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

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

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

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

Vibration with Nova chuck?
 

wrote:
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.

I too am not sure what you mean my 'vibration'. If you mean the bowl is
not turning concentrically it could be due to:

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

http://www.seafoamwoodturning.com
http://chipshop.blogspot.com - a blog for my customers
http://www.seafoamwoodturning.com/TheToolrest/ - a blog for woodturners

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

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.

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

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

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