Thread: A couple of quick questions re chisels.

Originally Posted by mattocks

Hi all, I'm a bit confused about back and secondary bevels for chisels. Are they one and the same thing or different. Is a back bevel on the back of the chisel, if so how do you do it and is it worth it? Also can you lap the back of a chisel on the side of a slow wet grinder wheel? I have spent some time procuring good chisels and have been sharpening them with diamond stones and japanese waterstones using a Veritas MkII honing guide. I have got reasonable results, well the chisels I have done seem sharp enough. But I seem to have quite a number now, I think they may breed on their own!! Lapping the backs is not as easy as it looks and I've held off trying to do the good chisels until I improve.
Cheers
Frank

Hi Frank,

Back bevels are used on plane blades to increase the angle of attack on wood likely to tear out. It has a similar effect to fitting a high angle frog. The back of a chisel should be flat without a back bevel. I've used a slow wet grinder to flatten the backs of chisels but use the flat side of the wheel/stone, not the curved rim.

A secondary bevel or micro bevel is used to speed up subsequent sharpening. After the primary bevel is formed, say at 30 degrees, a small secondary bevel at 35 degrees is honed on the chisel or plane blade. Once the plane or chisel is dull, the blade can be honed at 35 degrees to return the edge. Doing this avoids the loss of metal that would be experienced if you had honed to 30 degrees as you would lose metal across the whole of the bevel.

Sharpening is a personal issue and there are as many methods to sharpen as there are brands of chisels. I do not use back bevels on my plane blades or secondary/micro bevels on either chisels or plane blades. I usually use a coarse diamond stone or sandpaper on glass to flatten the backs. I use a wet slow grinder to form the bevel then use the Mk2 honing guide with 800 and 6000 grit water stones to finish the edge. Sometimes I will polish the edge with green cutting compound on MDF.

You seem to on the right track. Good luck with your chisels!

homesy135

Frank - whatever else you do, DO NOT PUT THE BACKS OF YOUR CHISELS NEAR ANY PART OF THE GRINDER! The backs have to be dead flat on a chisel, particularly any used for paring. The slightest rounding will detract enormously from the function. So only clean up backs on dead flat stones, diamond plates or lapping plates - whichever floats your boat.

OK - we've got that settled - now to the other questions.

Be prepared for a barrage of advice on how to get the perfect edge. My advice is that since you have already chosen a path, stick with it - it does take some practice, even with a honing guide. A sharp edge is nothing more than two intesecting planes, so the finer the polish and the straighter the edge, the 'sharper' it will be.

As to bevels - the two bevels are, respectively, a grinding bevel and a sharpening bevel. The grinding bevel is the one which takes off the bulk of the unwanted metal. On most chisels it is recommended this be around 25 degrees, but on some of the harder steels like LN's chisels, they recommend a steeper bevel of 30 degrees.

The secondary, or sharpening bevel is used so that you don't have to remove much metal to touch up your chisel between times. The secondary bevel is the one that has always been applied by hand, so you want to minimise the time & effort on this bit & get back to work. You just tip the tool up a bit on the stone, & hone a thin 'flat' along the edge. It also increases the amount of metal supporting the pointy end, making it a little sturdier. It is generally recommended that this be around 30 degrees, or 35 on the more brittle metals.

I am not into the masochistic stuff, so I grind my chisels on a slow-speed dry grinder. Using a 'soft-bond' wheel and a light touch (& keeping the stone well-dressed!) it is not a dangerous exercise, and a hell of a lot easier than taking it off manually! It does take a bit of practise, and it is easy to burn hifgh carbon steels if you are heavy-handed, so the next best thing is the wet grinder - slower, over-priced to blazes, but safe. I have only tried using a honing guide briefly, but I found it a waste of time. We were taught to hone freehand back in grade 7, which was a while ago, now, and I can get my tools plenty sharp enough that way. However, they are probably good for a beginner, & probably save a lot of metal in the long-run.

Bear in mind that the quoted sharpening angles are average figures - for some applications it is desirable to either increase or decrease these angles. For a chisel that will be belted into hard, siliceous woods, an increased honing angle helps preserve the edge a little longer. A low angle gives better penetration, but is much more fragile. For example, on my paring chisels, I drop both grind & honing angles considerably, but these chisels are never struck (or very rarely, & then only the gentlest tap or two), so they can stand the more fragile edge.

Happy sharpening....

IanW's advice is spot on!

I use a honing guide (Eclipse) for creating a secondary bevel, because I found that freehand I was honing an uneven rounded bevel - the guide helps me to keep it flat and uniform across the blade.

"Different strokes for different folks" as they say in relation to sharpening methods and recipes, but we all agree on keeping the backs of chisels dead flat and finely honed and lapped so as to maximise the benefit from all the work that goes into grinding and honing a really sharp fine cutting edge.

Cheerio