Mill plus power-feed circuit protection

[Gone AwayParticipant @goneaway]

My mill (WM16 lookalike) was imported into Canada under approval from the local electrical authority rather than CSA because of the low volumes. Part of the approval required that the original 8A fuse be replaced by a 6A component. I have to assume they knew what they were doing but it did make the mill rather sensitive to any slight heavy-handedness, particularly in high-gear, and it became a nuisance replacing fuses (assuming I had one at the critical time).

I considered replacing the fuse with a circuit breaker but then, rather than modify the machine I decided to do that with an external box with two outlets: a local-breaker-protected (6A) outlet for the mill and a separate outlet for the power-feed that I have on the mill. The fuse on the mill was replaced with the original 8A fuse.

This works very well – except under one condition. If the mill breaker trips during a cut with the power-feed, the feed continues for a second or two until I can react enough to turn it off. Usually, the upshot of this is that the force on the cutter rotates the milling head against its locknut and leads to subsequent re-alignment attempts without tearing down the whole setup to do it properly.

What I need is for the electrical outlet for the power-feed to be controlled by the same circuit breaker that protects the mill such that if the mill trips, the power-feed will shut down too. I don't want to directly run both from one circuit breaker since then it would react to the sum of the two (variable) currents. What I think I need is for the mill circuit breaker to also be wired to the coil of a relay whose contacts switch the power-feed outlet.

Is there a better way? Are there any commercially available devices that will do this?

[Gone AwayParticipant @goneaway]

[AndyfParticipant @andyf]

Sid, all I can think of is what you suggest near the end – use the downstream side of the 6A breaker (or fuse) to feed not only the spindle controller+motor but also the coil of a relay which has a separate mains supply to its contacts (with a fuse/breaker appropriate for the power feed upstream of those contacts). This means that your 6A breaker will have to carry the additional current required by the relay coil, but on the 230V UK mains that would only amount to something like 30mA, or 0.03A. If you are on 110-115V mains, it would be 60mA or so, but that ain't much – check the specs of relays with mains voltage coils available in your area which are capable of switching the power feed current .

A simple thing to make up if you are confident with wiring up mains voltage contraptions and earthing/grounding any metal box containing the relay.

Andy

[DustyParticipant @dusty]

I have both motor and power feed fed through the on/off switch. This means that unless the spindle is running you cannot turn on the power feed, conversly if for any reason the power to the spindle motor fails it cuts power to the feed. Simples.

[Gone AwayParticipant @goneaway]

Andy, I don't have any problem with building something like that – just wondered if there was a better way.

…. Well there is (a better way) as Dustin suggested. That would involve modifications to the mill itself though which I'm loath to do. Also, I suspect, Dustin, that both the mill and power-feed are both fed through one fuse or CB in that case, which is not what I want.

I have this "itch" in my brain about somehow using the same kind of zero volt dropout switches (what do we call those?) that the mill uses, externally to the mill somehow. Can't quite formulate it.

Edited By Sid Herbage on 31/05/2013 22:52:36

[Ed DuffnerParticipant @edduffner79357]

I'm just wondering if a 4-pole contactor with overload protection would suit this requirement. Any overload on either of the circuits would switch off both mill and power-feed.

Although just thinking about it a bit more. If you had to hit the Em-Stop button on the mill, the feed would still continue to run. So you might need to control the circuit to the power-feed via the EM-stop circuit as well.

Edited By Ed Duffner on 31/05/2013 23:54:18

[Gone AwayParticipant @goneaway]

Sounds interesting, Ed …. could you point me to one?

[Ed DuffnerParticipant @edduffner79357]

Here's something that might work but it could be a costly and over engineered solution. It has 4 normally open contacts. Usually used for 3 phase equipment or switching banks of lighting. I can't see why it can't be used two switch 2 individual circuits. It's basically a relay with a self latching coil mechanism.

(2nd row up from the bottom, right hand side, CA2KN40G7)

**LINK**

That one is rated at 10 amps. Some of those types of contactors utilise plug in overload protection so pehaps there's one availbe at 6 amps. You'd have to do some research into what's available, maybe have a chat with a local supplier?

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