I have recently done a lot of testing with splicing cables.
I have tested a number of different urethane and 3M potting compounds. This was done using 3D printed molds.
The aim was to test joining of BlueROV R1 7.5mm tether and BlueROV Slim 4mm tether with MCIL connectors 8.5mm.
- Vaseline (Petroleum Jelly) works well as mold release (available, easy to apply and effective)
- Silicone grease, technical oil, silicone spray, olive oil
- Bonding to 7.5mm BlueROV R1 is nearly impossible
- Scotchcast 2131B worked best
PUR80 worked well
- Adding a small amount of coloured mica powder had no effect on adhesion
- Flame treating the cables makes a positive difference
I took some inspiration from Oultland Tech here.
Here are the molds I made.
Mating faces of the molds were wet sanded on 320grit sandpaper until smooth and internal faces were lightly sanded.
The aim here was to get some experience splicing cables. I had some spare pieces of MCIL pig tail to play with. I have 300m of old R1 tether and wanted to try get that to pot well. I have never succeeded in the past.
I also wanted to test some different potting compounds. Scotchcast 2131B is hard to get in South Africa and expensive. I found that PUR80 works quite well and can be coloured with mica powder for extra style points. In mission critical applications use 2131B.
I found that nothing sticks to the R1 Tether. I think it is jacketed in Polyethylene. In the end I cheated. I applied a thing film of Gorilla Glue to the cable and then applied heat shrink over the top. I could not source the right size of adhesive heat shrink. Getting a bond with the heat shrink was no problem.
@magnusmyklebost suggested flame treating the cable here. I found that this helped, but it is hard to quantify how much.
If you need a really soft potting material, I would suggest Vytaflex. It seemed to adhere well, but only goes up to 60A.
Hope this help someone. If you need a custom size mold and have a 3D printer, I will happily modify for you.