Looking for ideas to affix graphite electrodes to a copper block

[ca2n]

Hello,

I hope everyone is in good health and keeping safe.

I had 2-mm-diameter 303 stainless steel rods press-fitted into C101 copper blocks as shown below:

The SS rods protrude from the copper block surface at equal lengths and I've had good results for my experiments. I'm now moving on to replacing the stainless-steel rods with graphite rods.

A vendor has supplied MCCA(?) grade rods to me which are 3 mm in diameter and cut to my desired length. I'm looking for ideas on how to affix these graphite rods to the C101 copper block. I don't think press-fitting them as I did with the 303 SS rods would work.

What is most desired from the connection between the graphite and copper is good electrical conductivity. As an added bonus, integrating a convenient way of replacing the graphite rods, when they break, would be beneficial.

Among the ideas that have been bounced around:

• Interference fit of the graphite rods within graphite sleeves, which themselves are press-fitted to the copper block.
• Use of mechanical clutch contraption (like that used on mechanical pencils) to hold the graphite rods in place.

Each of these ideas has its pros and cons. And we're still looking for other options.

I would greatly appreciate some thoughts from this wonderful community on how I might be able to achieve my desired outcome.

Thanks.

 

[implmex]

Good morning ca2n:
As I see it, your best bet is to put collets into the copper block.
They need not be complicated, and they need not have a large collapsible range.
They can either be integral with the block or they can be separate pieces depending on what you hope to accomplish.
If it were my project (and not knowing what these rods need to do or how strong the connection needs to be, I'd look at wire EDM cutting my collet shapes through the copper plate and putting a tapered pipe threaded collar on the back or front of each shape to allow each too be collapsed with a little collet nut.
That will be the most secure and accurate and still allow easy interchangeability of the graphite rods.

If you can't see your way to something this elaborate, can you just tap an M2 or so hole into the back of each graphite rod and make blind pockets into the copper into which you can run a little screw from the back?

If you don't like that idea either, you could just put an angled setscrew into each pocket and nip the rods with the setscrews.
You'd have to populate the copper block from the center outward, but it would work.

Last, you could do the split collet idea as before but instead of a collet nut for each collet, you could run a tapered pipe plug on each side of the split so the collet is collapsed as the pipe plug is advanced.
Attached is a picture.
Obviously the tapered holes are where the pipe plugs go.
If you want better alignment of the rods, take out the flex relief slot and the two pipe plugs on one side and collapse only the other side.
If you do it right, you can use only one pipe plug per collet like the second picture.
However if you do this, the graphite rods MUST be very consistent in size. (better than 0.001")

Cheers

Marcus
www.implant-mechnaix.com
www.vancouverwireedm.com

 

[Thunderjet]

Counter bore the face of the block to accept the rods.

Drill a clearance hole thru to the back side to allow for a 2-56 flat head screw and drill and tap the rods to accept the screws.

Simple easy and replaceable.

 

[boslab]

Graphite conductive adhesives ( seem to remember them in the electron microscopy room)
Water based stuff
Mark

 

[Joe Gwinn]

Copper-plate the graphite rods at the ends that will go in the block.

Sweat-solder the copper plating to the copper block using 63-37 eutectic tin-lead solder. This is most easily done by putting all the rods in the block, each with a solder collar and some flux, and heating the block up until the solder joints all form.

 

[DDoug]

I always wondered what the electric motor brush people use. The braided copper lead goes into a hole in the brush, and you can see a copper glue of some sort extruding out.

 

[9100]

I once had a tachometer generator that developed voltage on the brush but nothing came out of the wire. Finally, the dingbat temporary helper I had at the time said that the wire had fallen out and he put it back in with superglue.

I also wondered about copper plating the graphite. I never tried it, but it should work.

Bill

 

[jim rozen]

" And we're still looking for other options. "

1) drill and tap a hole in the graphite. Thread the end of the copper part.

2) drill and tap a hole in the end of the copper, and put threads on the major diameter of the graphite.

3) drill a hole slightly larger than the graphite OD in the copper. Use Epo-Tec silver epoxy (H20S) to glue the graphite in place.

 

[ca2n]

These are all brilliant ideas, guys, thanks.

I'll discuss these with my colleague to see what might work the best.

Again, many thanks.

 

[Joe Gwinn]

Also look on the website of a few graphite manufacturers -- they usually discuss how to attach to graphite or carbon.

 

[EPAIII]

A self holding taper?

 

[snowman]

not sure of space behind, but tig torch collets could save you time

or just 2mm tubing compression ferrules...using a combination of double flare brake nuts then a custom ground seat tool