riding the bevel and ridges

[Derek Voigt]

So I'm getting back into bowl turning after not having much time to turn bowls in the last year or so. I'm getting a ridged surface when I hollowing out the insides. I'm trying to ride the bevel and make it as smooth as possible but can't seem to avoid ridges and grooves. My gouge is sharp and I can get fine shavings.

What is the most likely problem? Angle the gouge is sharpened? Angle the tool is being pushed through (tool rest too high or low), something else?

I need to get better at the final finish off the tool so I can cut down on my power sanding time...

Thanks,
Derek

[Dennis Ford]

You may be riding the bevel too hard, the bevel should barely touch for best results. If the bevel is too long, that can cause problems on the inside of bowls. Grinding a secondary bevel is helpful for interior cuts.

[Bob Bergstrom]

Slow the travel speed of the gouge or speed up the lathe.

[Prashun Patel]

Lighter touch. Flatten and wax the rest for smooth travel. Think of the gouge as a plane blade; don't aim to cut all the way from rim to base during final cuts; aim for smooth travel, that contacts the high spots preferentially. I know, that's a 'duh' comment, but it's true.

[Reed Gray]

The bevel should rub the wood, but the wood should not know it.

Hold the sword (tool) as you would a bird. Too tight and you kill it. Too loose and it flies away.

Probably biggest causes of uneven surfaces. The inside is far more difficult to turn than the outside, in part because you can't see as well. If you have the death grip on the tool, the ridges get worse. Grinding off most of the heel of the bevel also makes it go much more smoothly because your bevel rub is closer to the cutting edge. On the outside, with a convex surface, you don't need to grind off the heel. On the inside, with a concave surface, you do. Also a sharp heel will push the cutting edge into the wood more than you want as well as leaving bruises on the wood that you can never seem to sand out. Learning to move with your body and not just your arms also helps smooth out the cuts. I have a bunch of clips up on You Tube that address all of this. Just type in robo hippy. Others do as well.

robo hippy

[Dale Miner]

"Grind the heel" is exactly right.

If you measure the spacing of the ridges, and measure the width of the bevel on your gouge, you will find that they are very close to the same dimension.

The hollow ground bevel cuts to match the shape of the bevel. As cutting progresses, eventually pressure builds against the heel and levers the cutting edge off the bevel immediately behind the edge. This creates a bruise at the bottom of the ridge the heel is in, and creates a bit of tearout when the bevel immediately behind the edge is lifted. Once the cutting edge progresses a short distance the bevel behind the edge makes contact and the ridge pattern is repeated.

If the bevel were ground with a convex shape that exactly matched the curvature of the inside of the bowl instead of the concave shape that results from using a jig, then it would be impossible to cut ridges without deliberately trying. BUT, it is near impossible to grind a gouge to match the changing curvature of the inside of a bowl.

Putting a secondary bevel and a tertiary bevel can approximate the curvature of the inside of the bowl and reduce the size (width and depth) of the ridge to the point that it is not apparent. Also, the tearout and bruising in the bottom of the ridges will be greatly reduced or eliminated.