High Pitch Chatter?

[Steve Mathews]

I just finished a small bowl using Pecan wood and experienced for the first time a high pitch chatter. Is this because the wood was so hard?

[Fred Belknap]

Steve I'm not sure just what you mean by chatter but you will get vibration on the outer edge of bowls quite often. One of the most simple things to do is use a steady rest. Usually the thinner the bowl is the more it vibrates. It sometime is better to pretty much finish the outer inch or so of a bowl and leave more thickness toward the middle to help dampen vibrations. Sometimes just changing the speed a bit will help.

[John K Jordan]

I can usually stop any chatter/squeal by supporting the opposite side with my hand. As Raffan says, if the fingers get hot there is too much pressure with the tool.

Sharper may help. Sometimes I switch to a different grind or a different tool entirely, for example a Hunter Hercules instead of a gouge or vice versa. I agree with thinning in sections, then smoothing as needed with NRS.

JKJ

[Richard Coers]

Too high lathe rpm, too much pressure on the bevel of the tool, dull tool, wrong tool choice, wrong approach angle, wrong direction of cut, too long of tool overhang over the tool rest, etc....

[Al Launier]

Would a rubber band help, i.e. like from a tire tube?

[Bill Boehme]

It's usually because the walls are thin. It is best to work in stages from rim to bottom ... turn the first inch or so at the rim to final thickness while the lower part is still thick and has enough supporting wood to prevent vibration. After that stage is complete do the next inch or so and turn it to final thickness. Continue in this fashion until you reach the center of the bottom. One word of warning is to never go back to touch up a previously finished stage. If you do theere is likely to be chatter and possibly even a bowl wrecking catch.

[Reed Gray]

Without even finishing reading your post, I said to myself, 'inside bowl tool pressure on the rim'. A common problem. This is the main reason most finish turn the inside of the bowl in steps rather than one cut from rim to bottom. Especially at higher speeds, the bowl will warp from grain orientation alone, and then when you rub the bevel, you can make that worse. Once the inside of the bowl is pretty much done and I am doing clean up cuts, when it comes to working any where near the rim, it is a shear scrape only (I have one video dedicated to shear scraping). This is no bevel rubbing, so you don't get distortion from that. Another thing, much more so with beginners, and some what with more 'experienced' turners, we use way too much bevel rub.... "The bevel should rub the wood, but the wood should not know it." Unknown author.... That is an art I am still figuring out...

Oh, from some one, a while ago, who was using a scraper near the rim, "my bowl made this strange screeching and howling sound and then blew up!"

robo hippy

[John K Jordan]

...Another thing, much more so with beginners, and some what with more 'experienced' turners, we use way too much bevel rub.... "The bevel should rub the wood, but the wood should not know it." Unknown author.... That is an art I am still figuring out...

When I first started turning I learned from Darlow's "Fundamentals of Woodturning" book that the part of the bevel that contacts the wood is extremely short. He has some great photos of cuts in action that illustrate this (the book is well worth buying for that and many other reasons.)

This photo of Darlow's illustrates just how much of the bevel is "rubbing". I think this photo is OK to post since it is on one of the "Look Inside" pages on Amazon, available to the world. (Get the book, the photos are so much clearer there!)
peeling_Darlow.jpg

Later, I heard Chris Ramsey explain just how little of the bevel is needed. His grind leaves a bevel of less than 1/16". I took this photo of the gouge he uses for cowboy hats. The cellphone photo is poor - I highlighted the actual bevel with red:
Ramsey_gouge_comp.jpg

Over the years, every time I heard someone say to "rub the bevel" I thought it was a figure of speech, not actual bevel contact. When I did let the bevel, and worse, the heel contact the wood I sometimes got rough, undulating surfaces and/or the wood was burnished by the tool. It's real easy to mess up a planing cut with the skew by letting the bevel contact - any imperfection can be amplified by the bevel making the surface worse and worse and difficult to correct unless you know how. End grain cuts in hard woods can also be easily ruined with too much bevel contact. Most finish cuts are so much smoother and more controllable if the tool is positioned to touch the bevel then lifted every so slightly so it's only contacting at the very edge and the touch is light. Too much lift or force and the edge will dive into the wood, more than that and it starts scraping. Just right it cuts so cleanly.

I've heard others talk of "gliding" the bevel. Maybe that's a better way to think about it.

JKJ