Tuning up carving chisel innards

[Lawrence Brown]

So if there are any wood carvers here, I'm dabbling with some basic carving and wanted to get some sharpening advice. I've picked up a couple of V-chisels, both used but in good condition. When I was talking to the guy at the hardware store (Hardwicks for those of you in the area) about tuning up the inside of the V, he just said never do it because you don't want a bevel on the inside.

Now, this makes sense. You want the bevel on the outside to control the cut. The trouble is, to me it looks like the flats on the inside of the steel aren't so flat. Nothing drastic, just a bit of what looks like waviness from the steel extrusion or something.

From my experience with regular chisels and hand plane blades and so on, the first thing I want to do is flatten the back. Should I be doing this or are carving chisels a whole different beast? Is this a case of me just being too picky? I'd assume I'd be fine with something like a flat diamond hone as long as I was careful to keep it flat against the back.

[Kari Hultman]

With V-tools, use stones to sharpen the outside bevel, being very careful to maintain the original bevel. I drag the tools towards me on the stone, not back and forth, to maintain better control. Do the same number of passes on each side of the tool. You can hone the inside with slipstones, shaped with a sharp edge, that you slide toward the cutting edge. You just have to be very careful to not rock the stone. I use strops/honing compound following stones on the outside bevels. For the inside, you can use a thin piece of leather—slide it toward the cutting edge. You can also cut a piece of hardwood to match the inside shape of the tool, add honing compound to the wood, and use it the same way as a slipstone. I wouldn't worry about the inside steel not being perfectly flat unless it's very close to the cutting edge.

[Beechwood Chip]

I think you flatten the back of flat chisels because you sometimes rest the back against a flat surface to continue that line. In other words, the back of the chisel is often that part that rests against the work. That's not the case with a V chisel - you never rest the inside of the V against a guide or the piece. At least, that'd be my guess.

[Lawrence Brown]

Beechwood, a sharp "edge" consists of two surfaces. On the chisel or a planing blade its the back and the bevel, so if you only flatten one side, you still end up with a rough edge. that's why they recommend you always start by honing the back of a blade to a mirror finish. Once that's done you should never have to touch it again. You just resharpen the front until it makes a nice intersection with the back again, but you're right about the V and it's proper use I was talking more about roughness in terms of a technically sharp edge. Just wasn't quite sure how to describe it.

Kari, thanks for the honing tips and the confirmation of my suspicions. I just didn't know if there was some secret thing where normal sharpening logic didn't apply in this case. Glad to know it does. I think I'll do an ever-so-light honing pass on the inside and call it done.

[lwllms]

There's so much behind your question. I wish I had still photos to show you but all I have is video that went into a DVD on sharpening profiled tools for Lie-Nielsen. It'd be unethical for me to post any of that.

First of all, most carving is done in mild woods and the carving tools are often pushed by hand. For this reason, you want a pretty acute cutting angle of about 25º as a general rule. Gouges are honed at 20º and have a 5º inside bevel so you can use them upside down and carve convex profiles. You want all your tools to operate in a uniform fashion so the vee tool needs to have the same cutting geometry.

Depth of cut on carving tools is controlled by riding the bevel. Simply lifting or lowering the handle will cause depth of cut to increase or decrease. This is where the vee tool gets difficult. When you hone the two wings with the 20º and 5º bevels the small skate that's formed at the bottom of the vee is the result of a compound angle and not the 20º you want. You have to form this independently by grinding a 20º with the tool balanced on the chisel body's vee. Don't grind past the cutting edge. This will result in a small diamond-shaped flat where your skate or bevel you ride needs to be. Obviously, if you try to use the vee tool this way, the leading edges of that flat will act as a wedge that'll lift your tool out of the cut. You need to then grind again to form the skate that'll ride in the bottom of the vee-shaped groove you're cutting. Grid the sides of that diamond flat so that you end up with a single straight line that runs from the bottom of the vee at the cutting edge to the bottom of the vee on the body of the tool. You need to grind enough material away from the sides of that small diamond flat so there's clearance for the tool to work properly. It takes patience and some tweaking to get things right and the cutting edge formed properly. The vee tool is the most difficult to sharpen tool I know of but, once you understand the process, isn't all that difficult.

[Lawrence Brown]

Hehe. Here I thought the vee would be the simplest to start with I do have a couple videos that go into technique and basic sharpening, but no real technical info. Thanks for the additional explanation.