Old lathe, chuck accuracy

[Mark Smith 3Participant @marksmith3]

Hi I am new to engineering and I have a very old lathe. My problem is the 3 jaw chuck has always been inaccurate, as anything I put in it wobbles visibly. I got sick of this and decided to check the runout (without a DTI) and it was about 1/32″ out. I removed the chuck from its back plate and checked that and it was bad. I took a skim off it and got it running true and reassembled the chuck. Things are better but not perfect – if it is ever possible to get a perfect 3 jaw. My question is what else,  besides a new lathe, can I do to improve matters? Shims? there are no marks that I can see that register the chuck with the back plate.

Mark

[Mark Smith 3Participant @marksmith3]

[Fred MillerParticipant @fredmiller19582]

Mark. If you are having trouble getting things true, use soft jaws lock in and bore to suit.

Or if your jaws are hard  lock them in and using a Dremal or the like grind the grip face true. See MEW no. 145 – 146 for using soft jaws.    Fred.

Edited By Fred Miller on 25/01/2010 05:26:34

[Jens Eirik Skogstad 1Participant @jenseirikskogstad1]

Are the centerhole in the backplate worned out? Are there no play between the spindle and backplate?

 

In case make a new backplate or buy a backplate then make it true before the chuck are mounted at backplate without play. Best to use cast iron as material.

 

And in case there are worned out  jaws or chuck, buy a new set  jaws or new chuck.

 

I am using ER32 collet set with ER32 spindle with MK3 taper to fit the spindle, there are allways true than chuck. Above 25 mm diameter i am using chuck.

 

Jens Eirik

[KWILParticipant @kwil]

Mark says that there are no marks that register the chuck with the back-plate. It is quite normal to have stepped backplate, the raised portion of which, if machined correctly locates the chuck body radially, this register needs to be carefully machine to a “dead” size fit. Thus ensuring that the body runs true.

 

Which make of chuck are we discussing and does it have a recess in the back face for the purposes of centring the chuck body?

Edited By KWIL on 26/01/2010 15:49:16

[Mark Smith 3Participant @marksmith3]

Hi, Kwil, the chuck is of the same vintage as the lathe, which is a Barns (american) and yes it does have a recess that locates with the back plate. I didn’t machine anything from that edge just the wobbly face. But I wondered if the three hole that the bolts go through should go back in the same location thats what I mean’t about register marks.

Thanks for your replies.

Mark

[chris stephensParticipant @chrisstephens63393]

Hi Kwil,

Re the register on the back plate and the matching one in the chuck, you might be right in theory but not necessarily in practice. If the register is a sloppy fit the chuck can be what has become known as “bump” trued. I refer you to the section in GHT’s model engineering “bible” where he describes the benefits and credits a Commander Barker with the idea.

chriStephens

[KWILParticipant @kwil]

Mark, since the three holes are usually a clearance size it probably does not matter, but you can try moving around in 1/3.

Chris, I know about bump alignment but my chucks are better than that and again if it is bumpable then it can also get out of true again unless the bolts are very tight to prevent this.

 

Another thought since the chuck is old on Mark’s machine, even if the body is running true, uneven wear on the scroll will throw the jaws out so that it may only run true at one daimeter setting only Make sure the back of the jaws are clean with no swarf trapped.

[chris stephensParticipant @chrisstephens63393]

Hi Kwil,

 I used to think that, too.

chriStephens

[Ian S CParticipant @iansc]

Thank you David for fixing the site,I don’t understand the working of these things.Ian S C

[Mark Smith 3Participant @marksmith3]

Thanks Ian I might try your suggestion. I tried to reply  to your email but it bounced back again.

Kwil I thought about turning the chuck to different positions. The chuck might have been dismantled several times in its history and not reassembled properly.

Another suggestion i heard is to check the spindle, I didn’t think of that.  So now I have several ideas to work on as the chuck is otherwise in good condition and I don’t think a chinese one will fit as my spindle is only 25mm outside Dia.

Mark

[Les Jones 1Participant @lesjones1]

Hi Mark,

                Have you verified with a dial gauge that the register on the backplate is running true ? I imagine that this register would be machined on the backplate with it fitted to the lathe on which it will be used on. If I am wrong I’m sure someone will correct me.

Les.

[KWILParticipant @kwil]

Mark, I for one would not buy a chuck of that origin.

[Ian S CParticipant @iansc]

KWIL,Chinese chucks are the only ones you can get here, although you might get a second hand one of British origin. Mark if you did have to get one you’d need to make a bake plate, or obtain one regardless of what lathe it was for. If you have no DTI, put a bar in the tool post and use feeler gauges to messure any runout. Most of the Chinese chucks are fairly good here.Ian S C

[CirclipParticipant @circlip]

Surprising how many three jaw chucks have been distorted over the years with the application of a “Tube Lever” on the end of the chuck key.

 

  Small point Mark S3, if using a three jaw, put in bar bigger than you want to finish with and turn down all diameters to finished sizes and part off.

 

  Three ways to turned accuracy and non using the three jaw as a refference:-

 

   Between centres,

 

   Collets,

  

   Four jaw and “Clock”

 

  Regards   Ian.

[Mark Smith 3Participant @marksmith3]

Thanks Ian, I’m learning everyday,

Mark

[Mark Smith 3Participant @marksmith3]

Hi, all. thanks to your suggestions, i have got the runout below 2thou as against 1/32, Using feeler guages I can’t insert the 2 thou but the 1 thou does.

The chuck jaws are not even as witnessed by the wear pattern which is tapered towards the back of the chuck; so it is gripping first at the back and on light grip not at the front at all.

 Ian has suggested putting a ring, internally gripped, and passing a high speed grinder a few thou to true them and make them parallel. The scroll is in good condition, no chips or breaks and the jaws don’t move so there is very little backlash that I can detect. Maybe now I can make flywheels that don’t wobble.

Mark

Edited By Mark Smith 3 on 28/01/2010 07:37:42

[Mark Smith 3Participant @marksmith3]

I bought a DTI yesterday, an american one, now I have to learn how to use it. I have taken Fred and Ian’s advice and trued the jaws with a high speed air grinder mounted in the tool post; that is how I hone my cylinders as well. Now the chuck is nearly true and grips evenly. Ian, (cirlip) I have yet to learn about collets, do these mount directly in the morse taper? I have been trying to make small parts with just the chuck, that is wrong it seems.

Mark

[Jens Eirik Skogstad 1Participant @jenseirikskogstad1]

Posted by Mark Smith 3 on 30/01/2010 19:08:01:

 I have yet to learn about collets, do these mount directly in the morse taper? I have been trying to make small parts with just the chuck, that is wrong it seems.

Mark

 

There are the collet chuck with morse taper direct mounted to the spindle, to example ER32 Milling Collet Chuck Sets, see this link: http://www.arceurotrade.co.uk/Catalogue/Collets/ER-Collets-Collet-Chucks/ER32-Collets-Collet-Chucks

 

The collet chuck are true than traditional chuck and are practical if you need to make parts true without adjusting with DTI and 4 jaws chuck. It save much time in working time.

Edited By Jens Eirik Skogstad on 30/01/2010 20:29:51

[Mark Smith 3Participant @marksmith3]

Thanks, Jens, I trued up my flywheel today… no wobble!

[CirclipParticipant @circlip]

Re-read what I wrote Mark, I didn’t say Wrong, many roads to Rome, but for accuracy, forget the three jaw. It only takes a rism of swarf on the teeth of one jaw and you are tearing your hair out trying to chase the ellusive thous. of eccentricity. You can use one to turn true, but note the limitations, just don’t try to turn press fit registers for wheels on axles that are 3/8″ dia. using 3/8″ dia. bar as a starting point which you COULD using the other three options I showed.

 

      Regards  Ian.

[Ian S CParticipant @iansc]

Mark have you got a 4 jaw chuck? If so stick with that for now,its slower, but I’m not sure of availablity of collets. Did you get the bearings sorted? Ian S C

[Mark Smith 3Participant @marksmith3]

Sorry,Ian I wasn’t refering to anything you said. Thankyou for the advice though.

Ian SC yes the bearings seem ok now.

[CirclipParticipant @circlip]

No agopolies required Mark, just trying to stop you falling into the three jaw trap that most starters do, as SC has said, if you havea four jaw stick with that one.

 

  Regards  Ian.

[Mark Smith 3Participant @marksmith3]

Thanks Ian, yes I have a four jaw, it is a monster. I am thinking of getting a small one but will have to make a back plate to suit my spindle. I also now have a DTI just need to buy or make a stand. But good news I have trued up a flywheel and for the first time no wobble.

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