Hi Barry. Just read your post but see it was written a week ago. Have you had success since then? Here's a situation where instruction from a professional turner would be valuable. An expert would see the cause of the problem at a glance and help you overcome it easily. In lieu of that, here are some things to consider:
When you say ripples, do you mean chatter marks versus ridges that are even all the way around the bowl, or do you mean shiny rings that are basically flush with the surface, or do you mean rings of torn grain? If you are getting chatter, it can come from either the tool flexing or the wood bouncing against the tool. Is your lathe heavy enough? Does it vibrate as you turn? Is your bowl supported adequately? Bring up the tailstock and see if that helps. If it does, then your headstock or bearings or chuck/faceplate may be the problem. A 6" bowl should be well within the capabilities of even a small lathe.
Ripples in the traditional meaning of the term (shallow ridges) often come from less than perfect tool control. Are you moving the tool with body motion (good) or hand and arm motion? Is the tool held firmly against the tool rest? Ripples usually sand out easily. Is your sandpaper fresh and sharp? Are you using a coarse grit to start? Is your wood too wet to sand easily? Is a wet slurry clogging your sandpaper? Are you sanding with the grain or against the grain?
If the grain is torn, are you cutting from base to rim on the outside of the bowl (with the grain) or from rim to base (against the grain). Is your tool angle 45 degrees or more (the part of the cutting edge touching the wood, not the tool shaft/handle angle)? Are you using the best tool for the finishing cut? A small gouge with a thin bevel (not so small that it chatters) will make a cleaner cut than a bigger tool or coarser bevel.
Shiny rings are caused by too much bevel pressure and can be difficult to sand out. Rubbing the bevel is a bit of a misnomer. Touch the bevel lightly against the wood, as close to zero pressure as possible. Keep pressure against the tool rest but don't put pressure against the wood.
If your ridges are truly too deep to sand out easily, they can be levelled with shear scraping. Scraping with the tool flat on the tool rest usually causes some tear out. Hold a freshly sharpened scraper so that the part of the metal touching the wood is at 45 degrees (like a clock hand pointing at 10:30), moving the tool from base to rim. Use a light touch against the wood. Stop and resharpen every 5 seconds when shear scraping.
Let me know if any of this helps.
-mike paulson, fort collins, co
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I am turning a bowl (about 6" in diameter by about 6" deep, side grain) from green Black Walnut. I have shaped the exterior of the bowl. When I started to power sand, I noticed that the outside of the bowl had several concentric ripples. These ripples are a bit too deep to remove by power sanding, but have eluded removal with a bowl gouge or scraper. I have not hollowed the bowl yet, so it shouldn't be moving too much.
I have tried taking a very fine cut with a sharp bowl gouge, but the new surface had just as many ripples. What is going on here? I'm pretty new to green wood turning. Do I just need to rough the bowl and let it dry for a couple of weeks before I proceed? Any suggestions will be much appreciated. Thanks.
Barry