Carbide Tipped Versus Solid Carbide Knives

The comparison between high-speed-steel, carbide-tipped, and solid-carbide knives depends in part on what material you're machining. August 12, 2007

Question
I am currently running HSS planer knives in my planer. I am considering carbide tipped or solid carbide. Can someone help me out with information?

Forum Responses
(Architectural Woodworking Forum)
From contributor R:
The type of material can be a big factor in your knife type. HSS knives will give you a cleaner cut because you can get a sharper edge. Don't get me wrong - carbide tipped or solid carbide are very sharp, but not quite the same.

The big factor in the carbide tipped and solid carbide is the life. You will increase your run time between sharpenings a great deal, therefore less down time and less setup time is required.

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From contributor A:
The carbide used in inlayed tipped knives is usually not as long lasting as solid carbide knives because the harder carbides will crack when they are brazed into the HSS backer. Carbide tipped can still give very good results, though, and they are generally a lot less expensive that solid. Remember, different wood species do better with different tooling. What type of lumber are you mostly planning on planing and how much?

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From Professor Gene Wengert, Sawing and Drying Forum technical advisor:
A couple rules of thumb... The softer the wood, the more HSS will give a clean cut. Carbide fuzzes softer woods. The denser and knottier the wood, the more chance that you might hit a dry knot and fracture the carbide. Sharpening is more technical with carbide. In a planer, jointing is not really sharpening carbide. Carbide will outlast HSS by at least 30x, unless you hit something harder than wood.

Are you planing rough lumber that has been air dried? If so, a segmented knife is best, as you only damage one small segment when you hit a small stone, etc. Because carbide is brittle, care must be used to avoid damaging the carbide edge (hitting, dropping, etc.). Carbide gets dull and must be sharpened. Oftentimes I see carbide used too long between sharpenings. When you have the need for sharp edges in a profile (not a question when you are using a planer), HSS may do a better job.

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From contributor S:
Some personal experience, for what it's worth. I am not a production shop - mostly custom furniture and boat work. I don't joint/plane a ton of lumber, but a fairly high percentage of what I do is teak. And teak is murderous on HSS. I put carbide edged knives in both my jointer (Jet 6") and planer (Delta 15"). The jointer knives were approximately C$60 each (times 3) and the planer knives were C$130 each (times 3). This is not trivial... and solid carbide was substantially more expensive. I went with tipped knives because of expense, and the fact that solid are more brittle.

The finish from the carbide knives is not as good as HSS, no question. However, my theory was, and has proven true, that I never need a finished surface right out of the machine. A jointed edge gets glued (typically) or finish sanded anyway. And a jointed face ends up going through the planer, and again, the planed faces end up getting sanded anyway. And the difference in sanding time is negligible. But the kicker was/is, that even though the carbide is not as smooth a finish, if you're running teak, by the time you have pushed a couple of sticks through it, the HSS has dulled to the point where it is no better than the carbide. And finally, I hate changing knives. I did not know about Shelix heads when I made my decision.

Having said all that, even though I'm glad I've got carbide instead of the stock knives, if I was going to do it again I would either look more closely at:
1) A Terminus or some such head that is very simple and easy to change knives (and the knives are not all that expensive). Then you get the advantage of a HSS cut and finish.
or
2) Shelix heads. This is most likely.