Sherline Lathe question????

[Jeff02]

What is Acceptable run out for a 3-jaw chuck?
If I chuck a 3/8 reamer in my 3-jaw chuck and Indicate off of the reamer as close as possible to my chuck I get a 5 thou run out, when I take my chuck off and indicate off the spindle I get 0, is this acceptable for a 3-jaw chuck or should I expect better?
Because of this I have switched to a 4-jaw chuck for just about all of my turning, it takes longer to set up but it’s more accurate.

Thanks for your Help!

 

[Mainer]

It might be a little high, but not unheard-of. Typically I think one would expect a 3-jaw, new, to be within 0.003".

Whether 0.005" (or 0.003") is "acceptable" is entirely up to you. It depends on what you're trying to accomplish.

If you need concentricity, one really needs to plan to turn everything that needs to be concentric in one setup, i.e. don't plan to take the piece out of the chuck until it's complete. If for some reason you absolutely do need to remove and re-chuck a part, you can improve your odds by marking its position relative to the #1 jaw (or some jaw) and putting it back the same way.

Bottom line: you can't count on a 3-jaw chuck for precision workholding. If you need better accuracy, either use a 4-jaw (as you're doing) or a collet.

 

[rake60]

A 3 jaw chuck is not usually a high precision piece of equipment.
If the threads and faces are all clean and free of burrs that may be as good
as it gets. A slight burr or high spot on a thread or one of the faces will cause
a measured run out 2X the flaw.

Rick

 

[BillH]

You can always turn between centers as well.

 

[greenie]

Re-read the reply from MAINER, he hit it on the head with that reply.

If you really want to persist with the 3 jaw, then throw away the HARD jaws and just use SOFT jaws. OK, it's a bit of a pain having to re-cut the soft jaws all the time, but if you want accurate from the 3 jaw chuck, then it's the ONLY way to go.

That's why Sherline's main competitor, TAIG, ONLY sells it with soft jaws fitted to the 3 jaw chuck.

regards greenie

 

[black85vette]

I read an article on line about this and the author suggested opening up the jaws and running the chuck at a fairly high speed to force the jaws to the outside and then make light cuts on the inside of the jaws with a boring bar to get the jaws concentric and centered.

Does this seem reasonable to you guys?

When my lathe was new I did check my chuck which has 3 studs holding it. I measured it in each of the 3 positions for run out and then made a punch mark on the chuck where it was the best. At least I can put it back the same way every time.

 

[mklotz]

Grinding the jaws on a 3jaw, even if done properly with preload (not an easy task), will only make the jaws accurate at the particular jaw opening at which the grinding was done.

My advice is to meditate until you've finally convinced yourself that the native 3jaw is not a precision workholding device.

Any of the other suggested methods,

turn between centers
4jaw
collets
soft jaws

will, used properly, be better than a 3jaw.

The most flexible approach is the 4jaw. It's well worth your time to learn how to center work in it. I've written some hints on how to simplify that process.

http://www.schsm.com/html/centering_work_in_the_four_jaw.html

 

[rake60]

Cutting unsupported jaws could be a hazardous venture.

Tiag has their recommended method here:
Tiag Tools 3 Jaw Chuck

Rick

 

[D.C.Clark]

Sherline claims "a few thousandths" run out for their chucks. See http://www.sherline.com/1040inst.htm Mine average around 2 or 3. If you're seeing 5, consistently, at different diameters, I'd call Sherline and see if they'll regrind or replace it. Sherline's customer service is excellent.

David Clark in Southern Maryland, USA

 

[AlanHaisley]

I read an article on line about this and the author suggested opening up the jaws and running the chuck at a fairly high speed to force the jaws to the outside and then make light cuts on the inside of the jaws with a boring bar to get the jaws concentric and centered.

Does this seem reasonable to you guys?

Not a good idea with the Sherline 3 jaw chuck for several reasons:
1) As Marv says, it will only be accurate at that specific diameter.
2) Sherline chuck jaws are hardened. You would have to grind rather than bore.
3) The Sherline 3 jaw rotates the back plate against the front to move the scroll. Running it loose is likely to spin the jaws out. Bad Things will happen.