Brake acts on the input pulley and at 65 revs you won't harm anything.

Stomp away.

If it has a thread dial on the lead screw, the half nuts can be released. They must then be re-engaged as the lathe is started in reverse, as the dial passes the number it was cutting at. A s

imple alternative that avoids any drastic braking.

Whether or not the brake acts before, within or after the gearbox is bound to increase momentary loadings, which cannot be seen as the most ideal mode of operation. As an extreme, a gear could fail, but unlikely at that speed. Won't do the brake any good, either, I would think.

if the lathe has reverse and a rear toolpost you can cut a thread in the "unscrewing" direction which saves the panic to stop the lathe. The tool needs to be upside down and even if between centre turning there is usually more space at the right hand end to bring things to a gentle halt.

(Edit: sorry missed the bit about limited space either side of the thread. I'll get my coat)

John

Edited By Journeyman on 02/11/2016 09:02:41

Thats the official way of cutting non-native threads on a Smart & Brown 1024 VSL. Albeit via the big red button rather than a foot bar. So nowt wrong with the principle unless serious engineering cock-up has been made so the brake engages before the motor drive drops. On my 1024 there is a very short, but distinct, pause after the motor power is cut before the brake hits. About 1/2 turn of the chuck at the 55 (ish) rpm I was using to do 14 tip on my metric 1024 yesterday.

Motor may be a bigger issue. Single phase ones don't like too many starts in quick succession as the starter winding doesn't get a chance to cool down and can eventually overheat. Even high quality ones tend to be specified for around 10 or less starts per hour. In practice how bad too many starts is probably depends on loading. I guess the book refers to the motor being used at its rated start load capacity so the starter winding would be working hard. Lathe spins up under pretty light load viz:- chuck, work, drive and gearbox innards. Not insignificant but nothing like full motor capacity.

This is the one time where VFD driven three phase motor is not an advantage as you need a finite time to spool down the motor unless you want to trespass on the overload safety margin by simply dropping the input contactor out. Can be OK if you have a decently oversize VFD with a inherently good overload capability, like the Whole Shop set-ups Drives Direct sell, but pretty much a no-no for a matched VFD & motor combination.

Clutch is nicer. I keep wondering if there is a way to get one on my 1024.

Clive.

TNot when he is cutting imperial threads on a metric lathe, surely?

It does not make a jot of difference whether metric to imperial or vice versa. One is only reversing the screw until the same point on the dial, the rest of the reversing is with the half nuts engaged. It is simple and it works. One does not leave the lathe running for an unlimited time, so reversing the screw after stopping the lathe immediately simply drops those half nuts in exactly the same place as a few seconds before. Try it. I think doubleboost has demo'd it as he was as sceptical as I was (had always been told you could not disengage the half nuts, even for an instant, during a threading operation such as this). Think of actually stopping the lathe, disengaging the half nuts and re-engaging. Not a lot of difference, really, but an extension of just a few turns of the chuck past and back.

Since fitting a variable speed drive to my Warco BH600 I find that I never bother to disengage the half nuts when screw cutting. Just slow down and stop the spindle when the cutter reaches the desired point then retract the cutting tool to clear the threads then reverse the lathe before advancing the cutting tool again.

> With a VFD, optimising the decel ramp parameters, enabling DC injection and possibly fitting a braking resistor (if the option is available in the VFD) would be the way to go.

Probably. A braking resistor to suit a hobby sized lathe won't 'brake' the bank, one for my 0.4kW inverter is 100R 200W and costs lest than £15.

Neil