Jet Lathe

[Sparky_NY]

What is the model number of the jet lathe? The manuals for many of them are online. I have a Jet GHB1340 and the manual is online which includes the wiring diagram.

[Sparky_NY]

3 HP, 240 V single phase motor should be rated around 16 FLA. My 1.5 HP motor has 8 FLA.

Those lathes could be configured for either 120V or 240V. On 120V the FLA is 34A for 3hp thus the 50amp contactor rating.

[Bented]

Each contactor has a manual over ride on the front, pushing this in closes the contacts operating the relay manually.

If the machine runs with the contacts closed there is a control problem, if it does not run it is a power problem.

This is a diagnostic tool.

[wmgeorge]

Each contactor has a manual over ride on the front, pushing this in closes the contacts operating the relay manually.

If the machine runs with the contacts closed there is a control problem, if it does not run it is a power problem.

This is a diagnostic tool.

As someone who has worked in the field since 1962, that is good way to A. Burn out a motor B. get burnt from the flash if there are shorted wires. If you zoom in on that contactor on the left it looks like something is burnt. If you don't own a meter then you should step back and let someone who does check the circuit.

[Doozer]

As someone who has worked in the field since 1962, that is good way to A. Burn out a motor B. get burnt from the flash if there are shorted wires. If you zoom in on that contactor on the left it looks like something is burnt. If you don't own a meter then you should step back and let someone who does check the circuit.

Then why the fuk do contactors have the ability to manually over-ride
if YOU say they are never to be used ? ? ?

-D

[wmgeorge]

Then why the fuk do contactors have the ability to manually over-ride
if YOU say they are never to be used ? ? ?

-D

For power off testing of the contacts and aux switches, do as you wish have you ever seen a flash across a 3 phase contactor? They are also there for a visual indication of the contactor pulling in.

[CPeter]

Back a ways, a VFD was mentioned. I have a Grizzly 12x24 and it had motor issues and I converted it to a 2HP 3 phase motor and VFD and used the existing control locations on the apron and headstock for FWD/OFF/REV and speed control. I run it in gear configuration C-6 (600 RPM at 60HZ) most of the time and use the speed control from the VFD. Also the quick reversing is nice for threading. IMHO, the only way to go!
Peter

[mikey553]

Peter, I also have a Grizzly lathe, but 12 x 36. My single phase motor is fine, but I was thinking about converting many times. So you use apron lever for FWD/OFF/REV. What existing controls do you use on the headstock? Emergency stop? And you probably added the speed control potentiometer there.

600 RPM is my favorite speed on this machine as well. It is C-III in my case. Do you still experience gear "clunk" at startup and reversing? I do and it is bothering me. The only way I found to reduce it is to rotate the chuck manually in the opposite direction before start. If I would use a VFD for a slow start, this problem should go away.

[Doozer]

For power off testing of the contacts and aux switches, do as you wish have you ever seen a flash across a 3 phase contactor? They are also there for a visual indication of the contactor pulling in.

I can see that.

-D

[Doozer]

Off topic but...
Man those EU or ISO rated contactors are so much
smaller than the NEMA rated contactors. I can't see
getting the same service life out of them.

-Doozer

[mikey553]

Off topic but...
Man those EU or ISO rated contactors are so much
smaller than the NEMA rated contactors. I can't see
getting the same service life out of them.

-Doozer

A few years back we were using a 400A Furnas contactor for the plug reversing motor tests. It was burning its contacts badly and we were forced to file them after not too many cycles. Finally we redesigned the whole control circuit and replaced the contactor with 600A Leroy Somer. It was about the same size as Furnas. What a difference this made! It is possible that Furnas contactor was overloaded, but 600A vs 400A is not a very big change. We were testing 250 HP motors at 460 VAC and I am sure both contactors were overloaded momentarily during plug reversal.

[Sparky_NY]

For power off testing of the contacts and aux switches, do as you wish have you ever seen a flash across a 3 phase contactor? They are also there for a visual indication of the contactor pulling in.

I used to do a lot of work on large printing presses with tons of contactors. Guys in the plant would sometimes push one manually when they were having problems and on more than one occasion caused considerable damage. A example would be pushing in a motor contactor while the brake contactor remains engaged. Often multiple contactors/relays are used to accomplish logic functions especially in older equipment. Some lathes have relay logic to prevent forward and reverse from being engaged at the same time as another example.

The owner of one of those printing plants did it once, he told me how he burned his hair and melted the frame of his glasses. After that he wouldn't change a light bulb !

Pushing in a contactor by hand under power is a really bad idea except for a very skilled electrician (few electricians are versed in motor controls). Measuring the coil voltage and then across the contacts is the safe way.

[J Tiers]

Off topic but...
Man those EU or ISO rated contactors are so much
smaller than the NEMA rated contactors. I can't see
getting the same service life out of them.

-Doozer

You may not. Lifetime is one of the considerations for sizing them, along with selecting the "exact" type of service they will see from a list of about 30+ possibilities. It's supposed to take a PE to do it.

All that to avoid putting "needless resources" into constructing the contactor and/or applying it. They are not fans of over-design in the EU. Heck, they even figured out how to make the neutral the absolute smallest that was possible and still work. That's why there are such strict limits on line harmonics.

It's a design choice, and that's how they chose.

[Doozer]

My presumption (maybe wrong) that the person pushing in the contactor
knows it's function or what it powers. On a lathe with criss cross wires
between 2 contactors, a pretty sure bet is that they are reversing contactors
and they control the main motor. Another presumption (again, possible
wrong) is the machine worked previously and is recently having a problem.
It is good advise not to just walk up to a previously unknown machine and
just start pushing in coils. All of my machines I have either made the control
panel from parts myself or am intimately familiar with from having worked on
them before. So I know what things do. But if I was at work, I would not be
randomly trying contactors without being absolutely sure what they do.
So right on with that.

-D

[CPeter]

Peter, I also have a Grizzly lathe, but 12 x 36. My single phase motor is fine, but I was thinking about converting many times. So you use apron lever for FWD/OFF/REV. What existing controls do you use on the headstock? Emergency stop? And you probably added the speed control potentiometer there.

600 RPM is my favorite speed on this machine as well. It is C-III in my case. Do you still experience gear "clunk" at startup and reversing? I do and it is bothering me. The only way I found to reduce it is to rotate the chuck manually in the opposite direction before start. If I would use a VFD for a slow start, this problem should go away.

First, I meant C-3 for the gear set up. The FWD/OFF/REV is via the lever on the apron. The speed control knob is on the headstock as is a "jog" knob and the power control for the input to the VFD and a greeen "power on" light. No gear knock, just great performance. I love it. Photos tomorrow. I did retain one relay and transformer for the main power to the VFD as the wiring from the electrical box to the electrical box on the lathe was not up to line voltage.