Is this chuck too big/heavy?

I bought myself a brand new Pratt Burnerd 160mm independent 4-jaw a little while ago for my Warco WM250v lathe. The chuck weighs 5.4kg without a backplate. Is this too heavy for my lathe and likely to damage the spindle bearings? I used it for one project and the lathe seemed to run/spin up no different to when the standard chuck was fitted but I'd rather get other peoples opinions to help decide if I should keep it or sell it and buy a 125mm sized chuck?

If your lathe has tapered roller headstock bearings they should take the extra load ok. Not sure what your model has though. Heavy chucks were mostly a concern on older lathes with plain bearings such as whitemetal etc. But tapered roller bearings will carry more load -- think automotive wheel bearings.

The lathe will swing 150mm over the cross slide? You could mount a lump of steel about half a metre long?

How much would that weigh? About 70kg? Supported at both ends would mean 35kg at each end?

Certainly would not be turning at full speed, of course, but gives an idea of how much load the bearings should cope with. Unfortunately, chinese bearings may not be up to snuff, so therefore there is more to consider than just the chuck weight. How long would it be run at full speed might be important, so Hopper is spot on with his assessment.

Would you want to chuck a 150mm or larger diameter workpiece with a much smaller chuck? I think probably not.

Myford supply 150mm chucks - 160mm is not so much bigger?

Probably asking Warco might be your best bet. They should know...

It is not just the weight but the inertia that puts load on the motor at start up that also needs to be considered, once up and running its OK.

Myford 6" and other 160mm chucks are fine if they are "slim body" designs which as the name suggests are slim body but also hollowed out at the back to reduce weight. I run the Bison 160mm slim chuck on my 280 and that is about 6kg with backplate and that seems fine.

Edit. Just weighed the supplied 5" and that also comes out at 6KG with backplate due to it being deeper and solid. So really comes down to what PB chuck you have got though going by your stated weight sounds like a slim one.

Edited By JasonB on 29/06/2019 10:35:12

I went from a 100mm chuck to 125mm on my SC4.

The change was worth it for the extra capacity.

Jim

Please note that the supplied chucks 125mm on the wm250 will clear the cross slide (150mm) even with the jaws sticking out, the 160mm Pratt chuck obviously will not, a crash might prove catastrophic .

PS, a 160mm 3jawSC chuck normally weighs in at about 8 to 9 KG so your Pratt must be a lightweight.

Its not just about the overall weight of the chucks, with a larger diameter chuck for example that weighs the same as a smaller diameter deeper more solid body chuck. The larger diameter has more weight further out from the axis which will be more load on the motor on start up to get things spinning up to speed.

Not sure if its classed as one of the slim type, it's exact the same chuck as this.

I think I'll keep hold of it, I use the collet chuck for smaller items but for larger stuff I'll use this. It wont be on the lathe permanently and looking at the Warco website their 125mm chucks aren't a lot lighter anyway. My WM250 lathe is the type with the inverter and didn't sound or appear to struggle spinning the chuck up. Thanks for the advice and opinions.

.

If it's a genuine Pratt Burnerd, I would say that's exactly the right decision.

MichaelG.

Nice looking chuck but jaws look on the chunky side for a slim body / light duty type. For ME work the true light duty type with slimmer, more pointed jaws are generally much better. What you loose on ultimate holding power you gain in the ability to hold smaller, trickier parts.

Given our, generally, lighter machines we probably can't take the sort of cuts, especially the clunk-clunk-clunk interrupted ones, that need the grip of a normal duty or even heavy duty 4 jaw. But we can get seriously frustrated when the part is too small or oddly shaped to get all four heftier jaws gripping.

My light duty 8" PB is very good and looks to have slimmer jaws than that one but, even so, one day I shall get round to mounting up a slim body 4" on a 5C arbor for the teensy stuff.

It would be a great help if chuck suppliers give jaw dimensions. Regrettably now the numbers of professional buyers of manual lathe chucks in our size range have dropped so much there is no pressure for the more niche types and everyone goes for the middle market.

Clive

Have to agree with Clive the narrower and also more pointed jaws are a bonus, not only for holding smaller items but also big flywheels where you may not the able to get the jaws between the spokes when holding by the inside of the rim.

Isn't that a bit like saying that the load capacity of a Ford Transit is 15 cubic metres so it can carry 120 tonnes of steel?

That said 'Chinese bearings' should happily take vastly higher loads than that - I'd be worried about other issues.

Neil

The thing that will really test you bearings (and lathe as well), seeing that its an independent 4 jaw, is mounting a relatively heavy job off centre to the chuck and then running at too high a speed. Your centrifugal forces far exceed the static loading!

Bob D

I've a couple of PB 110mm independent 4-jaws that are tiny by comparison. The one on the left is really nice, the one on the right has a couple of tight spots. Not sure if I'll ever use them but they were cheap enough and perhaps they'll come in handy one day.

I have a choice of two 4 jaw independent chucks on the S&B model A. A 160mm Chinese and a 6" Toolmex lightweight originally intended to screw directly onto a Myford. The Toolmex weighs half the weight of the Chinese one, and the jaws are half the size, so the size the workpiece dictates which chuck is used.

I bought a serrated jaw Burnerd of 6 3/4" which is as heavy as both the four jaws put together. It only gets used occasionally, no worries about speed as it is Ductile iron and the lathe max speed is only 1400 rpm and the plain bearings are easily able to cope with the load. I always check clearances and set stops if necessary whether or not the chuck is in danger of fouling parts of the lathe.

 One slight drawback of larger chucks is that you loose length which can be a problem with shorter machines, the model A is only about 21" between centres.

Edited By old mart on 29/06/2019 22:00:15

I have not done a comparison but imagine a large and heavier chuck will resonate less and therefore be less prone to chatter as long as the power train is adequate to power it up. Like a flywheel on an old treadle lathe!

That said I do like smaller chucks for turning small work pieces (and collets even more so).

The weight of the chuck itself will have a negligible effect on the spindle bearings. The cutting forces when turning are greater than the weight of the chuck. A greater problem is the total thickness of the chuck. Bigger chucks are thicker. The effect is similar additional stickout of the workpiece.

I don’t think so. Would you hire a transit van to transport a single dust bin contents (unless of extremely hight density material such as tungsten!)?

We choose our machines to cope with the largest item we are likely to work with. One hires a transit when you need the volume, most of the time. But that is OK as long as the other limits are not exceeded (gross vehicle weight, axle loading, etc). Lathes are not quoted for load, just maximum sizes which can be swung and supported between centres. Little point in having a lathe that will swing 150mm over the carriage if it will only machine an item of one third that size, I would suggest?

-As for the quality of chinese products - bearings (or lathes) - I thought that most of us know that there can be a considerable (or even great) differences between best and worst. Cheap lathes likely include cheap bearings. Maybe not the worst (**LINK**), but not the best, all the same.

Somehow, I don’t think that some machines on the market would be blessed with ‘bearing longevity’ if used at the maximum capacity for too long! Many are only rated for ‘light use’ by the supplier, so are clearly limited in the amount of work they can be expected do in a ‘working lifetime’.

Many on here advise fitting better quality bearings (than the original manufacture) when replacements are deemed necessary after early failure, orbpre-failure symptoms arise.

An extra couple of kilograms should not be too bad when that is only a small fraction of the machine’s gross capacity?

Edited By not done it yet on 03/07/2019 08:49:06

The 160 mm three jaw that came with my Atlas lathe weighs 9.4 kg. The only problem with it is lifting it with a bad back! Most of the time I stick to a 100 mm chuck.

Russell