Battery contacts

[tvodrd]

I have been using silver relay contacts cannibalized from old octal KRP relays for my positive battery contacts. (Yeah, anal.) It's a little more classy than a "blob" for the back of Wayne's boards. Well, I ran out of relays. Salvaging and lapping contacts to useful size was always a PITA, so on a whim, I Googled "silver sheet." The stuffs all over the place. I ordered an oz of .020" thick sheet from a supplier in AZ. ($20 for $5 worth of silver but try making it yourself by pounding out a coin.) I made a .150" punch and die. Stuff arrived and I punched a few. I got to
thinking. (uh oh /ubbthreads/images/graemlins/grin.gif ) Gold-plated silver would be better and Cobalt gold(over twice as hard and much better wearing) would be better still. I pulled out my SoCal Thomas Register and found a local precious metals plater. I stuck my head in their door with 2 pieces (masked with laquer on
one side, and totalling 8 sq in) and inquired. $125 lot minimum! /ubbthreads/images/graemlins/faint.gif I told them I didn't need any certs or even a receipt for that matter and it would be cash. I have to admit they were cool and answered all my questions. Got .0002" two days later for $80. I'm out a C-note, but it will make well over 200 contacts.

Larry

 

[paulr]

Wow, cool! Gonna sell any of those little discs?

 

[Chief_Wiggum]

Mmmmm...gold over silver. Where's my punch set? /ubbthreads/images/graemlins/grin.gif

 

[PhotonFanatic]

Wouldn't a gold filled sheet have worked just as well for considerably less money, i.e., double clad in gold, brass interior?

 

[tvodrd]

Oeo2oo,

I'll have to plead clueless on that one. High-end relays/contactors use coinsilver contacts- usually a pretty thick layer. High-end connectors, like the pins on your cpu are gold plated albeit veeery thin. Gold-plated connectors for frequent make/break seem to typically be Cobalt gold alloy-plated for durability/wear. I'm told the Cobalt gold process results in a little organic carbon in the alloy matrix which "lubricates" the interface with a mating connection. Not sure where to get gold filled brass sheet in .020" thickness.

Larry

 

[CNC Dan]

nice punch.

 

[tvodrd]

From you, Dan, Thanks /ubbthreads/images/graemlins/blush.gif It was Q&D to the max- used a screwdriver bit for the punch. Punching .020" silver isn't much of a challenge.

Larry

 

[PhotonFanatic]

Larry,

Try this site for starters:

http://www.silversupplies.com/catalog/metals/gold_filled/sheet.shtml

There should be plenty of other suppliers though.

24 ga is .020 inches.

 

[Justintoxicated]

if your going to sell them I'll take a couple...I was going to smash some copper wire to plate the solder bolbs, but this sounds much better...I don't have a drill press or a punch like that...

 

[chalo]

I make silver button contacts-- not as pretty as yours, mind you-- by heating small scraps of .999 silver with a plumber's torch on a firebrick or charcoal block until they form beads.

A couple of smacks with a hammer on an anvil or vise top, and silver beads become silver buttons, ready to solder to a PCB or a contact spring and file true and clean afterwards.

Chalo Colina

 

[Doug S]

I love that photo. It tells a complete story all by itself. The individual items in the photo are artfully arranged IMHO.

 

[mrsinbad]

Really nice work. Can you post a pic of the face of the cutter? Thanks.

 

[tvodrd]

Mrsinbad,

I made the punch from a screwdriver bit. (Fairly tough steel.) I just ground the end reasonably square/flat on a pedestal grinder. /ubbthreads/images/graemlins/grin.gif Not worthy of a pic. The punch/die clearance is abt .005" total. I used .002" shim stock to act as a bearing in the guide portion in the die. I think the die is annealed 440C stainless. It's held up for 130 contacts so far and shows no sign of dulling. Silver is soft!

Larry