rotary table 3 jaw chuck runout

[garrygunParticipant @garrygun]

I have a soba 150mm rotary table with 125mm chronos chuck (all new) i machined a boxford mount plate to suit, it fits quite snugly, i put a piece of ground silver steel in the chuck then clocked it to check runout 0.12 mm.so i checked the mt 2 to boxford adaptor found ok, so checked back plate register that ok, so the chuck is out, the chuck is very tight, would it be advisable to shuffle the jaws? (no numbers on them)…

What would be the best way to grind the jaws if i have to?

Thanks Garry..

[garrygunParticipant @garrygun]

[I.M. OUTAHEREParticipant @i-m-outahere]

Hi Garry,

Before you go grinding anything I would suggest that you strip the chuck down and give it a good clean and inspection.

There could be a small burr or some swarf from machining that could throw things off centre .

Is the runout consistently in the same spot ?

If after re assembly there is no improvement try indexing the jaws around to another slot ( keep them in the same order though ) and see if the runout follows them , if it does then I would say there is an issue with one or more of the jaws and if it does not follow the jaws around it would be in the chuck body or the scroll.

Unless you want to spend some serious money on a chuck you won't find many cheap 3 jaw chucks that will run perfect or less than a few thou but this is not a problem as a light tap with a soft hammer usually improves things or a thin shim under the jaw that reads high with your indicator will sometimes help.

IF you really must have perfection then an independent 4 jaw chuck is the way to go.

Another thing to check is whether the chuck is sitting on the adapter properly as it could have a burr behind it so check to see if the runout gets worse as you move the indicator further away from the chuck

Ian

[garrygunParticipant @garrygun]

Thanks Ian, i will do as you say, try it out see what happens, i must say it is very tight.

[garrygunParticipant @garrygun]

Just stripped it down, removed all the burrs washed it out lubed it up & its smooth and easy action now, still out 0.12mm i swapped the jaws one place i will try again tomorow.

[Brian WoodParticipant @brianwood45127]

Hello Garry,

I have just caught up with this post, so I may already be behind the times.

A few things I would try as well.

!. Try the chuck on something you know and trust, 0.12mm runout is after all only 5 thou, but you don't say if it gets markedly worse measured further out from the chuck jaws, indicating a 'leaning' error [jaw problem] rather than simple displacement parallel to the body of the chuck.

2 Take off the backplate and check the mating face to the chuck, a small error there will be magnified by distance.

3. The fit of the backplate to the chuck, ie it it snug in the recess? Is there a burr or tiny piece of dirt there? All these can be additive. As Ian observed, a careful tap with a soft faced hammer followed by retightening securing screws can sometimes do wonders

4 And finally, how well does the adaptor fit the table? The trouble may be in that.

Regards Brian

I doubt you will get better than 0.05mm whatever you do

Edited By Brian Wood on 30/10/2013 10:01:43

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by garrygun on 27/10/2013 20:53:17:

Thanks Ian, i will do as you say, try it out see what happens, i must say it is very tight.

Make sure it's not tight on the threads of the adaptor. It should be a good fit on the register and fairly loose on the threads so that the threads don't play any part in the alignment.

Have you tried checking the chuck and backplate by mounting it on the lathe and clocking it?

Russell.

[Ady1Participant @ady1]

The solution on a lathe 3-jaw is to use a tailstock centre and I can't see any "simple" reliable system bettering this approach

Would be a pain to implement, but would give a lifetime of usage and benefit

[Howard LewisParticipant @howardlewis46836]

It would be surprising if any, let alone an amateur market, three jaw chuck holds work absolutely true.

Even collets are not infallible, unless direct in the mandrel / quill taper. And that assumes that the taper bore has no eccentricity relative to the bearing surfaces!

If you want to start talking REAL tenths of a thou, or better, you are going into the realms of Standards Room conditions with CLOSELY controlled temperature and humidity.

There won't be many of us with those sorts of environmental controls!

If you want the workpiece to run absolutely true, use a four jaw and adjust until the DTI shows Zero eccentricity.

Allow plenty of time for this.

A good Industrial grade three jaw chuck will probably not do much better than 0.005" (0.127mm) total eccentricity. And to complicate matters, it will probably alter as the diameter changes.

(I know of one venerable three jaw, not mine thank goodness, which has an eccentricity of 0.036", but still being used to produce good work!)

Eccentricity in a three jaw is only a problem in second operation work. If you do all the turning / milling without moving the workpiece, the machined diameters will all be on the same centreline. Once you take the job out, you have to centre it up in a four jaw for subsequent work.

Howard

[garrygunParticipant @garrygun]

Thanks for all your replys guys,

Russel, one of the retainer bolts is a little tight also c/sunk so i will take out the hole slightly&use std hex bolts with a heavy washer then try again.

Brian, i will check for burrs again incase i missed any, i will also try clocking piece ground s/steel further out the chuck see if it gets worse.

Garry.

[Author]

Posts