Three JAW CHUCKs

Hello all

Three jaw chucks, can they be made to run True! the one I have came with my Mini Lathe, every time I put a bit of bar stock in the chuck, I have to keep messing around trying to get it centered, is it just the Chinese three jaw chucks do this or is it all three jaws have this problem, I haven't got the money at the mo to buy a decant four jaw ,

Do I have any other options?

Thanks

lee

What is the run out? Put say a bit of 1/2" bar in the chuck and clock it with a DTI, once we know how much runout you have it will give us an idea if its withing the usual runout that you get with 3-jaws they are never 100% true .

There was a thread about a month ago and a lot of the far eastern chucks were as true as the expensive named brands.

Have you tried giving the jaw teeth and scroll a good clean, also they can sometimes be tweaked on the backplate.

Hi Lee.

Most three jaw chucks that are bundled with the smaller lathes tend to be hit and miss, sometimes you get a good one... Other times, well you know about those.

To my mind, and I am quite prepared to be corrected by other members, you have a few choices to choose from.

1. You could buy a "brand" name chuck at something approaching the price of the lathe itself usually.

2. You could buy an independent four jaw chuck. These tend to be more useful as the four jaw will hold square stock too, and setting the work piece central is not as difficult as you might imagine.

3. If all you do is turn smaller stock you could invest in a ER 32 collect chuck and collets, but this can become a limiting factor if you want to turn something larger than the collets will hold.

4. You could try grinding the jaws parallel, but this usually results in a wasted few hours as the jaws may well be perfect at the diameter you ground them on but any other diameter will see them shift again, this is because the jaws of the chuck are usually just fine, it's the scroll which opens and closes the jaws where the issues lie.

Myself, I went with a 100mm four jaw independent and have to say that it is possible to get your work piece to within a gnats whisker of dead centre, more if you take the time.

I might add that it MAY be worth your while looking at fitting a slightly larger version of whichever chuck you go with as there are back plates available that will allow you to fit a 100 or 125mm chuck rather than the 80mm that they come with.

Just remember though that with a larger chuck there is more inertia and momentum, so it's wise to ramp the speed up slowly to save you the cost of replacement fuses and be a little more patient when waiting for the lathe to spin down from the higher speeds.

Regards.

Bill.

Have a look at this thread: **LINK**

and this: **LINK**

Personally I think the TOS chucks are very good and don't cost an arm and a leg.

Russell.

if chucking bar not re chucking part. three faults are shown

concentricity...unless massively out then a concentic part can be made{ if too eccentric then oversize stock required}

bell mouth..grips poorly and part can move in chuck...

poor grip.see above..

using a tailstock reduces/removes most of the above.

in my mind eccentricity is least.

if rechucking.. well self centering {Scroll } chucks( 2,3,4,6 jaw)can be made to work well over a range of diameters..saddly not the full range of the chuck...

the collet is just a small range chuck..but closed via ramps not gears...this makes it more repeatable from day one

the independent jaw chuck and face plate can of course be set to the limits of your instruments or patience

Lee

Before you spend any money may I suggest (if you have not already done so) that you check to make sure the chuck body itself is running true.

It is a good idea to remove the chuck and give the back plate and the chuck a good clean.

When refitting the chuck make sure it seats well on the backplate, you may find that it runs 'more true' in one of the three (or four) positions dictated by the mounting screws. If so mark the backplate and the chuck with a centre dot for future reference.

Once you are sure the body is running reasonably true then you can check the jaws. Check the jaws using a piece of silver steel or at least something with a good finish and don't let it protrude too far from the chuck for starters. If you don't have a DTI your eye will give you a good idea how true it is, alternatively, turn the chuck by hand with a tool just touching the bar. If you can get it somewhere near for your immediate needs, worrying about exact run out can wait a bit.

Lee

Firstly follow John's excellent advice!

There is another option- see HERE . I've not made one but the principle is just the same a " Griptru" chuck which allows small adjustment to overcome small degrees of eccentricity. I would buy one and try it but I came across a good S/H Griptru at a reasonable price so the "need" is not there really.

In truth, most of the time, the fact that a 3-jaw does not hold work truely is not a problem as long as you can complete all the concentric critical turning on a component without removing it from the chuck. That is mostly a case of thinking ahead.

A 4-jaw independant chuck should be on your list for Santa - you WILL need one some day!

( Oh yes - by the way- pretty nearly all 3-jaw chucks suffer, to a greater or lesser extent. from the problem you are finding)

Cheers

Norman

Edited By NJH on 11/10/2013 13:57:50

Hello, thank you all for your replies

You have gave me lots of food for thought.

Since I bought this mini lathe a month back, I have cursed about it, should I have waited to get a second hand myford or similar quality second hand, when I got it the spindle did not run true, looking at it, it was seen that tell tell signes it was not finished off at the factory, so I told the person/company I bought it from, they sent me a new spindle straight away no hassle, so I fitted that plus I did the Taper Bearing conversion also put the Metal gears in as well, But now I am not happy with these Chucks, Going back last year I restored a very old Cromwell lathe , do you know the old batter chucks that came with it ran as sweet as a nut and was spot on for any sort of runout. Anyway I am lumbered with this mini Lathe that is a project in it's self to get it running at any sort of quality, the lathe I have takes a 100mm chuck, these new spindles do not need Back plate, the new spindle I fitted runs dead true now or should I say I am happy with it, tomorrow I am going to strip the chuck right down and give it a good clean like John advised.

Regards

lee

My first 3 jaw chuck had 1/16 inch runout (3 inch chuck).

Sometimes you just have to start with bigger bar stock

We can get a bit obsessed with these things.

The old timers would produce a steam engine with a drill and a file, so a bit of runout shouldn't be too much of a worry.

Steve

Edited By Steve Withnell on 11/10/2013 16:59:42

Hi Lee,

Mini lathes usually come with an 80mm chuck.

I haven't come across a mini lathe that took a 100mm chuck without a backplate. is it possible that yours insn't properly matched to the spindle register.

Neil

Hi

The ones from Amadeal do, they also sell the spindle as an up grade. SPG sell them as well but out of stock.

Cheers Michael

Interesting, very different tailstock to most others.

In have a Zither 100mm 3-jaw from Arc which I have found to be accurate (as 3-jaw chucks go).

Neil

Edited By lee hawkins 1 on 11/10/2013 18:44:25

Most Minis have chucks that aren't even as good as your average hand drill.. Take it from someone who's been there.. Don't waste your hard earned money on them.. Get a half decent machine and it will last a lifetime.. !!

Sorry Geoff,

I have to disagree, the chuck that came with my Clarke CL300M is still in the same thou-or-so accuracy range as reported recently for chucks of all origins, even after 14 years of (ab)use..

Neil

By now I do think this really should be just standard and pretty well general knowledge on any of these forums. None of this is at all secret. A three jaw self centering chuck is a relatively recent invention for the lathe if you consider when the very first modern screw cutting lathe was invented. But that ultra accurate or even any 3 jaw is or should be considered as just a convenience more than any real actual necessity. And as others have already mentioned, we have for some illogical reason gotten incorrectly fixated on a very low run out chuck that requires large money to obtain and keep accurate. Yet one single swarf chip in it's internals will ruin that high cost accuracy till it's cleaned. It is IMO much more important that any chucks jaws are directly inline and dead true to the the lathes ways.

So nothing could ever be accurately machined before an accurate 3 jaw was invented? Of course not, prior to the invention of the 3 jaw self centering, and the 4 jaw independent chuck, they used a faceplate, then a faceplate with screw adjustable jaws, then the obvious invention of the 4 jaw independent. And then finally that 3 jaw independent. Shaft work was always done between centers, and that's still the most accurate way today no matter what level of accuracy your own personal 3 jaw or collet system will repeat to. The amount of time and posts that have been wasted on somehow obtaining that magical ultra low run out 3 jaw is a very bad example and should be judged as more than un-nessisary for the people here trying to learn. Chuck your part up once, fully machine it and then part it off. Your part is then as accurate as the surface finish, headstock bearings, and machine condition will ever do no matter how cheap or expensive your chuck is. If you really do think a high end low runout chuck is going to somehow make your lathe more accurate? I just might have some super expensive but very magical 3 bean chuck grease for sale that I just invented, but please keep it quiet as it's still not on the market yet.

If your parts need X amount of accuracy and due to the part shape and layout, they do require re-chucking, then yes an accurate 3 jaw just might be handy, But I do have a very accurate heavy duty Emco chuck that will average right around .001 on any diameter I've ever checked it with that I bought long before I knew what I do now. But if the part requires some real accuracy? I still turn shaft work between centers, or I'll do plate type work in a 4 jaw independent, or on that faceplate. I can assure you that for any work I can think of from a M.E. or HSM perspective, one of those high cost ultra repeatable low run out 3 jaw chucks isn't at all necessary. An industrial high volume situation is of course or might be a different thing. But a good low run out chuck could help speed things up in the right situation. They aren't a total waste, just not needed as much as some would like to think or imply.

But exactly why do subjects like this just keep repeating themselves? Aren't these forums in place to help educate all of us? So why aren't we getting or at least doing that? Simple common knowledge subjects such as this should have been dealt with and solved a long time ago IMO.

Pete

Hi Pete

You ask |.... "why do subjects like this just keep repeating themselves?"

I suggest this is probably because there is a constant stream of new members coming to the forum. The question is raised - folk respond. In this thread Lee asked the question and folk gave helpful responses which he says were useful to him. So maybe this was common knowledge to many here but not to him. Sure we could say go read a book or look it up on the internet etc. but, I suggest, a personal response is much better and , of course interactive. What's more threads digress from time to time and, quite often, little nuggets of information can appear which challenge our own perceptions. Yes stuff does keep recurring but I welcome that.

When the site was first launched I thought that it would provide a vast catalogue of information that could be accessed and searched at will to answer all our questions. Of course, although the old posts ARE there, finding what you want in them is not too easy. Far easier to just ask the question!

Regards

Norman

Horses for courses. I needed to put a 1/8" spigot and an 8BA thread on each end of a length of 3/16 bar. My 3-jaw was ample to achieve the concentricity required (actually it could have been done with a much worse chuck). The saving in faff over changing to a collet chuck wasn't worth it.

The 3-jaw chuck makes workholding very easy for beginners, and easy means safer too. They just need to know its limitations and the options if greater precision is needed.

The point about cleaning is well made - the bar mentioned above was obviously out when turned end for end - a bit of swarf on one of the jaws. Knowing how good your chuck is and looking out for this kind of problem can save a lot of worry.

Neil