Would anyone know if a 7.5 HP 16x40 lathe would be able to run from a
10 HP idler. I am sure that power reversing would not be possible, but
would it be able to start it at higher RPM?

i

Ignoramus2991 wrote:
Would anyone know if a 7.5 HP 16x40 lathe would be able to run from a
10 HP idler. I am sure that power reversing would not be possible, but
would it be able to start it at higher RPM?

i
Not a good idea, use at least 15 HP idler, 20 is better.

Ignoramus2991 wrote:

Would anyone know if a 7.5 HP 16x40 lathe would be able to run from a
10 HP idler. I am sure that power reversing would not be possible, but
would it be able to start it at higher RPM?


At Names I think Bob Swinney indicated 1.5x the driven is the minimum mulitiplier. Bob
put on a very nice seminar on power conversion.

Wes

On 2009-05-13, Wes wrote:
Ignoramus2991 wrote:

Would anyone know if a 7.5 HP 16x40 lathe would be able to run from a
10 HP idler. I am sure that power reversing would not be possible, but
would it be able to start it at higher RPM?


At Names I think Bob Swinney indicated 1.5x the driven is the minimum mulitiplier. Bob
put on a very nice seminar on power conversion.

Would the same minimum apply if the machine in question never puts out
its nameplate horsepower? This is a 7.5 HP lathe, used for hobby
purposes.

As an argument for more idle horsepower rating, I would mention that
it takes extra power to start a lathe in high gear.

As an argument for less needed idle horsepower, I would mention the
fact that the lathe never needs nameplate horsepower.

This is in regards to a guy who wants to use one of my motors for a
phase converter. I want to make sure that he gets good advice.

i

Just a suggestion. i got in real trouble trying to start a large idler. Tell
him to use that 10 hp. if there is any trouble, add another idler motor. In
that case, you need a delay start on the second motor.

Karl

On 2009-05-13, Karl Townsend wrote:
Just a suggestion. i got in real trouble trying to start a large idler. Tell
him to use that 10 hp. if there is any trouble, add another idler motor. In
that case, you need a delay start on the second motor.

That's what I told him also 10 minutes ago. I have a unwanted 7.5 HP
motor that I will offer to him for $50. I agree with you 100%. My own
phase converter also has two idlers. I do not have time delay, but I
have a separate button to start the second idler. It is wired so that
it can only start if the first idler is running.

i

"Ignoramus2991" wrote in message
...
Would anyone know if a 7.5 HP 16x40 lathe would be able to run from a
10 HP idler. I am sure that power reversing would not be possible, but
would it be able to start it at higher RPM?

i
I'm running a mill with a 7.5HP motor on a 10HP idler, it starts at top
speed no problem although it dims the lights a bit! The mill is a horizontal
with a complex gearbox and a vertical adapter so there's a lot of mass to
get moving, I would imagine a lathe wouldn't be any more difficult to start.
One it's running, the motor load should be immaterial as the motors are
running together and act as a larger idler.
Martin
--
martindot herewhybrowat herentlworlddot herecom

On 2009-05-14, Martin Whybrow wrote:

"Ignoramus2991" wrote in message
...
Would anyone know if a 7.5 HP 16x40 lathe would be able to run from a
10 HP idler. I am sure that power reversing would not be possible, but
would it be able to start it at higher RPM?

i
I'm running a mill with a 7.5HP motor on a 10HP idler, it starts at top
speed no problem although it dims the lights a bit! The mill is a horizontal
with a complex gearbox and a vertical adapter so there's a lot of mass to
get moving, I would imagine a lathe wouldn't be any more difficult to start.
One it's running, the motor load should be immaterial as the motors are
running together and act as a larger idler.


That's very good to know. Did you try to power reverse it at top
speed, I wonder if instead of reversing the mill, the idler would
reverse instead.

i

"Ignoramus2991" wrote in message
...
On 2009-05-14, Martin Whybrow wrote:

"Ignoramus2991" wrote in message
...
Would anyone know if a 7.5 HP 16x40 lathe would be able to run from a
10 HP idler. I am sure that power reversing would not be possible, but
would it be able to start it at higher RPM?

i
I'm running a mill with a 7.5HP motor on a 10HP idler, it starts at top
speed no problem although it dims the lights a bit! The mill is a
horizontal
with a complex gearbox and a vertical adapter so there's a lot of mass to
get moving, I would imagine a lathe wouldn't be any more difficult to
start.
One it's running, the motor load should be immaterial as the motors are
running together and act as a larger idler.


That's very good to know. Did you try to power reverse it at top
speed, I wonder if instead of reversing the mill, the idler would
reverse instead.

i
I haven't tried it but I suspect the lights would go out instead! Assuming
the breaker held, then it may well cause the idler to reverse, I hadn't
thought about that; of course the feed motor and suds pump would also
reverse which could be rather confusing.
Martin
--
martindot herewhybrowat herentlworlddot herecom

On May 13, 10:24*pm, Ignoramus2991
wrote:
On 2009-05-14, Martin Whybrow wrote:



"Ignoramus2991" wrote in message
...
Would anyone know if a 7.5 HP 16x40 lathe would be able to run from a
10 HP idler. I am sure that power reversing would not be possible, but
would it be able to start it at higher RPM?

i
I'm running a mill with a 7.5HP motor on a 10HP idler, it starts at top
speed no problem although it dims the lights a bit! The mill is a horizontal
with a complex gearbox and a vertical adapter so there's a lot of mass to
get moving, I would imagine a lathe wouldn't be any more difficult to start.
One it's running, the motor load should be immaterial as the motors are
running together and act as a larger idler.

That's very good to know. Did you try to power reverse it at top
speed, I wonder if instead of reversing the mill, the idler would
reverse instead.

i

To reverse the idler, you would have to actually stall the idler and
then force it to reverse. Actually you would just need to slow it
enough to throw the phasing out of whack enough to cause the poles to
flip, but .... Anything is possible, but it's unlikely you will cause
that to happen.

More likely cause a surge on the idler mains and trip the breaker
first (assuming those are properly sized).

JW

On 2009-05-14, jw wrote:
That's very good to know. Did you try to power reverse it at top
speed, I wonder if instead of reversing the mill, the idler would
reverse instead.

i

To reverse the idler, you would have to actually stall the idler and
then force it to reverse. Actually you would just need to slow it
enough to throw the phasing out of whack enough to cause the poles to
flip, but .... Anything is possible, but it's unlikely you will cause
that to happen.

More likely cause a surge on the idler mains and trip the breaker
first (assuming those are properly sized).

Think about this. In a running phase converter, that drives a load,
the two motors form a dynamic system. You call one idler and another
load, because the "load" does something useful and the "idler" just
spins. But the motors do not really "know" who is the idler and who is
the load.

So if you reverse one of them via a reverse switch, they will both
generate forces that act against their rotations, until one stops and
reverses. Which would would it be, seems to depend on either their
rotational momentum, or their energy, or something of that sort, but I
can see how it could be the idler motor.

i

"Ignoramus2991" wrote in message
...
Would anyone know if a 7.5 HP 16x40 lathe would be able to run from a
10 HP idler. I am sure that power reversing would not be possible, but
would it be able to start it at higher RPM?

i

I have a 10HP idler in my shop and have started my 7.5HP mill motor and a
7.5HP(or 10HP, don't remember) 18" X ~72" lathe. The lathe started very
slow but it did start. I never tried power reversing.

RogerN

On 2009-05-15, RogerN wrote:

"Ignoramus2991" wrote in message
...
Would anyone know if a 7.5 HP 16x40 lathe would be able to run from a
10 HP idler. I am sure that power reversing would not be possible, but
would it be able to start it at higher RPM?

i

I have a 10HP idler in my shop and have started my 7.5HP mill motor and a
7.5HP(or 10HP, don't remember) 18" X ~72" lathe. The lathe started very
slow but it did start. I never tried power reversing.

Good to know Roger. Thanks a lot.

i

On Thu, 14 May 2009 15:03:41 -0500, Ignoramus12712 wrote:
On 2009-05-14, jw wrote:

That's very good to know. Did you try to power reverse it at top
speed, I wonder if instead of reversing the mill, the idler would
reverse instead.

To reverse the idler, you would have to actually stall the idler and
then force it to reverse. Actually you would just need to slow it
enough to throw the phasing out of whack enough to cause the poles to
flip, but .... Anything is possible, but it's unlikely you will cause
that to happen.

More likely cause a surge on the idler mains and trip the breaker
first (assuming those are properly sized).

Think about this. In a running phase converter, that drives a load,
the two motors form a dynamic system. You call one idler and another
load, because the "load" does something useful and the "idler" just
spins. But the motors do not really "know" who is the idler and who is
the load.

So if you reverse one of them via a reverse switch, they will both
generate forces that act against their rotations, until one stops and
reverses. Which would would it be, seems to depend on either their
rotational momentum, or their energy, or something of that sort, but I
can see how it could be the idler motor.

The dynamics of the relation between the two motors is "angels
dancing on the head of a pin..." If you swap the two Utility phases
to the load motor only, the RPC idler should keep turning in the same
direction and producing the phantom third leg to the load motor - but
I still would not suggest plug-reversing any motor in a home shop. For
openers, might be a bit hard on the RPC phase balancing capacitors
getting their voltages slammed around like that.

Unless the power feed to the equipment and the house Main Panel is
ridiculously oversized (and it never is...) and fortuitously
under-loaded because all the major loads are off (and they never
are...) all you are going to do is trip a breaker or blow a fuse.

If you are really unlucky and you beefed up your house panel, the
breaker or fuse that goes open is going to be on the Edison side of
the demarcation line, where you can't fix it yourself. Power
utilities use /very/ generous derating fudge factors on how many
houses they can put on one Pole Pig, and throwing huge mLocked Rotor
Amps shorts across the line is not something they allow much cushion
for - about the biggest motor they plan for is your air conditioner.

All the neighbors that share that transformer or distributuion
circuit with you, and are going to be sitting in the dark for an hour
or three until Edison comes out to reset the line, will not be very
pleased to hear about your hobby...

Industrial 3-phase power feeds *are* sized to handle the extra loads
of plug reversing - which is why commercial power rates are so much
higher, because they have to build excess system capacity that only
gets used for a few seconds a month. Where a house with a 200A Main
might be on a 10 KVA Transformer by itself (there's that over-generous
derating) an industrial building with a 200A Main and nobody sharing
the feed would have anywhere from a 25 KVA to 75 KVA can, depending on
how often you throw hefty loads on.

Not to mention you are running Locked Rotor Amps through that motor
till it spins down to a stop and then spins up in reverse. If the
power feed is hefty enough to feed 20X rated current and hold, that
still isn't good on the motor windings and normally should be avoided.
You get a deep burn in the winding insulation, and the Magic Smoke
will soon escape from that motor.

And if you must plug reverse and the equipment is up to it, you
can't do it more than two or three times in an hour with a bunch of
cool down running time in between.

-- Bruce --

On 2009-05-15, RogerN wrote:

"Ignoramus2991" wrote in message
...
Would anyone know if a 7.5 HP 16x40 lathe would be able to run from a
10 HP idler. I am sure that power reversing would not be possible, but
would it be able to start it at higher RPM?

i

I have a 10HP idler in my shop and have started my 7.5HP mill motor and a
7.5HP(or 10HP, don't remember) 18" X ~72" lathe. The lathe started very
slow but it did start. I never tried power reversing.

The *real* test is to put a heavy chuck (e.g. the typically
larger 4-jaw) on the spindle, close the jaws on something so they don't
spin loose, set for the highest spindle speed (within the safety range
of that chuck, of course), start it at that setting, and once it is up
to speed, reverse it and see what happens. The only more sever test
would be to have a maximum diameter workpiece (which will clear the
cross-slide) the length of the lathe between centers -- or perhaps
reversed jaws and the largest diameter workpiece which is short enough
to not walk out of the jaws without tailstock support. :-)

If you have variable speed pulleys, you may have to start it
first to be able to run the speed up, then stop it and re-start. With a
gearhead lathe or pure step pulleys, you should be able to set it up for
maximum speed without jumping through those hoops.

But be sure that you aren't in the path of chuck jaws or
workpieces coming loose at high speeds. They can be quite dangerous.

Good Luck,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On 2009-05-16, DoN. Nichols wrote:
The *real* test is to put a heavy chuck (e.g. the typically
larger 4-jaw) on the spindle, close the jaws on something so they don't
spin loose, set for the highest spindle speed (within the safety range
of that chuck, of course), start it at that setting, and once it is up
to speed, reverse it and see what happens. The only more sever test
would be to have a maximum diameter workpiece (which will clear the
cross-slide) the length of the lathe between centers -- or perhaps
reversed jaws and the largest diameter workpiece which is short enough
to not walk out of the jaws without tailstock support. :-)

So, DoN, do you think that with the chuck heavy enough and RPM high
enough, plug reversing the lathe would actually reverse the idler?

(I believe that it is true, based on general symmetry considerations).

i

On 16 May 2009 04:18:47 GMT, "DoN. Nichols"
wrote:

On 2009-05-15, RogerN wrote:

"Ignoramus2991" wrote in message
...
Would anyone know if a 7.5 HP 16x40 lathe would be able to run from a
10 HP idler. I am sure that power reversing would not be possible, but
would it be able to start it at higher RPM?

i

I have a 10HP idler in my shop and have started my 7.5HP mill motor and a
7.5HP(or 10HP, don't remember) 18" X ~72" lathe. The lathe started very
slow but it did start. I never tried power reversing.

The *real* test is to put a heavy chuck (e.g. the typically
larger 4-jaw) on the spindle, close the jaws on something so they don't
spin loose, set for the highest spindle speed (within the safety range
of that chuck, of course), start it at that setting, and once it is up
to speed, reverse it and see what happens. The only more sever test
would be to have a maximum diameter workpiece (which will clear the
cross-slide) the length of the lathe between centers -- or perhaps
reversed jaws and the largest diameter workpiece which is short enough
to not walk out of the jaws without tailstock support. :-)

If you have variable speed pulleys, you may have to start it
first to be able to run the speed up, then stop it and re-start. With a
gearhead lathe or pure step pulleys, you should be able to set it up for
maximum speed without jumping through those hoops.

But be sure that you aren't in the path of chuck jaws or
workpieces coming loose at high speeds. They can be quite dangerous.

Good Luck,
DoN.


I once worked in a shop that had a couple of lathes with screw on
chucks - the mount by screwing them onto the headstock spindle. One of
the blokes used to use reverse to brake the lathe and tried it while
he was polishing something, in high gear. The chuck came off and made
about two laps around the shop bouncing off machines and walls.
Luckily, no one was hurt.

But it is kind of exciting to see a 16 inch three jaw chuck do a burn
out and launch on a concrete floor :-)


Cheers,

Bruce in Bangkok
(bruceinbangkokatgmaildotcom)

On May 16, 6:12*am, Bruce in Bangkok wrote:
On 16 May 2009 04:18:47 GMT, "DoN. Nichols"
wrote:





On 2009-05-15, RogerN wrote:

"Ignoramus2991" wrote in message
...
Would anyone know if a 7.5 HP 16x40 lathe would be able to run from a
10 HP idler. I am sure that power reversing would not be possible, but
would it be able to start it at higher RPM?

i

I have a 10HP idler in my shop and have started my 7.5HP mill motor and a
7.5HP(or 10HP, don't remember) 18" X ~72" lathe. *The lathe started very
slow but it did start. *I never tried power reversing.

* *The *real* test is to put a heavy chuck (e.g. the typically
larger 4-jaw) on the spindle, close the jaws on something so they don't
spin loose, set for the highest spindle speed (within the safety range
of that chuck, of course), start it at that setting, and once it is up
to speed, reverse it and see what happens. *The only more sever test
would be to have a maximum diameter workpiece (which will clear the
cross-slide) the length of the lathe between centers -- or perhaps
reversed jaws and the largest diameter workpiece which is short enough
to not walk out of the jaws without tailstock support. :-)

* *If you have variable speed pulleys, you may have to start it
first to be able to run the speed up, then stop it and re-start. *With a
gearhead lathe or pure step pulleys, you should be able to set it up for
maximum speed without jumping through those hoops.

* *But be sure that you aren't in the path of chuck jaws or
workpieces coming loose at high speeds. *They can be quite dangerous.

* *Good Luck,
* * * * * *DoN.

I once worked in a shop that had a couple of lathes with screw on
chucks - the mount by screwing them onto the headstock spindle. One of
the blokes used to use reverse to brake the lathe and tried it while
he was polishing something, in high gear. The chuck came off and made
about two laps around the shop bouncing off machines and walls.
Luckily, no one was hurt.

But it is kind of exciting to see a 16 inch three jaw chuck do a burn
out and launch on a concrete floor :-)

Cheers,

Bruce in Bangkok

That sounds like a good argument for a single phase motor on a belt-
driven lathe. My belt drive, threaded spindle lathe came with a 3
phase motor which I swapped for a 1 phase TEFC. If I accidentally push
the drum switch to Reverse instead of Stop the lathe just keeps
running forward. It won't reverse until it has slowed down enough to
close the start switch.

What is the lathe operation that is said to require instant reverse?

jsw

On Sat, 16 May 2009 04:08:09 -0700 (PDT), Jim Wilkins
wrote:

On May 16, 6:12*am, Bruce in Bangkok wrote:
On 16 May 2009 04:18:47 GMT, "DoN. Nichols"
wrote:





On 2009-05-15, RogerN wrote:

"Ignoramus2991" wrote in message
...
Would anyone know if a 7.5 HP 16x40 lathe would be able to run from a
10 HP idler. I am sure that power reversing would not be possible, but
would it be able to start it at higher RPM?

i

I have a 10HP idler in my shop and have started my 7.5HP mill motor and a
7.5HP(or 10HP, don't remember) 18" X ~72" lathe. *The lathe started very
slow but it did start. *I never tried power reversing.

* *The *real* test is to put a heavy chuck (e.g. the typically
larger 4-jaw) on the spindle, close the jaws on something so they don't
spin loose, set for the highest spindle speed (within the safety range
of that chuck, of course), start it at that setting, and once it is up
to speed, reverse it and see what happens. *The only more sever test
would be to have a maximum diameter workpiece (which will clear the
cross-slide) the length of the lathe between centers -- or perhaps
reversed jaws and the largest diameter workpiece which is short enough
to not walk out of the jaws without tailstock support. :-)

* *If you have variable speed pulleys, you may have to start it
first to be able to run the speed up, then stop it and re-start. *With a
gearhead lathe or pure step pulleys, you should be able to set it up for
maximum speed without jumping through those hoops.

* *But be sure that you aren't in the path of chuck jaws or
workpieces coming loose at high speeds. *They can be quite dangerous.

* *Good Luck,
* * * * * *DoN.

I once worked in a shop that had a couple of lathes with screw on
chucks - the mount by screwing them onto the headstock spindle. One of
the blokes used to use reverse to brake the lathe and tried it while
he was polishing something, in high gear. The chuck came off and made
about two laps around the shop bouncing off machines and walls.
Luckily, no one was hurt.

But it is kind of exciting to see a 16 inch three jaw chuck do a burn
out and launch on a concrete floor :-)

Cheers,

Bruce in Bangkok

That sounds like a good argument for a single phase motor on a belt-
driven lathe. My belt drive, threaded spindle lathe came with a 3
phase motor which I swapped for a 1 phase TEFC. If I accidentally push
the drum switch to Reverse instead of Stop the lathe just keeps
running forward. It won't reverse until it has slowed down enough to
close the start switch.

What is the lathe operation that is said to require instant reverse?

jsw


The shop still had some belt drive lathes, although they had all been
converted to use individual motors. Of course none of them had a brake
or any method of slowing them down and as they were 3 phase they were
all wired with forward/reverse switches so we used reverse as a brake.

As far as I can remember reverse was never used for actual machining.

Cheers,

Bruce in Bangkok
(bruceinbangkokatgmaildotcom)

On May 16, 8:13*am, Bruce in Bangkok wrote:
On Sat, 16 May 2009 04:08:09 -0700 (PDT), Jim Wilkins
[reversing a motor?]

As far as I can remember reverse was never used for actual machining.

Cheers,

Bruce in Bangkok

In a discussion of 1 vs 3 phase motors, someone once posted that
several important lathe operations require instant reversing.

Maybe I never do anything important, but I've never needed to reverse
it without stopping first. The lathe stops very quickly at the end of
a thread when the belt tension lever is released.

jsw

Iggy sez:

"So, DoN, do you think that with the chuck heavy enough and RPM high
enough, plug reversing the lathe would actually reverse the idler?

(I believe that it is true, based on general symmetry considerations)."

Give it up already, Iggy! You are not likely to find anyone that will agree with you.

Bob Swinney



"Ignoramus26671" wrote in message
...
On 2009-05-16, DoN. Nichols wrote:
The *real* test is to put a heavy chuck (e.g. the typically
larger 4-jaw) on the spindle, close the jaws on something so they don't
spin loose, set for the highest spindle speed (within the safety range
of that chuck, of course), start it at that setting, and once it is up
to speed, reverse it and see what happens. The only more sever test
would be to have a maximum diameter workpiece (which will clear the
cross-slide) the length of the lathe between centers -- or perhaps
reversed jaws and the largest diameter workpiece which is short enough
to not walk out of the jaws without tailstock support. :-)

i

On Sat, 16 May 2009 17:12:24 +0700, Bruce in Bangkok
wrote:

On 16 May 2009 04:18:47 GMT, "DoN. Nichols"
wrote:

On 2009-05-15, RogerN wrote:

"Ignoramus2991" wrote in message
...
Would anyone know if a 7.5 HP 16x40 lathe would be able to run from a
10 HP idler. I am sure that power reversing would not be possible, but
would it be able to start it at higher RPM?

i

I have a 10HP idler in my shop and have started my 7.5HP mill motor and a
7.5HP(or 10HP, don't remember) 18" X ~72" lathe. The lathe started very
slow but it did start. I never tried power reversing.

The *real* test is to put a heavy chuck (e.g. the typically
larger 4-jaw) on the spindle, close the jaws on something so they don't
spin loose, set for the highest spindle speed (within the safety range
of that chuck, of course), start it at that setting, and once it is up
to speed, reverse it and see what happens. The only more sever test
would be to have a maximum diameter workpiece (which will clear the
cross-slide) the length of the lathe between centers -- or perhaps
reversed jaws and the largest diameter workpiece which is short enough
to not walk out of the jaws without tailstock support. :-)

If you have variable speed pulleys, you may have to start it
first to be able to run the speed up, then stop it and re-start. With a
gearhead lathe or pure step pulleys, you should be able to set it up for
maximum speed without jumping through those hoops.

But be sure that you aren't in the path of chuck jaws or
workpieces coming loose at high speeds. They can be quite dangerous.

Good Luck,
DoN.


I once worked in a shop that had a couple of lathes with screw on
chucks - the mount by screwing them onto the headstock spindle. One of
the blokes used to use reverse to brake the lathe and tried it while
he was polishing something, in high gear. The chuck came off and made
about two laps around the shop bouncing off machines and walls.
Luckily, no one was hurt.

But it is kind of exciting to see a 16 inch three jaw chuck do a burn
out and launch on a concrete floor :-)


Cheers,

Bruce in Bangkok
(bruceinbangkokatgmaildotcom)
Sounds somewhat similar to the errant hard drive disk assembly from a
few years back, or the high speed bearing episode from around the same
time.
Gerry :-)}
London, Canada

On Sat, 16 May 2009 09:57:50 -0700 (PDT), Jim Wilkins
wrote:

On May 16, 8:13*am, Bruce in Bangkok wrote:
On Sat, 16 May 2009 04:08:09 -0700 (PDT), Jim Wilkins
[reversing a motor?]

As far as I can remember reverse was never used for actual machining.

Cheers,

Bruce in Bangkok

In a discussion of 1 vs 3 phase motors, someone once posted that
several important lathe operations require instant reversing.

Maybe I never do anything important, but I've never needed to reverse
it without stopping first. The lathe stops very quickly at the end of
a thread when the belt tension lever is released.

jsw

Threading toward a face is one of those - but IMO it would be both a
whole lot safer and easier to go the other way and go from the face to
off the open end. If your timing on hitting that Stop button isn't
dead-nuts perfect, you have a crash.

Or do it on a CNC machine that has a lot better reflexes than you
do, and should know precisely where the tool is at all times.

-- Bruce --

On 2009-05-16, Ignoramus26671 wrote:
On 2009-05-16, DoN. Nichols wrote:
The *real* test is to put a heavy chuck (e.g. the typically
larger 4-jaw) on the spindle, close the jaws on something so they don't
spin loose, set for the highest spindle speed (within the safety range
of that chuck, of course), start it at that setting, and once it is up
to speed, reverse it and see what happens. The only more sever test
would be to have a maximum diameter workpiece (which will clear the
cross-slide) the length of the lathe between centers -- or perhaps
reversed jaws and the largest diameter workpiece which is short enough
to not walk out of the jaws without tailstock support. :-)

So, DoN, do you think that with the chuck heavy enough and RPM high
enough, plug reversing the lathe would actually reverse the idler?

Yes, I do. Of course, that depends in part on the relative
horsepower ratings of the idler motor and the lathe's own motor. I have
read here postings by people who have experienced that with equal
horsepower on each. And *that* might be something which could be
improved somewhat by a flywheel on the idler motor -- but expect the
housing to jump around during the reversal. :-)

Tuning and balancing capacitors might change the threshold at
which this reversal happens in that they will be applying a bit of
rotational bias -- but with equal sized or smaller idlers, you still
will have the idler reverse at some set of parameters.

(I believe that it is true, based on general symmetry considerations).

Indeed so.

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On 2009-05-16, Jim Wilkins wrote:
On May 16, 6:12*am, Bruce in Bangkok wrote:

[ ... ]

I once worked in a shop that had a couple of lathes with screw on
chucks - the mount by screwing them onto the headstock spindle. One of
the blokes used to use reverse to brake the lathe and tried it while
he was polishing something, in high gear. The chuck came off and made
about two laps around the shop bouncing off machines and walls.
Luckily, no one was hurt.

But it is kind of exciting to see a 16 inch three jaw chuck do a burn
out and launch on a concrete floor :-)

[ ... ]

Bruce in Bangkok

That sounds like a good argument for a single phase motor on a belt-
driven lathe. My belt drive, threaded spindle lathe came with a 3
phase motor which I swapped for a 1 phase TEFC. If I accidentally push
the drum switch to Reverse instead of Stop the lathe just keeps
running forward. It won't reverse until it has slowed down enough to
close the start switch.

I have never *accidentally* pushed the switch through stop to
reverse.

What is the lathe operation that is said to require instant reverse?

Well ... I'll tell you why *I* want to put a three phase motor
on my lathe to replace the single phase motor which it came with, and
to add a VFD which I can program to slow down to a stop and then speed
in reverse at a reasonable rate).

1) The lathe came with a bed turret which will hold up to six 1"
shank tools.

2) It has a lever closer 5C collet setup, so there is no problem
with chucks unscrewing. (Actually, since I have replaced the
2-1/4x8 spindle with a L-00 spindle, there is no problem even
with the chucks.)

3) In the turret, among other tools, I have a releasing tap
holder. I bring the tap into contact with the pre-drilled
spinning workpiece, it bites and starts self-feeding until the
turret ram reaches the preset stop for that station, at which
point the ram stops but the tap continues into the workpiece for
another 1/8" or so before a dog clutch disengages allowing the
tap to spin with the workpiece.

4) To withdraw the tap, I must switch the spindle motor to stop,
wait for it to slow enough so the centrifugal switch clicks, and
then continue through stop to reverse. Once running in reverse,
the dog clutch re-engages so I can back the tap out of the
workpiece. (And yes, I can take the releasing tap holder apart
and reassemble with the operation of the dog clutch reversed, so
I can use it for tapping with left-hand taps as well as right
hand ones.

5) This internal threading is just one of a number of operations
on the workpiece, including knurling, turning down to a specific
diameter, and then threading that diameter (using a Geometric
die head) -- all of which can be done without stopping the lathe
spindle -- *except* for backing out the tap.

6) As a result, the tapping takes more time than most of the other
operations, since the spindle has to be slowed to near a stop,
reversed, and then (once the tap is clear) slowed to near a stop
again and started forwards.

7) Yes, I do stop the spindle to feed the stock to a stop set
in the turret -- but if I had that near-instant reverse (the VFD
will be a bit slower than plug reversing, but still pretty quick
by comparison to waiting for the single phase motor to coast
down to near a stop), I would also take the time to set up a
pneumatic stock feed tube so I could do it all with the spindle
turning. After all -- I can release the collet with the lever
when the spindle is still turning.

So -- this is at least one reason for reversing a lathe under
power, which is what you asked about.

Another reason for a three-phase motor instead of a single phase
one is that a single phase motor's start capacitor suffers from frequent
start cycles. A three-phase motor does not have that capacitor
available to fail.

Hmm ... when metric threading to a shoulder on an inch lathe or
vise versa, when the threading dial is useless, it is nice to be able to
switch the spindle to reverse as you quickly wind out the threading tool
so you don't run into the shoulder, since you don't dare disengage the
half-nuts (or you will lose the sync between the spindle and the
leadscrew).

So -- even without having the instant reverse ability on my
lathe, I have two reasons to want it.

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On 2009-05-16, Jim Wilkins wrote:
On May 16, 8:13*am, Bruce in Bangkok wrote:
On Sat, 16 May 2009 04:08:09 -0700 (PDT), Jim Wilkins
[reversing a motor?]

As far as I can remember reverse was never used for actual machining.

Cheers,

Bruce in Bangkok

In a discussion of 1 vs 3 phase motors, someone once posted that
several important lathe operations require instant reversing.

Maybe I never do anything important, but I've never needed to reverse
it without stopping first. The lathe stops very quickly at the end of
a thread when the belt tension lever is released.

This assumes that you have a belt tension lever within easy
reach. Not all lathes are made the same.

My 12x24" Clausing 5418 has the motor in the pedestal, and I
have to turn a knob several turns to open the door, and then bend down
and swing the lever from one side to the other to lift the motor and
relax the tension in the V-belt. Even relaxed, it still has significant
drive and will not simply stop -- at least until it throws the V-belt.

I presume that your lathe has a flat leather belt with the motor
mounted behind the headstock (common with South Bend lathes, at least.)

Some versions of my Clausing (but not mine) have a dog clutch
which allows switching from forward to stop to reverse while the motor
continues to run forwards. These also have a variable speed pulley
assembly controlled by a crank on the front of the pedestal.

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On 2009-05-16, Robert Swinney wrote:
Iggy sez:

"So, DoN, do you think that with the chuck heavy enough and RPM high
enough, plug reversing the lathe would actually reverse the idler?

(I believe that it is true, based on general symmetry considerations)."

Give it up already, Iggy! You are not likely to find anyone that will agree with you.

So, just to make sure, do you think that it is impossible?

Specifically, do you think that it can never happen that plug
reversing a motor, with load, running on a phase converter, would
reverse the idler instead?


Think of it as this picture.

/~~~~~\--L3---/~~~~~\
L1 -----|Idler|--L1---|Load |
L2 -----| |--L2---| |
\_____/ \_____/

As you can see, there is symmetry between idler and load and the
distinction can only be made by their relative size. So which one
reverses and which one keeps rotation, depends on which one has more
momentum. Not on which one is called "idler" and which one is called
"load".


i

On 2009-05-17, Bruce L Bergman wrote:
On Sat, 16 May 2009 09:57:50 -0700 (PDT), Jim Wilkins
wrote:

[ ... ]

Maybe I never do anything important, but I've never needed to reverse
it without stopping first. The lathe stops very quickly at the end of
a thread when the belt tension lever is released.

[ ... ]

Threading toward a face is one of those - but IMO it would be both a
whole lot safer and easier to go the other way and go from the face to
off the open end. If your timing on hitting that Stop button isn't
dead-nuts perfect, you have a crash.

Assuming that you are forced to not use the half-nuts (such as
when threading metric on an inch machine or vice versa). Otherwise, the
half nuts result in a lot quicker stop of the feed -- though you do need
a runout groove for that.

And -- you need a start groove when threading away from a
shoulder with a machine whose threading dial and half-nuts can be
trusted for the thread being cut.

I experimented while straight threading some bronze pipe and
discovered that on my Clausing I was able to withdraw the cross-feed
reliably enough to have the thread taper out instead of need a runout
groove -- though of course there was no shoulder to worry about there.
:-)

Or do it on a CNC machine that has a lot better reflexes than you
do, and should know precisely where the tool is at all times.

Indeed so -- and my Compact-5/CNC, at least, does a tapered
pull-out at the end of the thread, so it is a clean looking thread
without a runout groove (which can weaken the workpiece -- especially a
fairly thin-walled pipe.)

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

I think the backlash involved in the carriage feed on most lathes would
result in some damage to the utting tool, or the closest end of the thread.
The operator would also need to back the cutting tool away (quickly) from
the workpiece when switching to reverse (at the same time, actually).

As Jim suggested, there probably aren't many good uses for rapid reverse on
a lathe (common, manual models).

--
WB
..........
metalworking projects
www.kwagmire.com/metal_proj.html


"Bruce L. Bergman" wrote in message
...

Threading toward a face is one of those - but IMO it would be both a
whole lot safer and easier to go the other way and go from the face to
off the open end. If your timing on hitting that Stop button isn't
dead-nuts perfect, you have a crash.

Or do it on a CNC machine that has a lot better reflexes than you
do, and should know precisely where the tool is at all times.

-- Bruce --

On May 17, 1:14*am, "Wild_Bill" wrote:
I think the backlash involved in the carriage feed on most lathes would
result in some damage to the utting tool, or the closest end of the thread.
The operator would also need to back the cutting tool away (quickly) from
the workpiece when switching to reverse (at the same time, actually).

As Jim suggested, there probably aren't many good uses for rapid reverse on
a lathe (common, manual models).

--
WB

OK, so instant reverse is important for turret production and for
threading to a shoulder on a gear-head lathe that doesn't have a
brake. The other manual lathe available to me is a geared 15" Jet with
a foot brake, I haven't threaded on it or the CNC lathe yet.

My flat belt drive, back geared, threaded spindle South Bend does fine
without it. A while ago I posted about stopping a thread cold to
within thousandths by using a dial indicator. In back gear I can ease
out the bit while turning the pulley by hand, then dress up the rather
rough tapered thread end with a triangular needle file.

Maybe a threaded-spindle lathe that shouldn't instantly reverse also
doesn't need to, and can use a single phase motor.

jsw

Don Sez:

"Yes, I do. Of course, that depends in part on the relative
horsepower ratings of the idler motor and the lathe's own motor. I have
read here postings by people who have experienced that with equal
horsepower on each. And *that* might be something which could be
improved somewhat by a flywheel on the idler motor -- but expect the
housing to jump around during the reversal. :-)

Tuning and balancing capacitors might change the threshold at
which this reversal happens in that they will be applying a bit of
rotational bias -- but with equal sized or smaller idlers, you still
will have the idler reverse at some set of parameters." " Indeed so."

That "set of parameters" would have to be a reversal of polarity on the idler's two input line
leads. I'm afraid you are caught up in the erroneous premise that an idler motor and load motor
constitute a generator and load. They do not. Irrespective of rotational mass and any series
capacitance present, current flow (and torque) in each motor depends on the polarity of applied
voltage. Swap the two input (line) leads in either idler motor or load motor and that motor will
change direction. The other motor will continue to spin in the same direction as before.

In a RPC, the idler motor and load motor are not in parallel with respect to current flow. This
because of the way current must flow in the "3rd" leg to return to either side of the single-phase
line. There is no "parallel" way to connect a single phase source to a 3-phase load. For that
reason, only the inut line leads of either motor can be considered for polarity swapping in order
to achieve plug reversal.

Bob Swinney

When I'm cutting threads under power, the spindle speed is so low (about
50-70 RPM as seen on the Trexon Tachulator) that a crash into a shoulder
isn't very likely, as long as I'm paying attention.

The motor is a TEFC PM 90V DC motor, and the drive doesn't even have a
braking circuit/resistor. The spindle stops within about 1/2 revolution, so
there isn't any need for evasive action.
The 3L V-belt provides enough resistance/friction, and the combined mass of
the spindle, chuck and motor armature isn't great enough to keep
freewheeling for several rotations.

--
WB
..........
metalworking projects
www.kwagmire.com/metal_proj.html


"Jim Wilkins" wrote in message
...
On May 17, 1:14 am, "Wild_Bill" wrote:
I think the backlash involved in the carriage feed on most lathes would
result in some damage to the utting tool, or the closest end of the
thread.
The operator would also need to back the cutting tool away (quickly) from
the workpiece when switching to reverse (at the same time, actually).

As Jim suggested, there probably aren't many good uses for rapid reverse
on
a lathe (common, manual models).

--
WB

OK, so instant reverse is important for turret production and for
threading to a shoulder on a gear-head lathe that doesn't have a
brake. The other manual lathe available to me is a geared 15" Jet with
a foot brake, I haven't threaded on it or the CNC lathe yet.

My flat belt drive, back geared, threaded spindle South Bend does fine
without it. A while ago I posted about stopping a thread cold to
within thousandths by using a dial indicator. In back gear I can ease
out the bit while turning the pulley by hand, then dress up the rather
rough tapered thread end with a triangular needle file.

Maybe a threaded-spindle lathe that shouldn't instantly reverse also
doesn't need to, and can use a single phase motor.

jsw

On Sun, 17 May 2009 15:58:26 -0400, "Wild_Bill"
wrote:

When I'm cutting threads under power, the spindle speed is so low (about
50-70 RPM as seen on the Trexon Tachulator) that a crash into a shoulder
isn't very likely, as long as I'm paying attention.


50-70 RPM????????

Geeze

I cut threads at 500-800 rpm on a manual machine.

Course..I do have Hardinge HLV-hs......

giggle


Gunner

"Somewhere a True Believer is training to kill you. He is training with
minimum food or water,in austere conditions, day and night. The only thing
clean on him is his weapon. He doesn't worry about what workout to do---
his rucksack weighs what it weighs, and he runs until the enemy stops chasing him.
The True Believer doesn't care 'how hard it is'; he knows he either wins or he dies.
He doesn't go home at 1700; he is home. He knows only the 'Cause.' Now, who wants to quit?"

NCOIC of the Special Forces Assessment and Selection Course in a welcome speech to new SF candidates

"Ignoramus8051" wrote in message
...
On 2009-05-16, Robert Swinney wrote:
Iggy sez:

"So, DoN, do you think that with the chuck heavy enough and RPM high
enough, plug reversing the lathe would actually reverse the idler?

(I believe that it is true, based on general symmetry considerations)."

Give it up already, Iggy! You are not likely to find anyone that will
agree with you.

So, just to make sure, do you think that it is impossible?

Specifically, do you think that it can never happen that plug
reversing a motor, with load, running on a phase converter, would
reverse the idler instead?


Think of it as this picture.

/~~~~~\--L3---/~~~~~\
L1 -----|Idler|--L1---|Load |
L2 -----| |--L2---| |
\_____/ \_____/

As you can see, there is symmetry between idler and load and the
distinction can only be made by their relative size. So which one
reverses and which one keeps rotation, depends on which one has more
momentum. Not on which one is called "idler" and which one is called
"load".


i
I think Bob Swinney is saying the same thing, the motors are not identical.
One does not have its power connection momentarily disconnected, and likely
has capacitors which also remain connected.

I understand the idea that the idler might reverse and have read some
reports of it doing so. I have also read that a flywheel does and does not
effect the surge capability of the idler. The opinions of those I feel most
likely correct are that the idler will not reverse. I personally start a 5HP
K&T mill or a 7.5HP Cincinnati 24" shaper almost instantly on a pretty well
balanced 5HP idler. Both machines have clutches and I have to need to
reverse the motor on either.

If one must or wants to plug reverse from an idler, I would suggest that
they try it and see whether it works or not as I am not sure there is a
definitive answer for all cases. It seems rather hard on the motor,
contactor, etc.. I do enjoy the discussions.

Don Young

On 2009-05-18, Don Young wrote:
I think Bob Swinney is saying the same thing, the motors are not identical.
One does not have its power connection momentarily disconnected, and likely
has capacitors which also remain connected.

Well, capacitors are somewhat extraneous to the question, as there are
phase converters without capacitors.

I understand the idea that the idler might reverse and have read some
reports of it doing so. I have also read that a flywheel does and does not
effect the surge capability of the idler. The opinions of those I feel most
likely correct are that the idler will not reverse. I personally start a 5HP
K&T mill or a 7.5HP Cincinnati 24" shaper almost instantly on a pretty well
balanced 5HP idler. Both machines have clutches and I have to need to
reverse the motor on either.

If one must or wants to plug reverse from an idler, I would suggest that
they try it and see whether it works or not as I am not sure there is a
definitive answer for all cases. It seems rather hard on the motor,
contactor, etc.. I do enjoy the discussions.

I have a 4 HP Ametek motor, and a 3 HP lathe. (same proportion as a
7.5 HP lathe on a 10 HP idler). I need to finish a couple of projects,
and I may try to do an experiment.

i

On Sun, 17 May 2009 11:32:33 -0500, "Robert Swinney"
wrote:

Don Sez:

"Yes, I do. Of course, that depends in part on the relative
horsepower ratings of the idler motor and the lathe's own motor. I have
read here postings by people who have experienced that with equal
horsepower on each. And *that* might be something which could be
improved somewhat by a flywheel on the idler motor -- but expect the
housing to jump around during the reversal. :-)

Tuning and balancing capacitors might change the threshold at
which this reversal happens in that they will be applying a bit of
rotational bias -- but with equal sized or smaller idlers, you still
will have the idler reverse at some set of parameters." " Indeed so."

That "set of parameters" would have to be a reversal of polarity on the idler's two input line
leads. I'm afraid you are caught up in the erroneous premise that an idler motor and load motor
constitute a generator and load. They do not. Irrespective of rotational mass and any series
capacitance present, current flow (and torque) in each motor depends on the polarity of applied
voltage. Swap the two input (line) leads in either idler motor or load motor and that motor will
change direction. The other motor will continue to spin in the same direction as before.

In a RPC, the idler motor and load motor are not in parallel with respect to current flow. This
because of the way current must flow in the "3rd" leg to return to either side of the single-phase
line. There is no "parallel" way to connect a single phase source to a 3-phase load. For that
reason, only the inut line leads of either motor can be considered for polarity swapping in order
to achieve plug reversal.

Bob Swinney


This thread is getting a bit tangled. Back to basics

Take an equal sized "idler" plus "motor" system. No starting or
balancing capacitors. Mechanical or pony motor start.

This is in all respects a true parallel connected system. Both
motors receive power from the two single phase input lines and
power is exchanged on the common phantom phase link line.

If the motors are identical and zero, or equally loaded, the
phantom phase voltages are identical. No current flows in this
line so there is no power exchange.

The ONLY differentiation in this system is the historical
fact that one of the motor was spun up to speed. Once that has
happened, the motors are identical twins.

If either or both the motors is mechanically loaded, current
will flow in the phantom phase line, power flowing from the
lightly loaded motor to the more heavily loaded.

If, in this perfect twin motor system, ANY pair of the
interconnecting wires is reversed the relative direction of
TORQUE is also reversed.

In this fairy tale case of plug reversing precisely identical
motors the two torques will oppose in their respective rotors
reducing the spin speed of both motors to below minimum start
speed stalling BOTH motors.

In a practical case various mismatch factors may be sufficient
to enable one motor to remain above minimum start speed and this
will eventually reverse the second motor. With roughly equal
sized motors this can be either motor.

Run capacitors don't make any difference because the phase
shift they provide is equally valid for both motors in both
normal and reverse connection.

A high inertia load (heavy chuck) favours reversing the idler
because equal reverse torque is more successful in reversing the
lower inertia idler. For the same reason a flywheel on the idler
favours the idler. However these are minor differences - safe
plug reversing needs a big idler.

Jim

On 2009-05-18, wrote:
This thread is getting a bit tangled. Back to basics

Take an equal sized "idler" plus "motor" system. No starting or
balancing capacitors. Mechanical or pony motor start.

This is in all respects a true parallel connected system. Both
motors receive power from the two single phase input lines and
power is exchanged on the common phantom phase link line.

If the motors are identical and zero, or equally loaded, the
phantom phase voltages are identical. No current flows in this
line so there is no power exchange.

The ONLY differentiation in this system is the historical
fact that one of the motor was spun up to speed. Once that has
happened, the motors are identical twins.

If either or both the motors is mechanically loaded, current
will flow in the phantom phase line, power flowing from the
lightly loaded motor to the more heavily loaded.

If, in this perfect twin motor system, ANY pair of the
interconnecting wires is reversed the relative direction of
TORQUE is also reversed.

In this fairy tale case of plug reversing precisely identical
motors the two torques will oppose in their respective rotors
reducing the spin speed of both motors to below minimum start
speed stalling BOTH motors.

In a practical case various mismatch factors may be sufficient
to enable one motor to remain above minimum start speed and this
will eventually reverse the second motor. With roughly equal
sized motors this can be either motor.

Run capacitors don't make any difference because the phase
shift they provide is equally valid for both motors in both
normal and reverse connection.

A high inertia load (heavy chuck) favours reversing the idler
because equal reverse torque is more successful in reversing the
lower inertia idler. For the same reason a flywheel on the idler
favours the idler. However these are minor differences - safe
plug reversing needs a big idler.


What you have explained so well, is that there is a symmetry between
an "idler" and a "load", once both are spinning. They are both motors,
tied together, with current flowing from one to another depending on
their respective slip, size etc.

i

Jim,

Thanks for lending some clarification to a confusing issue. Perhaps I am totally dense and
hopelessly lost in an overly-simplistic way of looking at RPCs. Please, if you will bear with me, I
would like further clarification on your response "back to basics" below:

{ To begin let's label the respective terminals of 2 motors as A B C . . and . . A B C. In an
idler / load set up, one side of a single-phase line is connected to A, A and the other side of the
single phase-line is connected to B, B; and terminals C,C are together. This, I believe, defines
basic connectivity of a "RPC". The term "plug reversing" is taken to mean reversing (turning over)
a pair of leads feeding the load motor.}

Jim wrote: "This is in all respects a true parallel connected system. Both
motors receive power from the two single phase input lines and
power is exchanged on the common phantom phase link line.
If either or both the motors is mechanically loaded, current
will flow in the phantom phase line, power flowing from the
lightly loaded motor to the more heavily loaded." Agreed. This would be the case whether we are
considering a practical RPC or a perfect pair of identical motors.

Jim wrote: "In this fairy tale case of plug reversing precisely identical
motors the two torques will oppose in their respective rotors
reducing the spin speed of both motors to below minimum start
speed stalling BOTH motors." This is where I am confused, Jim: Your statement seems to imply plug
reversing both ("precisely identical") motors.

The scenario, depicted in the opening, is with the motors connected A B C to respective A B C as
described in the opening paragraph above: The single-phase input, A A and B B is reversed. This
would reverse inuts to both motors and torques, thus direction of rotation, of both motors would
reverse. In essense, plug reversing of both idler and load.

Jim, my confusion arises in that AFAIK if we were to "plug reverse" only the load motor, the
connections would be single-phase line to A, B of the idler, A of idler to B of load, and B of idler
to A of load, With C terminals together. It seems to me this connectivity would reverse only the
load motor, not both motors.

Please explain if this is not the case.

Sincerely,

Bob Swinney








wrote in message ...
On Sun, 17 May 2009 11:32:33 -0500, "Robert Swinney"
wrote:

Don Sez:

"Yes, I do. Of course, that depends in part on the relative
horsepower ratings of the idler motor and the lathe's own motor. I have
read here postings by people who have experienced that with equal
horsepower on each. And *that* might be something which could be
improved somewhat by a flywheel on the idler motor -- but expect the
housing to jump around during the reversal. :-)

Tuning and balancing capacitors might change the threshold at
which this reversal happens in that they will be applying a bit of
rotational bias -- but with equal sized or smaller idlers, you still
will have the idler reverse at some set of parameters." " Indeed so."

That "set of parameters" would have to be a reversal of polarity on the idler's two input line
leads. I'm afraid you are caught up in the erroneous premise that an idler motor and load motor
constitute a generator and load. They do not. Irrespective of rotational mass and any series
capacitance present, current flow (and torque) in each motor depends on the polarity of applied
voltage. Swap the two input (line) leads in either idler motor or load motor and that motor will
change direction. The other motor will continue to spin in the same direction as before.

In a RPC, the idler motor and load motor are not in parallel with respect to current flow. This
because of the way current must flow in the "3rd" leg to return to either side of the single-phase
line. There is no "parallel" way to connect a single phase source to a 3-phase load. For that
reason, only the inut line leads of either motor can be considered for polarity swapping in order
to achieve plug reversal.

Bob Swinney


This thread is getting a bit tangled. Back to basics

Take an equal sized "idler" plus "motor" system. No starting or
balancing capacitors. Mechanical or pony motor start.


If the motors are identical and zero, or equally loaded, the
phantom phase voltages are identical. No current flows in this
line so there is no power exchange.

The ONLY differentiation in this system is the historical
fact that one of the motor was spun up to speed. Once that has
happened, the motors are identical twins.


If, in this perfect twin motor system, ANY pair of the
interconnecting wires is reversed the relative direction of
TORQUE is also reversed.

In a practical case various mismatch factors may be sufficient
to enable one motor to remain above minimum start speed and this
will eventually reverse the second motor. With roughly equal
sized motors this can be either motor.

Run capacitors don't make any difference because the phase
shift they provide is equally valid for both motors in both
normal and reverse connection.

A high inertia load (heavy chuck) favours reversing the idler
because equal reverse torque is more successful in reversing the
lower inertia idler. For the same reason a flywheel on the idler
favours the idler. However these are minor differences - safe
plug reversing needs a big idler.

Jim

"Robert Swinney" fired this volley in
:

Jim, my confusion arises in that AFAIK if we were to "plug reverse"
only the load motor, the connections would be single-phase line to
A,
B of the idler, A of idler to B of load, and B of idler to A of
load,
With C terminals together. It seems to me this connectivity would
reverse only the load motor, not both motors.

Please explain if this is not the case.

My read on this is that, in the absence of start or run capacitors,
the motors could be spun up in either direction. When the attempt is
made to plug-reverse the load motor, it won't reverse the idler
(alone) What it's actually trying to do is reverse BOTH of them, and
it'll simply stall both in the effort.

In this perfect parallel connection, there's nothing to distinguish
the idler from the load motor except where it's physically located.

LLoyd

Lloyd,

That's the way I read it too. In a perfectly balanced system, as Jim depicted, both motors would
stall. Of course, that is as Jim sez, a fairy tale system. In the stark world of actuality, even a
slight imbalance would eventually reverse the idler.

Bob Swinney
"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote in message
. 3.70...
"Robert Swinney" fired this volley in
:

Jim, my confusion arises in that AFAIK if we were to "plug reverse"
only the load motor, the connections would be single-phase line to
A,
B of the idler, A of idler to B of load, and B of idler to A of
load,
With C terminals together. It seems to me this connectivity would
reverse only the load motor, not both motors.

Please explain if this is not the case.

My read on this is that, in the absence of start or run capacitors,
the motors could be spun up in either direction. When the attempt is
made to plug-reverse the load motor, it won't reverse the idler
(alone) What it's actually trying to do is reverse BOTH of them, and
it'll simply stall both in the effort.

In this perfect parallel connection, there's nothing to distinguish
the idler from the load motor except where it's physically located.

LLoyd