By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Forum House Ad Zone

What to do,what to do.

All Topics | Latest Posts

Search for:  in Thread Title in  
Roger Hulett27/06/2019 10:27:26
131 forum posts
9 photos

I have now saved up enough RDG vouchers to buy a self centering 4 jaw chuck.

I have a South Bend lathe with both 3jaw and 4 jaw chucks. A small Pools horizontal mill.vertical slide and boring table.

Am I doing the right thing, or is it going to be a waste of vouchers

Andrew Johnston27/06/2019 10:41:17
6668 forum posts
701 photos

Not for me to say, but I've never used, owned, or missed, a 4-jaw self-centring chuck.


John Haine27/06/2019 10:59:15
4712 forum posts
273 photos

I agree, I can't see the point. The whole beauty of 4 jaw chucks is that you can accurately centre things, where you want the centre. If your 4-jaw SC chuck is not dead accurate it won't even centre square material! Personally I'd prioritise a collet chuck.

SillyOldDuffer27/06/2019 11:10:36
8862 forum posts
1995 photos

I guess they're good if you have a lot of square stock to machine?

Wouldn't get much use in my workshop. Although adjusting an independent 4-jaw to centre is a bit of a faff, it's not worth me having a special chuck just for square stuff.


Nicholas Farr27/06/2019 11:12:57
3414 forum posts
1590 photos

Hi Roger, I have to agree with Andrew and John, to the letter.

Regards Nick.

P.S. you may think it has more gip on round material, but it would have to be truly round, otherwise you may well get one jaw not taking much load.

Edited By Nicholas Farr on 27/06/2019 11:41:48

JasonB27/06/2019 11:31:29
23022 forum posts
2763 photos
1 articles

Another one who has never had one or felt the need for one.

I do have a 5C chuck and 4 or 5 square collets but even then they don't get used that often, if I want something with a square head I'm more likely to machine from round and then mill the head in the spin indexer. Most small square stock has rather soft corners for my liking so I mill them to get a crisp part.

Plasma27/06/2019 11:39:31
443 forum posts
1 photos

Hi Roger.

I have a large self centreing 4 jaw and I use it a lot.

It's better for thin walled jobs and the extra capacity is useful for so many things without the faff of an independent chuck.

As well as the already mentioned square stock use I would not be without mine, it sits on one lathe with a 3 jaw or collet chuck on the other.

Regards mick

mechman4827/06/2019 11:40:11
2947 forum posts
468 photos

I've often thought it would be a 'Nice to have' item ; but then again I've asked myself 'do I really NEED it?. I would go for something more beneficial... collet set, DRO's etc


Former Member27/06/2019 11:59:26
1329 forum posts

[This posting has been removed]

HasBean27/06/2019 12:00:46
141 forum posts
32 photos

I would appear to be in the minority.

I use mine a lot, in fact I can't remeber the last time I took it off the lathe except for using my ER32 collet chuck. It's only a 4" job but is consistently accurate to within 0.03mm, more than good enough for my meagre skills blush & I've never noticed any issues with holding round stock.


Bazyle27/06/2019 12:46:33
6379 forum posts
222 photos

Perhaps a double 2 jaw would be a better invention. Ie two opposite jaws linked so they centre up one plane then the other two jaws linked to handle the 90 degree faces. That way rectangular stock, round and square could all be held with assured contract on all jaws.

Edited By Bazyle on 27/06/2019 12:47:01

not done it yet27/06/2019 13:00:10
6876 forum posts
20 photos

Posted by HasBean on 27/06/2019 12:00:46:


It's only a 4" job but is consistently accurate to within 0.03mm, more than good enough for my meagre skills blush & I've never noticed any issues with holding round stock.


Many three jaw self centering chucks can be just as accurate, or possibly better than that

Think about a 40mm aluminium ‘round’ bar (topical) that is only 39mm in one plane. When the two jaws are tight on the 40, the other two might still have 1mm to take up. Not good, when both pairs of jaws are mechanically interlocked!

I put one on my rotary table and have regretted it. There was one on my lathe, but I prefer the usual three jaw or the four jaw independent. The independent one probably gets most use.

The self centering 4 jaw is rather better than 0.03mm runout, but I would still not want to re-chuck an already machined item in it (which is where you might notice it?). I avoid using it for anything that may not be perfectly round - it might only be gripping on two jaws!

I would recommend the OP to spend his vouchers on something else (ER collet chuck, maybe).

Clive Foster27/06/2019 13:58:44
3172 forum posts
113 photos

Very much an "if you need it you will know" thing. Although it has its advantages in certain jobs its not really a general purpose device.

If you are wondering, shall I - shan't I, you don't need it.

Over the years I've bought a fair bit of stuff after the shall I - shan't I debate most of which ended up as cupboard queens and bragging rights. When it takes 25 years between purchase and "I couldn't have managed without it" you are probably doing something wrong. Especially in that case as if I'd not had it I'm not have been lumbered with the job which turned out mega grief!


MalcB27/06/2019 14:31:08
257 forum posts
35 photos

I have an RDG SC 4 jaw for my Harrison M300.

As others have said its a luxury unless you have an abundance of chucks and frequent need for square bar stock.

I have 3 x 3 jaws, 3 x ind 4 jaws and 2 x collet set ups ( 1 x ER40 and 1 x Pratt ) all gained at various times etc.

They do make a good backup for round stock to the 3 jaw and the RDG one i have is excellent on running true.

My advice ( again as others mention ) is to save further for a good collet setup first.

Chris Evans 627/06/2019 14:42:21
2067 forum posts

I would put the money towards a 5C chuck and collets. 80% of my work is in collets.

Baz27/06/2019 14:42:34
756 forum posts
2 photos

I have one, used it a couple of times and now it holds the workshop door open. For it to be any use the work must be square to within .001”, if one side is larger than the other it will only grip on two jaws and rock on the other two.

roy entwistle27/06/2019 15:24:19
1549 forum posts

Note also that not all square stock is square


HasBean27/06/2019 15:57:21
141 forum posts
32 photos
Posted by MalcB on 27/06/2019 14:31:08:

My advice ( again as others mention ) is to save further for a good collet setup first.

I agree, my ER32 collet set would definately be higher up on the list than the 4Jaw SC if I was buying again.


Brian Wood27/06/2019 19:10:21
2578 forum posts
39 photos


Clearly opinion is divided.

I found a 4J self centreing Pratt chuck on the RDG stand at the last Harrogate show and after I put the fitting right on it's backplate [ it was at least 1 mm in error] it has proved to be truly accurate and I prefer to use it for most work now.

It was almost brand new at the time of purchase, the previous owner must have been deeply disappointed with it's performance, all down of course to a sloppy job he made of fitting

So, your choice really


Hollowpoint27/06/2019 19:26:03
476 forum posts
59 photos

I like them and prefer them to 3 jaw chucks. That said a collet chuck would be much higher up on my list.

If you're just looking to spend some money and treat yourself one of the best upgrades is a QCTP without doubt. DRO scales are another time saver as is the often overlooked tailstock turret.

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Sign up to our Newsletter

Sign up to our newsletter and get a free digital issue.

You can unsubscribe at anytime. View our privacy policy at

Support Our Partners
Eccentric July 5 2018
Eccentric Engineering
Rapid RC
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest