ON/OFF/Brake lever does not wsork on the Clausing

Was it powered from a VFD before? VFDs do not like their motor load switched, and are likely to emit magic smoke if one does this. So, people bypass the switch.

In my lathe, I pulled all AC wiring out of the switch, instead having the motor wired directly to the VFD 3-phase output. The switch is instead wired to the VFD 24-volt control inputs, and tells the VFD what to do. The switch works as it always did, with one exception - if one is spinning at full speed with a big chuck and (using the switch) tells the VFD to stop, it may instead trip because the motor is overrunning the VFD. There is no harm in this, but it is a nuisance.

I also added an external braking resistor to the VFD, which helped a lot, but I can still trip it.

One odd thing to look for: As received, the green wire in the cord was not connected to the machine frame, instead flopping around in the 4" square box, probably because there was no convenient ground screw. No attempt had been made to attach it to anything. I discovered this when I noticed that I was getting a tickle when I touched the machine frame. The tickle is due to leakage in the motor, and is quite common in old motors, especially if they are dirty. Changed the 4" square box for a modern one with grounding screw, and finished the job. No more tickle.

You also want that ground to work so if the motor shorts the VFD will trip, rather than putting 240 volts on the machine frame.

Joe

It was never wired for a VFD, that's for sure.

I think that a quick stop is a big safety advantage.

You may opt for a lower resistance and higher watt rating.

But still leakage, right?

Interesting. I think that the limit switches operated by this lever, are not working right.

One theory shot to hell.

Yes, up to some limit.

Oh, yes. It's harmless unless it gets large. The 5914 measured ~100 volts to ground using a DMM (with 10 Mohm input resistance), so the leakage was something like 10 microamps. A layer of dirt can easily achieve this.

One always grounds the frame of a washing machine because they always have a little leakage from the motor as well. And sometimes a lot of leakage, if the washer leaks water onto the motor.

When I was maybe 16, the widow next door, a friend of my Mother, was getting shocks from her washing machine, and Mother sent me over to fix it. The ground wire was missing, and probably was never installed. When the machine was new, no problem. But it grew on you. I made and installed a ground wire, and no more shocks.

I would not be surprised. Does the manual say much about how this is supposed to work? On my 5914, there is a mechanical clutch and brake that does work, but I never use because it always trips the 3 HP VFD, which is a little small for a 2 HP motor with lots of spinning mass.

Joe Gwinn

The lathe, with its big chuck and gear train, is a tough application for a braking resistor. Much more so than a Bridgeport.

Since I fixed the problematic lever this afternoon (see separate post), I must say that I kind of like the mechanical safety stop embodied in this lever. I flip it up to turn on, down to turn off, and force down to brake almost instantly.

Agreed.

I did not realize the extent of this issue. I tended to think that all leakage was bad and needed to be fixed.

The mass is rather enormous, all gears, chuck, work piece, possibly two lead screws etc, spinning at 1,800 RPM.

I would think that if I wired my lathe for a VFD, I would continue to use my ON/OFF/BRAKE lever exactly as intended, in ON position it would start the VFD, in OFF position it would turn off and let it coast (or slowly brake as in, like, 8 seconds), and I would still be able to use the mechanical brake as originally intended.

Since I screwed around with its electrical system a lot today (and got it fixed), I think that the VFD application is rather obvious and easy on my lathe.

Adding a VFD properly integrated with control levers (ie, no new buttons), I think would increase the resale value of this lathe if I decide to sell it. I have a 5 HP VFD that has a cracked cover, which would not matter much here, so I could use it.

True. The Millrite vertical mill has no such problem.

I read that posting. Classic problem - clueless repair. The 5914 had its fair share of that.

Nor did it occur to them to call Clausing and ask what might be wrong that they could not figure out.

Leakage is bad, but unavoidable. So one always provides a path. Nor do ground-fault interrupters work well with big industrial equipment.

The other reason for the hardwired ground is to ensure that if the worn old motor shorts to the frame, the breaker will pop, versus the operator frying.

Yep. I will probably lengthen the slowdown period the VFD aims for.

Actually, with the clutch/brake lever, I get trips on starting only, when the motor is suddenly asked to accelerate all that metal. I get trips on stopping if I order the VFD to stop spinning the motor, and all that metal tries to keep on spinning. The 3-jaw and 4-jaw chucks are the big issue. If I recall, I could mechanically start and stop with the collet chuck.

The mechanical brake on the 5914 does still work, and can be used for emergency stops. That is if I think of it, which is a problem because I don't normally use the clutch/brake handle.

This is exactly what I did.

Yes. And DoN had another point, that it's best to train oneself on the standard switch (and controls) in the standard way, so when you operate some other machine, or buy a new machine, you don't have to unlearn and endanger man and machine in the process.

Joe Gwinn

Joe, that seems kind of odd to me. My 5914 runs from an older Mitsubishi VFD with out of the box settings and the clutch/brake has never tripped the VFD.

Happens a lot. Clueless repair is the #1 source of great stuff for cheap that "does not work".

Clausing has some very nice ladies to talk to.

Should help.

How many seconds acceleration do you have set up?

Can you lengthen that?

On my lathe, I am not even sure if I would use VFD braking altogether, since I have a mechanical brake that is right where it should be, on the on/off/brake lever. If I set up the VFD to brake, I would use a very long braking time like 10 seconds.

good to know

Plus, any extra weird controls are a big minus when selling the lathe.

I think that Joe was talking about electric braking not being able to stop all that mass of metal.

Yes, but I think Mike understands that too. Mike and I will need to compare notes.

Joe Gwinn

Tell me more about this VFD. Model? Size?

What I have is a Hitachi SJ100-022NFU 200 volt class 3 HP, being fed with 220 volt single phase. Automation Direct has the manuals, although the unit is now discontinued.

The SJ100-022NFU is fitted with a Hitachi JRB120-3 braking resistor (120 ohms 50 watts).

Joe Gwinn

So, it's a silver lining for you?

They also have some fellows in the back that seem to know what they are doing.

I recall that it's 10 seconds. Yes, I can set it to just about anything I like. But it won't help, as that delay applies only while the VFD is accelerating the motor and load. If the motor is up to speed, and a big load is suddenly imposed, the motor will draw too much current from the VFD, which will trip. The motor is in no danger, even if this is done with the lathe powered by a real 3-phase industrial power system.

There is no harm in doing both.

Yep.

Joe Gwinn

Mitsubishi seems to include larger brake resistors than other mfrs, at least on their full-featured drives. The 3HP Mitsubishi on my lathe has a built-in 40 ohm 110W resistor.

If you do both, the drive will try to keep the motor speed on the decel ramp for the full set time and will fight the brake. Use one or the other.

Definitely.

They also have prices like $750 for a crossfeed nut. :)

Sounds like your VFD is not big enough.

Bingo! That's three times the braking effect. How hot does the resistor get?

The Hitachi can handle down to 35 ohms, according to the manual.

Joe Gwinn

Not on my 5914, which has both a clutch and a brake, operated simultaneously by the one lever. The motor keeps on spinning unless I also use the Rev-Off-For switch.

Part of the economic rationale for the lever is that one can get the chuck up to and down from operational speed more quickly, thus eliminating labor time and money spent waiting for the the lathe to accelerate and deaccelerate.

Joe Gwinn

I have some 18 ohm high power resistors for sale. (IIRC, I am on train right now)

This is also a big safety feature. Stop the lathe instantly with left hand without fumbling.

I'd just assumed that you were talking about the 5914 mechanical brake/clutch. If you weren't, never mind .

Mike