Full disclosure, since I bought some of these from Germany, and I am re-selling them in the US, I really can't say too much...since I'm also a moderator. That being said...
Based on feedback from customers, I am trying to improve the electrodes and the electrode holders. Part of the reason is also that I want to make the cables and electrodes here in the USA, so I don't have to pay the high shipping cost, plus customs fees.
The holders need to have more mass, so they don't get as hot so quickly, these are longer and fatter.
For those who wish to also make their own, here is the criteria I used in the parts selection. In order to make the "conductive" holders easier to hold, I made them longer. Right now 4-inches long seems to be the minimum to achieve this (it feels like holding a sharpie brand felt marker)...
Pure copper is very soft and hard to machine. I found an alloy called C14500. It is almost pure copper to make them very low resistance, but it has a tiny amount of tellurium to make it harder, so drill bits don't bog-down when cutting. You must still clear the drilling chips frequently to keep the bit from bogging down, drill 1/8th inch at a time, and then clear the chips before going deeper.
If you put the 1/2 inch rod in the drill chuck, and mount the bit below (facing up), then...when you raise the spinning work piece off of the fixed bit, the chips clear by themselves.
The C14500 alloy is specifically made for electrical contacts that need to be machined. It's IACS conductivity is 93/100 of pure copper, which is a huge improvement over using brass parts in the chain of current-flow (brass is IACS 28/100 conductivity of pure copper). Brass conducts well, but it will get much hotter than the same part made of copper.
The pic of the 3-inch electrode holder below is a rod that is almost 1/2-inch diameter (so it can fit in a 1/2-inch drill)...it's 7/16...11mm...0.437-inch...$9 per foot (plus tax and shipping).
https://www.onlinemetals.com/merchant.c ... top_cat=87
The fatter tip shown below [on the left] is a 1/4-inch copper rod, and the smaller tip is a 6AWG copper grounding wire (easily found at local hardware stores), both solid copper. The 4AWG solid copper grounding wire is halfway between the two (no 4AWG shown). The smaller 6AWG hole can easily be drilled out to fit a fatter wire. I think the 6AWG will work the best, new tips will be dirt cheap and NON-proprietary...
Part of my interest in the 1/4-inch diameter is that I can also get carbon rods and tungsten rods in 1/4 inch.
name___drill bit size__inch__metric
6-AWG____5/32______0.15___3.9mm (this is the smallest diameter that I would recommend)
When using the 1/4 inch copper rod, there was not enough "meat" left in the wall of the electrode holder to have enough threads to allow the set-screw to have a decent amount of hold. I even filed a flat area along one side of the 1/4 inch replaceable rod to allow the set screw to penetrate deeper. When I went to a smaller tip, I could also off-set the drilled hole, and I feel that doing this worked well. I think the 6AWG solid copper wire will work great, but if anyone wants the slightly fatter 4AWG, you can easily drill the hole out fatter.
Since the copper electrode holder is relatively soft (C14500 is harder than pure soft copper, but...still not as hard as brass). I wanted to use the largest possible diameter of set-screw, while still using a commonly available thread. The ones I tried here (and I am happy with them) are 1/4-20. That is also the fattest bolt I can easily get in brass, which would be the preferred material for the set-screw.
A brass (or aluminum) set-screw with a straight slot (for a screwdriver) is less likely to strip out the holder threads.
Electrode tips need to meet several requirements. They must conduct high currents with low resistance in order to avoid getting so hot that they begin melting (sticking to the work-piece), but...
Copper is cheap and available, IACS conductivity is 100/100, but...melts at 1080C
Tungsten melts at 3420C, IACS 31/100 (conductivity/resistance is better than brass, worse than copper. Will get hot, but will not melt)
An alloy of 70% tungsten and 30% copper is sometimes used for industrial electrodes (need to research more). They run cooler and cost less than pure tungsten.
Experiments with carbon gouging rods are on-going. Will post results when a definitive conclusion is achieved. They are very affordable, but brittle. I easily shaped the tips with a pencil sharpener.