Repairing an electromagnetic coil on a machine brake

My Rambaudi Mill has an electromagnetic brake on the spindle that hasn't worked. The sheave has a steel plate with dogs but the brake wasn't engaging it. Turns out the wires leading into the coil were broken as they entered. Can the coil be repaired and new leads brought out? The brake is a Baruffaldi and replacing will be difficult without swapping sheaves. Coil and plate on machine. Front of coil Back of coil with wires barely in sight. Is this a job for a motor shop? thanks, Dave

Can you get it apart without damage? If so it looks like solder new leads to the cut ones or replace the cut ones altogether. If you can pull them out a little to solder and heat shrink you might not even need to take it apart.

It's entirely possible to burn the potting compound out, exposing the magnet wire, which is then taken out, turns counted, wire size matched and a new coil wound, installed and potted. If you're crafty you can do it, if not so crafty, a competent motor shop has all the resources to do it.

I've done it before...it works!

Stuart

beckerkumm said:

My Rambaudi Mill has an electromagnetic brake on the spindle that hasn't worked. The sheave has a steel plate with dogs but the brake wasn't engaging it. Turns out the wires leading into the coil were broken as they entered. Can the coil be repaired and new leads brought out? The brake is a Baruffaldi and replacing will be difficult without swapping sheaves. View attachment 285603 Coil and plate on machine.View attachment 285604 Front of coilView attachment 285605 Back of coil with wires barely in sight. Is this a job for a motor shop? thanks, Dave

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If you cut yerself a couple of short lengths of insulating tubing, slip them over the two stub wires, you should be able to get first, meter probes on the pair without shorting to each other or the frame..

- See if you have continuity.

If so..

- go the next step - apply appropriate power and see if you have a strong magnetic field rather than smoke or stink.

IF.. the coil is good, then it is tedious as-in eye surgery to splice-on new leads when those are so hard to get at.

But it CAN be done.

Then sleeved with heat-shrink tubing OR salvaged soft insulation jacketing from larger wire plus liquid tape if yah need more flexibility.

No rewinding needed. Hopefully. Unlesss... a PO CUT the wires because it HAD shorted turns?

BTW: Baruffali is still in bizness, but they were never "cheap", so "spare part" might be a joke.

You might also see if the size is close enough you could adapt a coil - or an entire clutch - from an ag/groundskeeping mower-drive electric clutch.

They are about a hundred bucks, complete, on ePrey, new. Stewart-Warner or Dings motor-brake coils or complete units are another possible source.

"Personally"... I'd be tempted to rig a bellcrank, lever, cable, or rod and make it into a "manual" brake. or simply do without and move on to some other more important project.

It's a mill, not a motor vehicle. Not all of them ever HAD a spindle brake.

If the coil proves to be good I would open up the hole on the mill with a small end mill
Using a turntable if you want it perfect
Beeing carefull not to mangle the wires and then solder on a extension

Peter

Peter from Holland said:

If the coil proves to be good I would open up the hole on the mill with a small end mill
Using a turntable if you want it perfect
Beeing carefull not to mangle the wires and then solder on a extension
Peter

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I was thinking something like a hollow end mill to clear the region around the wires. Carefully. Maybe
leaving a 0.005 rim of steel around them for safety. Then going in there under a microscope and cutting
the remaining metal away. I suspect if you go 0.100 inch deep that will give enough room to solder
on the extension leads. Teflon insulated exention leads, thin teflon tubing to insulate. Rosin flux
only. Often old wires like this don't tin up well when they've been exposed to who knows what from the
ends for a while. Don't use anything more than rosin flux. The insulation will try to melt when you tin it,
if you can slide some thin teflon tubing down along the wires that helps before you start.

And the comments about ohm the thing out for continuity and ground isolation before you go heavy at it,
excellent advice.

Thanks, all. My retired motor guy said he will take care of it. He still does work for me because I always have weird stuff for him. He rewound the Italian motor that came with the mill. Gives me an excuse to visit. Dave

Here are pictures of the plate that sits in the sheave. I had expected the brake to pull the plate free of the dogs but as usual, I'm likely wrong. The pads must sit lightly on the disk but just stop it when current is applied. There was no spring to push the plate in either direction. Does that sound like how it should work? Dave

Cost $30 to get the coil on the brake fixed. Works well once I realized I had the two wires in reverse so it was repelling. Sometimes i self inflict. Dave

beckerkumm said:

Cost $30 to get the coil on the brake fixed. Works well once I realized I had the two wires in reverse so it was repelling. Sometimes i self inflict. Dave

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Since when is it that a electromagnetic coil is repelling a iron brake disk when polarity is reversed
Peter

I probably didn't explain it right. There is a steel plate that sits in the sheave with dogs to catch it. What i thought were brake shoes were just shoes to adjust how far from the coil the steel plate sits so when the coil is energized, the plate stops but doesn't rub against the coil. The shoes rub against the steel as it is rotating rather than stopping the steel plate by having the magnet pull the plate to the shoes. Probably obvious to everyone but me. Dave