Newton Tesla lathe package

[John HaineParticipant @johnhaine32865]

Afternoon all. I've got one of these on order for my Super7 and, absent detailed information from NT like a downloadable manual, I was wondering if anyone could help me with a query please.

The lathe in question is CNC'd and I would like to have a single e-stop to halt the CNC and the lathe motor. I gather from NT that they don't have any spare contacts on the internal e-stop to bring out and anyway the warranty would be void if the box is opened.

The alternative is to have an external e-stop that just turns off the power to the drive as well as halting the CNC system. I have the usual NVR starter/estop switch for the Myford which will be redundant when the NT unit is fitted, this could supply the NT drive as well as operating a suitable relay to feed an e-stop to the CNC.

So my question is, does anyone know what the NT estop function is, does it just operate on the mains or is it more intelligent (e.g. braking the motor quickly)?

Thanks in anticipation!

[John HaineParticipant @johnhaine32865]

[EmgeeParticipant @emgee]

Soinds like you need to pass control of the VFD from the unit and any remote station to the cnc control system being used so start/stop/fwd/rev/speed is controlled by the program running.

Emgee

[egaParticipant @ega]

I have the NT CL750 package on my S7. I just did a quick subjective comparison between the estop and normal red stop button and there seemed to be no difference.

[John HaineParticipant @johnhaine32865]

Thanks EGA. Is there a pilot light on the unit, does it go out if estop is pressed?

[SteviegtrParticipant @steviegtr]

My Super7 with the Omron has both soft stop (timed as required) & a e-stop which is instant. From what you say it seems there is not that function on the NT. I'm just going to do a experiment on the lathe.

Ok so i ran the lathe & switched off the power to the inverter. The lathe did not stop instantly as it does using e-stop. So i guess using a contactor at the power source will not stop quick enough if timed to cnc.

Steve.

[duncan webster 1Participant @duncanwebster1]

I've always found NT very helpful, have you tried asking them nicely to fit an e stop with a spare set of contacts. I've bought 4 inverters from them, not the cheapest, but only a few miles away, so if advice needed I can call in.

[egaParticipant @ega]

Posted by John Haine on 23/01/2022 18:09:38:

Thanks EGA. Is there a pilot light on the unit, does it go out if estop is pressed?

No pilot light on my unit which dates from 2004 since when it has functioned flawlessly according to its rather basic lights. The more recent TECO drive I have on my other lathe was a challenge to install but it does have user-programmability.

[John HaineParticipant @johnhaine32865]

Thanks for the information everyone. I've now got a pdf of the manual and it confirms that the estop removes all power from the inverter so the motor coasts to a stop. So an external estop should do the job, switching the supply off and also generating an estop signal for the controller.

[peak4Participant @peak4]

Posted by John Haine on 24/01/2022 17:35:00:

Thanks for the information everyone. I've now got a pdf of the manual and it confirms that the estop removes all power from the inverter so the motor coasts to a stop. So an external estop should do the job, switching the supply off and also generating an estop signal for the controller.

John, I can't speak for the NT unit. but at least one inverter I have suggests limiting how often you stop it by killing the mains power feed. Without searching for the manual I can't remember now, but it's something like keeping it to less than once per minute.
I've no idea why.

Bill

[John HaineParticipant @johnhaine32865]

Bill, indeed, as does the NT manual. But with an "upstream" estop the estop frequency will be no more than with the integral one. They suggest operating the estop at the end of a machining session just to isolate the machine.

[peak4Participant @peak4]

Posted by John Haine on 24/01/2022 17:35:00:

Thanks for the information everyone. I've now got a pdf of the manual and it confirms that the estop removes all power from the inverter so the motor coasts to a stop. So an external estop should do the job, switching the supply off and also generating an estop signal for the controller.

John, any chance of a copy of the pdf please, mine came fitted to my second hand Warco720 (Super 7 clone)
The NT package was brand new, but without any paperwork.
I did have a look, but there didn't seem to be a download option on NT's site.
Many Thanks
Bill

[John HaineParticipant @johnhaine32865]

Bill, I sent you a PM.

[Mike PooleParticipant @mikepoole82104]

A controlled stop which is when you just want to stop the motor with the normal stop button which will bring the motor to a stop under the control of the VFD and can be programmed to be a very fast stop. Perversely an emergency stop will be uncontrolled and probably slower than a normal stop, many VFDs now have a safe torque off feature which can inhibit the drive to the output stage thus being a safety stop, the other option is to kill the supply to the VFD which results again in a coast to stop. An emergency stop must be able to halt the drive in the event of the VFD control failing in such a way that it is unable to halt the motor, safe torque off is a safety circuit that should fail safe if it fails itself or will effect a stop when requested. Wiring a mushroom estop button to the motor off control is not an emergency stop.

Mike

Edited By Mike Poole on 25/01/2022 14:27:07

[John HaineParticipant @johnhaine32865]

Quite possibly Mike, but that is not what I am proposing. The internal estop clearly just removes the supply from the inverter/motor. Connecting another switch in series with the supply to the unit does exactly the same thing.

From the manual…

"Emergency Stop.
Pushing this will cut off all power to the inverter and the machine will coast to a standstill. To release the stop button, the head is turned clockwise allowing it to return to its’ normal position. The machine can then be restarted with the green start button."

[John HaineParticipant @johnhaine32865]

Just to finish this off, I have adapted the original lathe switch box by removing the reverser and fitting a 13 socket to the front with the "e-stopped" supply brought out to this from the contactor. Also across the switched output is an opto-isolated sensor that gives a logic "low" when the output mains is "on" to the estop input to the CNC BoB. This is on a little board from a supplier on eBay. Box mounted on the RHS of the lathe cabinet, the NT box will mount where this used to be.

[Mike PooleParticipant @mikepoole82104]

Killing the supply to the VFD via a NVR is an effective EStop. It would be best to not use the EStop for stopping the motor unless in an emergency but operating the EStop with the is drive stationary is the same as turning it off. If you are going to work on the drive train then pulling the plug is the ultimate safety device but if the EStop button latches then an accidental restart would be most unlikely as it would require the button to be released the NVR reset and the drive start button to be pressed. Having two EStop buttons that do different things is not ideal but if you can live with the button on the NewtonTesla box only stopping the motor then the NVR can be wired to stop the CNC and the motor. Personally I would invalidate the warranty and open the Newton Tesla panel but I understand the downside of doing this.

Mike

[John HaineParticipant @johnhaine32865]

I'm struggling to understand what you're getting at here Mike. It's clear from their manual that the NT estop just switches off the mains supply to the inverter, nothing else! I suspect that there is also an NVR function of some sort since normally the box just replaces the normal Myford unit.

So what I am doing is simply replicating their estop function with a switch upstream. So there are two estop buttons that DO EXACTLY THE SAME THING as far as the drive is concerned.

Just in case it isn't clear, in normal operation the estop WILL NOT BE USED to stop the motor, only the stop button on the NT controller.

Just as a little sidelight, when I took the back swarf guard off the existing motor I found a short green wire connected at one end to the motor casing with the other end having just the fractured end of a crimp connector. It seems that this was supposed to be the way the whole machine was earthed, but once the connector fractured it clearly wasn't! Myford – British engineering at its best. People who have Myfords, you might care to check your earthing.

[EmgeeParticipant @emgee]

What you found John will apply to any machine with a resilient mounted motor, the earth (cpc) conductor will be connected to the frame of the motor and if required a bonding link will be taken from the motor frame to the metallic part/s of the machine.
A simple current injection earth continuity test between the earth source (earth pin if 13A plug) and the motor frame and the metallic parts would highlight any missing bonds.

Emgee

Edited By Emgee on 28/01/2022 18:41:57

[John HaineParticipant @johnhaine32865]

Indeed, but what I'm pointing out was the poor design that allowed the link to fracture. The fact that it was hidden under the swarf guard so you couldn't see it compounds the error.

[John HaineParticipant @johnhaine32865]

Just another question if I may. Could someone who has one of these units fitted please let me known the dimensions of the box and the spacing between the mounting holes (which I believe are M4)? There isn't an outline drawing in the manual. Also a photo of the unit in-situ would be useful. I'm going to have to make a little adapter to fit it to my lathe cabinet as the CNC electronics has moved into it and there's a cover on the front to keep swarf out of cyberspace…

Thanks in anticipation…

[Mike PooleParticipant @mikepoole82104]

I may have made an assumption that the NT box EStop will just stop the motor but the additional EStop would stop the CNC as well. In the event of a crisis with the CNC you will have to remember to hit the extra EStop as the NT button will not stop the CNC. As it is likely you will be the only user in your own workshop then the functionality of the 2 buttons will be known but in an industrial situation you would expect hitting the nearest EStop to stop everything.

A VFD normally behaves as though it has an NVR in it so in the event of a power failure or hitting the EStop it will not restart when power is restored, some VFDs have a parameter that will restart the motor when power is restored but this is usually used where no danger will arise from an automatic restart, applications like a pump in a remote unmanned location where it would be desirable to have the pump restart as soon as power is restored. Obviously restarting a manually operated machine unexpectedly could be dangerous.

Mike

[Clive SteerParticipant @clivesteer55943]

There are several different ways of providing emergency stop depending on the nature of the emergency.

If there is a mechanical/operator entanglement emergency the machine may need to be stopped as quickly as possible which may require a mechanical brake or an inverter to apply regenerative braking. Having an eStop that removes power from the inverter prevents regenerative braking.

However if there is an electrical emergency such as fire or electrocution, then an eStop that removes all power, is appropriate.

An inverter eStop will trip the inverter and will require power to be cycled to reset it or a dedicated input used as a reset.

In a complex machine a risk assessment and FMEA will govern what/who handles an emergency stop and how it is handled.

Modern electrical safety requirements requires any device made of a conductive material (metal) to be earthed whether there is electrical power connected to the device or not. The thinking here is that the device could become live if a device with an undetected fault came into contact with it. So for instance a steel central heating radiator in your house is required to be earthed. This is normally provided by the copper pipes but with the increasing use of plastic pipe and fittings earth continuity may be lost and supplementary earthing is needed.

An electrical machine such as a lathe would normally have two independent earth connections with one that can be visually checked for presence. The thinking here is that a single failure, ie broken earth wire, should not cause a machine to become unsafe and no special equipment is needed.

Domestic dwellings now have to have a residual current trip device (earth leakage trip) but there are many that have not been upgraded so good earthing practice is always wise and you can't have too many belts and braces.

Clive S

[John HaineParticipant @johnhaine32865]

Bump

[EmgeeParticipant @emgee]

Posted by Clive Steer on 31/01/2022 17:48:51:

An electrical machine such as a lathe would normally have two independent earth connections with one that can be visually checked for presence. The thinking here is that a single failure, ie broken earth wire, should not cause a machine to become unsafe and no special equipment is needed.

Clive S

Clive, I am retired now but have never recalled a regulation calling for 2 independent earth conductors being required to the frame of any machine in a normal home or industrial installation.
Is this a recent requirement ?

I do remember that when testing fixed equipment the maximum cpc resistance had to be below a certain level to ensure any fault current could flow to earth so rupturing the supply fuse or tripping an mcb.
Such tests were carried out by injecting a 25A current into the earth lead to measure the impedance.

Emgee

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