Benefits of a Secondary Bevel

[Michael Ray Smith]

Another thread about bevel geometry reminded me of a question that I've had for a long time but have never asked, probably because I was afraid of asking a stupid question. But stupid or not, here goes. The question applies to both chisels and plane blades, but for the sake of discussion, let's stick to bevel-down plane blades.

The question: After one has just put a primary bevel on a plane blade, say 25 degrees, why would one immediately add a secondary or microbevel? As I understand it, the benefit of a secondary bevel is to make subsequent sharpenings quicker. If it's bevel-down, the bevel angle doesn't (or theoretically shouldn't) have anything to do with how well or easily the blade cuts because the angle at which the blade attacks the wood is fixed by the angle of the frog, not the angle of the bevel. As I understand it, the idea is to make subsequent sharpenings quicker, but that doesn't apply when one has just put a fresh primary bevel on the blade, unless maybe the idea is to create the primary bevel with only a relatively coarse stone, limiting the use of finer stones to the narrow secondary bevel. But I've seen instructions that include the use of finer stones on the primary bevel as well (which is something else I've never quite understood -- why would one do that?). I understand that a higher angle bevel may last longer, or at least be less susceptible to nicks -- but that raises two other questions: (1) Why not just hone the primary bevel at the higher angle? (2) Some sources recommend secondary bevels that are only a few degrees higher than the primary bevel -- does the difference between 25 degrees and, say, 27 degrees really make that much difference?

I've taken to using only a primary bevel at whatever angle I want the final bevel to be -- usually 35 degrees -- especially when I'm using my Work Sharp 3000. I don't see that it it's any harder or more time-consuming (again, at least with the Work Sharp) to re-hone the primary bevel than it is to use a secondary bevel or that it uses up the blade any faster (because even with a secondary bevel, you eventually refresh the primary bevel anyway). What am I missing?

[Daniel Rode]

When I make the primary bevel, I grind the angle using a coarse stone, or bench grinder it but do not work it any further than that. Then I create the secondary bevel with the finer stones. So even the very first time sharpening the iron benefits from using a secondary bevel.

[David Weaver]

A 25 degree final effective bevel on a hand plane is going to take a lot of damage in regular use, especially if you're relying on it to do a clean smoothing job with no chipout. I think the most effective total bevel angle for smoothing is probably somewhere in the 32-34 degree range, and above that you're quickly fighting reduced clearance. On a jack or fore plane iron, it might be less critical since the chipout doesn't threaten anything, but it's nice just to have irons fail from wear. That'd be the reason I'd think of.

I don't like to keep any primary bevel angles at that high of a point, though, because like most of us, I'm not using something that will mechanically hone the entire bevel for me and thus a primary bevel and a secondary bevel of some sort that is more than 2 degrees more steep is handy. It maximizes the time between grinding without compromising the strength of the edge.

Chisel edges can be closer to 25 degrees because they fail differently and they're quicker to sharpen.

[Judson Green]

Michael, are you confusion a secondary bevel with a back bevel; micro bevel on the back,flat side of the iron?

Or maybe I'm confused... your mention of the angle of the frog lead me to this line of thinking...

[Malcolm Schweizer]

The idea is that when you hone the microbevel, you are taking off less metal when you sharpen, so it is quicker to sharpen the small bevel than the whole primary bevel. I personally polish the primary bevel because I live in a humid climate and things rust. I find that a coarse grind is more prone to rusting than a polished surface. Other than that, you can grind the primary bevel rough, then hone the secondary bevel fine.

[Sean Hughto]

- Why bother with a secondary bevel until the first resharpening?
No reason except possibly if your practice is to hone between sharpenings with something like a strop and you want to hone only the secondary angle.

- Why polish the primary bevel if you are using a secondary?
There is no reason to do so. However, many fellas really like their tools as pretty as possible. ;-)

- Does a couple degrees matter?
Nope. I almost never know the actual degrees and don't care.

[David Weaver]

(2) Some sources recommend secondary bevels that are only a few degrees higher than the primary bevel -- does the difference between 25 degrees and, say, 27 degrees really make that much difference?

A secondary bevel that's significantly steeper is one intended to strengthen the bevel (or in some cases plane highly figured wood) or give you a lot of sharpenings before touching the primary bevel. A secondary bevel that is only slightly steeper is just a bias to make sure the next finer stone works all the way to the edge of a tool. (goes back to the sharpening by hand instead of machine - that bias can be a nice thing, especially for someone new to sharpening).

[bridger berdel]

If your machine can reliably hone your blades as single bevel without unnecessarily shortening the blade, no reason not to.

I generally grind the primary and hone the secondary. They often start out hollow ground and end up convex bevel from honing before taking them back to the grinder. The bottom line is that no sharpening method that produces the edge you need without wasting steel is "wrong".

[Michael Ray Smith]

A 25 degree final effective bevel on a hand plane is going to take a lot of damage in regular use, especially if you're relying on it to do a clean smoothing job with no chipout.

Yep. That's why I mostly use about 35 degrees.

[Michael Ray Smith]

When I make the primary bevel, I grind the angle using a coarse stone, or bench grinder it but do not work it any further than that. Then I create the secondary bevel with the finer stones. So even the very first time sharpening the iron benefits from using a secondary bevel.

That makes sense.

[Michael Ray Smith]

Michael, are you confusion a secondary bevel with a back bevel; micro bevel on the back,flat side of the iron?

Or maybe I'm confused... your mention of the angle of the frog lead me to this line of thinking...

Nope, not at all. The comment about the angle of the frog was probably a little off topic. Just making the point that for a bevel-down plane, a 35 degree bevel should not cut much differently than a 25 degree bevel, except the 35 degree bevel should last longer.

[Michael Ray Smith]

- Why bother with a secondary bevel until the first resharpening?
No reason except possibly if your practice is to hone between sharpenings with something like a strop and you want to hone only the secondary angle.

- Why polish the primary bevel if you are using a secondary?
There is no reason to do so. However, many fellas really like their tools as pretty as possible. ;-)

- Does a couple degrees matter?
Nope. I almost never know the actual degrees and don't care.

Thanks. All that makes perfect sense.

[Michael Ray Smith]

A secondary bevel that is only slightly steeper is just a bias to make sure the next finer stone works all the way to the edge of a tool.

Makes sense.

[Michael Ray Smith]

The bottom line is that no sharpening method that produces the edge you need without wasting steel is "wrong".

I like that. I believe in finding something that works for you and going with it, regardless of what works for someone else. Maybe later you'll find something that works better for you and then start going with that. That said, I do tend to favor techniques that seem to have some underlying logic and common sense to them. Chris Schwarz wrote something a while back on sharpening card scrapers. He found something like fourteen different techniques and tested them. I'm glad he did that, bless his pea-pickin' heart, but he makes his living doing that sort of stuff. I don't have the time for it.


Thanks to everyone for their comments.

[ian maybury]

Hi Michael. Just gearing up here now to properly go after the sharpening of plane blades, and thinking in terms of using the WorkSharp too. Another reason (related to what the guys have said) why a low angle primary bevel can be useful on plane blades is because it can where required make putting on a camber while honing on waterstones etc relatively easy - because it sets up a situation where it can be done by removal of a minimal volume of metal right at the edge.

Derek Cohen discusses methods and some of the issues in the sharpening section of his website: (the situation changes a little between bevel down and bevel up blades) http://www.inthewoodshop.com/Woodwor...aneBlades.html Sorry i can't give the exact link but the site is not opening at the minute. David Charlesworth describes the technique for bevel down baldes in his writings too, as do others...