I bought a 5914 Clausing lathe last weekend. I"m running it off of a
rotary phase converter, that at this point does not have balancing
The drum switch on the lathe has a set of momentary contacts inside
that activate the magnetic switch when you move the handle a little
past the forward or reverse position. When the momentary contacts are
closed, the switch pulls up and the motor runs, but the mag switch
drops out as soon as the momentary contacts are released.
I have tried exchanging the different leads from the RPC to the lathe
so that the wild leg wouldn't be part of the mag switch circuit and
that didn't solve the problem.
The wiring inside the drum switch was not standard, and connecting the
power lines to the places it had been when previously, it didn't run.
Same symptom - switch would pull up ,but not latch and motor ran with
a pulsation / vibration. I got the wiring diagram from Clausing and
rewired it to factory standard. Still won't latch. Using the drum
switch and bypassing the mag switch works fine. The motor itself
seems to be OK.
What I can see from the wiring diagram supplied by Clausing and from
the diagram inside the mag switch box, it appears that all is wired
correctly. I am having difficulty following the flow of power in the
switch. The diagram has me confused.
Any thoughts on trouble shooting?
Contactors need an extra NO ancillary switch ("latch switch") which bridges
across the momentary start switch, keeping the relay coil energized.
A momentary stop switch is then in series this switch/coil.
If there were a 4th pole on the relay, this could be used, also.
This latch switch could be bad, or just not wired in. I've seen these
switches go bad.
Or, the mechanical connection of this switch to the relay is loose, so it is
not "making". Sometimes the switch itself is loose, as these switches can
be often be added on, taken off, etc.
Please do balance yer rpc! I burnt out a lot of shit with that goddamm wild
It's actually perty simple to do, much simpler than many of diy sites (and
std web refs) recommended here make it out to be -- imho. Altho some of
those setups are indeed enviable...
I did a very complicated multi-motor (staged) and switchable multi-capacitor
system, whose magnitude of pita factor (and expense) I didn't really grok
until my buddy asked me to build one for him.... holy shit.....
So out of desperation, I did nearly as good a system for him, with *much*
First, these asshole rpc mfr's put starting caps that are way too large,
which further bumps up the voltage of the wild (generated) leg. You can
proly cut that down those caps by half to 1/3 -- which immediately improves
the V of the wild leg -- and which means if multiple caps were used, you
can use the extra caps to balance the rpc.
If line V is L1L2, and the starting caps were on L1L3, you add the balance
to L2L3. Except put a switch (S2) in the caps between L2L3.
How much capacitance to start the rpc? Whatever "sounds" reasonable. You
don't need the motor to instantly get up to speed (as these effing rpc mfr's
seem to think is so important), but you don't want it to take 10 secs,
About 1 sec seems OK.
I've forgotten exact values, but I seem to remember about 100 uF to start,
60-80 to balance. Season to taste.
If you have a good ear, you'll notice that the right balance of caps
(tightest V) results in the lowest hum/buzz of the motor.
So now, to start the rpc, make sure S2 is off, and start the rpc as normal.
Then, just flip S2. Wahlah....
Iow, the reduced value starting caps also stay in as balancing caps, and are
The other balancing caps are switched in only after the motor is running.
Using this method, my buddy's rpc measured (the other day) 241, 242, 246 --
not bad, eh?
Mine is even tighter -- on the order of 241,243,245, on a good day -- but
with just too much effing electrical drama.
You'll get proly 100 other opinions, and altho ahm no 'spert, I grappled
with this for a long time, and bought $200 worth of caps from Graingers at
1/3-1/2 price, and did some amount of experimenting.
I don't think it gets much simpler or cheaper than my buddy's system, and
the voltage speaks for itself.
Just remember to flip in S2!!! Which, on my system, I sometimes forget to
If you want to go "cap wild", you can have two banks of caps, ranging from
100 uF down to 10 or 20 caps, with a switch for each cap. One bank gets
switched across legs L1-L3, the other bank across L2-L3.
Thus, depending on what rpc idler you plan on firing up, you can choose your
starting caps, and then switch those in/out, and the other balancing caps
in, as needed. You can have 3 cheap digital VOMS attached, for on-the-spot
This is easier described than done, and is really a wiring pita, altho it's
not rocket science either.
I used regular 49c wall switches, screwed to wood, with zip cord.
Altho my set up is not as nicely done/automated as some diy setups you'll
find, it is the most versatile and "tune-able" that I've seen anywhere on
Bear in mind that a bunch of small 3 ph motors pack as much oomph as one big
honking idler, a point much de-emphasized in rpc discussions.
This way, you just need starting caps for the 1st idler, which will start up
subsequent idlers, which can then be balanced with switchable caps, to
I breakered my wild leg(s) separately, fwiw. Too much effing drama, tho.
A quick/dirty "fix" to this is to put a simple HD light switch in parallel
with the momentary on switch.
The problem is then, the Off momentary will not work; you'll have to switch
off the light switch to turn off the motor.
Which is not a big biggie, imo.
But you should be able to find the defective or mis-wired latch switch
sooner or later.
[ ... ]
You've done quite a bit of the right troubleshooting, but one
thing comes to mind as a possibility. The switch probably has overheat
coils which trip a set of contacts open when too much current is drawn
through them. These interrupt the current to the contactor (relay)
coil, thus dropping it out and stopping the motor.
The momentary contact apparently bridges over both the heat
switches, so it engages the relay coil -- until you release the
There is probably a ratchet to reset the heat coils -- there
will be at least two, and perhaps a full three, though two is all you
If the motor was originally wired for 240 VAC and it has been
rewired for 120 VAD, the current the motor draws will have doubled, so
you need a new set of heat coils rated for the new current.
Of course -- it could be something else -- but this is what I
would check first.
You just described how these Clausings are wired. The NO contactor is
the 4th terminal in the drum switch. It goes to the 4th pole on the
relay. Over time I figured out how the switch worked and realized
there should be a jumper wire to the 4th contactor, so that it
continues to be powered once the NO switch is released. I added the
jumper and voila! - well almost. With the motor disconnected from the
mag switch it latched when the drum switch was moved in either the
forward or reverse direction. Add the motor and it runs in forward
but not reverse - just chatters and won't latch. That's because the
wild leg of the RPC is feeding the other end of the coil in reverse.
I did a variation of that to solve my problem. I connected a 2nd
jumper from one of the line feeds to the other end of the coil so that
the line feeds always power the mag switch. If my RPC supplied better
power on the wild leg, I wouldn't have to do that.
I've thought about putting a light switch in the 2nd jumper wire to
use as an emergency stop.
Yes. Definitely miswired. I got the wiring diagram for these from
Clausing and as purchased, this lathe had clearly been rewired for
some reason. Perhaps it worked on genuine 3 phase from the power
company, but not when I hooked my RPC to it. The only thing missing
from the Clausing wiring diagrams is the first jumper you need to keep
the mag switch latched. For anybody reading this thread in the
future, the jumper needs to go from T3 to the terminal labled #2.
Thanks for all the suggestions.
It is a 220 / 440 V coil. There is a wiring diagram right on the coil
showing you how to make it either 220 or 440 and I had the darndest
time figuring out where those terminals were that they showed. I was
wondering if it had been wired for 440 at the knitting mill where it
used to live. When I finally realized where those terminals were, it
was a "doh" slap your head moment". Then it was clear that it was
wired for 220 and that wasn't my problem.
I had been wondering about that too. As I mentioned in reply to Don,
it took me until this afternoon to figure out where the terminals are
that change between the two voltages. I confirmed it as wired for
One problem was that a jumper was missing between T3 and the 4th
contator terminal #2, which maintains power to the coil once the
momentary switch has caused the coil to pull up. The second problem
was that the wild leg of my rotary phase converter was part of the
circuit when I was trying different things, and that leg would not
hold the coil up despite the voltages being within 11 volts of each
other between the lowest and highest pair of legs in the RPC.
Shoot me an email and I'll send you the wiring diagram Clausing sent
me. That's not part of the manual. You can put the diagram on your
I'm using a 270-300 uf start capacitor on a cheap wall switch to get
it going. It beats the pull cord I had been using. Currently I have
24 uf between L1-L2 and L2-L3. - cause that's the caps that I had at
hand and wasn't sure what total uf to shoot for.
With the two run capacitors in place, I'm getting
240 - 251 - 244
(L1-wild leg, wild leg-L3, L1-L3)
I have a couple of more capacitors, but the one I'd like to try has me
a little confused. It's 370 V so it *should* be a run capacitor, BUT
it's a plastic case rather than metal like the others. The second
confusion is that it's 40 uf and 5 uf. How do you tell which
terminals to connect to get the 40 uf? I don't see anything on the
lable although I believe one terminal is a little smaller than the
other two. Which of the two terminals to use on that cap?
No need for me to get that complex. The two largest motors in the
shop are both 2 HP and the idler on my RPC is 3 HP so that should
handle both machines if I want to use it on both. The lathe would not
work well with my VFD without rewiring. The Bridgeport uses the VFD
and doesn't have a magnetic switch.
That's why I'm hanging onto the 5HP motor. If I ever get something
that needs a larger RPC, I'll gang the 3 and 5 HP motors together to
start the large machine.
Check the coil voltages..make sure they are whatever is the proper value
and make sure the secondary control transformer is wired with the proper
This is the normal fast check..look at the wiring configuration of the
internal control voltage transformer to see what its wired for.
Whenever a Liberal utters the term "Common Sense approach"....grab your
wallet, your ass, and your guns because the sombitch is about to do
something damned nasty to all three of them.
[ ... ]
Is it possible that they had the wires from those terminals run
off to an external panic stop switch somewhere? Perhaps a full-width NC
treadle switch between the cabinets, or a master control for the shop to
force *all* machines to stop in an emergency situation? (The best way
to get the machinist's/operator's attention is to stop his machine. :-)
Glad you solved it.