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SB 2 speed motor wiring problem

Mr Bridgeport

Stainless
Joined
Nov 27, 2002
Location
Burlington, NJ
Working on a SB 16" lathe from about 1970 or so. It has a two speed main drive motor (Reliance Duty Master) and the control panel has 4 contactors. There is two sets of push button switches by the tailstock, each with Forward, Reverse and Stop.

Having trouble getting the motor to start.

Does this sound familiar to anyone? I'm looking for a wiring schematic if anyone has one. As soon as I figure out how to post pictures I will add some.

I already have a post going with more info.

https://www.practicalmachinist.com/vb/south-bend-lathes/help-id-sb-lathe-380627/

Thanks for any help.

Mr Bridgeport
 
If it's a 3 phase motor and your other post suggests it is, then if it doesn't start that means one of the phases is not being connected. I'd be looking at the points in the contactors or the line connection into the contactors. If it has resistors for a "soft" start then there could be trouble there as well. 3 phase motors are so simple it should run if all phases are connected for either speed. Unless, of course, there's a winding out in the motor but since you have two sets of windings, at least one set just about has to be intact. If the current can get to the motor, it just about has to run.
 
OK, a little cumbersome but now I know how to post pictures.

I appreciate the tutorial on how 3 phase motors work but I'm past that. I've been servicing machine tools for over 35 years.

One of the first things I did was to check the windings of both the high and low speed ranges. Phase to phase on one set of windings I get a nice balanced 3 ohm and across the other set of windings it's 1.8 ohm with nothing to ground. Motor should be healthy.

Let me see if I can explain what I have found so far. One set of windings is marked L1,L2 and L3 and the other set is marked L11,L12 and L13.

The overloads only protect 2 legs. On the top left contactor/overload L11 and L13 are connected through the overload. L12 is found on the lower right contactor and will not receive power until that is pulled in.

Yet if I push forward or reverse one at a time on both set of switch stations each switch will only pull in one of the four contactors. Cycling through the four switches every one of the contactors will pull in.

As you can see this panel consist of two commercially available Forward/Reverse panels wired together to get to this configuration. If this was added after market someone did a very professional job of it. That's why I'm thinking it was factory wired like this. I think I've seen this before else where on a SB lathe, not 100% sure. Most places either don't use SB lathes or are not willing to pay someone to work on it.

So does this look familiar to anyone?

Mr Bridgeport
 
Two speeds plus two rotations equalling 4 contactors/relays makes sense. Each individual switch only pulling one contactor would be my expectation.

I cant read voltage connection on picks, but the push button to activate relay. . . The button will use one hot leg and a neutral/ground to activate a relay, or two indivdual hot legs.

My expectation is all 3 legs to run through relay to power motor, regardless speed or rotation, but all 4 speed/rotation options are covered with the 4 relays.

Now there's a lot going on with jumpers, You need one or two hot legs for button to activate, plus 3 legs for motor. All of which is suppllied by only 3 legs of power source. . . So maybe L12 is on the side as an activation leg, but its not really the L12 to motor, but because of jumpers your getting funny readings.

Or maybe L12 is just wired wrong.

Ultimately you need incoming supply voltage A, B, C to connect to motor L1, L2, L3, through two relays, one fwd, one rev.

Then a,b,c to L11,12,13 through the other two relays, also fwd and rev.

You could disconnect motor, Then live, activate each switch position, take voltage readings at disconnected leads at motor to see what is what.
 
I "think" that it requires two contactors to pull in at once to operate the motor. L12 is on the right lower contactor and is not connected to anything until it gets pulled in. I used that point when I took my ohm meter readings and used L11 and L13 on the bottom of the top right contactor. So the top right contactor pulls in and latches but nothing happens with one phase (L12) missing.
I searched the internet for "3 Phase Two Speed Reversing Motor Wiring" and didn't come up with anything useful yet.

Further searching shows that SB had other switching schemes including a 5 position drum switch.

I know where this machine came out of, it was used for repair work in a big steel distribution plant. I repair the saws. I'm friends with the maintenance man as well. Wiring is bone stock.

I'm going to open up the switches on the push button station next. There may be multiple poles in those switches.

Mr Bridgeport
 
You could be right there. Might be doing something more interesting. Like a push button activates, but once motor or one of two relays is activated, then those completed circuits hold a particular relay powered. Thus a stop button to break the connection.

Then to give third leg, you're alternating which relay, Then depending which relay, could be swapping for fwd or rev. That would explain 2 legs per relay. No doubt fun or more interesting for a regular electrician. :D

I'd need to write it out while testing which relay does what, and what the result is at motor, in which leads are live, and the orientation of a,b, or c to leads at motor, per given relay.

To me, the needed end result at motor is a given, as well as 3 legs of supply. So I'd need to work from either of those ends to figure it out. My only other question would be are they using neutral or a neutral bonded ground as neutral for buttons or relay activation. Like if relay activation is like a light bulb, 110 single with a neutral. And if so, are you running a neutral.

My guess is they don't use neutral, as you have got relays to close, but if they do, and you are working on a straight ground, might not be a clean connection, so you'd get "some" operation.
 
Ok, it's running!
But boy do I feel like a dumb-ass!

So when I first started working on this I just glanced at the pushbutton stations and somehow read Forward/Reverse on both stations. That turned out biting me in the ass.

So after an hour of tracing wires I was convinced that two contactors had to be pulled in to get motion. I put power to the machine and had my buddy Timmy, the proud owner of this lathe, operate the control station. I told him to hit the forward button on the top station and after that contactor latched in I manually closed the bottom left contactor and the spindle started as I figured it would. He turned it off and as I was pondering why the second contactor wouldn't pull in Timmy says to me, "Why don't we push Hi or Low on the bottom station and than hit forward".

Me: "There is no Hi or Low station, just forward and reverse".
Timmy: "Yes there is, look at the labels on the switch".
Me: Walks around to the front of the machine and just groans....

So yea, feel like a dumb-ass tonight.

Bottom line, it's working.

Next to do is free up the taper attachment, don't think it's ever been used and see why the oil cups on the spindle are half full. Should have drained after sitting for about 3 years I would think.

Mr Bridgeport
 
My favorite part is you gave us a result. Its really irritating bouncing a problem off my skull and never hearing what the results are. :D

On taper attachment, on bottom of main overhanging portion, there can be 2 screws locking the assembly, not always there, but maybe. They just get run up like set screws. Also lube the two points here: Looks like two tapered holes, on either side of sliding through shaft. They are open, so chips, dirt, moisture can get in and hold that shaft from sliding. They'll be under chip guard with long slot:

159.jpg 163.jpg

The passages in headstock for oil is larger than you might expect. The hole that cups screw into, is the low point to drain, without tipping headstock over. The rest of the passage is a dead end, no way to get out. I'd recommend un-screwing the cups to dump it. Have a coffee can, diapers or something to catch it. Won't come out fast, and will probably need a day to drain out. If you fish around the hole with a small screw driver, probably get a bunch of mung out too.
 
Ok, I'll drain that out. I don't intend to get into the spindle bearings unless I have to. I grew up with a 1921 Monarch lathe so I'm familiar with plain bearing headstocks. I have to train my buddy Timmy to always keep an eye out on the bearing temps. It's second nature to me. Drain and clean and add some fresh oil. Looks like 0W synthetic is an acceptable substitute.

I always give results even if it makes me look bad. When I worked for Bridgeport all those years I was on the support desk about 10% of the time instead of in the field. So I took in a ton of calls and helped a lot of folks out. It was rare when I got a call back when trouble shooting an issue if my advice fixed it. I knew it was fixed though if they didn't call back after giving them a list of things to do/check. To me a follow up is just the correct thing to do but most folks just move on. Thanks for the help and I may have other questions along the way, SB lathes are not my forte.

Mr Bridgeport
 








 
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