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Nightmare removing 3 jaw chuck

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Mark Salzedo23/02/2014 12:49:02
49 forum posts
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I am not too sure if this is the correct category to post this but perhaps someone will kindly let me know if not. In any event, just over two years ago I bought a 7 x 12 Chinese lathe (not a mini-lathe) from a dealer who sells model engineering and industrial lathes and milling machines. It is probably best that I do not mention the name of the company concerned. Since I have had the lathe it has had very little use and regularly cleaned and oiled. All the work to date has involved just using the 3-jaw chuck. But last weekend I needed to turn between centres with a MT3 centre in the headstock and a MT2 centre in the tailstock. This is when my problems began. Firstly, I just couldn't remove the nuts at the back of the chuck back plate. There were so tight that no amount of leverage could move them. So, I had to judicioulsy use heat (a propane blow lamp) to assist the process and then direct some WD40 around each nut to help with removing them. Eventually they did budge but not without badly cutting myself in the procecss as one of the nuts turned very quickly and I caught my finger on the headstock housing as the spanner broke away in its travel.

Nonetheless, at this point I thought my problems were over. But, unfortunately, not so. With the nuts removed the chuck also appeared to be 'welded' onto the backplate. At this point I rang the company to ask for their advice. It was mentioned that as the chuck hadn't been removed in the time that I had had the lathe that this was the cause of the problem and that the protective coating that is smeared all over the lathe had probably 'glued' up between the chuchk back plate and the chuck. There suggestion was to use a rubber mallet and to strike the chuck loose which I thought might budge it quite quickly. Not so. I couldn't see any movement in the chuck at all. I then contacted the company again and they suggested using a cold chisel prise the chuck off between the backplate and the back of the chuck (there is a small groove that interfaces them both). I then proceeded to 'judiciously' strike the chuck at appropriate positions probably in excess of a 100 times in order to remove it. I am now concerned that that there may be damage to the spindle in not running true. The chuck did eventally loosen and I was able to remove it but I had probably spent in excess of 4 hours from start to finish. The back of the chuck and the front of the back plate were spotlessly clean without any evidence of corrosion or of the red protective coating.

It is now difficult to refit the 3 jaw chuck without having to use a rubber mallet to strike it onto the backplate. Also its removal still requires the use of the mallet and a chisel. The company suggested that I use fine emery paper and a cutting compound to remove any 'high spots' on the back plate. I put a DTI on the backplate and there was only about half a thou difference in a full revolution of the plate.

I have yet to hear from the company concerned as to how they propose to rectify the problem. I do not think that the lathe is 'fit for purpose'. I have offered to take the lathe down to the company (a round journey of about 250 miles), in my time and at my expense, but they have been very vague as to when I can do this as they are moving offices in the next week or two.

I was asked to ring them this morning at an arranged time to discuss the matter further but no one answered the phone.

I would be grateful to hear from anyone who has experienced similar problems in removing chucks from fairly new Chinese lathes and what the outcome was. I have had one or two Chinese lathes in the past and one expects some rough edges with them, such as slides too sloppy or stiff, setting up the alignment of the tailstock and the like, but nothing like this.

Thank you for listening.

Tony Pratt 123/02/2014 13:12:51
1233 forum posts
5 photos

Not a good state of affairs to say the least! There is no way you want to fit the chuck back on with the aid of a mallet as you will be back to square one. As suggested you need to rework the backplate but without photos I am not sure of what set up you have.

Tony

JasonB23/02/2014 13:26:15
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A lot of the Imported lathes with a short straight spigot to locate the chucks are very tight particularly the 3-jaws where you don't want any play to affect runout.

Rather than hitting the chuck to remove it just loosen the nuts and then slip a piece of flat bar between the head and the nut and just wind the nut off until it jacks the two apart, not too much to avoid jamming things then move to the next nut and so on jacking say 0.5mm at a time.

To make this less of a problem you can do what I have done and suggested to others and that is to machine a very slight taper along 80% of the internal hole in the chuck backplate so it will slide most of the way over the spigot on the spindle and you then just nip up the nuts to pull it teh last 1.5mm or jack off the first 1.5mm. I'll take a picture of mine later this afternoon to show the cure.

J

John McNamara23/02/2014 13:44:26
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1313 forum posts
113 photos

Hi Mark

I am not sure why you needed to remove the chuck from its back plate? It appears that the manufacturer was a little over zealous in tightening the machine screws that attach it to the back plate, and that the light press fit normally used between the shoulder on the chuck was more a press fit, the fit is easily fixed by turning a couple of tenths off the back plate shoulder. (Be careful it is easy to take too much)

Getting the chuck off is a different matter. and more importantly does it go back on easily turning all the way until it hits the spindle face? If it does then all is well.

My old lathe had a screwed spindle nose. It can be pretty hard to release a chuck sometimes, particularly if you have done a lot of heavy cutting and it is screwed on tight.

A little trick I used to release my chucks was a short stout piece of hardwood 100 x 50 x the exact length required to fit between the bottom of a chuck jaw that is aligned parallel with the lathe bed. and the top of the lathe bed.

The wood was placed firmly against the lathe bed with the left hand while the right hand was used to rotate the chuck so the parallel jaw was moved up and away from the operator until the next jaw hit the side of the wood, then with firm hand force the chuck was rotated until the jaw hit the piece of wood stopping the chuck abruptly. The spindle having developed some inertia in the process tries to continue and breaks free.

It always worked for me mostly first time The wood does not damage the lathe bed or the chuck, Do not use metal. And don't even think of doing this under power, The result could be serious injury to your hands.

Please also take great care to position your hands and fingers (Particularly the one holding the piece of wood, Maybe it would be better to just prop it there the first time you try it)

Regards
John

Bazyle23/02/2014 13:54:43
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5471 forum posts
206 photos

You are lucky it is too tight rather than too loose so you can easily correct it. The change needed is a fraction of a thou so be carefull.

Two things to avoid are running the lathe then trying to get the chuck off as the spindle will have warmed and expanded into the cold chuck register. The other is never put a warm chuck onto a cold spindle as it can shrink fit itself. The same applies in reverse for fitting morse tapers (especially in milling machines) so always think about your remperatures and expansion direction.

For anyone else getting in the same position as well as Jason's advice above use an electric paint stripper to warm the chuck and soften the gunk if it might be a contributor. If you have a screw on chuck don't whack the chuck key but put a bar through the jaws such that the force is distributed along the side of a jaw. Better grip a bit of hex and put a socket set on that. Beware using the back gear to lock the spindle.

Mark Salzedo23/02/2014 15:30:18
49 forum posts
4 photos

Hi,

I am grateful for all the feedback which will take me a little time to absorb. I have uploaded a few pictures of the backplate assembly in 'My Albums' under 'Lathe back plate'. It's on the last page of 'Albums':

www.model-engineer.co.uk/albums/default.asp?p=182

When all is said and done, I don't think that it would be unreasonable of me to contact the supplier and inform him that under the 'Sale of Good Act', I consider the lathe 'not fit for purpose'. Nonetheless, because the lathe is over six months old, I think that I might have to have to prove that the problem was present when I bought the lathe.

Many thanks.

Involute Curve23/02/2014 15:31:43
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337 forum posts
107 photos
Posted by John McNamara on 23/02/2014 13:44:26:

Hi Mark

I am not sure why you needed to remove the chuck from its back plate? It appears that the manufacturer was a little over zealous in tightening the machine screws that attach it to the back plate, and that the light press fit normally used between the shoulder on the chuck was more a press fit, the fit is easily fixed by turning a couple of tenths off the back plate shoulder. (Be careful it is easy to take too much)

I'm also puzzled as to why the chuck is removed from the back plate, or is this common practice on these lathes.....

wheeltapper23/02/2014 16:06:18
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421 forum posts
98 photos

It looks like the way my Comet chuck fits, It's not technichly (sp) a backplate, its a flange integral with the spindle.

the chuck itself has no backplate as such, not like a screw on chuck.

Roy.

JasonB23/02/2014 16:31:58
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Your locating spigot is a bit shorter than teh larger Warco lathes so the second pat of this may not work.

As I said earlier rather than knock the chuck off you can jack it which is a lot kinder to the machine.

1. loosen nuts and then unsert metal packer, preferably non ferrous.

imag2472.jpg

2. Turn nut with spanner, working round giveing each about 1/3rd of a turn.

imag2473.jpg

3. Or you can use the bar as a lever, again small amounts as you work round so teh chuck does not get cocked at an angle.

imag2474.jpg

Now my parallel spigot is about 8mm long so I turned a shallow taper in the first part of teh chucks backplate. This may not work for your shorter setup. This means its only tight for the last littel bit so does not need a lot to jack it free

imag2478.jpg

And this is the setup to machine the taper

imag2481.jpg

imag2482.jpg

Edited By JasonB on 23/02/2014 16:32:34

Mark Salzedo23/02/2014 16:44:46
49 forum posts
4 photos

dscn2567.jpgInstead of going to 'Albums' you can view the images here.

Edited By Mark Salzedo on 23/02/2014 16:45:50

Mark Salzedo23/02/2014 16:46:24
49 forum posts
4 photos

dscn2568.jpg

Mark Salzedo23/02/2014 16:46:36
49 forum posts
4 photos

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Mark Salzedo23/02/2014 16:46:52
49 forum posts
4 photos

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Bazyle23/02/2014 18:28:53
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5471 forum posts
206 photos

Just like my Hobbymat. A small register is more normal that the 8mm mentioned and I repeat you are better off having a tight fit to ease down than a sloppy one. Read back a few months posts to find the advice about the nuts with integral washers and ways of fitting them more easily. Once you start using a 4 jaw too you will appreciate why this was a discussion topic.

Tony Pratt 123/02/2014 18:44:49
1233 forum posts
5 photos
Posted by Bazyle on 23/02/2014 18:28:53:

Just like my Hobbymat. A small register is more normal that the 8mm mentioned and I repeat you are better off having a tight fit to ease down than a sloppy one. Read back a few months posts to find the advice about the nuts with integral washers and ways of fitting them more easily. Once you start using a 4 jaw too you will appreciate why this was a discussion topic.

Mark would be better off having the correct fit i.e. about .001" clearance! He wants to use and enjoy the machine not fight it.

Tony

Mark Salzedo23/02/2014 19:03:18
49 forum posts
4 photos

I am much obliged for all the valuable advice and suggestions. I measured the diameter of the spigot, boss, register whatever is the appropriate terminology and it is about 10 thou wider than the recess on the back of the chuck which it fits into (onto). Personally, I think this is not a good fit and finish on a relatively new lathe. I have spent quite amount of time using emery to reduce the diameter of the boss but I don't think I am getting too far on ground steel. I do think the supplier has a responsibility to rectify the problem. What should have been a 2-3 minute job in taking the 3-jaw chuck off and inserting a MT3 centre in the headstock has turned into something far more complex and problematical.

DMB23/02/2014 19:38:04
1014 forum posts

Fizzy,
I believe this thread is about being practical, after all, we all have to snuff it sooner or later - cant take it with you!
Surely far better to downsize belongings while you can and are able to control what happens to them?
Clubs I have belonged to over the years usually have at least one member prepared to spend time sorting pricing selling tools+metal in clubhouse,usually with a donation to club funds. .
John

Edited By JasonB on 23/02/2014 19:55:53

Michael Gilligan23/02/2014 19:40:17
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16372 forum posts
714 photos

Ten thou bigger diameter !!! [expletive deleted]

MichaelG.

Tony Pratt 123/02/2014 19:57:03
1233 forum posts
5 photos

Hi Mark,

With the greatest respect if the spindle spigot was .010" larger in diameter than the chuck bore diameter they would have been impossible to assemble together. However what is obvious is that you have ended up with an interference fit between the spindle and chuck which is totally wrong for this type of application and I am sure who ever assembled the chuck onto the spindle would/should have known this.

You need to sort this out with the supplier.

Tony

JasonB23/02/2014 20:00:17
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18884 forum posts
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The downside of any clearance in the fit is that you will increase the TIR of the chuck, thats why I stuck with the last little bit a tight fit. The 4-jaw I opened out but kept it parallel as a thou or so sideways has no effect on teh way teh chuck works.

J

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