Hook Angle for Large Radius Cutters
To cut the right profile, very large cutters need special attention to hook angle. September 10, 2007
Question
I make log cabin parts on a Pinero moulder and cut very deep and wide radii on the faces of the logs. I have problems getting knives that will cut the correct radius I want. My current knife manufacturer makes me the knives and a sharpening template. Both the knife and the template look right but don't cut correctly. Does anyone know how to fix this?
Forum Responses
(Solid Wood Machining Forum)
From contributor T:
The problem you are having is due to a lack of compensation for hook angle. In profiles that are very deep, the hook angle in your head can distort the profile depth. To remedy this problem the knives must be ground to a compensated profile based on the hook angle of your knife head and the cutting diameter. This will make the knives appear to have a much deeper profile ground in them but when they are run, they will cut the intended profile.
From Dave Rankin, forum technical advisor:
I agree with contributor T; the knives should be ground in a cutter head the same diameter and hook angle as you are using in order to maintain the exact profile. Another to talk to your grinderman about is the condition of his machine. There are problems on grinders than can also cause profile distortion.
From contributor A:
I agree with the above. Most likely it is just a hook angle thing. Sometimes it may be a good idea to have your cutter head checked for hook angle. I've had guys that think they had a 12* hook, but when they send me an image of their head, it turns out to be 20*. All you should have to do is put your head, hole down, on a piece of paper and trace around it. Fax it to your grinderman, so you guys can both be sure you're on the same page.
From contributor R:
I agree with all of the above. Imagine that, everybody agrees with each other. Good luck.
