After reading several articles, including the last issue of Woodworker’s Journal eZine, about spiral cutterhead on jointers and planers, I understand the advantage of being able to just turn the cutter insert for a new edge. My question is, when you change one of the cutter inserts to a new edge, should you change just the one insert or should you change all of the inserts? Could there be an uneven, though slight, cut on the surface? – John Mahoney
Tim Inman: If your cutterhead uses inserts that have only one cutting edge, then I would change out the whole set. If your cutters can be turned to reveal a new surface, then I don’t see why you couldn’t just alter the one nicked one. Chris is probably our best resource here, since he has that type machine.
From our last set of questions, where Chris had a bit different opinion of spiral cutter than did I, I would like to just point out the one very important point we both completely agree on: Whatever type cutter you use, straight blade or spiral insert, the cutters must be razor-sharp to do the best, safest, work. No disagreement there. Period.
Chris Marshall: As I suggested in the last eZine issue, these carbide inserts stay sharp for a very long time. So, to answer your question, John, if I noticed a telltale sign of a nick on my jointed or planed stock (a tiny raised “track” on the wood where the knife edge no longer is making full contact with the lumber), I would be inclined to rotate just the inserts that are affected by the nick. There will be several, because the edges of the inserts overlap. I would leave the other inserts as is. But, if I was noticing more tearout than usual across the full faces of my stock, or if the jointed or planed surfaces were generally not as smooth as usual, I would rotate all of the knives to sharp edges. So, the same reasoning as a straight-knife cutterhead owner would do when the knives would need to be removed and re-sharpened. More to your point, when I’ve rotated just a few of the inserts, I haven’t noticed a measurable difference in surface smoothness between the areas where the fresh insert edges are at work, versus the rest of the inserts that are not as micro sharp anymore. Again, I think some degree of overlap helps here, as does the long edge retention of these inserts over time. I should also add, even if there was a slight noticeable difference, I don’t have “finished quality” expectations for my jointer or planer, only what I’ll call “glue-up” quality. I scrape and sand all of the edges and faces anyway to remove evidence of machining, except for those surfaces I’m edge- or face-gluing.