Question
As a general rule, it is well known that for a fixed speed, the more knives, the better the quality. Our company is facing a problem with this. We purchased a 12" planer running at 360fpm maximum. We have purchased 12" heads with 12 knives. This gives us a very good quality with 17 marks per inch. When we run widths going from 3 to 8", the machine could run to 280 to 360 fpm and the quality is okay. When we need to process pieces 10 and 12" wide, the speed should be slowed down to 150 to 180 fpm. But the quality we get is worst, showing some signs of chatter marks. The manufacturer of the machine says the problem is that there are too many knives for the speed. I don't agree with that. Is the manufacturer right?
Forum Responses
(Solid Wood Machining Forum)
From contributor C:
More knives is not always better. Your rpm's are a key component of determining the best feed rate. Feed rate directly affects the finish quality of the work. If the rate is too slow, knives dull more quickly and burning occurs. By running too many knives in a cutterhead at too slow a feed rate, you may also be experiencing hammer marks. These are caused by inadequate dust collection, or by the next knife in the cutterhead catching a chip cut by the previous knife and hammering it back into the work piece. Too many knives can also glaze (burnish) your work piece surface and create problems on the finishing end as well. Be mindful of maintaining proper chip loads to achieve the best possible material finish.
