Chucks running true

[Chumley]

G'day all,

Should a chuck run true without any visible wobble?

Reason I ask is 'cos I'm having no end of problems with my setup. I have an old lathe which was refered to on another post as a 'cheap clone' although it does normally run smooth and is good for between centres work. To try my hand at bowl turning I bought the cheapest scroll chuck from a reputable supplier. The chuck didn't come with an insert to fit my threaded headstock so I bought a blank unthreaded insert and got a local metal work shop to thread it. It fits nicely on the lathe and the scroll chuck fits nicely on the insert. But when I turn the lathe on I can see the chuck wobble until it gets going, then I can see the double image which is showing me its not running true.

I'm fine when I put a blank in using the chuck's centre thread and the tailstock and true it up, maybe turn the outside of a bowl or cup and make a foot - but when I turn the bowl around and put it in the scroll chuck I have to re-turn the outside of the bowl to get rid of that double image thing.

Hence my question - should the chuck be turning true? And if so, is the reason its not running true due to the lower quality lathe and chuck? Do more expensive modern lathes with more expensive modern chucks have this problem too?

Cheers,
Adam

[Big Shed]

Short answer? Yes it should run true.

So, why doesn't it?

I would start with the prime suspect, the insert. Take it out of the chuck and just put it on lathe head stock shaft by itself. Does that run true? If visbly true, put a dial indicator on it ($25, well worht the money). Run the shaft by hand and see the deflection of the dial indicator.

I had a similar problem with a Nova G3 chuck I bought, it didn't run true either. Turns out (sorry:rolleyes:) that the insert supplied with it was not a Nova insert. Once DJ got to it on his lathe and made sure it seated properly in the chuck all was well.

The chuck should seat properly on the shoulder of the insert, that could also be your problem.

Hope that helps:2tsup:

Oh BTW, I have a "cheap clone" wood lathe as well, AKA MC900.

[Ed Reiss]

Absa-posi-tuitly. If the shaft or chuck aren't running true problems just get compounded to the point where trying to get straight cuts just ain't happenin'.

Take the time to thouroughly check out the mechanical alignments...once those are set, it'll be "sweet" turning from then on.:2tsup:

[Chumley]

Thanks,
I'll check out the insert.
Cheers,
Adam

[NeilS]

Hi Chumley,

I know your problem very well. Had to get an insert made up for a left-hand thread that wasn't available for a Nova chuck. Despite several returns to the machine shop to get it fixed I never did get it to run true. As you say, the problem is always manifest when you reverse chuck a bowl, and the larger the diameter the more accentuated the 'wobble'. It seems to me that most 'local' machine shops don't work to the tolerances we need. Yes they can usually cut a thread to size, but don't get the two threads aligned. If they have to re-chuck the insert to cut the second thread the problem is almost inevitable.

If you can't find an off-the-shelf insert I suggest you look for a machine shop that specialises more in this type of work. A TAFE engineering school may be another option.

Sorry to say it, but that slightly more expensive chuck may start to look not so expensive before you have this one solved.

Neil

[RETIRED]

The machine shop needs to fit the insert to a threaded mandrel and seat against the shoulder and THEN cut the outside thread.

[Jim Carroll]

When the insert was drilled and tapped did the machine shop have the chuck.

The insert should be put into the chuck then the chuck inserted into a 4 jaw chuck and trued to run true. You can then be sure that the insert will be drilled and tapped true to your chuck then should run perfect on your lathe.

Make sure the insert fits into the chuck all the way and then seats up properly on the lathe spindle.

[Chumley]

G'day all,
Appreciate the replies.

,
It was the inside of the insert that I got threaded - the outside fits into the chuck.

Jim,
Yeah, realise that now - at the time I was young and foolish - just gave them the insert without too much thought about tolerances and accuracy.

Neil,
I might spend a bit more money before upgrading, but not that much. I think I'll try a longworth chuck - there's quite a bit of info around and I can make a chuckable faceplate - I figure if I keep it lined up the same way each time I chuck it up it should be pretty accurate.

I'm still trying to figure out if I want to spend lots of money on turning - I've done ok with spindle turning, but with bowls I can't keep the damn things on the lathe long enough to decide:-

Cheers,
Adam

[RETIRED]

G'day all,
Appreciate the replies.

,
It was the inside of the insert that I got threaded - the outside fits into the chuck. AH SO! In that case Jims is the best way to go.:D

Jim,
Yeah, realise that now - at the time I was young and foolish - just gave them the insert without too much thought about tolerances and accuracy.

Neil,
I might spend a bit more money before upgrading, but not that much. I think I'll try a longworth chuck - there's quite a bit of info around and I can make a chuckable faceplate - I figure if I keep it lined up the same way each time I chuck it up it should be pretty accurate.

I'm still trying to figure out if I want to spend lots of money on turning - I've done ok with spindle turning, but with bowls I can't keep the damn things on the lathe long enough to decide:-

Cheers,
AdamSounds like you need to go to a club and get some tuition.:D

[rsser]

+1 to tuition.

Course you learn most by your mistakes.

But life is short and you can get the benefit of other buggers having learned from theirs ;-}

[woodwork wally]

Hi chumley. Don't mess with the insert any longer Get another insert and do it right as per J.C. or . cos then you can turn till you are done. the insert has to but up to the shaft thread end and the chuck to the insert . If you cant get this part right then the longworth chuck is gunna be a hassle too. Been there done that If the shoulder on the lathe thread is true and all the mating surfaces mate correctly WOBBLEGONECHUMLYHAPPYBOWLSGREAT yes join a club if you can and pick the brains of those who have already walked the path No one can pick the real one now there are so many clones anyway Cheers and enjoy as a hobby that can be self supporting WW. Wally

[Chumley]

Sounds like you need to go to a club and get some tuition.:D


I know (and I agree), but the club here meets on wednesday nights and that's already taken.:C

Cheers,
Adam

[Robomanic]

I found that the insert screwed up the the shoulder on my first lathe, but the outer diameter of the shoulder was very close to the inner diameter of the insert. That combined with the flats cut on the shaft meant that as it screwed up the insert and shaft were actually deforming and throwing it off center. Treating it is tricky but it can be fixed if it is in fact contributing to your problem.

Good luck with it though, it is worth it :)