I Bought a(nother) Lathe

[Doc Nickel]

You haven't yet mentioned which part is unfixable, which would force you to scrap it.

Doc.

[The Metal Butcher]

2 speed tailstock ? If it is, and I rarely say this ... then you suck...
I always wanted a 2 spd tailstock..... closest I came to it l. My HERBERT 2D has a 2 spd cross slide.

Yeah. I've always wanted one as well. That was a pretty big feature for me.

You haven't yet mentioned which part is unfixable, which would force you to scrap it.

Doc.

The ballscrew and nut, for one. Guys on PM said they were quoted between $7k to $20k for a new one. It's a special, high lead thread, you're not going to get it anywhere. Looks ok though, and obviously the handle for the carriage drives through it.
Any gear over about $100 to 150.
Spindle bearings. They feel great though.
Any other combination of parts or repairs that I deem not worth it. Been there. Done that. Learned my lesson.

[Tundra Twin Track]

Congrats,as been mentioned the 2 speed tail stock is the ticket and the 3” spindle bore is nice to have.

[Bented]

Care to explain better what you mean?

Maybe this will help: as far as I understand it, the leadscrew is fixed. It never turns. The nut is secured between (I assume) angular contact bearings, and is gear driven for all functions by the feed rod. Even the handle is geared to turn the ball nut. There is no rack on this lathe.





.

Ball screws are close to 90% efficient, they will not hold a load unless the nut or screw is locked in rotational position, load on the nut/screw assembly will cause one or the other to unscrew away from the load, this is back driving.
Many gear/motor combinations require a brake to prevent this. Most CNC lathes use servo motors that rotate to the commanded position then stop and hold preventing back driving.
Square thread and Acme lead screws often have sufficient friction to hold position if the lead angle is low. If the lead is high even an acme lead screw will back drive.

[Bob Engelhardt]

Ball screws are close to 90% efficient, they will not hold a load unless the nut or screw is locked in rotational position, load on the nut/screw assembly will cause one or the other to unscrew away from the load, this is back driving.
...

How would TMB's leadscrew be back driven? I.e., what operation would back drive it when it isn't already being forward driven?

[Bented]

How would TMB's leadscrew be back driven? I.e., what operation would back drive it when it isn't already being forward driven?

The longitudinal ball screw is not always driven.
Facing will load the carriage during a cutting operation and may back drive the screw away from the desired position if not locked.

I have had the cross feed lead screw (square thread) on manual lathes back drive during interrupted cuts, it was fascinating to watch the feed dial slowly back off in rhythm with the interruptions.
This is caused by vibration.

[754]

I cant see it ever being scrap, still useful as maybe a driveshaft lathe, or a positioned

with a pulley mounted on end of spindle could still be used for drilling..... but it takes up room..

[The Metal Butcher]

The longitudinal ball screw is not always driven.
Facing will load the carriage during a cutting operation and may back drive the screw away from the desired position if not locked.

I have had the cross feed lead screw (square thread) on manual lathes back drive during interrupted cuts, it was fascinating to watch the feed dial slowly back off in rhythm with the interruptions.
This is caused by vibration.

Manual lathes will back drive since the rack doesn't resist motion either. That's what the carriage lock is for. Thankfully, with my wonderful WNMGs, I notice very little side force even on the heaviest of facing cuts.

[boslab]

Don’t you need the motor running to shift those, some hydraulic contraption?, never used one but looks nice
mark

[The Metal Butcher]

Don’t you need the motor running to shift those, some hydraulic contraption?, never used one but looks nice
mark

Nope. All mechanical shifted.

[boslab]

Oh well lid off, selector fork must be snapped or padless
fixable though if there the right number of teeth on the gears
mark