How much back bevel?

**silentC** · 21st September 2007, 11:56 AM

OK, trying to get my head around this.

With a bevel-down plane, like the Stanley #5, without a back bevel, the cutting angle is the same as the bed angle. The primary, secondary or micro bevels that you put on the blade actually make no difference to this, as they are clearance angles and don't affect the angle of blade presentation to the wood.

When you grind a back bevel however, this does change the cutting angle, which is a result of the combination of the bed angle and the back bevel. So a back bevel of 15 degrees would give you a cutting angle of 45 + 15 = 60 degrees, regardless of the bevels on the other side of the blade.

However, the clearance angle has a bearing on the life of the edge and I think it may also have a bearing on the degree of difficulty in pushing it through the wood. So a sharper angle is easier to push but will be less durable than a more obtuse one.

**kman-oz** · 21st September 2007, 12:20 PM

Originally Posted by silentC

... the clearance angle has a bearing on the life of the edge and I think it may also have a bearing on the degree of difficulty in pushing it through the wood. So a sharper angle is easier to push but will be less durable than a more obtuse one.

Exactly, this has been my experience. I can't say I completely understand all of this but the upside of the sharper iron angle also seems to be less need for a higher over all cutting angle. In my example I've gone from a presented cutting angle of 70 degrees to a cutting angle of 60 degrees with no significant effect on finish while the effort involved was considerably lower.

I'm going to continue building a HA plane anyway to verify my results against. With a 60 degree bed and 30 degree primary bevel the presented angle and clearance angle will be the same as my experiment, then I just need to see if the results differ.

**silentC** · 21st September 2007, 12:22 PM

Well let us know how it goes and don't forget the photos!

**Caliban** · 22nd September 2007, 10:59 PM

Originally Posted by silentC

You can tell us from the rest by the crooked thumbs

and the unmistakeable smell of burning flesh.

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