I put my roughed-out box elder bowl back on the lathe yesterday. Its about
10" in diameter by about 6" tall. It had dried some, so I had decided to
thin down the walls to hasten drying by taking a few hollowing cuts off the
inside of the bowl. Although the bowl walls are well over an inch thick (1
1/8"), I get a low frequency vibration when I start the cut near the rim of
the bowl. As I near the bottom, the vibration diminishes and goes away.

The bowl is mounted in my Super Nova chuck with a 2" stub tenon. The chuck
is tightly seated against the spindle....no plastic washer or anything. The
2" standard jaws are tight on the tenon. The tenon is intact....not cracked
or anything I am no longer using tailstock support as the bowl is now
hollowed. The Crown PM 5/8" Ellsworth grind gouge is freshly sharpened.
Still I get the vibration. Any ideas would be appreciated. Thanks.

Barry

PS Is it time for me to replace my Super Nova with a new Stronghold
chuck? Do I just need to put this blank on the rack, wait a few weeks and
let it finish drying before I come back to it?

"Barry N. Turner" wrote in message
...
I put my roughed-out box elder bowl back on the lathe yesterday. Its about
10" in diameter by about 6" tall. It had dried some, so I had decided to
thin down the walls to hasten drying by taking a few hollowing cuts off the
inside of the bowl. Although the bowl walls are well over an inch thick (1
1/8"), I get a low frequency vibration when I start the cut near the rim of
the bowl. As I near the bottom, the vibration diminishes and goes away.

The bowl is mounted in my Super Nova chuck with a 2" stub tenon. The
chuck is tightly seated against the spindle....no plastic washer or
anything. The 2" standard jaws are tight on the tenon. The tenon is
intact....not cracked or anything I am no longer using tailstock support
as the bowl is now hollowed. The Crown PM 5/8" Ellsworth grind gouge is
freshly sharpened. Still I get the vibration. Any ideas would be
appreciated. Thanks.

Barry

PS Is it time for me to replace my Super Nova with a new Stronghold
chuck? Do I just need to put this blank on the rack, wait a few weeks and
let it finish drying before I come back to it?

=========================
Barry,
I'd say it's not too unusual. you probably have some distortion from the
drying it has already done. That, combined with the normal tendency for a
bowl wall to vibrate when cutting near the rim, is not abnormal, and may be
more or less pronounced depending on wood species, size and shape of the
turning. If you can put your left hand against the back side of the bowl
opposite the cut, (Or have someone else do it for you, the vibration should
either go away or be greatly damped. If not, I'd start looking for a crack.
FWIW

Ken Moon
Webberville, TX.

Barry N. Turner wrote:
I put my roughed-out box elder bowl back on the lathe yesterday. Its about
10" in diameter by about 6" tall. It had dried some, so I had decided to
thin down the walls to hasten drying by taking a few hollowing cuts off the
inside of the bowl. Although the bowl walls are well over an inch thick (1
1/8"), I get a low frequency vibration when I start the cut near the rim of
the bowl. As I near the bottom, the vibration diminishes and goes away.

The bowl is mounted in my Super Nova chuck with a 2" stub tenon. The chuck
is tightly seated against the spindle....no plastic washer or anything. The
2" standard jaws are tight on the tenon. The tenon is intact....not cracked
or anything I am no longer using tailstock support as the bowl is now
hollowed. The Crown PM 5/8" Ellsworth grind gouge is freshly sharpened.
Still I get the vibration. Any ideas would be appreciated. Thanks.

Barry

PS Is it time for me to replace my Super Nova with a new Stronghold
chuck? Do I just need to put this blank on the rack, wait a few weeks and
let it finish drying before I come back to it?


There could be any number of things going on here.

First, the wood is now drier and therefore harder than before. The
cutting action is therefore going to place more force on the bowl and
hence the tendency to create vibration. Sharp tools and light cuts are
in order.

The tenon, and the shoulder that the chuck jaws mate against, will have
distorted as the bowl dries. The flat surface is probably no longer
flat, and the tenon is no longer round. This may be enough to allow the
bowl to move a little in the chuck.

The bowl will have distorted, so as it rotates the depth of cut is going
to vary. This might cause vibration.

I use a SuperNova and don't think I would have a problem. What size
lathe spindle do you have? When I moved up from a Delta (1 inch) to the
Nova (5/4 inch), I noticed a lot of vibration problems disappeared and
my turning improved considerably.


FWIW, when I skim roughed out bowls, I usually do the outside first.
Holding the inside of the rim of the bowl in cole jaws allows me to work
on both the walls and the recess (in your case the tenon). Gripping the
rim gives a much bigger mechanical advantage compared to the base.


--
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

First of all, it's only been about 10 days since I roughed out the bowl. I
guess I'm rushing things, but I was just trying to thin down the walls more
so the bowl would dry faster. Initially, the walls of the bowl were about 1
1/4" thick.

A few days after I roughed out, I put the bowl back in the chuck and took a
couple of passes off the inside. Yesterday, about 10 days after initial
roughing, I noticed the bowl was drier and decided to rechuck and thin the
walls a bit more. A bowl with walls over an inch thick is going to take a
long time to season. The tenon and bowl may have distorted some, but its
just not dry enough to have distorted a lot. There is no visible distortion
yet.

My lathe spindle is 1 1/4" (Stubby 750). On the advice of a friend of mine,
I also checked to make sure the threaded insert in my Super Nova Chuck had
not loosened. (It hadn't)

Your comments about mechanical advantage make sense, I'm holding this bowl
on a 2" stub tenon and I'm making cut on a 10" diameter part of the bowl.
Therein probably lies the problem. Thanks.

Barry


"Derek Andrews" wrote in message
...
Barry N. Turner wrote:
I put my roughed-out box elder bowl back on the lathe yesterday. Its
about 10" in diameter by about 6" tall. It had dried some, so I had
decided to thin down the walls to hasten drying by taking a few hollowing
cuts off the inside of the bowl. Although the bowl walls are well over
an inch thick (1 1/8"), I get a low frequency vibration when I start the
cut near the rim of the bowl. As I near the bottom, the vibration
diminishes and goes away.

The bowl is mounted in my Super Nova chuck with a 2" stub tenon. The
chuck is tightly seated against the spindle....no plastic washer or
anything. The 2" standard jaws are tight on the tenon. The tenon is
intact....not cracked or anything I am no longer using tailstock support
as the bowl is now hollowed. The Crown PM 5/8" Ellsworth grind gouge is
freshly sharpened. Still I get the vibration. Any ideas would be
appreciated. Thanks.

Barry

PS Is it time for me to replace my Super Nova with a new Stronghold
chuck? Do I just need to put this blank on the rack, wait a few weeks
and let it finish drying before I come back to it?


There could be any number of things going on here.

First, the wood is now drier and therefore harder than before. The cutting
action is therefore going to place more force on the bowl and hence the
tendency to create vibration. Sharp tools and light cuts are in order.

The tenon, and the shoulder that the chuck jaws mate against, will have
distorted as the bowl dries. The flat surface is probably no longer flat,
and the tenon is no longer round. This may be enough to allow the bowl to
move a little in the chuck.

The bowl will have distorted, so as it rotates the depth of cut is going
to vary. This might cause vibration.

I use a SuperNova and don't think I would have a problem. What size lathe
spindle do you have? When I moved up from a Delta (1 inch) to the Nova
(5/4 inch), I noticed a lot of vibration problems disappeared and my
turning improved considerably.


FWIW, when I skim roughed out bowls, I usually do the outside first.
Holding the inside of the rim of the bowl in cole jaws allows me to work
on both the walls and the recess (in your case the tenon). Gripping the
rim gives a much bigger mechanical advantage compared to the base.


--
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

"Barry N. Turner" wrote: (clip) Any ideas would be appreciated. Thanks.
^^^^^^^^^^^^^^^^^
All the ideas that have been offered seem valid. But no one has mentioned
speed. Have you tried raising or lowering the speed, in order to get away
from possible resonances?

Another comment, though. The wall thickness you have may be necessary after
the bowl is dry, to restore roundness. I think it would be better to bag it
and wait for slow drying to take place. As the bowl dries and distorts, it
will be inevitable that you will experience uneven cutting. If you do this
more than onece during the drying process, you will probably have the
problem each time, so why not just wait, and suffer only once?

Barry N. Turner wrote:
A bowl with walls over an inch thick is going to take a
long time to season. The tenon and bowl may have distorted some, but its
just not dry enough to have distorted a lot. There is no visible distortion
yet.

Roughed out bowls dry surprisingly quickly because there is so much end
grain exposed. In fact I usually slow down the drying by putting endseal
on the areas where end grain has been cut right across.

It won't take a lot of distortion for the chuck to be unable to seat
properly on the tenon.

--
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

Your comments about mechanical advantage make sense, I'm holding this bowl
on a 2" stub tenon and I'm making cut on a 10" diameter part of the bowl.
Therein probably lies the problem. Thanks.

That's a pretty small tenon for a 10" bowl. Either Mike Mahoney or Stuart Batty (I don't
recall which), at the AAW Symposium in Pasadena (2004) (where they recorded the Two Ways
to Make a Bowl video), says that the tenon should be about 40% of the bowl diameter. That
would be 4" on a 10" bowl.

Barry


Matt Heffron

a few things
- reverse the bowl against your chuck holding it in place with the
tailstock.

- True up the tenon or cut a new larger one. I bet you have enough wood
with the thickness but if all you have is the 50mm jaws on the super
nova you may not. With larger bowls I use the power grip jaws.

- While it is reversed also round of the outside of the bowl so when you
put the tenon back on the chuck it will be more balanced.

- Look for cracks. I find that little cracks in the wood can cause more
vibration resonance. You can almost tell that something is not right
when your bowl startes to sing. You can expect something to come flying off

- How fast are turning the bowl? Always start slow.

- Test your nova chuck by spinning it without anything mounted.

I've recently started putting my roughed turnings in a scale and putting
the information into excel so I can plot the drying rate and know when
it is dry.

Barry N. Turner wrote:
I put my roughed-out box elder bowl back on the lathe yesterday. Its about
10" in diameter by about 6" tall. It had dried some, so I had decided to
thin down the walls to hasten drying by taking a few hollowing cuts off the
inside of the bowl. Although the bowl walls are well over an inch thick (1
1/8"), I get a low frequency vibration when I start the cut near the rim of
the bowl. As I near the bottom, the vibration diminishes and goes away.

The bowl is mounted in my Super Nova chuck with a 2" stub tenon. The chuck
is tightly seated against the spindle....no plastic washer or anything. The
2" standard jaws are tight on the tenon. The tenon is intact....not cracked
or anything I am no longer using tailstock support as the bowl is now
hollowed. The Crown PM 5/8" Ellsworth grind gouge is freshly sharpened.
Still I get the vibration. Any ideas would be appreciated. Thanks.

Barry

PS Is it time for me to replace my Super Nova with a new Stronghold
chuck? Do I just need to put this blank on the rack, wait a few weeks and
let it finish drying before I come back to it?

Barry - it's not the chuck.
several others have posted valid ideas as to cause, but you will
almost always get resonance at some RPM with a bowl because you are
making a bell and gee, bells ring.

I disagree with teh 40% rule - I've turned a platter that was about 24
inches across (asymetric, that's the long dimension) using a tennon
that was a lot less than 10 inches (I'd say about 3 inches), no
problems with the tennon, though I was unusually careful to not have
the wings smack me - I'm not particularly fond of splattering my own
blood on my nice black lathe.

As Leo suggested, you can be patient and let it dry. Or you can do
what I do and cut to finished dimensions in one pass and then deal
with any distortion bycalling it a "feature" - in that case, turn thin
(1/4 inch or so) and declare victory.

To cut and avoid the vibration, sharp tools, and a light touch, adjust
RPM, and thin from the rim down in about 1/2 inch to 1 inch steps -
more vibrational energy is transmitted for cuts near the rim, so keep
the mass inthe bowl as you thin the rim.

On Sun, 19 Mar 2006 21:17:05 -0700, william kossack
wrote:

a few things
- reverse the bowl against your chuck holding it in place with the
tailstock.

- True up the tenon or cut a new larger one. I bet you have enough wood
with the thickness but if all you have is the 50mm jaws on the super
nova you may not. With larger bowls I use the power grip jaws.

- While it is reversed also round of the outside of the bowl so when you
put the tenon back on the chuck it will be more balanced.

- Look for cracks. I find that little cracks in the wood can cause more
vibration resonance. You can almost tell that something is not right
when your bowl startes to sing. You can expect something to come flying off

- How fast are turning the bowl? Always start slow.

- Test your nova chuck by spinning it without anything mounted.

I've recently started putting my roughed turnings in a scale and putting
the information into excel so I can plot the drying rate and know when
it is dry.

Barry N. Turner wrote:
Bill

www.wbnoble.com

to contact me, do not reply to this message,
instead correct this address and use it

will iam_ b_ No ble at msn daught com
*** Free account sponsored by SecureIX.com ***
*** Encrypt your Internet usage with a free VPN account from http://www.SecureIX.com ***

"Barry N. Turner" wrote in message
...
I put my roughed-out box elder bowl back on the lathe yesterday. Its about
10" in diameter by about 6" tall. It had dried some, so I had decided to
thin down the walls to hasten drying by taking a few hollowing cuts off the
inside of the bowl. Although the bowl walls are well over an inch thick (1
1/8"), I get a low frequency vibration when I start the cut near the rim of
the bowl. As I near the bottom, the vibration diminishes and goes away.

The bowl is mounted in my Super Nova chuck with a 2" stub tenon. The
chuck is tightly seated against the spindle....no plastic washer or
anything. The 2" standard jaws are tight on the tenon. The tenon is
intact....not cracked or anything I am no longer using tailstock support
as the bowl is now hollowed. The Crown PM 5/8" Ellsworth grind gouge is
freshly sharpened. Still I get the vibration. Any ideas would be
appreciated. Thanks.



OK, as others have mentioned, you're not supporting the piece in a way
calculated to keep it from swaying. Gripping a tenon that has certainly
distorted from drying, especially without a true reference face at right
angles to the tenon, won't do it. If you buy a set of jaws that chew the
tenon as you tighten you have all the problems above plus artifact from the
original torn/crushed fibers to contend with. Derek has found a way to get
around some problems of drying distortion. He re-trues the tenon and face to
get full support and hold.

I do the same, but with the pin chuck, I just run a 1" Forstner down the
narrowed (cross-grain drying distortion) hole I used when roughing the wet
blank, put on the lathe, and do the outside. Easy, extremely close to the
original turning axis, and when I'm ready to reverse, I have a circular
mortise and a flat bottom inside for my expansion dovetail. BTW, that
safety talk from the manufacturers is probably pretty well padded for legal
purposes, so use the size mortise or tenon that brings success. It may get
smaller as your proficiency improves. You might even do things that look
dumb to prove you can do it at all.
http://photobucket.com/albums/d160/G...able-Again.jpg
Red oak, and you can bet the bottom is heavy to hold it from tipping.

Last, the bowl has distorted, and until you get it back to circular, a task
which will be difficult if not impossible without proper chucking, you'll be
shaving the side grain and missing the end, which makes the balance worse,
of course, as it shifts the center of mass outward. Your tool hits twice
each revolution, but the effect diminishes toward the bottom of the bowl,
because shrink is in proportion. You are also putting much less strain on
the piece, as the force varies with the square of velocity, and your force
is therefore much less the closer to center you go. Which is why, of course
you're rotating as close to slow as your patience can support, else you
exacerbate all the out-of-balance problems.

Speculation of the walls being too thin is just that. They're not going to
move much until they get below 1/2" green or 3/8" dry and have some
reasonable force placed on them by spinning too fast or "riding the bevel"
too hard. . When you get close to that, it's time to resharpen or rehone,
your preference, and peel easy to desired thickness.

Oh yes, boxelder has approximately the same drying characteristics as soft
maple, so you can get to 20% MC from green in 160 above-freezing days
according to FPL experimental data on _planks_ 1" thick. Means one tenth
of that time through the end grain. Under winter rules, if you've got that
blank open to the warm air, you're probably talking 4-6 weeks to ambient 6%
, tops.

I think everyone's missing the real problem here. I'm guessing that by
using a gouge with an ellsworth grind, you're using it much like a
scraper. When you do this, you put a force on the edge of the bowl that
is radial (outward). This complicates rounding because every time you
cut, you're distorting the shape of the bowl. The vibration won't go
away once it's round. It may even get worse because it's thinner and
flexes more.

You need to use a tool in a way that puts the force axial (parallel to
the axis) which will drastically reduce vibration near the edge of the
bowl.

2 ways to do that, off the top of my head:
1. Use a regular gouge with a different grind in a cutting mode .
2. Use a scraper with a sharp corner to get the cut started near the
edge and define the round circle. Do not push the tool in a radial
direction, align it so you're cutting on the top edge of the bowl,
cutting straight back toward the headstock, just as if your tool is a
drill and you're going to push the drill into the bowl to make a
perfectly round hole. Once you have a round rabbet half an inch or an
inch deep (o two inches deep) you can use a gouge in a cutting mode
(not the ellsworth grind in a scraping mode) to move deeper, rubbing
the bevel on the already cut surface.

I have a couple gouges with a straight grind on them which can be used
to do both cuts... the first cut I do with the very corner edge of the
grind as if it were a skew, with the tool parallel to the lathe axis.
Works like a charm. You get rounder circles and cleaner edges on the
bowl, especially if it's a natural edge.

Once it's round, you can use the ellsworth grind to clean up the
surface as long as you use a feather-light touch., but it may sometimes
chatter, and you'll need to clean it up with sandpaper.

"Mark Fitzsimmons" wrote in message
oups.com...
I think everyone's missing the real problem here. I'm guessing that by
using a gouge with an ellsworth grind, you're using it much like a
scraper. When you do this, you put a force on the edge of the bowl that
is radial (outward). This complicates rounding because every time you
cut, you're distorting the shape of the bowl. The vibration won't go
away once it's round. It may even get worse because it's thinner and
flexes more.

You need to use a tool in a way that puts the force axial (parallel to
the axis) which will drastically reduce vibration near the edge of the
bowl.

2 ways to do that, off the top of my head:
1. Use a regular gouge with a different grind in a cutting mode .
2. Use a scraper with a sharp corner to get the cut started near the
edge and define the round circle. Do not push the tool in a radial
direction, align it so you're cutting on the top edge of the bowl,
cutting straight back toward the headstock, just as if your tool is a
drill and you're going to push the drill into the bowl to make a
perfectly round hole. Once you have a round rabbet half an inch or an
inch deep (o two inches deep) you can use a gouge in a cutting mode
(not the ellsworth grind in a scraping mode) to move deeper, rubbing
the bevel on the already cut surface.

I have a couple gouges with a straight grind on them which can be used
to do both cuts... the first cut I do with the very corner edge of the
grind as if it were a skew, with the tool parallel to the lathe axis.
Works like a charm. You get rounder circles and cleaner edges on the
bowl, especially if it's a natural edge.

Once it's round, you can use the ellsworth grind to clean up the
surface as long as you use a feather-light touch., but it may sometimes
chatter, and you'll need to clean it up with sandpaper.

I think you're mis-characterizing the ellsworth grind here. As with any
grind on any gouge (or any tool) you can scrape with the cutting edge, but
the ellsworth gouge is definitely used in a cutting mode (riding the bevel)
the majority of the time.

Jr.

"Mark Fitzsimmons" wrote in message
oups.com...
I think everyone's missing the real problem here. I'm guessing that by
using a gouge with an ellsworth grind, you're using it much like a
scraper. When you do this, you put a force on the edge of the bowl that
is radial (outward). This complicates rounding because every time you
cut, you're distorting the shape of the bowl. The vibration won't go
away once it's round. It may even get worse because it's thinner and
flexes more.


Seems an Ellsworth grind allows cutting at many places on its edge depending
on the presentation angle. Wouldn't be my choice, even if I could afford
one however, because I'm a devotee of flatter forged gouges. They can be
held firmly on the rest and present the same edge to the piece that a badly
supported deep gouge cutting with its ears can do.

Some pictures of the action and the result at
http://georgephoto.photosite.com/FlatGougeAngles/ for feeding your thoughts.
#4 - Bevel Reference In shows a hogging-depth cut used to establish round
for a finer pare in progress. Remember, the bevel doesn't guide on the
surface as it was, but the surface as created. Make your entry cut under
firm control, muscles locked and shift your weight as you roll in.

Won't to a bit of good if the piece is allowed to move at will, of course.

Sometimes if you turn your gouge slightly steeper down into the bowl than
you would normally for bevel rubbing, you can alleviate vibration of this
type. This helps keep the bevel from bumping.

I personally grind a second bevel to slightly reduce this problem.
Additionally, the gouge does a better job following tight radii on the
inside of small bowls.

Derek

I think you are right on. I did just that tonight with another bowl, this
time about 12" in diameter. I took the bowl walls down incrementally an
inch or so at a time and had no problems with vibration at all. I took the
walls to about 3/8". I'm still a little timid on thin walls. I generally
turn slow, probably 700 to 900 RPM.

Barry


"William B Noble (don't reply to this address)" wrote
in message news
Barry - it's not the chuck.
several others have posted valid ideas as to cause, but you will
almost always get resonance at some RPM with a bowl because you are
making a bell and gee, bells ring.

I disagree with teh 40% rule - I've turned a platter that was about 24
inches across (asymetric, that's the long dimension) using a tennon
that was a lot less than 10 inches (I'd say about 3 inches), no
problems with the tennon, though I was unusually careful to not have
the wings smack me - I'm not particularly fond of splattering my own
blood on my nice black lathe.

As Leo suggested, you can be patient and let it dry. Or you can do
what I do and cut to finished dimensions in one pass and then deal
with any distortion bycalling it a "feature" - in that case, turn thin
(1/4 inch or so) and declare victory.

To cut and avoid the vibration, sharp tools, and a light touch, adjust
RPM, and thin from the rim down in about 1/2 inch to 1 inch steps -
more vibrational energy is transmitted for cuts near the rim, so keep
the mass inthe bowl as you thin the rim.

On Sun, 19 Mar 2006 21:17:05 -0700, william kossack
wrote:

a few things
- reverse the bowl against your chuck holding it in place with the
tailstock.

- True up the tenon or cut a new larger one. I bet you have enough wood
with the thickness but if all you have is the 50mm jaws on the super
nova you may not. With larger bowls I use the power grip jaws.

- While it is reversed also round of the outside of the bowl so when you
put the tenon back on the chuck it will be more balanced.

- Look for cracks. I find that little cracks in the wood can cause more
vibration resonance. You can almost tell that something is not right
when your bowl startes to sing. You can expect something to come flying
off

- How fast are turning the bowl? Always start slow.

- Test your nova chuck by spinning it without anything mounted.

I've recently started putting my roughed turnings in a scale and putting
the information into excel so I can plot the drying rate and know when
it is dry.

Barry N. Turner wrote:
Bill

www.wbnoble.com

to contact me, do not reply to this message,
instead correct this address and use it

will iam_ b_ No ble at msn daught com
*** Free account sponsored by SecureIX.com ***
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