Adan – Not sure about the 8" chuck on your lathe. The 4 jaws supplied with these lathes are the 160mm as you know. The suppliers obviously reckon that 160mm is the most suited – a bit easier on the headstock bearings perhaps?

I have a 200mm as supplied to go on my WARCO BH600G but the lathe is that much more heavy duty . By the way – the 200mm chuck is a bit of a beast. I have to use a winch to lift mine as I cannot even lift it of the floor where it lives.

So my advice would be to stick with the 160mm although it would be interesting to hear what others think.

Rik

I have got a 290 lathe, and the 4-jaw I use is a 6" lightweight – 4.5kg without backplate. It handles the work I do well. A standard 200mm might be around 15kg, so considerably heavier, Too heavy for my back at least.

Thor

As a rough rule of thumb chuck weight nearly doubles for each extra 20mm diameter. In cast-iron.

80mm – 1.5kg
100mm – 2.5kg
120mm – 4kg
160mm – 7kg
200mm – 15kg

Another factor is max rpm falls off with increasing chuck diameter. One brand quotes 4000rpm max for their 80mm chuck and drop 500 rpm for each 20mm increment, so their 200mm is "only" rated to 2500. The big chuck is expected to be turning large diameter work where the surface speed will be plenty high enough, but the surface speed might be low for small diameter work. Probably not a problem.

I'd still be a tad nervous of putting a big chuck on a small machine. As well as the extra weight on the bearings, the additional overhang increases leverage. And the extra stress is before any work is mounted and cutting pressure applied.

How heavy is the work? An oversized chuck suggests turning larger than average diameter jobs and maybe more weight than the machine is designed to take. I think the effect of persistent overloading would be to reduce the life of the bearings rather than cause instant damage. But Adan might be turning light large diameter rings, and if heavy jobs can be done successfully for 5 years, so what. Fit new bearings!

The bigger chuck also stores a lot more energy, which might damage a VFD or resistive load during braking. Maybe.

Dave

I have an 8" 4 jaw chuck which came with my Craftsman lathe, and yes it is heavy to lift.

That,s why I made my lifting hoist, as shown in my Album, which works a treat. That chuck falling on your foot would not be a good experience.

I don't see a particular problem either. The original faceplate supplied with my Harrison L6 is almost 2' in diameter and the slots go pretty much all the way to the edge so by implication there is an expectation items will be clamped to it to enable machining at a large radius so load on the headstock bearings could be quite large. 15kg of weight on the bearings is hardly massive. The only rider is keep the speed down to the limitations of the chuck and as Nigel says watch the out of balance forces from irregular shaped work. Not sure who might be trying to machine say a slug of 6" diameter steel bar at 1000's of rpm though!

Paul.

I bought an 8" slim body PB chuck about a month ago, they have the cam lock pins built into the body so it sits closer to the headstock, I just weighed it with some spring type baggage scales, so not very accurate, it showed about 9kg, they seem to be quite sought after, how much was the one you missed?

I agree, you would need thicker aluminium than cast iron.

When I had a Fiat Panda multijet, I had two sets of wheels, alloys and steel. The alloys were 5J X 14 and the steels were 5 1/2 J X 14 and with the same size tyres on them, the steels were 1 Kg lighter each.

Now imagine the difference if you compared the 17/18/19" diameter and 6/7" wide wheels common on modern cars. They're bloody heavy as alloys, and a lot more manageable as steels. If you can find any.

And lets not forget how easy it is to damage a large alloy wheel beyond repair