Milling Machine issue

[Ian Patrick 2Participant @ianpatrick2]

Hello all first post on this forum hoping someone can help.

I recently purchased a used hobby milling machine off of ebay and am having some issues getting it to function correctly.

The milling machine in question is a Chester Champion 16vs.

When i went to pick it up it had the main wire cut. Once i got it home I opened up the control box to replace the wire and most (almost all) of the wires were disconnected from the board. Over the past couple of weeks i have been working on it in the evenings after work, i removed all the wires and started again, reassembling it but i have got to a point where i am stumped.

I have re wired it according to the wiring drawings available for that model. When powered up the speed display is working & the motor starts, but as soon as i let go of the ON button, the machine switches off again.

Does anyone have any ideas what the problem could be? Perhaps i have missed something. I have even gone as far as stripping down the ON OFF switch to check inside.

The DC motor itself looks barely used, i decided to replace the brushes anyway and gave the commutator a clean to remove any previous carbon.

All the wiring looks ok, the tachometer is working, the potentiometer seems to be working (doesnt switch on unless the dial is turned down to the minimum) the interlock guard is working and the E stop is working too.

I am just stumped at what is causing it to only function when the ON button is held down ??

Atvb

Ian

[Ian Patrick 2Participant @ianpatrick2]

[David George 1Participant @davidgeorge1]

Hi Ian have you got the spindle guard switch wired up as it won't hold if isn't wired up or bypassed with a link.

David

[Jim MasonParticipant @jimmason14480]

I suspect this is something called a no volt relay that is not working. They are usually built into the start/stop switch and drop out if the mains supply is interrupted (so the machine doesn't auto start after a power interruption). It's a pointer if the unit only runs while you hold the start button down.

Can you post a picture of the on/off switches?

[SillyOldDufferModerator @sillyoldduffer]

Welcome to the forum Ian.

Sounds suspiciously like a faulty NVR switch, (No Volt Release). These have to be reset manually after a power cut as a safety feature stopping machines firing up on their own when the power comes back on – a common cause of accidents in the good old days.

NVR switches contain a relay coil that latches the switch 'ON'. The coil might fail, but as someone has been at your wiring, maybe be it's just not connected. Have a read of this recent thread. If it's connected correctly and not working NVRs are cheap and easy to replace. ebay, amazon and many other sources. The part number is usually printed on the side

Dave

[BC ProfParticipant @bcprof]

I can think of two possible faults. Either as Jim suggests , a faulty NVR ( of possible a missing link to the hold on coil), or SOD suggests a safety feature switch, possible on the spindle guard or the belt / gear cover. Both switches as wired in series so if either stays open circuit the NVR will not latch. If you can get access to the switches you can bridge the connections . Disconnect the machine the mains and take care with the insulation of any links you use.

Brian

[Ian Patrick 2Participant @ianpatrick2]

Thankyou for the advice,

The guard switch is still in place, with the switch pressed down the mill doesn't light up or move at all, only once it is depressed does it work.

I have ordered a new NVR which should hopefully arrive tomorrow. I have (hopefully) attached some photos of the current NVR, i took the unit apart to have a look and noticed there is some scorch marks between the contacts, one in particular looks really bad, could this possibly be the fault?

All the best

Ian

[Ian Patrick 2Participant @ianpatrick2]

Posted by BC Prof on 27/04/2021 22:49:39:

I can think of two possible faults. Either as Jim suggests , a faulty NVR ( of possible a missing link to the hold on coil), or SOD suggests a safety feature switch, possible on the spindle guard or the belt / gear cover. Both switches as wired in series so if either stays open circuit the NVR will not latch. If you can get access to the switches you can bridge the connections . Disconnect the machine the mains and take care with the insulation of any links you use.

Brian

Would the Gear cover inside have a limit switch? It has a low and high gear setting. I will see if the new NVR unit solves the issue tomorrow but if not i shall have a look inside for another limit switch, i hadn't thought of that!

Atvb

Ian

[Jim MasonParticipant @jimmason14480]

If that thinner black wire in the right of the photo on the switch is on a fifth switch connection then I'll bet pounds to pennies that is the supply to the NVR, and the NVR had gone to meet it's maker. A new switch should sort it.

Jim

[David George 1Participant @davidgeorge1]

Hi Ian I have just checked my mill as I have same and I can start motor with gear position in any position. I can start motor with spindle potentiometer in any position, it just rotates slowly if turned down to bottom setting. I wonder is there a problem with the potentiometer as well. If i can check anything on my mill against yours please ask.

David

[John ShepherdParticipant @johnshepherd38883]

Ian

It has to be an NVR issue. If there was a fault with the interlock switches etc the motor would (or should not) run when the on button is held down, it would be dangerous otherwise.

Good luck.

[Ian Patrick 2Participant @ianpatrick2]

Hi all,

New NVR arrived today, however there is only 4 possible connections? Would the 5th connection (To create the magnet) be internal?

Thankyou all for far for the help!

Atvb

Ian

[Ian Patrick 2Participant @ianpatrick2]

Hey all, just a update!

I tried the new switch, removed the extra wire, hoping it was an internal connection on this one and boom, worked!

So must of been a worn out NVR

Thankyou for all of the help! Now I can start ordering some tooling for it!

Atvb

Ian

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