Mellor lathe.

[Richard.]

Run out on a 3 jaw isn’t really a huge deal. Providing it’s not massively excessive. Don’t forget what a 3 jaw chuck is meant for. You put in stock that’s over sized and the moment you take a cut greater than the chucks run out that stock is now perfectly round. The run out doesn’t matter any more. You then part off. If your placing a job already finished on one surface and trueing another surface to the finished surface you use an independent 4 jaw. If your removing the job and replacing it back you use a 4 jaw. 3 jaw chucks with a bit of run out used for there intended purpose isn’t a big deal at all. Looks like you’ve got about 3 thou of run out on that. I’ve seen worse. My 3 jaw is adjusted on the back plate with tapered screws so I’ve trued it up to some round stock in the jaws to about 1/2 a thou. Not essential though.

 

[Richard.]

Also like said above there is no point measuring run out on the chuck body.
The two places to check are the spindle which id expect to be near on spot on and a piece of round stock placed right in the jaws. I have a couple of drill blanks which I know are extremely true so ideal to give true runout indications.

 

[Richard.]

Turn a piece of bar a few inches long, see what its like. The dial gauge isnt that far out for an old machine

If you turn the bar in the 3 jaw and don’t remove it I’d expect that isn’t a good indicator for telling run out because you’ve cut it in its position. So the run out would still be there but the bar will read true.
This is why run out on a 3 jaw doesn’t really matter cos you can still make something true.
I would be more concerned with checking spindle run out and work piece taper. Put the dti on the spindle and see what that shows. Then turn a piece of stock in the lathe unsupported and measure the OD at both ends to see they measure the same. Then take the stock and drill a centre in it and support it with the tail stock then cut it and measure both ends to see if you’re tail stock is running through centre. These are more important checks. I wouldn’t worry about 3thou of run out on a 3 jaw.

 

[addjunkie]

Micing a piece turned in the 3 jaw over its length is the best indicator I know to check lathe performace, but once you incude the tail stock you add additional error potential, as that also needs to be correctly centered.

A test bar in the spindle is the correct way to check, but having the right bits on an old machine is usually rare. As the morse reducer to go in the headstock is normally missing.

 

[eLuSiVeMiTe]

Micing a piece turned in the 3 jaw over its length is the best indicator I know to check lathe performace, but once you incude the tail stock you add additional error potential, as that also needs to be correctly centered.

A test bar in the spindle is the correct way to check, but having the right bits on an old machine is usually rare. As the morse reducer to go in the headstock is normally missing.

I'm assuming I could use a collet to the same effect?. No Mt on my spindle. It's bored for its own collets.

 

[addjunkie]

Yes but there was probably a suitable test bar to fit to the spindle when it was new

 

[Ian James]

@spencer 427 if you are concerned about the run out and the mandrel is running true you could just slightly skim the back plate to true things up the chuck could of taken a knock in the past that has thrown things out

 

[God mode restorations]

Thanks for the information guys.
I just like things to be correct. It's a big learning experience that I have to suss out .

 

[Pete.]

Micing a piece turned in the 3 jaw over its length is the best indicator I know to check lathe performace, but once you incude the tail stock you add additional error potential, as that also needs to be correctly centered.

A test bar in the spindle is the correct way to check, but having the right bits on an old machine is usually rare. As the morse reducer to go in the headstock is normally missing.

If you are checking headstock alignment it the only thing you worry about is if the jaws are bell mouthed. Other than that put a sturdy piece in the chuck, turn it and check diameters. Once it's turning a nice parallel part put a live between centres and turn that to set the tail stock and you're done.

 

[Richard.]

If you are checking headstock alignment it the only thing you worry about is if the jaws are bell mouthed. Other than that put a sturdy piece in the chuck, turn it and check diameters. Once it's turning a nice parallel part put a live between centres and turn that to set the tail stock and you're done.

Exactly.
That’s what I was trying to say

 

[Richard.]

Micing a piece turned in the 3 jaw over its length is the best indicator I know to check lathe performace, but once you incude the tail stock you add additional error potential, as that also needs to be correctly centered.

If you place something you know to be round in a 3 jaw and put your dial on it you can see how far it’s running out. If you then turn it and put a dial on it you cannot check run out no more. The chuck jaws are still out but you’ve machined the stock true so any run out on the jaws won’t be indicated on the stock. If However you remove the stock and turn it round you’ll see the run out again . The only thing you’ll be able to check on the stock after machining will be taper. Ensuring it’s parallel. Doing this unsupported will tell you if your chuck or spindle is causing any taper and if not doing it supported will tell you if your tail stock is running true through centre. That’s my understanding anyway

 

[God mode restorations]

If you place something you know to be round in a 3 jaw and put your dial on it you can see how far it’s running out. If you then turn it and put a dial on it you cannot check run out no more. The chuck jaws are still out but you’ve machined the stock true so any run out on the jaws won’t be indicated on the stock. If However you remove the stock and turn it round you’ll see the run out again . The only thing you’ll be able to check on the stock after machining will be taper. Ensuring it’s parallel. Doing this unsupported will tell you if your chuck or spindle is causing any taper and if not doing it supported will tell you if your tail stock is running true through centre. That’s my understanding anyway

Ok. Got ya. Understand now. Will have a go tomorrow . Cheers Richard.

 

[addjunkie]

Yes the taper is what you are looking for, the accuracy of the jaws is really not relevant if your looking for accuracy as once you remove the work you loose you're accuracy.

Supporting once if parallel or usung a test bar is to set up the tail stock. Many an unwated taper has been turned using tail stock support that wasnt where it should be.

Personally speaking Ive never used a 3 jaw that was spot on in my 40 years of machining. Most have been near enough not to worry about.


Its actually time for @spencer 427 to make some swarf and see what all his restoration work will produce. Then his headaches will really start

 

[Richard.]

Personally speaking Ive never used a 3 jaw that was spot on in my 40 years of machining. Most have been near enough not to worry about.

From what I’ve been told nothing on any lathe is going to be 100% perfect. absolute zero run out or taper just doesn’t exist. Mine tapers and my chuck has run out. I’ve messed about with mine for hours and got all inaccuracies to within 1/2 a thou. I’m quite lucky with my 3 jaw as it is fully fine adjustable between the two halves so I’m able to clock it a bit like a 4 jaw.

 

[Richard.]

Funny thing is my chuck body is waaaaaaaaay out.
I clocked up on the stock and got the stock turning with minimum run out and it’s knocked the body right out. 4 thou plus of run out on the body.

 

[Richard.]

Ok. Got ya. Understand now. Will have a go tomorrow . Cheers Richard.

You can faff about with the things forever and you’ll never get it quite as close as you want. Just throw in some stock and start using it mate. Then take some measurements of what you’ve turned.
If you can turn a piece of material in your 3 jaws to a specific measurement within decent tolerances then that’s all it’s got to do. Take a piece of 2” bar 4” long and aim to turn it down to 48mm
See how close you can get.
I know I could get that to 48 +/- 0.01 on the ml10 but I will always work to a 0.02 tolerance at the worst. I know with my limited skills this is repeatably achievable.

 

[God mode restorations]

You can faff about with the things forever and you’ll never get it quite as close as you want. Just throw in some stock and start using it mate. Then take some measurements of what you’ve turned.
If you can turn a piece of material in your 3 jaws to a specific measurement within decent tolerances then that’s all it’s got to do. Take a piece of 2” bar 4” long and aim to turn it down to 48mm
See how close you can get.
I know I could get that to 48 +/- 0.01 on the ml10 but I will always work to a 0.02 tolerance at the worst. I know with my limited skills this is repeatably achievable.

Will do mate. I will get some turning and measurements on the go tomorrow. I will of course post my results. Thanks for the help chaps. Very appreciated all of you.

 

[God mode restorations]

Morning guys.
I have set the machine up and took some long cuts to determine if it's in line. I used a long piece of stock. Used the tailstock centre and took some cuts. And all looks good. Both ends are the same measurement and a reasonable finish considering I am using an old cutting tool. Think it's ready for action.

 

[Richard.]

Morning guys.
I have set the machine up and took some long cuts to determine if it's in line. I used a long piece of stock. Used the tailstock centre and took some cuts. And all looks good. Both ends are the same measurement and a reasonable finish considering I am using an old cutting tool. Think it's ready for action. View attachment 136722 View attachment 136723 View attachment 136724 View attachment 136725 View attachment 136726

Officially christened. Well done.

 

[Richard.]

Take some diameter readings see what tolerances you can hit.
These are as good as I can get
Top middle and bottom of a 90mm cut. Aimed for as close to 32mm as possible.