End-to-End Knife Marks in Maple
Knives in bad condition caused linear scratch marks in Maple moulding. What's the fix? May 11, 2011
Question
I have been manufacturing a 3/4" x 3/4" picture frame moulding for a customer for the last 5 years. I use a tinted topcoat to achieve a cinnamon color finish. The company that did my milling went out of business. I have tried two different mills since with no luck. Both companies had the same problem - the moulding looked fine with a natural finish, but when I use a tinted topcoat to achieve the cinnamon color, I can see lines running the length of the moulding. I purchase 3,000 ft when ordering, so I need to find the best way of sanding the lines out. I’ve tried a hand held orbital sander, but the lines are too deep. I have also tried using my old 4 headed Makor profile sander using an 8" sandpaper and scotch-brite combo wheel at 180 grit, but I still see the lines. I do not own a drum sander, but I could purchase one if I was sure it would work. I really need some good advice on how to sand hard maple.
Forum Responses
(Solid Wood Machining Forum)
From contributor M:
Sounds like small bugs in the knife. Should be reground or stoned out. Can you put up a photo of the problem? What does your moulder guy say is going on?
From contributor T:
The mill should have known better. Carbide knives are the only way to fly with hard maple to avoid what you are seeing. They are nicks in the knife where the edge is rolled back and polishing the wood and closing the cells so it won't take stain. Carbide virtually eliminates this, but it comes at a cost. It's going to take a lot of sanding. Try to go back to the mill to recover some of your time.
From the original questioner:
Thanks. I think you’re correct, because the lines almost look burnished into the wood. Should I purchase a drum sander, and if so, which grits of sandpaper should I use?
From contributor M:
I agree that a run of 3000 lf should have carbide tooling. High speed steel will require several regrinds and the quality will deteriorate as you near the regrind. I also feel that the cost of resanding may eat up a lot of your profit. Will the mill replace the stock at no charge or a lesser charge? They may ask for a one time tooling charge for new carbide, but it shouldn't cost too much for such a small knife. You will still have to sand to get the smooth surface you need for your finish, but you won't have to fight with sanding the bugs.
From contributor B:
Your most economical solution might be to seek out someone with a straight line profile sander. They will make a sanding block to mate the profile, just like the knives that produced the moulding mate to the profile. I'm not sure what all this will cost.
From contributor N:
Try spraying it with a spray bottle of water, let dry (only takes a minute or two), just to raise the grain. Then try the orbital.
From contributor H:
Knife marks end-to-end are nicks in the knife. I run a M3 HSS (machined from German made steel, and not the cheaper Chinese steel). I do mostly hardwoods, including quite a bit of hard maple, and I can do 3,000 lineal feet with some not so aggressive profiles, but most I would have to hone at 1,500 to 2,000 feet. You may want to consider carbide, but I don't think that it is necessary. Probably it is a quality of knife problem.
