Back-Beveling Tips
Fine points of back-beveling jointer knives. May 13, 2005
Question
I want to back bevel my Powermatic 60a jointer knifes to help prevent tearout of figured woods (curly cherry and maple). Does anybody do this? I read that a net angle of 10 degrees was fine.
Forum Responses
(Solid Wood Machining Forum)
From contributor R:
Feeding slower will work just as well!
From contributor K:
Yes, I grind a small bevel on the face of my knives to change the cutting angle. Memphis Machine catalog has good info on cutting angles/sharpness angles/feed rates/knife cuts per inch for each wood species. For cherry, they show 10 degrees hook or cutting angle and 35 for sharpness. For maple it is 5 and 40. I feel that it made a big improvement for my jointer, although it may require a little more power.
From contributor J:
I've had my planer knives ground with a 10 deg back bevel to net about 10 deg cutting angle for my cutterhead. Works great in all of the hardwoods I've tried, but still needs to be sharp to prevent fuzz in curly maple, etc. I've just ordered jointer knives with back bevel as well. I power feed my jointer, so the extra power requirement shouldn't be an issue, I'm hoping...
From the original questioner:
Are you back beveling the front or back of your knifes?
From contributor J:
There is some good info here in the Knowledge Base about sharpening and grinding. I've linked to the page. Anyway, the bevel is in the flat leading surface of the knife, so the manual refers to it as a "face bevel," but my sharpener and everyone else I've talked to about it call it a back bevel. Basically, you pay for a second sharpening, but the knives last longer (more steel behind the cutting edge) and drastically reduce tearout. I can run my 20" planer full speed and in most woods, can ignore the grain direction. This makes it much easier to have a helper run the machine.
Knife Grinding and Woodworking Manual
From the original questioner:
Thank you. My knife grinder will be happy, too.
From contributor K:
The 4 knives in my cutterhead were set at 30 degrees, so I used 20 for the face bevel to get the 10 that I wanted. My jointer is a Hall and Brown 12", which is cast a little different from most, but allows me to slide the outfeed back out of the way so that I can hand hone the knives about 4 -5 times between taking them out and grinding. I made a little wedge with a saddle groove in the butt end, which fits against the edge of the infeed bed to hold the knife at the highest point of the cutting circle. I then hone with a 2" X 6" medium and fine diamond hones which I have mounted onto handles. I can do this faster than I can take the knives out, and as I'm sure you know, installing the new ones usually takes a little longer. If your outfeed bed doesn't slide out of the way, you may not be able to do this, but if it will, it can save enough time that it makes it easier to keep the knives sharp without putting it off until you can't take it any longer.
