I have been thinking about making some race lines as well.
Do you guys buy some sort of splicing kit to make it easy or just use things from around the house?
Anyone found a good supply or thinner line?
I got some of these http://www.westmarine.com/buy/samson-rope--selma-splicing-fids-set--3736006
for splicing down to ~4mm. They're awesome for doing the 4:1 bits of a race bar, or chicken loops. You don't really need the set, the largest one would do docking lines I think. For flying lines I use a piece of hook up wire (solid core) with the insulation removed. Guitar strings work well. They both break where you fold them in half after a while, but are cheap to replace. You can buy fancy tool that are moulded wire with a handle. They're sometimes nice when you're doing sheathed rope and are trying to bury the cover. The biggest tip I got to make splicing easier is, taper the tail! You can pull the taper into the bury a lot easier than the full diameter, and it make for a stronger splice. This shows you how:http://www.animatedknots.com/longbury/index.php?Categ=splicing&LogoImage=LogoGrog.jpg&Website=www.animatedknots.com
I like the McDonald Brummel as it locks, no need to stitch it then.
I looked on alibaba.com for some dyneema, waiting to see if I can get some samples before buying 100kg spools of line!