How to prevent concave edge on chip carving knife?

[Brad I]

I've been having a problem for years where I hone my chip carving knife it eventually ends up with a concave edge. Very frustrating because the chips get stuck more often than not. What causes this concave edge and how can I avoid it?

[Randy]

Brad are you saying one side of the edge seems to be roled over or both edges sides are hollowed in? Do you use a flat stone or power sharpen?

[Brad I]

Hi Randy. Basically, the bevel is fine on both sides, just if you put the sharp edge down on a straight edge it has a bit of a concave instead of flat edge. Does that make sense?

oh and I'm using flat ceramic stones and leather strop

[pallin]

If there is some flex to the blade and you use too much pressure on the stones, it would be possible to take enough metal off the middle of the blade to cause a concave edge, but since you rarely use more than the tip for chip carving it may not matter.
Please describe what you mean by "chips get stuck."

[Brad I]

IPlease describe what you mean by "chips get stuck."

I'll do my best. I practice European style chip carving. So taking a basic triangle chip for example. I basically pivot and press the blade into the wood. In a basic triangle chip, I'd do this pivot 3 times. On the last time, the triangle should pop out as a chip. however, since my blade is concave (even a touch), there's enough wood untouched by the blade at each corner to hold the chip in place. That leads to me attacking cutting multiple times and different angles to get the chip to pop. This causes unattractive splintering, multiple blade marks - unlike the clean cuts one would expect.

[Brian T]

OK. I'd have to work the tip of the blade back with some 600 grit and check as you do to see a straight edge again.
Then, ever so gently, work up to 1500 and hone on a strop.

[Randy]

As Pallin suggested check how much pressure you a using on the stone as well as the strop. Pushing down to hard on a leather strop can cause a subtle curve in the cutting edge. The leather compresses and as the blade move down the strop and the strop decompress it can push up on the edge. Almost the same effect as rolling the edge if you turn your wrist at the end of the strop. This was a issue for me until another carver showed me what I was doing. From your above description could there be a issue with your angle or depth of cut on the last cut on the triangle?

[papasar]

Is it possible to show us the blade with a photo?

[pallin]

When I do European style chip carving I make two pressing cuts to define the sides of the triangle. These are followed by a slicing cut to release the chip. I have even done the slicing cuts with a fishtail gouge.

Plate 023.jpg

https://forum.woodcarvingillustrated...-sister-repost

[dave.keele]

... if you put the sharp edge down on a straight edge it has a bit of a concave instead of flat edge. .....and I'm using flat ceramic stones and leather strop

Assuming you start with a straight knife edge and the stone is flat, and the entire cutting edge of the knife remains in contact with the stone/strop during the sharpening process, there should be no way the center area of the edge should round-in (become concave).

Since I cannot see what you are doing, I can only take a guess... I'm assuming you're letting the edge closest to the handle come off the stone (a common issue if using a circle or figure 8 motion). If this is true, and you're applying a bit more pressure on the handle side, the edge of the stone will remove more material between the handle and the tip, causing the shape you're describing.

My suggestion is to pull the knife along the stone (avoiding circular motions) and ensure the entire edge stays in contact with the stone/strop. Applying pressure with an index finger at the center of the blade will help maintain even pressure along the entire edge.

[Brad I]

As Pallin suggested check how much pressure you a using on the stone as well as the strop. Pushing down to hard on a leather strop can cause a subtle curve in the cutting edge. The leather compresses and as the blade move down the strop and the strop decompress it can push up on the edge. Almost the same effect as rolling the edge if you turn your wrist at the end of the strop. This was a issue for me until another carver showed me what I was doing. From your above description could there be a issue with your angle or depth of cut on the last cut on the triangle?

You might be right here. I've had a heavy hand when it comes to stropping ever since I was 6 years old. I'm over 50 now. Tough habit to break.

[Brad I]

Is it possible to show us the blade with a photo?

I've already flattened the edge again. But can the next time if I don't solve this.

[Brad I]

When I do European style chip carving I make two pressing cuts to define the sides of the triangle. These are followed by a slicing cut to release the chip. I have even done the slicing cuts with a fishtail gouge.

Plate 023.jpg

Beautiful work there. Are you saying you are switching between chip knife and fishtail gouge between cuts?

My concave blade wasn't so much of a problem until I started doing this type of carving. If you zoom in, you can see around the edges evidence of unnecessary second and 3rd cuts. Virtually all of the internal triangles appear sloppy because it's impossible to get a clean cut without multiple passes. A slicing cut can be deadly to the carving as well because everything is so fragile and the angles are so weird.

IMG_0540.jpg

[pallin]

Yes, circular patterns are a special problem because the angles relative to grain direction are constantly changing. You have to think about where the cutting pressures will go.
In answer to your question about switching from knife to fishtail gouge - I often do the plunge cuts for multiple triangles before starting the slicing cuts with the gouge. It would seem that using a #3 gouge for flat, slicing cuts would increase the chances for misalignment of the final cut, but that's not the case.

Plate 021.jpg