As of now, I sharpen the primary bevil on my bench chisels (loose term, I know) to about 30 d. Last night killing time waiting to go to the vigil service (starts at 11:00) I started thinking that what I do as a matter of habit might not be optimal. So I searched a lot and found plenty of discussion of how to sharpen, with the posters diviede into at least three partisan camps, but, oddly, very little about angles. This was also true of what I found in searches in the rest of the FWW web site.
It is generally agreed that paring chisels are more delicate instruments with more acute angles — perhaps as fine as 20d to 25d, while heavier chisels have steeper angles to help withstand strain. Mortising chisels have step angles to match the solidity of their construction. But what is the accepted wisdom as to the best angles for each.
Related Qs –I just picked up some old socket mortising chisels. They have been sharpened with a kind of convex curve instead of a flat angle. I suspect this is just careless freehand sharpening over time — but is it? Should I take the time to flatten those out? Is it good or bad to have a hollow grind in a mortise?
Replies
Joe,
For general work, I prefer a 30º honing angle on chisels. Those I use for light paring I hone at 25º. In hardwoods a 20º edge on a chisel just doesn't stand up in any use I've found. I grind the bevel on all these chisels at 25º. Don, one of my partners, prefers to grind and hone at the same angle so he can both high ends of the hollow ground bevel on the stones for more accurate honing.
I like mortise chisels to have a convex curve on the bevel. Actually, the curve I try to maintain is more of a rounded heel on the bevel and I use this as a fulcrum when levering out waste during the initial mortising.
Ultimately, the important thing to remember is that edge quality depends on the surface quality of both surfaces that make up the edge. Both these surfaces need to be addressed during every sharpening.
Interesting. thanks. The rocker effect makes sense on a mortising chisel.
I am with you on the need to care for both surfaces.
Hi Joe
One other factor that should be mentioned with regard the mortice chisels is that the primary bevel is at about 20 degrees and the final microbevel is at 30-35 degrees. The shallow primary bevel aids in the blade entering the timber, while the higher final angle beefs it up for durability.
You can see the amount of "round" I have on mine - others have more.
View Image
Here are a few of the oval bolstered mortice chisels more for interest:
View Image
Most of my bench and detail chisels have a 30 degree bevel since I work in hard wood, but this is also a reflection of the steel used (laminated for Japanese and A2 for Blue Spruce). My Bergs, which are reserved for light paring, are bevelled at 20 degrees. Remarkably, they hold up very well. But I would not use them for general work.
Regards from Perth
Derek
Edited 4/8/2007 9:57 pm ET by derekcohen
Edited 4/8/2007 9:59 pm ET by derekcohen
Hi Joe,
In general I keep my chisel bevels at the lowest angle which will sustain an edge for the work I expect of them.
For my older Sorby paring chisels, this means that I use somewhere between 20-25 degrees of a primary bevel and a micro bevel of a few more degrees. When the micro bevel grows, the chisels are redone to the primary angle and the whole thing begins again.
Here's a link to a picture of a few of my mortise chisels. The one on top has too great a rounded profile, but works very well. The lower two will eventually transition to a slightly convex profile over time, but the top of the bevel will be more rounded.
http://www.wenzloffandsons.com/temp/mortise_chisels.jpg
This second picture shows all four I have [other than the newer sash mortise chisels I have]. It also shows on the largest one that I have reshaped the one mentioned above to a little flatter profile the last time I sharpened it.
http://www.wenzloffandsons.com/temp/mortise_chisels1.jpg
I use a convex shape to thrust the chisel slightly forward as it deepens the mortise, but the more rounded top of the bevel is as Larry says, to aid in leveraging the waste out.
For the bench chisels I probably use between 30 and 35 degrees. As I hand sharpen after grinding [no matter the chisel type] and rarely need to regrind, only following the grind can I know what the actual bevel degree is. Within a range, it really doesn't matter.
Take care, Mike
My view is similar to Mike's except:
I think wider chisels hold up better because the pressure (stress) on the edge is less (driving force is usually the same). Really small chisels typically punch into wood, so their edges are easy to manintain as well. Consequently, I grind my larger chisels - say 7/8"+ at lower angles. Ditto for chisels 1/4" and under. The middle sizes, sizes that get the most use chopping dts, are better ground higher.
Though I do wonder if we'd all be better off grinding lower. The issue isn't saving the edge, or at least, that's the stupid man's discussion (and we don't have any of those). That's like talking about saving your life. The issue is only how much work you can get done until you hone and how long it takes to bring the chisel back. Thinner chisels with lower angles seem to penetrate better. So tho their edges may beak down more readily, they may function fast enough for this to be okay. I like my chisels to get me through a project before they need sharpening. That's a lot to ask. Asking them to do more may be asking too much.
The convex edge is stronger than the concave. The problem area is near the tip, so don't worry about a little hollow gring mark left. Any convexity helps. Leonard Lee is a really sharp cookie. I recommend his book "Sharpening". I like the part where he has "that last page is really important, so if you didn't understand it, go back and read it again"!
Adam
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