Hi Adam,
As I recall, no matter what feed speed etc, there will always be scallops left as the timber is fed through the rollers, the relationship to its position on the block will differ, with the knife cutting and missing alternately, and of course, with the block being round and the timber flat, it will leave a scallop.
Slower feed rates and/or faster block rotation minimise this.
When I was learning my trade we were told that anything less than 25 cuts per inch, or one every millimetre was not acceptable as it is too easily spotted with the naked eye.
Most machines nowadays get up around this with ease, with some hitting about 2 cuts per mm or better, hence the better finish. The ratio between the feedspeed and cutter block rotation(allowing for number of knives in the block) will give you the cuts per mm.
The serrated infeed roller should in theory have little effect on the finish as the timber has to pass under the knives so these should be removed.
Excessive pressure from this roller and a very fine cut could result in these serrations still being evident after the timber has passed through though.
The outfeed roller can cause damage from stray chips though, which is where the rubber covered roller comes in. Any chips pressed into the surface with the outfeed roller should be cushioned by the rubber, minimising damage to the finished board. A steel roller can end up leaving dents in the surface.
Cheers,
Andy
