Reverse direction turning safety

[ALB]

Hello all,
A very noob question:

My lathe chuck screws onto the spindle, and is held tight by the spindle turning in the usual direction. If the direction of rotation is reversed, what is to prevent the chuck from gradually unscrewing and potentially flying off to destroy whatever it hits? It seems many lathes have a reverse function and I have not worked out how this is to be prevented. Is a particular chuck type required, or an accessory that will lock a chuck onto the spindle? Or something else entirely?

Thanks in advance,
Alun

 

[TRITON]

Can I ask why you need it to turn in the opposite direction ?.
Not that I have any helpful knowledge of this, its purely out of interest.

 

[Inspector]

The chuck would usually have a setscrew, preferably with a brass tip, tightened to a shoulder after the threads. Some spindles don't have a flat area and the screw bears on the threads.

Reverse is usually just for sanding but sometimes turning inside a deep vessel is easier on the opposite side. IE on the side away from where you stand rather than the same.

Pete

 

[alex robinson]

Unless there is a locking screw holding it in place, very little!

I would love a reverse function - it makes sanding a lot easier.

 

[ALB]

Thanks - I suspected some sort of mechanism was required.

I just bit the bullet and ordered one of the Axminster AT350s on clearance and noted it had a reverse option. I don't have a specific need for it, but have seen it done - particularly for sanding - and was curious! No specific plans to use it but I suppose it could be useful for work between centres.

 

[sawtooth-9]

Is it a wood lathe or metal lathe ?
With a wood lathe - probably not too important to have reverse.
But with a metal lathe - sometimes it is necessary.
Cam lock chuck mounts overcome this problem.There are some other systems ( seen on some Harrison lathes and US lathes ) - but none as good as cam lock.
So, if you just have a right hand threaded chuck mount - BEWARE

 

[Fergie 307]

Biggest risk is in stopping it if running in reverse. If the spindle stops too quickly the chuck keeps rotating and unscrews itself with sometimes spectacular, and terrifying, results. So make sure it is secured and take it easy, slowing down gently to a stop. As Sawtooth-9 says many metal lathes, in fact all decent modern ones, have locking systems that overcome this issue entirely.

 

[Phil Pascoe]

I can well imagine. If I stop my lathe without slowing it down it'll launch the chuck and large blank when it's running forwards.

 

[Sideways]

Biggest risk is in stopping it if running in reverse. If the spindle stops too quickly the chuck keeps rotating and unscrews itself with sometimes spectacular, and terrifying, results. So make sure it is secured and take it easy, slowing down gently to a stop. As Sawtooth-9 says many metal lathes, in fact all decent modern ones, have locking systems that overcome this issue entirely.

So true !
I renovated a Union Jubilee lathe once, screwed on the outboard turning faceplate (12" diameter or more ?) and had exactly this happen when I switched it off. The plate unscrewed itself, jumped off and rolled away down the workshop with me chasing after it ...

I really wouldn't want to see this happen with a 20lb plus engineering lathe chuck.

 

[Sandyn]

I had a chuck spin off my metal lathe while turning a screw thread. I leave the half nut engaged and spin the late back to the start for thread cutting. It gave me a fright, because my instinct was to catch it and I did, but it could have been nasty with some odd bit of metal in the chuck. I 3D printed a spindle lock which allows me to really tighten the chuck. I also regularly check if I run it in reverse. My chuck is just a small 5"

 

[johnwalls26]

Have you checked the chuck manufacturer's instructions for this? My Nova chuck has a set screw with a tiny leather disc to secure it to the spindle.

 

[Bob Chapman]

Biggest risk is in stopping it if running in reverse. If the spindle stops too quickly the chuck keeps rotating and unscrews itself with sometimes spectacular, and terrifying, results. So make sure it is secured and take it easy, slowing down gently to a stop. As Sawtooth-9 says many metal lathes, in fact all decent modern ones, have locking systems that overcome this issue entirely.

Fergie is correct in warning of this danger but has got his directions muddled. A sudden stop will unwind a chuck when the lathe is going forward. ( The chuck continues to turn when the spindle stops) With the lathe in reverse, a sudden stop will tighten the chuck onto the spindle. Either way it's a situation to be cautious of.

 

[Fergie 307]

Fergie is correct in warning of this danger but has got his directions muddled. A sudden stop will unwind a chuck when the lathe is going forward. ( The chuck continues to turn when the spindle stops) With the lathe in reverse, a sudden stop will tighten the chuck onto the spindle. Either way it's a situation to be cautious of.

You are quite right of course, doh.

 

[bertterbo]

I find the reverse functionality very useful but only in specific situations, and only really to make it more comfortable for me in that it means not having to bend over the bed bars so much. A rotating headstock can help, but sometimes you don't want to adjust the current setup.

Can't say I've tried sanding in reverse. If its power sanding or using a rotatory sander, you can just flip the direction. But for hand sanding, I guess its so you can flip the fibers back (and forth)? so makes it more efficient?

 

[Fergie 307]

Slightly off topic but i wonder if this is something to bear in mind when using a vfd on a three phase machine. Many of them incorporate quite powerful braking. I have a Huan Yang on my Harrison. Just on the factory default settings moving the lever from forward to stop will bring a heavy 8 inch chuck to a dead stop from 1200 rpm in about 3 seconds, dont know whether that might be enough to loosen a screw on type, especially with a heavy piece of work attached. Mine has an L00 taper fit so not an issuefor me.

 

[Phil Pascoe]

If you ran the lathe in reverse and suddenly stopped the workpiece, the chuck would unscrew. That's why the chuck need securing. In the normal direction it's the other way around - if the spindle stops and chuck doesn't it may unscrew and fly off.

 

[Fergie 307]

Yep, i was thinking of a stoppage, where of course the question was about reverse running. Senior moment on my part

 

[Duncan A]

Not always practical, but bringing up the tailstock will prevent the chuck unscrewing itself because it has nowhere to go
Duncan

 

[Paul Hannaby]

If you ran the lathe in reverse and suddenly stopped the workpiece, the chuck would unscrew. .

It's the other way round - Stopping the lathe sudddenly in reverse would wind the chuck on, not off.

Another reason for reverse on a lathe - one of my lathes has a right hand thread on both ends of the spindle so when turning outboard, you put the lathe in reverse.

 

[Phil Pascoe]

I said stopping the workpiece, not the lathe.