Reversing a lathe
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graduate_owner
Established Member
If you do manage to reverse the rotation, watch out for the chuck undoing while running. It happened to me - scary!!
K
K
CHJ
Established Member
Assuming your machine has the 3phase motor and electronic inverter variable speed then it is possible.
Any competent machine tool electrician should be able to do it for you.
Dependant upon which inverter is used within the control box, there should be an option to switch direction via a low voltage input connection on the inverter. It probably has a fixed wire link in it now, it would just need a two way switch to connect the common point to a Right or Left rotation terminal.
Alternate would be a mains rated two pole three position switch to swap any two of the three wires going to the motor, a copy of the wiring diagram or some good photographs of the box to motor wiring would be needed to point you in the right direction though.
Any competent machine tool electrician should be able to do it for you.
Dependant upon which inverter is used within the control box, there should be an option to switch direction via a low voltage input connection on the inverter. It probably has a fixed wire link in it now, it would just need a two way switch to connect the common point to a Right or Left rotation terminal.
Alternate would be a mains rated two pole three position switch to swap any two of the three wires going to the motor, a copy of the wiring diagram or some good photographs of the box to motor wiring would be needed to point you in the right direction though.
Chas
Does reversing via the inverter do a soft slow down/soft reverse ramp up? If not, is flicking the reverse switch while the machine is rotating likely to cause problems. (I've no idea, but was thinking of the problems that can occur with the Dewhirst reversing switch on a ML&/Super 7)
Does reversing via the inverter do a soft slow down/soft reverse ramp up? If not, is flicking the reverse switch while the machine is rotating likely to cause problems. (I've no idea, but was thinking of the problems that can occur with the Dewhirst reversing switch on a ML&/Super 7)
CHJ
Established Member
dickm":1impdjmr said:
On my Poolwood the Inverter soft ramps down and soft ramps up in the changed direction, that's the way I have the options set, I prefer a slow start up, gives me more time to react if somethings amiss or forgotten.
The inverter connections are shown below, other makes will have very similar wiring options, the direction FWD-REV. switch is in the digital inputs section..
Re- ML7 etc., that's why most reversing switches should be a drum switch with a center off posoition so that the NVR is in circuit and drops out.
Most older mechanical lathes have a motors with the start windings brought out so that the connections can be reversed, switching these without first stopping the motor can be quite destructive.
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CHJ
Established Member
![211314_s[1].jpg](https://cdn.imagearchive.com/ukworkshop/data/attach/9/9555-211314-s-1-.jpg "211314_s[1].jpg")
Sorry, I'll admit up front that I don't know a great deal about lathes, but is it not practical to work on the piece from the other side of the lathe so the piece appears to revolving in the opposite direction?
CHJ
Established Member
nanscombe":396s20so said:
Only for those folks that have access to both sides of the machine, even then it means turning 'left handed' for most folks, not easy without a lot of practise with a bowl gouge.
The other aspect is safety, a lot of lathes have fixed controls and can't easily be switched off in emergency from the rear face.
80% + of lathes are mounted close to a wall in small workshops so there is no access to the rear.
Even in a large workshop they are rarely out in the middle of the shop wasting floor space for the odd occasion when reverse turning would be useful.
chipmunk
Established Member
Hi Nigel,
It is pretty handy for scraping and sanding the inside of bowls to put the lathe in reverse and to work leaning across the lathe cutting on the opposite side. I'm not proficient enough to have tried wielding a bowl gouge on the opposite side, but in theory there's nothing wrong with that too I suppose.
The problem about the chuck or faceplate unscrewing is a real one though as graduate_owner says. Unfortunately only a few spindle thread options have a locking mechanism (usually set-screws biting onto the spindle behind the threaded section).
Certainly M33 x 3.5 threads often have locking means but I've never seen a 3/4" x 16TPI threaded chuck or faceplate with set screws. So I wouldn't risk it unless it could be modified, except perhaps at low revs for sanding.
It's worth considering that the length of 16TPI thread of a CL4 will unscrew completely in about 10-11 turns which even at 700 RPM gives you less than 1 second to react with a catch. That's quite a lot of time compared to say the 8TPI thread on a Nova where you need to develop Ninja-like reflexes ;-)
HTH
Jon
It is pretty handy for scraping and sanding the inside of bowls to put the lathe in reverse and to work leaning across the lathe cutting on the opposite side. I'm not proficient enough to have tried wielding a bowl gouge on the opposite side, but in theory there's nothing wrong with that too I suppose.
The problem about the chuck or faceplate unscrewing is a real one though as graduate_owner says. Unfortunately only a few spindle thread options have a locking mechanism (usually set-screws biting onto the spindle behind the threaded section).
Certainly M33 x 3.5 threads often have locking means but I've never seen a 3/4" x 16TPI threaded chuck or faceplate with set screws. So I wouldn't risk it unless it could be modified, except perhaps at low revs for sanding.
It's worth considering that the length of 16TPI thread of a CL4 will unscrew completely in about 10-11 turns which even at 700 RPM gives you less than 1 second to react with a catch. That's quite a lot of time compared to say the 8TPI thread on a Nova where you need to develop Ninja-like reflexes ;-)
HTH
Jon
CHJ
Established Member
Although not something you want to experience by choice a chuck unscrewing is not always as disastrous as it would first appear.
If the tool rest is is close to the face of the turning of course the piece will be jambed up against it and possibly damaged.
If the tool rest does not stop it then there is usually little inertia involved in the chuck when it disengages because it must be rotationally stationary or very close to it to unwind in the first place, the only real risk in this instance is it falling off the lathe bed onto your toes.
As far as lathe spindle noses that don't have a recess at the rear of the thread then a locking screw added to your chuck rear flange is still viable, you often see comments about this then damaging the threads but in reality it is of little consequence, it just means that the last one or two threads will have a small indent mark from a screw tip biting in.
Most older lathes will have this 'behind the threads' recess, it's a function of normal screw cutting procedures to allow the disengagement of the threading cutter before hitting the location collar.
On more modern machines made using fast acting CNC machines this is not always necessary as the tooling can be disengaged automatically and fast.
If the tool rest is is close to the face of the turning of course the piece will be jambed up against it and possibly damaged.
If the tool rest does not stop it then there is usually little inertia involved in the chuck when it disengages because it must be rotationally stationary or very close to it to unwind in the first place, the only real risk in this instance is it falling off the lathe bed onto your toes.
As far as lathe spindle noses that don't have a recess at the rear of the thread then a locking screw added to your chuck rear flange is still viable, you often see comments about this then damaging the threads but in reality it is of little consequence, it just means that the last one or two threads will have a small indent mark from a screw tip biting in.
Most older lathes will have this 'behind the threads' recess, it's a function of normal screw cutting procedures to allow the disengagement of the threading cutter before hitting the location collar.
On more modern machines made using fast acting CNC machines this is not always necessary as the tooling can be disengaged automatically and fast.
Having experienced chuck unscrewing on the Mystro (yes, I know, it has grub screws to prevent this, but memory isn't what it was 
) it seems like a good idea to fit a locking screw on any reversible lathe. But probably best to use a brass grub screw, not steel. (or to fit a small brass pressure pad under the grub screw) There's been some correspondence on the Yahoo Myford site about almost invisible damage to the nose threads, caused by a steel locking screw, making it very difficult to remove the chuck.
) it seems like a good idea to fit a locking screw on any reversible lathe. But probably best to use a brass grub screw, not steel. (or to fit a small brass pressure pad under the grub screw) There's been some correspondence on the Yahoo Myford site about almost invisible damage to the nose threads, caused by a steel locking screw, making it very difficult to remove the chuck.
