Pilot hole is always a good idea, needs to be 1/3 to 1/2 of next drill size, not more. Give the next drill something to do or it will grab.
Drilling down a pilot hole in cast iron always needs the drill rake modified to be nearly neutral, a standard drill grind will always grab and chatter or rip the corners off the drill. Same goes for green brass. Standard 118 deg point jobber drill perfectly OK for CI if the rake is backed off. Negative rake not necessary, neutral or about +5 deg is OK.
Speed – 1000 revs is too fast as others have said. Drilling cast iron keep the speed low and the drill cutting. Chips should come out as discrete pieces – say half the size of a match head – not dust. Slowness not critical; to success (that's in the grind of the drill) but suggest anywhere below 500 rpm for 10 mm hole is right ball park. Slower the better, keep the feed going.
If drill wanders and chatters on entering the pilot hole (leaving a nasty serrated edge as it throws the work piece around) fold up a small scrap of rag (old jeans ideal) and wedge it in the pilot so the advancing drill touches it first. This is sacrificial, but will stop the chatter and grab as the next stage drill edge meets the face of the work.
HTH Simon