, I'd be jacking up the headstock end first to put castors on in case jacking the tailstock end first tips the whole thing over.

In case this sounds over cautious to anyone, mine is a very top-heavy affair. And I've heard of one lathe where the whole caboodle must be bolted to the floor or the weight of the motor (which is pivoted backwards to help with belt tensioning) will tip it over.

[GB]

If you can easily remove any bits to lighten it, that would be a Good Idea!

[newshound]

A very valid warning. It won't seem over-cautious to anyone who has seen heavy kit tip over when being moved!

[newshound]

Whether you push or pull, you tend to increase the load on the leading wheels and reduce it at the trailing. But this does depend on the friction coefficient, and that should be low (or the castors are not much good). You are really going into a level of detail which the problem does not warrent. This is assuming you are pushing or pulling in a horizontal direction. Of course if you lean down on the end you are pushing, this increases the wheel load. If you are lifting, as you might be if you were pulling from low down, you might decrease the load. Any net moment applied will change the load distribution between the wheels, i.e. it will increase the load at one end and decrease it at the other.

[Brian Gaff]

Definitely, but the failure of castors in my experience is due to the off centre loading of the pivot, which when heavily loaded can shear off if it hits a bump or a small drop. Brian

[Cursitor Doom]

That's not quite what I'm trying to get at. See this:

m0016624.html

The 'other' force is gravity. When you use the parallelagram of forces to calculate the resulting vectors, you find that pushing an object results in adding to its weight; whereas pulling it reduces it. This has nothing to do with the angle you push or pull, which is a bit of a red herring.

[RobertL]

If one of the 'heavy end' castors fails then the whole 500kg will rest on the remaining 'heavy end' castor and it will therefore fail at once (500kg on a 200kg rated castor). So the risk is that both the heavy end castors fail together.

Robert

[newshound]

Sorry but you are getting confused. Gravity *is* acting on the lathe, but so is the upthrust from the floor. Otherwise it would be heading for the centre of the earth. So is friction at the wheels. With friction, as you slide it, the load increases at the leading edge and decreases at the traiing edge *unless* you pull it at floor level. If there is zero friction (i.e. perfect wheels) there is effectively no load transfer, whatever height you pull it at (provided you pull it slowly). But if you are pushing it *in practice* you are quite likely to be leaning downwards as well which would increase the load on the wheels.

[unknown]

I've used this with a 1500kg lathe - with a "bit of a tug" it's not that hard to slide the lathe along the rollers to get it to change direction. Remember that you'll need at least 3 rollers. Rollers are FAR safer and more effective than castors for a job like this.