Screwcutting away from a shoulder with the tool behind the work, facing the bottom of a recess from the ctr outwards, taper turning to keep the topslide set the same for the male & female part, left hand threadcutting, putting metal back on when you have cut too much off.

J

Edited By JasonB on 23/08/2015 14:14:06

reversing useful for tapping,and threading with sliding die holder.preferable with a lathe that has methods of securing the chuck other than a threaded mandrel. Single phase motors should not be continually switched to forward or reverse,they can overheat and burnt out,most single phase motors have a rating stating the maximum starts per minute,not stamped on the motor plate but with the manufacturers spec.

Hi, neat

Regards Nick.

Years ago I used a ML7 in a near production capacity. In all the years I owned this lathe I had the chuck come loose twice.

Note loose not unscrew and fall off. I feel that this problem is vastly over rated and just churned out ad hock every time this subject comes up.

In many case the operations being carried out on a small lathe require the revolting steady being used for support on a component that possibly wouldn't need it on a far larger and more rigid lathe. However it is this use of the steady that makes it impossible for the unscrewing action to start.

Both time my chuck came loose was because I was pushing the limit or doing something I shouldn't to get out of a mess.

.

No bog standard single phase motor initially and then later a two speed three phase motor, no inverter, this was pre affordable VFD's

Inverters, in my book bring an extra action to the equation in that because these things have start up and stop ramps and most can be fitted with dynamic braking then the operator tunes these to the limits.

Why I have no idea. In a commercial environment it could save 0.2 seconds and over a working day this can add up but we are talking hobby / shed environment here and it's not needed.

All it does is stress parts not designed to be stopped on a 1/12th scale model of a sixpence.

Another problem is that the back EMF from stopping a motor fast more than not errors the drive out, that's why dynamic braking was implemented.

Stop a big motor in less than 1.5 seconds and most VFD's will error out on a low volts warning meaning you have to reset the VFD.

Keep it around two seconds and it removes all the strain of having a spanner thrown in the works and you actually work faster as you don't have to keep setting the VFD.

So if you do have to run in reverse the answer is to check the chuck before hand and take things steady. Use the tailstock centre if you can and be aware it can happen.

Good thing is it never happens in a split second, unless you are running at 33,000 revs you get a warning.

You see the wobble or results of it in the work and the note changes.

Anyone who is both blind and deaf will be well advised to rest their white stick on the chuck and they will feel the vibrations.

Edited By John Stevenson on 23/08/2015 21:08:02

Michael, if the motor is single phase with a centrifugal switch on the start winding, switching direct from forward to reverse without waiting for it to slow down for the centrifugal switch to re set will surely result in the motor carrying on going forward.

This is because reversing a single phase motor alters the connection of the start winding, but if the start winding is disconnected by the centrifugal switch, it won't know.

John,

Thanks for the reply, but I still don't understand fully.

Say I'm screwcutting a metric thread and want to leave the drive nut permanently engaged, but rewind the carriage, all I need do is operate the tumble reverse. The drive to the shaft is reversed and so the carriage moves t'other way. I can retract the tool or not as preference indicates. Yes?

You may gather from the degree of incomprehension that I have yet to cut a metric thread.

Eug

Duncan, I think you have said what I meant to say, I should read my scribbling with more care.

Mike

Good grief, makes me glad to have a proper 3-phase supply! I not sure that using braking resistors is any different to swapping two phases in order to reverse a motor. On my repetition lathe it is quite normal to reverse the motor by simply flicking a switch in the headstock. This is an electrical switch and it simply swaps two phases; there is no stopping and re-starting in between. There is a second switch on the headstock which selects one of two speeds, by changing the number of poles the motor is using. I regularly flick both switches when tapping. So, for instance, tap at 500rpm forwards, and as soon at the dog clutch on the tapping head trips flick both switches and back the tap out at 1000rpm in reverse. This also puts the spindle in the correct state for any subsequent turning, as the turning tools are behind the spindle. So 'normal' operation is with the spindle running in reverse compared to most lathes.

Andrew