My ( Harrison M250 lathe ) I had it on a 2 pole motor for many years and ran off a VFD at 25Hz to get the right speed. It stopped on a dime ! I bought a new 4 pole motor and this improved the finish but now the same VFD needs 0.5secs to stop the machine. WAAAAY longer than before. Big irritation for threading as I am not a machinist and lack practice. I only use the lathe for simple things like making laps and the like. The VFD is an Altivar 2.2Kw single to three phase I bought around 2000 and until now was absolutely trouble free.
Anybody might now why the 4 pole motor takes much longer to stop and what's to be done about it ? Both motor 1.5Kw and same frame size.
You needed greater inertia for a smoother finish. You GOT greater inertia.
A half-second full-stop, no DC plugging, nor even braking resistor pak and a VFD as can even USE such.. read "not many" .. is actually rather remarkable.
A common default - even on four-quadrant AKA "regenerative braking" Dee Cee drives is around TWO seconds. That can be beaten with "active electronics", and by a LOT!
But why?
If you have an operational NEED to better that figure? You can add a seriously harder stop with a mechanical brake, be it foot, air, hydraulic, or electrically triggered.
Many, if not MOST Machinists have long been comfortable enough doing our work on lathes that had NO formal braking systems .... of
any kind.
So.....it makes far more sense at less stress - on the lathe, its systems, and even the operator - to use a method of working that just doesn't NEED anything special as to braking.
Threading? Full sixty years since I was taught... as MOST in the "no brakes" era were taught.. to thread AWAY from a shoulder or other feature as would otherwise have required a repeatable stop-point.. and no longer gave the least damn ...once the "end" ran ..... off.
Into ignorant
air. Instead of
into.. a shoulder!
It wasn't just clever old greybeards, nor young "superstars".
All-hands needed to know how to do this.
Some of our lathes? The workholder, spindle, drive train, then workpieces massed... in the multiple TONS. Lot of "drama" yah try to call a halt, abruptly, to a matched pair of massive railcar wheels already on on their axle. For any reason.
There are PM threads "reverse threading", "threading in reverse". Also search on "upside down" or "back tooled threading".
You Tube videos exist as well. Grain of salt. Not all those who publish such things are so good that they
should publish!
No fear. So long as you grok the concept, the "execution" of any new idea is on you, not they, in any case.
And you do good work. Because you give a damn. Yah?
PS: Altivar... year 2000? ISTR the "71" family wudda been their top-end around 20 years ago? My 10 HP one was made in Indohooliga, later ones in China. Group Schneider tends to "get around".
Welll it is about ten years overdue for a refresh of its capacitor bank with new cans. They die of old age as well as from stress. And phase-conversion, 1-P to 3-P IS "stressful". So "new", not "NOS", ELSE don't bother. Good luck even FINDING "new" that meet the spec and also FIT! I'd plan on having to mount them outboard.
Except that...
A new VFD will generally be cheaper, if not also better, than caps alone, yah but avoid the junque. Might want to start budgetting? A year 2000 VFD is getting rather ripe for failure. Even if it sat on the shelf 19 out of 20 years.