Mystery Out Of Round?

[Steve Mathews]

This one has me stumped. While using a push cut and riding the bevel on the outside of a bowl it seemed like the piece became out of round somewhere toward the middle of the pass. The same thing happened after repeated attempts. I get a similar effect while facing off the bowl. The cut is clean and smooth, then toward the middle the tool begins to jump around as if it's bucking up against out of round wood. I don't always get this, just sometimes. Any of this make sense? Cause?

[Steve Schlumpf]

How much pressure are you applying to the bevel during the cut? Sounds like you are pushing too hard and possibly even going though the cut faster than the wood and lathe speed allows. What happens is the wood bends away from you because there is not enough time for the tool to cut.

[John K Jordan]

Without more info (green, dry, small, large, oak, holly, ???) or seeing or trying it myself it I can think of several possibilities: running into a part of the wood with hard/soft or light/heavy areas, too much pressure, insufficiently sharp tools, insufficiently delicate cuts, technique/tool presentation issues, too much tool overhang, failure to relax while still directing the cut positively, bevel bouncing on an irregularity from a previous pass, you could even be releasing stresses in the wood (more likely with dry wood in my experience.)

The fix depends on the cause, of course. For example if running into an irregularity from a previous pass try shear scraping to remove the irregularity. Sharp tools and light passes will fix many things.

If you think it actually went out of round, you can stop and measure it. A dial indicator on a magnetic base is an easy way to check this.

JKJ

[Joe Kaufman]

Spend a little time on Vimeo watching Stewart Batty. His videos are very good and he addresses your specific question. They are well worth the time.

[Steve Mathews]

More than likely the issue is probably the result of more than one thing and I believe Steve an John are correct.

I do find myself getting heavy handed with the tool until realizing to relax. I'll try lighter cuts and to go more slowly. I became more aware of the problem with the last piece of wood used, which was described in my cracked bowl question. That piece of wood was dry and may have had stresses being relieved as evidenced by the cracks. I'm sharpening more often so I'll give less emphasis on that being the problem. I don't think it's a tool rest distance problem because the bouncing doesn't go away when it's moved closer. As for technique, I'm sure that could be improved and will be searching for ways to do that. I haven't seen much of Stuart Batty's videos but will do so now.
Thanks!

[Reed Gray]

There is always a little bit of 'bump' as you turn a bowl. It comes from 2 main things. One, is that for 1/4 turn, you cut with the grain, then 1/4 turn against the grain, then repeat for one full revolution. The tool reacts differently cutting with and against the grain. The other part comes from really trying to clamp down on your tool as you turn. The harder you clamp down, the more bounce you get. Your arms need to work more like shock absorbers. Old saying about swords, but it applies to tools: Hold the sword as you would a bird. Too tight and you kill it. Too loose and it flies away. A good shear scrape is about the only way I have seen to totally get rid of the bump because you are not using the bevel at all...

robo hippy

[Steve Mathews]

Only part way into a SB video I'm discovering the transition from end grain to side grain as causing bounce or the out of round condition. Working on the 7 fundamentals.

[Steve Mathews]

After watching the rest of the Stuart Batty video and a few more, the difference in side and end grain sets up the bounce but it's applying too much pressure on the bevel that causes it. I blame this all on Robo Hippy (just kidding Reed) for his constant reminder to rub the bevel. I now will glide the bevel and see if things improve. I'm only into part of the SB videos and they are proving to be very helpful.

[Reed Gray]

One quote I like to use, and have no idea who said it, "The bevel should rub the wood, but the wood shouldn't know it." If you ever get the chance, watch Ashley Harwood. Turning delicate long finials without using her other finger as a steady rest.... 'Ashley, I am going to have go home and practice my dainty skills.'

robo hippy

[Gary Baler]

I'm not too smart or scientific, but it sounds to me like a harmonic balance problem. It is kind of like what makes the wheels of your car shimmy. Speed up or slow down and they stop shimmying. I usually find this at about the top 1/2 to 1/3 of the bowl ... however it can happen on the lower section occasionally. To cure the problem I just turn the speed up a bit and make another clean pass taking enough of a cut to remove the bumps in the wood. For me, it doesn't happen often, but when it does, this solves the problem. Good luck.

[Steve Mathews]

Members Joe Kaufman and Reed Gray pretty much nailed the out or round or more accurately bounce that I was experiencing. Too much pressure was applied to the bevel. I plan to go back and practice the fundamentals as described in the Stuart Batty videos.

[Prashun Patel]

Steve, I am glad you solved your problem. 9x out of 10 in all of woodworking it appears the solution is 'sharper blade, lighter touch'.

FWIW, I experience the same thing. I experience it when shaping spindles more than anything. It happens about an inch away from the end of the spindle on the head stock side (which is held with a spur center or chuck). I get clean cuts right at the end, then chatter for a little bit, then clean cuts at the center all the way to the live center.

I also get this when cutting some bowls.

I notice - as Gary suggests that varying the speed helps. I cannot figure out if it's because it changes the harmonic resonance points, or if slowing down allows the tool to follow and cut better; but speed change helps.

In addition, for bowls, I also notice that varying the tool size helps. I can't find a pattern; sometimes a larger gouge that powers through the vibration helps; sometimes a smaller tool that is less aggressive helps.

I also notice that when I'm finish turning the outside and my rim extends the beyond the jamb chuck, it's hard to get a vib-free cut. I also dramatically reduced my vibration across all bowls on the inside when I switched to larger chuck jaws and larger tenons. All this is to say, explore your work holding as a culprit.