Best Hook Angle for Corrugated Insert Knives

      Here's some insight into hook angles. Different hook angles may work better for different woods, but other factors matter more. May 5, 2007

Question
I would like to find a chart for determining the correct set angle to grind in corrugated insert knives. I'll be cutting curved stair rails next week, and have the knives ground by a business associate who uses a Weinig profile grinder. He generally sets the angle at 19 degrees, but I'm wondering how different angles might affect the performance?

This particular rail is white oak, though I have a curved cherry rail to cut next month with the same knives... Also, I know that my 2-knife insert tool head's set is 20 degrees. Is this the same as a standard 1-13/16" moulder head like his machines use? Or is there an offset to calculate?

Forum Responses
From Professor Gene Wengert:
We need a hook angle, clearance angle and knife angle. The three total 90 degrees. Oftentimes with hardwoods, the clearance angle is 9 to 10 degrees (so the heel of the knife does not hit the wood). The hook ranges from 20 to 30 degrees, and may be controlled by the slot in the head when the knife is inserted. The remaining angle is the tool's angle. (To decrease hook, sometimes the knife is back beveled.)

Here is a quick summary: As the tool gets more slender (hook gets larger), chip out is more likely, but less energy and dulling occurs as the piece is usually splitting ahead of the knife. That is, the knife is acting like a wedge and splitting out the chips. If the hook is too small, the knife acts like a plow and more energy is needed, but there is no chip out, but there may be fuzzing. Moisture content of the wood affects the best knife angle as does wood density, feed speed (cut per knife) and depth of cut. With this information, you can see why it is hard to give you an exact angle that will work all the time. In my experience, the difference between 19 and 20 degrees of hook is hard to see. Other factors such as MC will have more effect.



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