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Woodturning (rec.crafts.woodturning) To discuss tools, techniques, styles, materials, shows and competitions, education and educational materials related to woodturning. All skill levels are welcome, from art turners to production turners, beginners to masters. |
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#1
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Vibration with Nova chuck?
I have a Delta 16" lathe that I thought had bad bearings or a spindle
that was bent because I get a lot of vibration especially on larger bowls. Hats off to Delta, they sent me new bearings and a spindle for free and a new belt (it was out of warrarty), but I'm still getting way too much bounce when the bowl is turning. On a 12" bowl it's hard to keep the tool edge on the wood! I have the supernova chuck and it seems to hold the piece very well, but if something in the worm gear was off would it cause the vibration? And if so how would I be able to check it. I'm at the end of my rope in trying to figure this out. Oh, and I have around 450lbs of sand on or in my lathe also. Any insight from anyone would be a great help. Craig |
#2
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Vibration with Nova chuck?
Run the lathe by itself, it should be very smooth. Install just the chuck it
should be very smooth as well. Put a known round object in the chuck and put the toolrest near it and turn it by hand. It should remain equal distant from the toolrest as it rotates. If you have a dial indicator even better. This will show if the chuck is holding the object on center. This could be caused by jaws not installed in the correct order. I trust you are concerned with vibration after the bowl blank has been trued and you are turning with a suitably low rpm for the piece. billh wrote in message oups.com... I have a Delta 16" lathe that I thought had bad bearings or a spindle that was bent because I get a lot of vibration especially on larger bowls. Hats off to Delta, they sent me new bearings and a spindle for free and a new belt (it was out of warrarty), but I'm still getting way too much bounce when the bowl is turning. On a 12" bowl it's hard to keep the tool edge on the wood! I have the supernova chuck and it seems to hold the piece very well, but if something in the worm gear was off would it cause the vibration? And if so how would I be able to check it. I'm at the end of my rope in trying to figure this out. Oh, and I have around 450lbs of sand on or in my lathe also. Any insight from anyone would be a great help. Craig |
#3
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Vibration with Nova chuck?
wrote in message oups.com... I have a Delta 16" lathe that I thought had bad bearings or a spindle that was bent because I get a lot of vibration especially on larger bowls. Hats off to Delta, they sent me new bearings and a spindle for free and a new belt (it was out of warrarty), but I'm still getting way too much bounce when the bowl is turning. On a 12" bowl it's hard to keep the tool edge on the wood! I have the supernova chuck and it seems to hold the piece very well, but if something in the worm gear was off would it cause the vibration? And if so how would I be able to check it. I'm at the end of my rope in trying to figure this out. Oh, and I have around 450lbs of sand on or in my lathe also. Any insight from anyone would be a great help. If you are turning a dried softwood bowl blank, there are at least two conditions that will give "out of round" vibrations even if the lathe and the chuck are in perfect contition: - The fibre directions will make your iron flutter and then jump if you don't have perfectly sharp tools, and sometimes even then if the wood is hard enogh, like some exotic woods, oak or elm. - The blank may consist of dark corewood and light sapwood in unequal distribution, and the difference in specific weight makes the bowl behave like "out of round", even if it is perfectly round. The only solution I know is to take your time; sharpen those irons and turn at slower speeds. Bjarte |
#4
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Vibration with Nova chuck?
wrote in message oups.com... I have a Delta 16" lathe that I thought had bad bearings or a spindle that was bent because I get a lot of vibration especially on larger bowls. Hats off to Delta, they sent me new bearings and a spindle for free and a new belt (it was out of warrarty), but I'm still getting way too much bounce when the bowl is turning. On a 12" bowl it's hard to keep the tool edge on the wood! I have the supernova chuck and it seems to hold the piece very well, but if something in the worm gear was off would it cause the vibration? And if so how would I be able to check it. I'm at the end of my rope in trying to figure this out. Oh, and I have around 450lbs of sand on or in my lathe also. Any insight from anyone would be a great help. You've already checked for runout at the jaws? Easy enough to do by clamping something to a toolrest and rotating by hand, checking for consistent gap. Bjarte suggests extending the axis, which could introduce more, even on a "known good" piece, but would also make any runout more obvious. Crapshoot. You're periodically snugging the jaws while making the turning? With the smooth holds, where the force is spread over a broader area, it's not as much of a problem as with the crush holds, where a misplaced tool can get the whole out of whack with a catch and dig-in. Make sure you have a good shoulder if gripping a tenon, and make sure you have full contact with it. Make sure you have a flat bottom on your mortise if using an internal dovetail, and make sure it's tight up against the nose of the jaws. If it wobbles, snug, don't crank. Cranking can exacerbate your problem. Use your tailstock until the last possible moment, when your bowl is at its lightest and most round. Be sure to snug - not crank - your hold before you release the tailstock, and as billh suggests, don't "ride" the bevel when cutting. Pressing into the piece leads to following its irregularities. Pressing into your unmoving toolrest and letting the wood cut itself against your sharp tool leads to a round piece. Might as well compound the heresy and say don't cut over about 600. With all kinds of kinetic energy available, you can fool yourself into thinking your tool is sharp enough, when in reality it's ripping the daylights out of things. When it rips, the wood flexes and recoils. http://personalpages.tds.net/~upgeorge/index.html |
#6
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Vibration with Nova chuck?
I have found that some pieces of wood will never run without vibrations
because the wood is out of balance, even when the bowl is perfectly round. Also, the set screws for my chuck jaws seem to work themselves loose over time, so I check them once in a while. robo hippy |
#7
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Vibration with Nova chuck?
"billh" wrote: (clip) This could be caused by jaws not installed in the correct order. (clip) ^^^^^^^^^^^^^^^^ I agree with everything you have said, except the part about the order of the jaws. It IS possible to assemble a chuck with the jaws in the wrong order, but the result will be so obvious that it could not go unnoticed. When you close the jaws completely, do they meet nicely on the center line? Look for one that is off a hair--you could have defective jaws. Do you belong to a club, or know other turners, where you could borrow a different chuck for a comparison run? You could be right that something in the chuck is out of whack. Following Bill's thinking, you have to do this by a process of elimination. Usually, even if a piece of wood is held unevenly in the chuck or on a faceplate, once it is turned round, it should run true. Your lathe, with the amount of sand you have added should tolerate a fair amount of unbalance without trouble. Otherwise, we'd all be in trouble trying to do off-axis turning or natural-edge bowls. |
#8
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Vibration with Nova chuck?
Derek Andrews sagely responded:
1- the bowl has been remounted. Even with 'perfect' technique there is still likely to be some lack of concentricity, but there is plenty of scope for poor technique and some woods lend themselves to better accuracy than others. 2 - the wood is green and warping as it dries out. 3 - the turning preocess is releasing stresses in the wood causing it to distort. -- Derek Andrews, woodturner I am with him. Check for runout as indicated by others above. But for me personally, I am thinking along the lines of Mr. Andrews. When remounting a piece, it is ALWAYS out of balance. How can you remount in exactly the right place with exactly the right pressure on your chuck to give you tolerances that are within a few thousandths? When giving my off center turning demo, I show the class how little it takes to get a kiln (OK microwave) dried piece off center. I take a cylinder that is about 3" across and 6 inches long. I turn it true between centers, and turn a 2" tenon on it to mount in the chuck. I mount it in the chuck with the shoulders of the blank firmly against the chuck, then turn on the lathe. It is now no longer balanced or true. But then to drive in the point of alignment, I loosen the scroll chuck a bit, and bring the tailstock up to the piece and put the point in its old hole. Add tailstock pressure, tighten scroll chuck, and remove tailstock and turn on the lathe. It is still not perfect, but it is 100% better. When you turn a bowl, you have no such realignment tool. Mount the blank, turn away, and then you go from there. I have also found that turning woods with large knots, or other features such as holes, occlusions, or punky areas are particularly bad about being out of round in just a few hours. Then if I fill a large void with some epoxy mixed with who knows what, watch out. When I started turning, I found this out these things well as the fact I needed to put an index mark on the piece and the chuck so I would remount as closely as possible. Still in frustration, I started doing things like leaving the piece on the jaws while out in the shop. Yup, after a day or two it was out of balance. It had begun to dry. So I tried bringing the piece in the house, still mounted on the jaws; same results, not as dramatic. With really green wood, I have turned it out for a while, gone to lunch, and some back and it is out of balance! Now I just accept the fact that they will be out of round and a couple of passes with the correct tool will get them back on track and ready to finish up. Robert |
#9
Posted to rec.crafts.woodturning
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Vibration with Nova chuck?
Thanks to everyone that took time out to offer help for my problem. I
have tried a few of the suggestions: put something I think is round in chuck place it against the tool rest and looked for gaps, none. My lathe does run without noticiable vibration even with the chuck mounted. The piece of wood that I have in there now is 12" sycamore with no knots and was rough turned a year ago to about 1" in diameter. The problem that I see I'm still having is, just like Leo states, even though the piece may not be mounted perfectly in the chuck it should be able to be turned round without the tool bouncing on the wood. I've turned in down to about 3/8" and just gave up trying to get a smothe surface just from the tool. Even with shearing cuts I still couldn't get rid of the bounce. I know you all have given me plenty of other things to try so I'll let you know how it goes. Craig |
#10
Posted to rec.crafts.woodturning
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Vibration with Nova chuck?
Is the problem all the way from the edge of the bowl to the centre?
It could be that having got the thickness down to 3/8" that the outside is flexing and giving you bounce which should get less as you get to the centre which has more support. The cure for this is to take light cuts and support the other side of the bowl with your fingers. If you smell cooking pork you are pressing too hard with your fingers. Good luck BillR "Craig S" wrote in message ups.com... Thanks to everyone that took time out to offer help for my problem. I have tried a few of the suggestions: put something I think is round in chuck place it against the tool rest and looked for gaps, none. My lathe does run without noticiable vibration even with the chuck mounted. The piece of wood that I have in there now is 12" sycamore with no knots and was rough turned a year ago to about 1" in diameter. The problem that I see I'm still having is, just like Leo states, even though the piece may not be mounted perfectly in the chuck it should be able to be turned round without the tool bouncing on the wood. I've turned in down to about 3/8" and just gave up trying to get a smothe surface just from the tool. Even with shearing cuts I still couldn't get rid of the bounce. I know you all have given me plenty of other things to try so I'll let you know how it goes. Craig |
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