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Bowl turning question

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Aug 12, 2011
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Often, when I turn bowls, the gouge starts to vibrate and leaves undulations in the surface. I have tried to maintain constant pressure to keep the bevel against the surface, but without consistent success. Can this be caused at least in part by vibrations in the lathe itself? I am using a midi lathe on a heavy metal stand, but it is not rock solid.

Harry
 
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bowl turning

Harry, When I experience this, I think of several things. My gouge needs to be sharpened, I need to try a smaller gouge and thus a smaller cut, I need to move the tool rest closer, I need to check that the chuck is firmly attached to the blank, I need to go back to a pull cut and make sure the blank is not out of round and then try a shear cut. If the lathe is vibrating, slow it down. Good luck and I'm curious to know what kinds of wood you have this problem with. I have some very hard and dry sugar maple that dulls gouges at an amazing rate, but it's worth the trouble.
 
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Often, when I turn bowls, the gouge starts to vibrate and leaves undulations in the surface. I have tried to maintain constant pressure to keep the bevel against the surface, but without consistent success. Can this be caused at least in part by vibrations in the lathe itself? I am using a midi lathe on a heavy metal stand, but it is not rock solid.

Wood is not uniform, so you get differential drag on different portions of the circle. If you're an underhand type you're more vulnerable to in/out tool movement as the ease of cutting changes than an overhand type who cuts with the tool firm to the rest. If you're a nose up type with little toolrest support (>45 degree angle) you're more vulnerable than the kind who cuts with the handle nearly horizontal. So, is this happening no matter where you are in the cutting process? If so, look to the above. If only when the piece is at or near its thinnest, all you can do is steady, because the wood's flexing. Lighten up. Think "guide" rather than "ride" the tool on the work.

Can also be the way you've mounted the piece and how many times you've hooked it en route. If you've dug in a time or two, especially with wet wood, you can loosen your screws a bit, or chew your tenon so that the wood's no longer getting full support. It'll flop toward the heavy side, or push away when you push instead of guide. Check you hold with a grab and rattle to see if you need more hold. I avoid most of those problems by spinning between centers until the piece is as close to symmetrical and as light as I will make it. Safer, too.

Could be the lathe, but I'm going to doubt. Does it shudder or walk when running unloaded? Can you static shake it? If so, shim or brace until you can't. I'll go with the first two paragraphs rather than that, though.
 
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Thank both of you for your comments. I am an underhand and nose up type, so I may try the alternative to see if that mitigates the problem. The problem seems to manifest itself about half way thru the cut so it may be a change of angle that causes the problem. I had the problem with Hickory which was a real bear to turn and keep the tool sharp, but I also ran into it with Cherry, which I would consider to be much more turner friendly.

The lathe does not move easily when not turning, it is fairly well grounded, but vibrates when the wood is out of round.

Harry
 

john lucas

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It sounds to me like your putting too much pressure on the bevel. Sharpen your tool and take a few light cuts to level the surface. You should put pressure down on the tool rest instead of pushing into the bevel. Once it starts bouncing pushing on the bevel just makes it worse.
 
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To be more specific, are you getting "chatter marks" which are more like small divots in the wood or are you getting an uneven surface in the piece which is resulting in your gouge moving in and out?

The solutions for either will be different but solvable. No mater what the answer is though is you need to have a stable lathe. Get your lathe stand nice and stable using shims and then add some weight to the bottom. A few hundred lbs of sand bags is best but in a pinch pile all of your scrap wood inside of your lathe stand. This will help in every situation.
 
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I have had both chatter marks and uneven surface. I think I have resolved the uneven surface by changing my position in relation to the work piece. I am 5'7" and the lathe is on a table that is the height of a work bench which makes the work piece several inches higher. I built a platform to allow me to level the tool and get better control. I have made pull cuts to even the surface and now have a very smooth surface. I have had chatter marks also but they are not now present. I thought perhaps the chatter marks resulted from too low speed.

Harry
 
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Chatter can come from anything that makes the wood move. It could be the wood flexing, your chuck not holding as tight as you might want. I have had chatter marks turning very wet Madrone and am still not really sure why it showed up. Im glad your tooling change made a difference. Changing the type of cut is always good if you are not having luck with the current one. Sometimes switching from a gouge to a skew works for me, at least on the outside of the bowls. Inside you can try a gouge, scraper or something like an eliminator tool.

Have fun and post a picture of it when your done.
 
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There could be a number of things going on here.

One, bigger, heavier tools are less likely to chatter on their own (ever twang a ruler on your school desk?). With a 1/4 inch gouge, I can't hang out more than 1/2 inch without getting chatter, unless I take half micron dust particle size shavings off. I did see a friend use a thin spindle gouge as a chatter tool to put marks in the lid of a box.

There is always some bumps put in the wood by the difference in how the tool cuts from going through end grain and side grain. If you have noticed, the more you fight it, the worse it gets. Thing here is you do not want a white knuckle grip on the tool. Hold the tool like you would a bird, too tight and you kill it, too loose and it flies away. You also do not want that heavy grip on the tool rest. I find myself more and more now days turning with my left hand on the tool shaft, and not on the tool rest, or barely touching it. You also want a light 'rub' with the bevel. The harder you push on the bevel, the rougher your cuts will be. I saw Mike Mahoney and Stuart Batty turn a bowl together that was 1/8 inch thick, 14 or so wide, and about 8 inches deep. They didn't use a steady rest, or hand support when turning the inside of the bowl. Rubbing the bevel is a very gentle guide, and a touchy/feely thing.

You will get more vibrations when turning the inside of the bowl. Most of the mass has been turned away, and the thin walls of the bowl will flex with tool pressure. Gentle touch.

If you are getting no marks near the bottom and more marks/vibrations near the middle and top, this can again be tool pressure. It can also mean that your bowl is loose in the chuck or on the face plate. With the lathe stopped, give it a hand push check. If it moves at all, tighten things up. The set screws in your chuck can also work loose.

robo hippy
 
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Welcome to turning, fellow Charlottesvillian.

In response to your question, I would have given the same advice that Reed suggested about tool control, and distance over tool rest. I've heard many people say, "a good turner adjusts the tool rest often".


Also, meet up with some local turners if you're able to. I'm an officer in the club nearest to Charlottesville. If you haven't been to one of our meetings yet, please check out Central Virginia Woodturners, meeting every 3rd tuesday of the month in Crimora, about 40 minutes from Charlottesville depending on where you live. (about 10 mins. past Waynesboro). Check out our AAW chapter website. http://www.centralvawoodturners.org/index.html
 
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All the responses address possible causes and considerations, but another one not mentioned is the point of contact. With a bowl gouge as you open and close the flute when making a cut from the center out or vise versa, vibrations can occur when the point of contact on your gouge gets too wide creating increased friction as your cut width becomes to great. Another part of this is caused by not having the flute open enough at the right point in the arch of the cut. If the flute is closed too much at the center of the arch, the gouge goes from a cut riding the bevel to a scraper. Likewise, if the flute is too open as you cut from outside in, and the gouge is near the center, the wood begins to feed itself to the gouge from the side rather than above.
 

john lucas

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Thomas I agree with what your saying but beginners have no idea what an open or closed flute is. Can you explain it for them.
 
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I have found open and closed terms confusing, or at least, not clear. I say, roll the flutes away from the cut. You do not want them straight up as the wings can catch. Between 9 and 11 o'clock when turning the outside of the bowl, and 1 and 3 o'clock on the inside of the bowl.

robo hippy
 
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I have found open and closed terms confusing, or at least, not clear. I say, roll the flutes away from the cut. You do not want them straight up as the wings can catch. Between 9 and 11 o'clock when turning the outside of the bowl, and 1 and 3 o'clock on the inside of the bowl.

Weeeeell, not really. If you cut above centerline outside and below inside you'd have to do some work to hook the piece. Especially when you're cutting from smaller to larger diameter outside. The key to catchlessness is the consistent angle bevel. If the tool rolls, it can't dig, because the heel will hit. Weakness of the cylinder with variable angle grind which has the smaller sharpness angle on the wings is that it will.

I'm sort of waiting on a definition as well. I use the standard woodworking terminology when describing working wood with an edge, from Hoadley via the net. http://homepages.sover.net/~nichael/nlc-wood/chapters/caop.html I had more or less assumed that John was thinking in two static dimensions, describing skewed and non-skewed as closed and open.
 
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Bowl turning

Good point John,


Generally, the term "open" when referring to the flute of the bowl gouge means that the flute is facing up, using the previous clock analogy the flute would be somewhere between 11 and 1. Having the flute closed would be somewhere between 9 and 10 or 2 and 3.

However I have to disagree with Robo regarding the issue of whether or not you want an "open" or "closed" flute. And especially his statement about the practice of turning the flute away from the direction of the cut. Its not possible to cut anything with the flute turned the oposite direction. Starting and finishing a cut with a closed flute (in the direction of the cut) can reduce the chance of a catch and is necessary for certain cuts or cut angles. But this is certainly not the case in all situations. I typically turn forms with an endgrain orientation that are thin walled (.5 mm to 4 mm) 10-12 inches deep and roughly the same in diameter, 1.5 mm being the most common thickness. I turn the vessel from chuck jaw tenon, to hollowing and finish cuts with a single bowl gouge. (Don't tell my wife, I like to buy other tools too) The only other tools I use are the hunter #6 for the very bottom of the vessel when I can't get the right bevel angle with the gouge, and a parting tool. Because of the type of turning I am doing, my pieces have to be free of tool marks or nearly so, straight off the lathe. So I know that cutting with an open flute is not only possible, but when done correctly provides a superior surface. And as the wood gets exceedingly thin, a closed flute cut requires too much sidewall pressure to make the proper cut.

When I am coring out the center I cut both directions i.e. from the center out, or from the outside to the center depending on several factors. During those cuts the flute is always pointed in the direction I am cutting and opens progressively from one end of the cut until I am at the apex of the cutting arch at which point the flute is at 12 o' clock. during the second half of the arch the flute is progressively closed in the direction of the cut. In doing this the bevel angle is maintained in the bottom of the vessel/bowl just as MM mentioned. But when trying to get the final wall thickness, those cuts are usually with a 12 o'clock position from the start, but the handle is held perpendicular to the woods point of contact so that the tip of the gouge makes contact not the wings.

I hope this helps explain the "open" and "closed" flute issue. It's probably best to watch a video of a pro turning a bowl. Reading how to turn is like reading how to properly swing a golf club, 20 things to remember and do at once. It's better to see it done.
 
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Good point John,


Generally, the term "open" when referring to the flute of the bowl gouge means that the flute is facing up, using the previous clock analogy the flute would be somewhere between 11 and 1. Having the flute closed would be somewhere between 9 and 10 or 2 and 3.

I hope this helps explain the "open" and "closed" flute issue. It's probably best to watch a video of a pro turning a bowl. Reading how to turn is like reading how to properly swing a golf club, 20 things to remember and do at once. It's better to see it done.

Are you cutting with the nose or the side? Side cut, flute open up. http://s108.photobucket.com/albums/n28/MichaelMouse/?action=view&current=PillarSmall.mp4

Nose cut, ears curving away from the surface. http://s108.photobucket.com/albums/n28/MichaelMouse/?action=view&current=CherryPeelIn.mp4

Easier to see on outside cuts. This one's got both. http://s108.photobucket.com/albums/n28/MichaelMouse/?action=view&current=35mmGougeRounding.mp4

With no ears rounded, cutting outside, right up to the corner. http://s108.photobucket.com/albums/n28/MichaelMouse/?action=view&current=1012052.mp4 Since the piece curves away at the top and the rear, the U shape becomes a skew, which can produce a great finish.
 
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