Using a fixed steady to support long work on a lathe

[digiex-chris]

I've got something to stick on my lathe that's longer than fits between centers. If I mount it with a steady at the tailstock end, how can I ensure I've got the work adjusted in the steady so that it's running on the centerline of the lathe and not flexed off center? Dial indicator doesn't work because the work is running true relative to the steady and only indicates out of round work. It's tough to eyeball that the rollers are only lightly touching, because I need a fair amount of pressure to keep deflection down because I'm cutting a hard material and need some pressure at the tool bit. Besides, there's going to come a day when eyeballing accuracy isn't good enough. Any ideas?

 

[MuellerNick]

There are three ways (or more):
DI on the saddle and move it along the work. Both in the horizontal and vertical plane. This assures that the work is along the bed's axis.

Clamp in chuck, do not support it with the steady rest, align to run true, and -while the DI touches work- adjust the steady rest's jaws. Might not work with long pieces.

Center bore, support with TS, adjust steady rest, retract TS.


Nick

 

[MachineTom]

In addition to the above, you can just measure the D, as you go, adjust the steady so there is no taper in the work, assuming you are turning the D, not just working the face.

 

[MuellerNick]

In addition to the above, you can just measure the D, as you go, adjust the steady so there is no taper in the work, ...

Not the best way.
If the TS-end is above or below CL, you don't detect that. But the workpiece will wiggle in the jaws and work lose.


Nick

 

[xpylonracer]

Hi Chris, In the case you describe I normally turn a stub in the chuck ( only long enough to fit the steady fingers) to exact diameter of the long bar, clamp the steady on the bed close to the chuck and adjust the fingers to give required contact on the turned diameter, once fingers set and locked off open the steady, reposition the steady to the tailstock end, lock down and then ready to fit the long bar to turn end or face/bore/thread or whatever. If your bed isn't twisted accuracy should be OK.
Rgds, Emgee

 

[digiex-chris]

wow, it's simpler than I'd expected. Happy for that! Thanks everyone! Sweeping the top and the side seems like it would account for any bed twist too, no?

 

[rcaffin]

I've got something to stick on my lathe that's longer than fits between centers.

However, what often happens is that you get a resonance of some sort or other and end up with a spiral ellipse rather than a straight surface. Not always, but it happens.

Cheers

 

[digiex-chris]

how would you deal with that? low rpm and a traveling steady as well?

 

[rcaffin]

I tried ... many ways. None were good.
The most successful, which was not very good, was to machine a few cm at the chuck end at a time, and to feed the machined bit through the chuck. But the result was that the machining drifted off-centre after a while because I could not keep the rod perfectly aligned to the axis of spin at the start. Yeah, only microns, but they grew.

In the end, I chopped the long rod into short lengths (which was what I really needed anyhow) and machined each one separately. That worked for me.

Now, if the rod you are trying to machine is sufficiently large in diameter, using a couple of steadies would work. That's how they machine prop shafts for destroyers ... on an enormously long lathe. Not many of them around the world though.

But if what you want to machine is thin and steel, centreless grinding is much the better solution. Get a quote.

Cheers

 

[lensman57]

I've got something to stick on my lathe that's longer than fits between centers. If I mount it with a steady at the tailstock end, how can I ensure I've got the work adjusted in the steady so that it's running on the centerline of the lathe and not flexed off center? Dial indicator doesn't work because the work is running true relative to the steady and only indicates out of round work. It's tough to eyeball that the rollers are only lightly touching, because I need a fair amount of pressure to keep deflection down because I'm cutting a hard material and need some pressure at the tool bit. Besides, there's going to come a day when eyeballing accuracy isn't good enough. Any ideas?

Hi,

I mabe a bit late with the reply but this is the way that I'd do this.
Forget turning between centers or the tail stock.
Use the 4 jaws independent and dial the work in to run true, then use the steady as close as possible to the chuck. Make sure that the fingers touch the work but do not put too much pressure on them so to deflect the bar.
Loosen the top finger only and move the steady to where you want it to be and then let the top finger come into contact with the bar and lock down . Grease the fingers and make the cut.

Hope this helps,

Regards,

A.G

 

[rake60]

You can indicate round at the chuck and at a fixed steady rest quite easily.
BUT, the height from the chuck to the steady rest is important!

It the steady rest center is low compared to the chuck, the stock will "walk" into the chuck.
If the steady rest center is higher than the chuck center the stock will "walk" out of the chuck.
That can become a potentially dangerous condition.

Rick