3 jaw chuck runout

[mike os]

just mounted a "new" (to me) 3 jaw & dialled in a piece of bright mild steel rod, I am looking at about 0.3mm/0.011inch runout ( checked with a drill shaft & its the same)

backplate register is bang on, and less than 0.01mm runout, turned on the lathe.

Should I worry? or is this about right ( bearing in mind second hand chuck on a roundhead student)

obviously I could turn down the register, but don't know if it is going to allow me to improve matters or not, the register is there for a reason

 

[Wallace]

Check the jaw faces for wear.

 

[mike os]

negligable

 

[Digger6135]

Most 3 jaw chucks exhibit run out, it can vary with the diameter you are holding, getting a previously turned part to run true after removing and re-chucking it is a
very tall order, this is where collett chucks come in to their own, they can re-chuck material and still run true.

Digger6135

 

[roofman]

try clocking it on the backplate you might claw in 0.1

 

[Mr shiney]

It doesn't make much difference, once you start cutting the piece will run true to the tool which is what you want. If you want truly accurate across a length that's not got part that's being cut off which is normally held in the chuck then turn between centres.

 

[mike os]

runout at the body is only 0.05/0.002, so guess it is the jaws/scroll that is worn a bit, still far better than the old one

now all I need is a couple of ******** L0 chucks.... all I want is the backplates so if anyone comes across one for scrap please bear me in mind

 

[Mr shiney]

Have you cut a test piece in it yet? What's the runout across the length of the test piece once it's cut parallel?

 

[mike os]

not yet cut anything... decided having cut a load of cast to fit new chuck the lathe needed a good clean,,,, was in a bit of a mess having not been used much in the last year... degrease & scrub some of the bits are even shiny again now, fresh coolant, looks a lot better.

 

[roofman]

not yet cut anything... decided having cut a load of cast to fit new chuck the lathe needed a good clean,,,, was in a bit of a mess having not been used much in the last year... degrease & scrub some of the bits are even shiny again now, fresh coolant, looks a lot better.

cutting cast on my lathes makes me cringe and cry at the same time...horrible nasty stuff. Then on the other hand i have a load of ally stock bar that gives off 10ft long razor blades and thats fun when it gets snagged on the chuck

 

[shedfull]

A 3 jaw chuck is best used for convenience, easy set up for non critical jobs or if you're going to finish the job in one go.
I've used soft jaws on the three jaw for odd jobs with not a lot to grip on.


A four jaw will let you set up for a second op and get the accuracy you want.

I use a collet chuck on my lathe ( multi size ) becausec i couldn't find a good 3 jaw

There are ways to make the 3 jaw come trule like makiing the register a bit smaller and bumping the chuck around each time then tighten the bolts but that's a bit irreversible.

I wouldn't worry about 11 thou

I hav some L0 backplates and a few catchplates I was going to convet.

Let me know if you want them

Lee

 

[mike os]

Agree Shedful et al... just wondering what would be "normal " runout for an old ish 3 jaw really... the last one was appalling, in some places there was nearly 1mm clear at the front of 1 jaw..

Been running on just a 4 jaw for a while and mentioned it in passing to a friend ( who owns the place I am borrowing machinery for the cnc build), and he said come with me... et voila as they say in mexico..... a 10" 3 jaw, which just happens to have the same PCD as the backplate, and does not fit anything he has for free , just needed to machine a spacer to adapt the 2 together, 15mm plate now 7mm thick at the edges but really pleased to have made it so accurate as having struggled with the old chuck I was not sure if the headstock was on the way out.

 

[Kent]

Ah,
Just look carefully if someone has marked numbers to co-inside with locations on each jaw (sometimes they like one way only). 4 jaw is mostly the option if you must centre to a part as other have said.

 

[mike os]

jaws are numbered and in right