High angle frog and primary bevel

[Randy Klein]

So with my 45* bedded frogs, I've been grinding a 25* primary bevel and working micro bevels finishing up at 30 degrees. This leaves 15* for a clearance angle which conventional wisdom says is more than enough.

But with the 55* frog from Lie Nielsen, is there any pros/cons to grinding the primary at 35* and honing to 40*?

[Jim Matthews]

I thought the whole point was to grind one blade, and put in a different Frog to change the effective angle.

Am I off-base, there?

[Randy Klein]

I'm not talking about changing the effective cutting angle since that is controlled by the frog (and any back bevel you may have). But what are the pro/cons of grinding a larger bevel angle. The first I can think of is that it gives you more meat behind the edge and this contacts the frog lower on it. Maybe this is good, maybe not. Maybe it provides greater edge retention or maybe it makes it more difficult to push. I was hoping someone has tried this and can pass on their experience.

[David Weaver]

So with my 45* bedded frogs, I've been grinding a 25* primary bevel and working micro bevels finishing up at 30 degrees. This leaves 15* for a clearance angle which conventional wisdom says is more than enough.

But with the 55* frog from Lie Nielsen, is there any pros/cons to grinding the primary at 35* and honing to 40*?

There's no advantage to it. Steve elliot or someone did some durability tests for A2 steel and found an angle in the low 30s on the blade he tested ceases unexpected chipout.

If you shoot for a 32 degree or so total final angle, you'll find that you basically wear out an A2 iron with wear with no premature chipping.

If you leave less clearance and have no increase in the toughness of the edge, you're essentially imitating the profile on a blade that instead has some wear. I wouldn't be surprised if you had less planing time between honings that way.

[Randy Klein]

There's no advantage to it. Steve elliot or someone did some durability tests for A2 steel and found an angle in the low 30s on the blade he tested ceases unexpected chipout.

If you shoot for a 32 degree or so total final angle, you'll find that you basically wear out an A2 iron with wear with no premature chipping.

If you leave less clearance and have no increase in the toughness of the edge, you're essentially imitating the profile on a blade that instead has some wear. I wouldn't be surprised if you had less planing time between honings that way.

Is this the test your are referring to: http://bladetest.infillplane.com/ ?

[Steve Elliott]

While I haven't done any controlled tests with higher bed angles I do have a few comments on the issues involved.

A higher cutting angle increases the force on the cutting edge and may need a somewhat larger bevel angle, maybe a couple of degrees. I doubt A2 would need anything over 35 degrees. The edge will wear faster at the higher cutting angle.

Your point about having more support behind the blade if the primary bevel angle is increased may be relevant if the plane has problems with chatter. This will depend on the stiffness of the blade itself and the amount of clamping pressure provided by the lever cap.

In general a blade will continue cutting well for a longer time if it starts with a larger clearance angle. The limit to this comes at the point where a smaller bevel angle makes the blade too fragile and it either chips or the edge rolls (depending on the hardness and toughness of the steel).

In a plane without chatter problems I think increasing the bevel angle past what is needed to give a strong enough cutting edge will provide no added benefit but will somewhat decrease the useful edge life.

[Randy Klein]

Ok, so I think I'll grind at 30 and hone a few degrees higher than that and recheck how that works. I was getting a bit of chatter every now and then, but I think my lever cap was looser than normal.

[Danny Burns]

I am wondering if edge durability will benefit from the added extra steel?