I agree I suspect the order of jaw installation. .
If they aren’t labeled. ( then do when you get this right)..
..line up the three jaws looking at the teeth on the back. .the face that engages the scroll..
You can get them in order such that the slots line up..jaws aligned slots diagonal…
The one with the slot nearest the clamping ( the bit the touches the outside of bar) face is “one “the middle one is “two” the last is “three”.
Now install them as described above..

Now if these jaws are reversed for use internal
. You install jaw three then two then one…

Edited By jason udall on 28/10/2014 22:22:52

Wrong order of installation will give bigger errors than 0.5mm. I would try the jaws with all three starting positions, and experiment with using all three key sockets for tightening. Tedious making 9 tests, but worth it if one set-up gives significantly better results.

My 4" Zither chuck gives a fraction of a thou runout, but only if:

1 every jaw is in the correct slot

2 I tighten using the socket marked '0'

3 The scroll and jaws are clean.

Mark the best socket, either centre pop next to it or use a drop of paint you can scrape off if you are worried about affecting your warranty.

If you still don't get good results check that the serial numbers on the jaws match the chuck's number (usually a three-figure number), but bear in mind it was OK when you took it apart so it should be possible to get it back in order!.

Neil

P.S. if you do a full strip down, make sure the socket bevel gears stay matched to their correct holes, or you have 27 tests to do…

I bought a Chinese lathe from the same supplier a few years ago

I had a new chuck sent out to try to fix a problem like yours, it was worse

A new tailstock arrived to try to rectify a problem it had

The gearbox worked a bit better after I removed all the sand and swarf from inside it

Finally a new lathe arrived to replace the one I had as the problem with the tailstock could not be fixed

My big mistake was taking two hours to load the faulty machine into the delivery waggon and setting the new one in the workshop before checking it. It had the same fault with the tailstock as the original !!

I got a refund and bought a second hand british machine, this was the advice I got in the first place

Dougie

Hello Robin.

Another thing worth checking on this type of Chinese lathe is the actual fit of the chuck backplate on the Camlock spindle. There can be the problem of the tapers mating together well before the flat faces of the spindle and backplate do.

This can lead to the chucks easily being pulled up unevenly when the cams are tightened, which would give the errors you have. It can take a great deal of force to get the backplate to mate up squarely, with even a small gap visible between the two flat mating faces on one side, and wobble of the chuck as it rotates, if it isn't done right.

My Warco 1330 suffers from this problem, plus a couple of other low cost Chinese lathes I have worked on. The higher quality lathes I use at work have Camlock spindles and these have a distinctly different fit. The taper and the flat mating faces on these make contact almost simultaneously, making repeated accuracy easy and with considerably less force needed on the cams when tightening them up with the key. They also release very easily when the cams are slackened, but on my 1330 the backplates remain stuck fast.

It seems to be a quirk of some of these low cost Chinese machines with Camlock spindles. I do know of someone who bought the same type of lathe as yours and did some work on all the backplates and face plate to get a better fit.

Edited By Lathejack on 29/10/2014 20:52:32

Surely putting the jaws in different slots shouldn't make any difference to the run out as such because they still engage with the scroll in the same sequence. Error here would be to do with the scroll not running concentrically. I would make sure the chuck is replaced in the same position on the back plate. mark this up with a spot to ensure you do this.

Check the jaw slots and jaws for burrs or bruises but this would only impact the lateral position of the jaw in the slot which if it was excessive you would feel.

Rob, It seems to me that the error is not likely to be caused by inserting the jaws in the wrong sequence as this would give a far greater error , at least 1/3 scroll pitch for a 3 jaw chuck. If the scroll is a close running fit on its spigot then the problem must be at the backplate interface due to poor fit or lack of parallelism on one or more mating faces between the business end of the chuck and the machine register. However if the scroll has a pitch error I would expect this to show up as change in error when different diameters are held although If the jaws are inserted in the correct sequence but in the wrong slots then I would expect this to show the variation you get. Colin

On cheaper chucks, it’s easily possible to get 020″ run out by assembling the jaws in the wrong slots.

Its logical to think that when being made that a chuck is assembled and mounted and then the jaws are ground internally and maybe externally with the separate jaws in there position in the chuck body. Any deviation from that position when in use is now all out of register so marking the jaws is essential. It is correct in 1 of 3 positions so set up the chuck jaws, marking the chuck jaws and the chuck and slowly set it up with each sequence of positions. Hopefully you will get it in the right position eventually.

Clive

Yes, grip a thin disk at the rear of the jaws, grind the jaws, remove the disk and grind the back of the jaws to slightly undercut the unground portion.

Rik

…. and yet, BF&R has a point, at least at first glance. If you imagine the jaws in the scroll in the correct sequence without the chuck body …. and then superimpose the chuck body …. it's hard to see why the orientation of the chuck body should affect the runout of the jaws. It's only providing slots to constrain the motion of the jaws.

And yet, intuitively I believe you Chris and I think perhaps the answer is that the above assumes the slots are truly radial. Any deviation in that respect (which may have been compensated in manufacture by final machining of the jaws in-situ) would mean that each slot should be used with its original jaw.

(Mostly just talking this through for myself )

PS I do take the point about the jaws all being shifted by one slot.

regards Martin