Untrue 4 jaw chuck ?

[Dave CParticipant @davec87625]

[Dave CParticipant @davec87625]

Evening guys. I bought a 4 jaw independant chuck last year and have not until last week used it. I noticed upon checking that the pieces I was facing were out of square in one plane.

On a 1" square axle box it was out by a few thou and clearly visible when checked with a square. After the initial panic that my lathe was knackered I came to the conclusion it was the chuck. It is a HBM chuck.

Unsure of the best way to check I placed a 12mm wide parallel in the jaws and ran a DTI along the length of the protruding part. There was a run out of 10 thou over a length of 5 inches. run out was plus 10 on one edge and then the chuck was turned 180 degrees and the run out was then found to be minus10 thou

I hope this is understandable. Is this the correct way to check the chuck or have I got it all wrong.The chuck was brand new but has been kept and stored unused for a long time so a refund is unlikely. I appreciate that this is a cheap chuck comparatively speaking but I would expect a lot better. I should have checked it when I bought it so my fault.

Is there any other way to check the chuck ? I am assuming that if the headstock was out of line then I would have a concave or convex turned face so I would appreciate others opinions.

I have been looking at a Toolmex Bison chuck which is availabe locally to me. What are the opinions of these chucks. It is a big outlay but better than the money wasted on this cheaper option. I would rather pay a little more and have a chuck which will last a lifetime than a cheap doorstop.

Is there anything I have missed or could alter or would I be better off just replacing the chuck.

Any help or advise greatly appreciated.

Thanks

Dave

[Les Jones 1Participant @lesjones1]

Hi Dave,
You do not say if the chuck was supplied ready to fit the lathe or if you machined a backplate to fit the chuck to your lathe. I would remove the jaws and check if the front face of the chuck is running true. You could also swap over the suspect pair of jaws (WITHOUT ROTATING THE CHUCK.) and note if the direction of the runout changes or remains the same. If it changes then I think the jaws are at fault in which case you could machine the jaws. To do this hold a ring of a suitable size from the inside, true it up and then skim the inside of the jaws. I would wait for some more replies before trying this suggestion.

Les.

[Ian PParticipant @ianp]

Dave

If you have a DTI and a ittle patience you should be able to see waht is causing the error. I would systematically check from the mandrel register to the tips of the jaws. To ellaborate,

With the chuck not fitted check the mandrel register and face, if OK fit the backplate only (or chuck on backplate) and check the register face of the backplate, and then the front face of the chuck (without jaws).

If the front face of the chuck is true you could check the jaw slots are all machined to the same depth (most likely they will be). If that is all true then you can do a quick on each jaw just by holding them against square.

If you lightly grip a small diameter piece of ground shaft you should be able to check if the jaws tips are gripping along the way along their length (bright light helps here). If for some reason the jaws are not square you could individually true them up with an oilstone.

Ian P

[Dave CParticipant @davec87625]

Hi Les

The chuck is a D1-4 type and so fits straight onto the lathe which is a Harrison M300.

I have removed the chuck and checked the mating face whis is clean and free from debri.

I will try changing the jaws over as you say tomorrow. I stupidly hadn't thought of doing this.

Many thanks for your help

[Les Jones 1Participant @lesjones1]

Hi Dave,
I had a few more thoughts overnight. First mark the jaws and slots so you can put them back in the original positions to avoid any confusion during the testing. Second with the two suspect jaws removed and the jaw slots horizontal mount a dial gauge on the cross slide with its tip against the jaw guide. Traverse the cross slide to see if the guides are perpendicular to the lathe axis. I am not familiar with the Harrison M300 chuck mounting so I can't make any suggestions regarding anything to do with that which could cause the problem.

Les.

[Anonymous]

I have a Harrison M300 and an 8" 4-jaw chuck that came with it. I can't see a makers mark on the chuck, but there is a small label in a circular indent on the face of chuck which has a stylised letter 'h' on it. I assume that means the chuck was supplied by Harrison?

I've measured the runout of the chuck body on the outer edge of the front face of the chuck, TIR is 0.05mm. That agrees roughly with the variation in thickness I would expect when 'snugging' a part against the body of the chuck. If I face off a part that is 'snugged' up against a step on the jaws I usually get a variation in thickness that is a little worse. On a 4.4" OD gear blank that I machined last week using the 4-jaw chuck the thickness variation is 0.04mm, so I must have been lucky that day.

I rough machined the crankshaft bearings for my traction engines using the 4-jaw chuck. Never again; the finish might have been good but they were not quite square or parallel. If I want a part square and parallel I now use the milling machine.

Regards,

Andrew

[John CParticipant @johnc47954]

HI Dave,

Try a search for 'D1 backplate fitting'. There appear to be some differences of opinion on how the two tapers engage. Personally I think that the taper should allow the two flat mating surfaces to touch firmly – there is not enough length in the taper to seat the chuck properly. Can you get a feeler or shim between the two faces? If so, is this consistent all round? If there is a gap that is not consistent this may be your problem.

Rgds,

John

[Dave CParticipant @davec87625]

Hi John

Once the camlocks are secured there is no gap at all between the back of the chuck and the mating face.

I have run a DTI on the spindle and all is spot on. A DTI test on the chuck body sides and face was also ok. I have borrowed another 4 Jaw chuck and faced off a 30mm square piece of stock and by checking with an engineers square across the end it is now spot on as hoped for.

I can only now assume it is the jaws which are the problem. A few more checks are needed tonight if time permits. I have spoken to the supplier this morning who was more than helpfull and has offered to run tests himself on the chuck however this will cost me two way postage. Another thirty quid gone.

Andrew thanks for your post. I agree some degree of runout is expected when snugged against the body or the jaw faces but I am having the problems when items are held in the jaws. I am holding the parts far back as near to the chuck body as possible and also being carefull to not over tighten the chuck too much. I understand that by holding parts at the jaw tips would give me problems but the parts are held by their full length pretty much.

The jaws when removed appear to be square so I only now have the registers in the chuck to check.

While I am at the computer I recieve emails to say there are new replies to my posts and I can read the replies but they do not appear on the actual forum post. I have had a couple from ADY regarding using a shaper instead of the lathe but they do not show here. Am I just having a very bad week ?!?!?!

Confused

Dave

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by Dave C on 04/07/2013 12:24:32:

I can only now assume it is the jaws which are the problem. A few more checks are needed tonight if time permits. I have spoken to the supplier this morning who was more than helpfull and has offered to run tests himself on the chuck however this will cost me two way postage. Another thirty quid gone.

Assuming that you bought it as a private individual and not as a business you have up to 6 years to raise problems with him under the sale of goods act. You are entitled to a product which is fit for purpose and the supplier should rectify it at his expence including postage.

Russell.

[John Stevenson 1Participant @johnstevenson1]

Posted by Russell Eberhardt on 04/07/2013 14:04:07:

Assuming that you bought it as a private individual and not as a business you have up to 6 years to raise problems with him under the sale of goods act. You are entitled to a product which is fit for purpose and the supplier should rectify it at his expence including postage.

Russell.

.

.

So when my Ipad goes tits up in 5 1/2 years , Apple will give me a new one.?

That's brilliant.

[Ian PParticipant @ianp]

Posted by John Stevenson on 04/07/2013 21:41:55:

Posted by Russell Eberhardt on 04/07/2013 14:04:07:

 

Assuming that you bought it as a private individual and not as a business you have up to 6 years to raise problems with him under the sale of goods act. You are entitled to a product which is fit for purpose and the supplier should rectify it at his expence including postage.

Russell.

So when my Ipad goes tits up in 5 1/2 years , Apple will give me a new one.?

That's brilliant.

 

John, that part of the sale of good act only relates to goods that have a purpose (to be fit for).

Apple have a clever get out, they never really say what things are supposed to do (apart from look good)

Ian P

Edited By Ian Phillips on 04/07/2013 21:48:19

[John Stevenson 1Participant @johnstevenson1]

But surely they expect it to light up when you switch on ? if it doesn't do i get a new one?

6 years dowen the line EVER iPad will still be working ? If not Apple with replace it.?

Pigs, theory of flight, comes to mind.

So take this chuck then.

Has the seller actually said what it does. It's a chuck after all.

I have a 4 jaw on my welding positioner, I expect it to be accurate to plus or minus the odd post code and that plenty good enough.

[AndyfParticipant @andyf]

I had a similar problem with a cheap 4-jaw. I labelled up the jaws 1 2 3 4 and the slots A B C D and tried a few combinations of jaws and slots. The error was always against one particular jaw, so as someone suggested earlier I worked on its gripping face with an oilstone until things straightened up. A bit of a hassle, but probably less than trying to get the chuck replaced and finding the replacement was just as bad.

Andy

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Dave C ,

You should bear in mind that ordinary grade self centering and independent chucks are only really very crude workholding devices . To put work randomly into such chucks and expect work to be set true by default is an unreasonable expectation .

In case of a four jaw independent which does not have any particular faults a nominal cube for instance can be out of position relative to the jaws by several degrees in rotation and up to a couple of degrees in tilt in two axes .

To set up a nominal cube properly requires positioning best guess in jaws and then clocking reference faces true in one , two or just sometimes three axes and progressively making small adjustments and tightening jaws at the same time .

Further notes :

Jaws are never going to be exactly square to chuck – might be somewhere near on a new and good chuck – but in general not .

The work will generally move as the jaws are tightened . You can keep track of movement and compensate while setting up as above but it helps to have some restraint where it can be arranged . One useful thing to do is to use the tailstock to prevent the work moving forward .

In many ways setting work in a four jaw independent chucK is the same as setting work in a milling vice – and its quite common practice to tap the work home as vice jaws are tightened .

For any particular chuck learn its defects – if you know that for instance that work is always cocked away from jaw no 1 then you can always bias the initial setting up of work to compensate .

Actuall knowing the defects of any particular machining set up is always useful and sometimes allows quite astonishingly accurate work to be done on dodgy equipment .

Regards ,

MikeW

 

Edited By MICHAEL WILLIAMS on 05/07/2013 13:42:43

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Editor wouldn't let me edit .

So PS:

Work may also be eccentric of course but that's a different problem which can be corrected by simple means .

[Sub MandrelParticipant @submandrel]

> I am holding the parts far back as near to the chuck body as possible

If you can't actually snug the parts up against the chuck body or the steps on the jaws, all bets are off – you can't blame the chuck.

Neil

[Ian PParticipant @ianp]

Posted by Stub Mandrel on 05/07/2013 18:12:45:

> I am holding the parts far back as near to the chuck body as possible

If you can't actually snug the parts up against the chuck body or the steps on the jaws, all bets are off – you can't blame the chuck.

Neil

Really?

What if the workpiece is a round bar (say 10mm) that passes through the chuck?

It would be nice to know that the axis of the work was parallel to the axis of the spindle.

Its an odd thing really, all the articles and engineering books tell you to grip a part machined component in the four jaw (and set it to run true) for second operations etc. l do not recollect ever reading about checking for squareness almost as if its a given fact that the chuck jaws will hold the job square.

Ian P

[Sub MandrelParticipant @submandrel]

An interesting point. The component in question is an axle box, and my experience does suggest that it's very different trying to grip a square (or round) component with only the outer part of the jaws to gripping a bar threaded right through the chuck. When I have to turn such a short part (in 3 or 4 jaw) I always insert a temporary parallel between it an the chuck face until the chuck is tightened up.

Neil

[Dave CParticipant @davec87625]

I appreciate that I can not just place a part in the chuck, tighten up and be within half a thou 12 inches away from the chuck.

However this is a brand new chuck. Not a second hand twenty year old worn out thing thats had a hard life.

As Ian says regarding second operations etc. I have read the books and watched all the you tube videos about getting a second chuck key and clocking to within a thou in a matter of minutes making the three jaw surplus to requirements. But as Ian says I have never seen anybody check for run out on axis. Everytime it is assumed or expected that the chuck jaws are holding the work on axis.

My chuck is holding work 10 thou out over 4 – 5 inches away when held between jaws 2 and 4.

Say I was to machine a part 25mm square by 120mm long. I do the long sides snugged against the chuck face. What do I do with the ends ? If all chucks are considered to be that inacurate why the vast price difference between them.

I am not a tool maker or anything close to being one so am I expecting too much ? Having spoken to the supplier today and explained the tests and results I have carried out he has offered to send out two replacement jaws free of charge and appologised. He obviously thinks it is unacceptable.

This is not a rant. I am just trying to get a bench mark for what I can expect from my equipment. In my innocence I assumed that I could hold work in the jaws and it would be in the correct axis with the lathe bed and it was just concentricity that was checked. If I am wrong then fair enough. My initial panic was that I had wasted a bag of money on something that was no good and its begining to sound like I am expecting too much.

Im off to cut some shim steel.

Cheers

Dave

[Dave CParticipant @davec87625]

PS The inacuracy was first noticed when squaring off the end of the axle box cast stick which had all been milled square along its long sides. The stick was 5.5 inches long. the only way of squaring off the end in the lathe was to pass it through the chuck and grip with the jaws. At this stage I had the minimum amount of material protruding from the chuck. I just assumed the end would be square after facing.

Dave

[Sub MandrelParticipant @submandrel]

Hi Dave,

In Peter Wright's book he describes his technique for axle boxes using a 4-jaw as you suggest claims to have achieved within 1 or 2 thou over 2 1/4 inches.

Neil

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

It's common practice when setting a round bar to run true in a four jaw independent chuck to clock the bar in two places – one very near the jaws and one as far as possible outboard .

If you want consistently true workholding without fiddling then you have to have very good chucks or start in a different place and use collets or things like V angle plates .

MikeW

[Dave CParticipant @davec87625]

Thanks for all the opinions and help chaps.

It seems I stupidly assumed too much. A bit more time setting up and a little less taking things for granted in future I think.

Many thanks

Dave

[John Stevenson 1Participant @johnstevenson1]

Dave

PM sent.

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