Lathe Chuck and Backplate Query

Another "What does the team think" query, or rather queries, as there are two!

I have an old but very good IMO lathe, but the 140mm dia chuck is a 3 jaw self-centering that has seen better days. It is OK and servicable, but the wear means it is not very accurate and stuff rarely runs anything like true. So I was thinking of maybe getting a new chuck. But which chuck?

I have a faceplate come 4 jaw independant chuck of about 200mm dia, so was looking at maybe another 3 jaw chuck. Then I read a couple of articles where the use of a 4 jaw self-centering was considered a better bet than the 3 jaw. Mr ArcEuroTrade's 160mm dia Indian made 4 jaw looked attractive, plus one can get soft jaws for it. But the weight is 9.6kg, which seems a lot. The 3 jaw is 7.7kg by comparison. The lathe is a Weiller 280Z, a German machine from the late 1960's early 70's BTW.

So, Query 1, is a 4 jaw self-centering a better bet than a 3 jaw self-centering, even though it is heavier?

The new chuck would also need a backplate, which would have to be made from a piece of material at least 160mm diameter by 60mm thick. I have looked at available material and I could get a lump of cast iron, or steel in either bright or black.

So, Query 2, which would be the best material, cast iron, bright steel, or black steel?

Regards,

ChrisH

Edited By ChrisH on 31/07/2012 15:17:16

Chris,

I have not used a 4-jaw self centreing chuck but have heard they are good, but not if you want to hold hex bar. That may be important to you.

Baldric

Hi There

I would go for steel especially if the lathe has high spindle speeds.
Four jaw self centreing chucks are good for holding round bar, they hold it tighter than a three jaw chuck.They are ok for square material but you have to make sure the square bar is fitted into the chuck right.

Could you get replacement jaws for your existing chuck?

Thame engineering used to make soft jaws for all sorts of chuck.

Might not be in existance now though.

regards David

Edited By David Clark 1 on 31/07/2012 16:16:44

Hi Chris

Well John has said it really. I have both 4 jaw and 3 jaw but mostly use the 3 jaw. If I had to chose just one it would be the 3 jaw as I use hex. stock more frequently than square. I guess the 4-jaw may gives a firmer grip.

It would be worth considering the secondhand market before rushing into a new purchase. I recently picked up a really good condition 3-jaw GripTru Burnerd chuck on a Myford ( Sorry John!) backplate for less than the price of a standard ( Imported) chuck. The good buys are out there but you need to look carefully.

Cheers

Norman

Edited By NJH on 31/07/2012 16:34:55

A four jaw in good condition will hold round and square section as true as you'l everl need for every day turning, if you want to turn hex bar it probably means your producing nuts and bolts, where the section can be tapped true in your old worn three jaw. I have a 4'' diameter TOS four jaw, which cost around the £75.0    I only really use my three jaw for holding turned parts in soft jaws.

Edited By mick on 31/07/2012 17:41:27

You can already hold a square bar but if you buy a self centering 4 jaw you won't be able to hold the more commonly used hex at all for the fine wok needed in so many parts. I have a cheap TOS 3 jaw which has given excellent service and still runs very true after 10 years. It is unlikely that you will ever exceed the speed rating for a cast iron backplate and a steel backplate has no advantage over cast iron unless a steel chuck is required. Cast iron is more stable than steel and so is my preferred choice. Colin

Edited By colin hawes on 31/07/2012 17:52:52

Many thanks to all who have replied so far.

Re the backplate, for me I was tossing up between the black steel and the cast iron, both quite similar on price. Still undecided!  Max chuck speed is supposed to be about 1600rpm, but I've not measured it.

Don't do much hex work so the 4 jaw would be OK as I would still have the 3 jaw for that. Both the 3 and the 4 jaw from Arc can come with soft jaws, which was an attraction. I have read Harold Halls method of making soft jaws which I was considering for my old 3 jaw - sounded like an interesting exercise to say the least!  I'm leaning towards a 4 jaw, just need to convince myself.

A quick look on the web established that Thame Engineering are still in business, and I will also check out second hand chucks.

Chris

Edited By ChrisH on 31/07/2012 18:57:08

Chris,

I have found Rotagrip are very good at sourcing replacement jaws for a very wide variety of chucks.

David

What makes everyone presume that hexagonal stock cannot be held truly in a 4-jaw self centering chuck. I have been producing hexagonal model engine parts for years in one, and have never had much trouble centralising the stock truly. It needs only care. My 4 jaw is therefore on the lathe more often than the three jaw.

That's just plain provocative, Thomas

Centreing round work in an independent 4-jaw is pretty quick and easy, but for quick turning of a round part from round bar a 3-jaw is convenient - but for really accurate and "second operation" work sometimes even round material is best held in the 4-jaw independent. 3-jaw s/c holds hex as well. I'd just replace the 3-jaw myself and get the best you can, second-hand or new. New chucks should have the benefit of a spec and warranty.

I have bought a couple of backplate castings over the years and machined them up with no problem, surely the best way to go?

A 4-jaw self centre-ing chuck will not hold bar that is not round - material that is supposed to be round but isn't, most stock bar that you will buy from suppliers - causing it to rock from side to side. We bought one at work and scrapped 3 jobs before the chuck was found to be the problem. It is still sitting on the shelf unused now.

3-jaw selfcentring will grip well and if in good condition hold true, soft-jaws can be trued for each job as needed - highly recommended.

If you want to grip a bar tightly then an independant 4-jaw is the best - a pain to set running true - but is more versatile in the long run if you are not in a hurry.

Trevor