Magnetic ground/probe

(mikep) #1

Inspired with the ongoing flurry of magnetic ground probes, here’s my take.

I took a male->male 3.5mm headphone cable and cut off the plug at the -end- of the housing. This didn’t work well using a female end and just attaching the magnet to that. I used a cheapo I found on amazon. I chose it because it was cheap and had a braided nylon jacket that I thought would hold up well.

Filed the end flat. Now the end is solid metal, and flat so there is something to attach things too.

Glue a single layer of aluminum foil to the end, and glue a magnet to that. The foil does a good enough job of bridging from the conductors that are left to the magnet (it’s a little wrinkly and pokes through the glue). Superglue is too brittle, the magnet snaps off after a couple uses. Conductive epoxy would be best (but I don’t have any). Regular epoxy is a little fussy, but seems to work well enough. I’ll see how it holds up.

(Scott Conant) #2

That looks sweet and neat Mike. Makes my OCD happy…lol

(mikep) #3

As a followup:
No surprises here, sticking onto the end like this isn’t very mechanically stable.

  1. Plain epoxy didn’t really work out. I wasn’t able to get consistent electrical contact. Worked for a a few jobs, then stopped. Stayed stuck, so I’m not sure exactly what went wrong here.
  2. Conductive epoxy worked great, but I’m having trouble getting it to stick well to the magnet.

I’ll try ways to get more “tooth” onto the magnet to make it easier to bond. If that doesn’t work…maybe on to plan “F.”

(Dan Nelson) #4

Been thinking about this a bit. What if you soldered the wire to the magnet (I’ve read heating these little magnets kills their magnetism). Then you stuck a second magnet to the first (to get the magnetism back). Then slather some epoxy across the whole mess (avoiding the conductive end). And heat shrink the whole thing (again not all of the way to the conductive end). Haven’t tried this myself, been busy with other projects, and so far my alligator clip is working like a champ.


(mikep) #5

Not bad ideas, just working from simpler to more complex. I think a few magnets (I have plenty) on the end with some silicone/epoxy and a heat shrink sleeve might be just fine. I haven’t had a lot of luck soldering to these. I had high hopes for the conductive epoxy, just makes for a really clean looking job.

(Craig) #6

I used the KISS magnetic clip, placed a rare earth magnet captured between the jaws of the alligator clip. IIRC it is a 3/8” x .1”. Works great, no adhesive or soldering required. The alligator clip is magnetized and grips the Collet well.

Another option you coul try are magnet cups, solder your wire to the cup, then insert your magnet into the cup. Lee Valley sells the cups, I’m certain they are available elsewhere.

(Dan Nelson) #7

I just did a little search inspired by this newly resurrected thread and came across these:

Don’t know if it’ll work, but I ordered some to give it a shot, will report my findings!


(Rich Knudson) #8

My solution was to use a 2.1mm x 5.5mm 18ga power cord. I also use magnets for both the spindle and touch block. I just embedded 1/4" x1/4" magnets into the block, securing with Locktite 638 retaining compound. For the cord to magnet connection a short piece of 1/4" ID brass tube served as a housing. A piece of 1/4" OD brass is soldered into the tube. The brass rod is drilled to allow the wires to soldered into the rod. Again 1/4" x 1/4" magnets are secured in one end of the tube with Locktite.
It should be noted that my block was made by me, only because the availability of the Carbide 3D block was sketchy. This was done prior to release of Carbide’s Block.
Thanks, Rich