Some key points with cable damascus, first, when you heat it up the first few times, dont bring it to a welding heat. Let the tar and oils and such burn out, and then flux it liberally, let the flux really soak into the center. The flux doenst only help prevent oxidization, but it helps clean the crud out.
As said, you'll ruin several steel brushes, every time you take i tout of hte fire, quickly brush off all the crud that has worked it's way to hte surface.
There are two good ways to set teh weld, using a pipe wrench and a vice and twisting it (you have to be fast out of the fire) is a good way, but i usualy hammer. Dont hammer hard, hammer lightly, you just need to set the weld, if you hammer hard you'll just break it apart again. Hammer along the twist of the strands with firm blows, continually twisting the cable as you go along to keep the part you'r ehammering at hte top. Move along one strand , and then if youv'e worked fast enough start on the next one BELOW it in the twist (that's important, because if you hammer on the one 'above' it in the twist you'll start to unwind the cable as a whole. Hard to describe that part, but in the few billets I've done now, it becomes readily apperant because one way of hammering it will tighten up the strands, the other will mke them looser.
brush it off and flux it again before putting it back in the forge. Once you've gone along each of the strands you should really start to feel that hte weld has set, instead of soft squishy blows, it will start to resist your hammer, at that point you're basically all welded. You can start taking your time now. Go along the surface of the bar, which should be probably around 3/4 as large around as it started once the weld is fully set and compressed, and pull / pick off with pliers any burnt out strands, these are decarbed and not good for the steel. What gives cable damascus its pattern is the pattern of the decarbed outer part of the cable strands, but some of the cables on the outside of the billet will likely be totaly burnt.
After you get rid of any burned steel, flatten it out at your leisure, though i still like to work at high heat, like i would wrought iron.
Once you've done it well once, it becomse much easier the next time.
(my problem now after a few billets... is i need to actulaly USE them and make knives!. I've got a pair of sigan dub in the works out of cable right now though)
edit: here's a pair of cable billets i made, ground flat, and ready to be turned into the sigan dub, as you can see, there's no 'sign' of them being cable if they're welded properly , not untill you etch it, either that or unles you hammer with a very polished hammer, in which case you can see the pattern in the polished hammer-print
http://www.tharkis.com/images/cablebillets.jpg
