I was hollowing a Sassafras bowl about 11" in diameter this afternoon. The
walls were about 1 1/4" thick and I was using my Crown PM 5/8" bowl gouge
with Ellsworth grind. Near the rim of the bowl, at the beginning of the
cut, I began to experience some vibration.

I put a fresh edge on the gouge and finished with little problem, but still
with some vibration. Then a thought entered my mind........had I switched
to a smaller gouge, say a 1/4" bowl gouge, which would remove less wood per
cut, would it lessen the amount of vibration? Thanks.

Not an easy question to answer! The situation is somewhat dependent on
the reason for the vibration. For example, if you are working green
wood, and the vibration arose because of imbalance, probably not.
You'd be adding the "flex" of the thinner shaft and might actually have
a rougher ride. When I run into this kind of a problem, my usual
tactic is to check all the fixings, then try whatever tool I think
might help until I come across something that behaves more to my liking
and stick with it. Probably not textbook, bt it's the best I can
offer: hope it's of some help

Kip Powers
Rogers, AR

Vibration occurs when the natural frequency (or a multiple of) matches
a harmonic or rotation. You might eliminate or reduce vibration by
slightly changing the speed. Also, a vibration can be reduced or
controlled by adding or changing mass and/or bracing.

Barry:

I'd start by changing the speed a little bit and see if that helps. You
can run into speeds at which the blank resonates.

I think that a 1/4" bowl gouge is an almost useless tool. There just
isn't enough metal there to resist flexing even with a minimum overhang.
On the other hand, you might have tried a 1/2" gouge -- it may or may
not help.

I'd also look for defects in the blank. If there is a problem with ring
shake it often will show up as vibration and you would like to get it to
the firewood pile before it comes apart at 500 rpm.

Also, since I happen to know what lathe you are turning on -- make sure
that all 4 legs are sitting on the floor.

Bill

Barry N. Turner wrote:
I was hollowing a Sassafras bowl about 11" in diameter this afternoon. The
walls were about 1 1/4" thick and I was using my Crown PM 5/8" bowl gouge
with Ellsworth grind. Near the rim of the bowl, at the beginning of the
cut, I began to experience some vibration.

I put a fresh edge on the gouge and finished with little problem, but still
with some vibration. Then a thought entered my mind........had I switched
to a smaller gouge, say a 1/4" bowl gouge, which would remove less wood per
cut, would it lessen the amount of vibration? Thanks.

Another friend of mine suggested that I take the bowl walls to final
thickness incrementally, say an inch at a time, rather than making one
sweeping cut from rim to bottom. I think that may work. I just didn't
expect to have vibration when the walls were well over an inch thick.

It's not the lathe. All four (4) feet are solidly on the floor. I don't
think it was the speed either, but it could have been. I tend to turn
slower than most people I know. The blank appears sound. I have some
doubts about the 1/4" bowl gouge too. I have one, but have never used it.
Thanks for the advice.

Barry


"Bill Rubenstein" wrote in message
om...
Barry:

I'd start by changing the speed a little bit and see if that helps. You
can run into speeds at which the blank resonates.

I think that a 1/4" bowl gouge is an almost useless tool. There just
isn't enough metal there to resist flexing even with a minimum overhang.
On the other hand, you might have tried a 1/2" gouge -- it may or may not
help.

I'd also look for defects in the blank. If there is a problem with ring
shake it often will show up as vibration and you would like to get it to
the firewood pile before it comes apart at 500 rpm.

Also, since I happen to know what lathe you are turning on -- make sure
that all 4 legs are sitting on the floor.

Bill

Barry N. Turner wrote:
I was hollowing a Sassafras bowl about 11" in diameter this afternoon.
The walls were about 1 1/4" thick and I was using my Crown PM 5/8" bowl
gouge with Ellsworth grind. Near the rim of the bowl, at the beginning
of the cut, I began to experience some vibration.

I put a fresh edge on the gouge and finished with little problem, but
still with some vibration. Then a thought entered my mind........had I
switched to a smaller gouge, say a 1/4" bowl gouge, which would remove
less wood per cut, would it lessen the amount of vibration? Thanks.

it does seem odd to have vibration with walls over an inch thick - in
my humble experience, that ususally indicates that there is a hairline
crack and it's time to stop and find it - or if you know there are
flaws, then it's your sign to use the sequential approach.




On Sat, 28 Jan 2006 22:57:20 -0600, "Barry N. Turner"
wrote:

Another friend of mine suggested that I take the bowl walls to final
thickness incrementally, say an inch at a time, rather than making one
sweeping cut from rim to bottom. I think that may work. I just didn't
expect to have vibration when the walls were well over an inch thick.

It's not the lathe. All four (4) feet are solidly on the floor. I don't
think it was the speed either, but it could have been. I tend to turn
slower than most people I know. The blank appears sound. I have some
doubts about the 1/4" bowl gouge too. I have one, but have never used it.
Thanks for the advice.

Barry


"Bill Rubenstein" wrote in message
. com...
Barry:

I'd start by changing the speed a little bit and see if that helps. You
can run into speeds at which the blank resonates.

I think that a 1/4" bowl gouge is an almost useless tool. There just
isn't enough metal there to resist flexing even with a minimum overhang.
On the other hand, you might have tried a 1/2" gouge -- it may or may not
help.

I'd also look for defects in the blank. If there is a problem with ring
shake it often will show up as vibration and you would like to get it to
the firewood pile before it comes apart at 500 rpm.

Also, since I happen to know what lathe you are turning on -- make sure
that all 4 legs are sitting on the floor.

Bill

Barry N. Turner wrote:
I was hollowing a Sassafras bowl about 11" in diameter this afternoon.
The walls were about 1 1/4" thick and I was using my Crown PM 5/8" bowl
gouge with Ellsworth grind. Near the rim of the bowl, at the beginning
of the cut, I began to experience some vibration.

I put a fresh edge on the gouge and finished with little problem, but
still with some vibration. Then a thought entered my mind........had I
switched to a smaller gouge, say a 1/4" bowl gouge, which would remove
less wood per cut, would it lessen the amount of vibration? Thanks.

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

"Barry N. Turner" wrote in message
. ..
Another friend of mine suggested that I take the bowl walls to final
thickness incrementally, say an inch at a time, rather than making one
sweeping cut from rim to bottom. I think that may work. I just didn't
expect to have vibration when the walls were well over an inch thick.

It's not the lathe. All four (4) feet are solidly on the floor. I don't
think it was the speed either, but it could have been. I tend to turn
slower than most people I know. The blank appears sound. I have some
doubts about the 1/4" bowl gouge too. I have one, but have never used it.

On a rim that thick, at relatively slow speed, I'd inspect the mounting.
Applies to wobble both free and with a load. You wouldn't be the first guy,
especially on green wood, to have squeezed too hard and crushed some fibers
so the chuck's no longer firm. Especially if you're holding wet sapwood.
Shake the piece. If it moves, re mount.

If it's not moving on its own, but only under load, it's the presentation of
the edge or the pressure on the bevel. With a 1/4" flute, you don't have to
be cutting too deep to bury the upper, non-cutting part of the profile, and
that will cause you to rip and slide over end and side grain. The pickup
fuzz should be obvious on green wood if this is the case.

Last, you could be riding that bevel. That will still give you a relatively
fuzz-free cut, but you'll get out-of-round really rapidly due to the
difference between end and face grain. If the gouge wants to move in and
out, that's what you've got. Sometimes you can even see compressed lighter
areas against a wet background where you rubbed the heel of the bevel too
hard trying to make a quick curve.

Changing speed is often suggested, but it's really the same as those folks
who say if you drive your car faster down a washboard gravel road you won't
feel it as bad. You'll still beat the crap out of your car, of course, and
increase the impact force with the square of the velocity, not to mention
the loss of control as your shocks are no longer able to get the wheels back
to the road. Same on the lathe. I turn slow, too. No problem, as long as
you sharpen and present properly. You can carve with only the gouge in
motion, after all.

A 1/4" gouge is a great tool where the curvature is fast, or the access
narrow. Use it where you have to, though mine has almost no grind at the
ears, making it more suitable for the above uses.

One last shot in the dark, though this one should have been obvious at the
get-go. I once cut a blank from wood that had been on its side for a while,
ending up with all the water on one side of the blank. That was a grin and
bear it. Not to mention, I had another blank to cut just like it,
afterward....

Thanks for the help. I'm still not sure what caused the vibration, but was
able to finish the bowl with little trouble. Thanks to you and some others,
I have several theories to check out. The blank was sound. It was green, but
had been cut and anchor-sealed several months ago.

I don't believe mounting was the problem. I used a SuperNova with standard
2" jaws snugged up tight on a short tenon. I stopped a couple of times
during turning and tightened the chuck. I also stopped to put a fresh edge
on my gouge a couple of times, the last time just before the final cuts.

Right now, the theory that seems most likely is the one my friend
suggested..........taking the walls down an inch at a time. Thanks for the
advice.

Barry

"George" George@least wrote in message
...

"Barry N. Turner" wrote in message
. ..
Another friend of mine suggested that I take the bowl walls to final
thickness incrementally, say an inch at a time, rather than making one
sweeping cut from rim to bottom. I think that may work. I just didn't
expect to have vibration when the walls were well over an inch thick.

It's not the lathe. All four (4) feet are solidly on the floor. I don't
think it was the speed either, but it could have been. I tend to turn
slower than most people I know. The blank appears sound. I have some
doubts about the 1/4" bowl gouge too. I have one, but have never used
it.

On a rim that thick, at relatively slow speed, I'd inspect the mounting.
Applies to wobble both free and with a load. You wouldn't be the first
guy, especially on green wood, to have squeezed too hard and crushed some
fibers so the chuck's no longer firm. Especially if you're holding wet
sapwood. Shake the piece. If it moves, re mount.

If it's not moving on its own, but only under load, it's the presentation
of the edge or the pressure on the bevel. With a 1/4" flute, you don't
have to be cutting too deep to bury the upper, non-cutting part of the
profile, and that will cause you to rip and slide over end and side grain.
The pickup fuzz should be obvious on green wood if this is the case.

Last, you could be riding that bevel. That will still give you a
relatively fuzz-free cut, but you'll get out-of-round really rapidly due
to the difference between end and face grain. If the gouge wants to move
in and out, that's what you've got. Sometimes you can even see compressed
lighter areas against a wet background where you rubbed the heel of the
bevel too hard trying to make a quick curve.

Changing speed is often suggested, but it's really the same as those folks
who say if you drive your car faster down a washboard gravel road you
won't feel it as bad. You'll still beat the crap out of your car, of
course, and increase the impact force with the square of the velocity, not
to mention the loss of control as your shocks are no longer able to get
the wheels back to the road. Same on the lathe. I turn slow, too. No
problem, as long as you sharpen and present properly. You can carve with
only the gouge in motion, after all.

A 1/4" gouge is a great tool where the curvature is fast, or the access
narrow. Use it where you have to, though mine has almost no grind at the
ears, making it more suitable for the above uses.

One last shot in the dark, though this one should have been obvious at the
get-go. I once cut a blank from wood that had been on its side for a
while, ending up with all the water on one side of the blank. That was a
grin and bear it. Not to mention, I had another blank to cut just like
it, afterward....

I core almost every bowl that I turn. On all of the larger blanks,
after it has been cored, as I start to turn the inside, there is
vibration. I think that this is due to there being little mass to
support the walls. I haven't ever had any vibration when turning the
outside. To counter this, I let my left hand act as a stead rest on the
outside of the bowl. Gentle pressu if your hand is getting hot, you
are pressing too hard. Also, I take very light cuts nearer to the rim.
Taking it down to final thickness in steps, rather than one long cut is
easier, but with practice, you can take that one cut from the rim to
the base in one pass. Have you noticed that the vibration is gone by
the time that you get half way or so down the inside of the bowl?
robo hippy

Hi Barry

I have had vibration in bowls that I did not think should have
happened, however they did and My thinking goes like this, the shape of
the bowl and the wood grain and stiffness that have to overcome the
force needed to cut the wood, sometimes set up a surging or vibration.
I have had more problems with flatter bottom bowl than with curved
bowls, especially the higher side bowl liked to start flexing.
And yes I think your gut feeling to go for a smaller gouge I think is
right, anyway that did help for me, making the force needed to overcome
the cutting edge smaller helps most, by either the presentation of the
cutting edge or using a smaller gouge and sharpening helps some also in
my experience , the problem with the smaller gouge though is of course
that you do have to take lighter cuts and you do have to be able to
keep the tool rest up close.
For finish cutting a dried previously rouged out bowl, going the
stepped way of 1" or 2" at the time is one way of minimizing the
flexing, but keeping a nice flowing shape becomes harder to do, but it
can be done.

http://homepage.mac.com/l.vanderloo/PhotoAlbum4.html

Have fun and take care
Leo Van Der Loo

Barry,
Some other answers have alluded to green wood. Two comments.

Wood isn't always homogeneous, there might have been areas in the wood that
were denser (or lighter) than the rest, and when you removed enough of the
inside of the bowl the difference was enough to cause the vibrations.

The other comment, an 11" bowl does take time to turn, and we all ( I do )
need to take some time out for a 'bio break', lunch, or just sharpening the
gouge. And I have a light close to the lathe. Make sure you turn that light
OFF when you don't have the piece turning for extended periods of time (what
ever that means). The heat from the light can dry one side causing warping,
or just enough drying to cause it to loose balance. For long times (lunch)
wrap the blank with a plastic bag. This will keep some of the moisture in the
wood but it may collect in the 'lower' side of the blank.

mike



Barry N. Turner wrote:
I was hollowing a Sassafras bowl about 11" in diameter this afternoon. The
walls were about 1 1/4" thick and I was using my Crown PM 5/8" bowl gouge
with Ellsworth grind. Near the rim of the bowl, at the beginning of the
cut, I began to experience some vibration.

I put a fresh edge on the gouge and finished with little problem, but still
with some vibration. Then a thought entered my mind........had I switched
to a smaller gouge, say a 1/4" bowl gouge, which would remove less wood per
cut, would it lessen the amount of vibration? Thanks.

On Tue, 31 Jan 2006 01:55:31 GMT, Mike wrote:

Barry,
Some other answers have alluded to green wood. Two comments.

Wood isn't always homogeneous, there might have been areas in the wood that
were denser (or lighter) than the rest, and when you removed enough of the
inside of the bowl the difference was enough to cause the vibrations.

The other comment, an 11" bowl does take time to turn, and we all ( I do )
need to take some time out for a 'bio break', lunch, or just sharpening the
gouge. And I have a light close to the lathe. Make sure you turn that light
OFF when you don't have the piece turning for extended periods of time (what
ever that means). The heat from the light can dry one side causing warping,
or just enough drying to cause it to loose balance. For long times (lunch)
wrap the blank with a plastic bag. This will keep some of the moisture in the
wood but it may collect in the 'lower' side of the blank.

mike

Good point, Mike... especially with the 500 watt halogen that I use... makes you
feel like an order of fries at Dennys
Mac
https://home.comcast.net/~mac.davis/wood_stuff.htm

My blank was green but had been cut a while and was Anchor Sealed. I didn't
get the impression that warping was the problem, but I may have been wrong.
I'll try some of your other suggestions. Thanks.

Barry


"Mike" wrote in message
ink.net...
Barry,
Some other answers have alluded to green wood. Two comments.

Wood isn't always homogeneous, there might have been areas in the wood
that were denser (or lighter) than the rest, and when you removed enough
of the inside of the bowl the difference was enough to cause the
vibrations.

The other comment, an 11" bowl does take time to turn, and we all ( I do )
need to take some time out for a 'bio break', lunch, or just sharpening
the gouge. And I have a light close to the lathe. Make sure you turn
that light OFF when you don't have the piece turning for extended periods
of time (what ever that means). The heat from the light can dry one side
causing warping, or just enough drying to cause it to loose balance. For
long times (lunch) wrap the blank with a plastic bag. This will keep some
of the moisture in the wood but it may collect in the 'lower' side of the
blank.

mike



Barry N. Turner wrote:
I was hollowing a Sassafras bowl about 11" in diameter this afternoon.
The walls were about 1 1/4" thick and I was using my Crown PM 5/8" bowl
gouge with Ellsworth grind. Near the rim of the bowl, at the beginning
of the cut, I began to experience some vibration.

I put a fresh edge on the gouge and finished with little problem, but
still with some vibration. Then a thought entered my mind........had I
switched to a smaller gouge, say a 1/4" bowl gouge, which would remove
less wood per cut, would it lessen the amount of vibration? Thanks.

Barry N. Turner wrote:
My blank was green but had been cut a while and was Anchor Sealed. I didn't
get the impression that warping was the problem, but I may have been wrong.
I'll try some of your other suggestions. Thanks.


Barry,
I meant warping on the lathe while you were taking a break - even a short
one while sharpening your gouges or taking a bio-break. The warping may be
small, but it is encouraged by by leaving a hot light near one side.

The other hint one of "the greats" told me once was to rough out a bowl,
leave it thick, let it sit for an hour or so, then after the internal stresses
have readjusted themselves it is time to finish turn, starting with the
outside of course, then the inside.


--
Mike Vore
http://andersonranchtrip.blogspot.com
http://arrowmont2006.wordpress.com
http://mike.vorefamily.net/twr

On Wed, 01 Feb 2006 01:34:47 GMT, Mike wrote:

Barry N. Turner wrote:
My blank was green but had been cut a while and was Anchor Sealed. I didn't
get the impression that warping was the problem, but I may have been wrong.
I'll try some of your other suggestions. Thanks.


Barry,
I meant warping on the lathe while you were taking a break - even a short
one while sharpening your gouges or taking a bio-break. The warping may be
small, but it is encouraged by by leaving a hot light near one side.


Jim Pugh, an occasional poster here, gave me a great tip on turning green
wood.... when you need to take a break, wrap the work in a plastic bag to slow
drying while you're away...

I was turning a bunch of almond last year and it would crack on the lathe if I
got a damn phone call!



mac

Please remove splinters before emailing

Jim Pugh is an accomplished turner and he can offer a lot of good tips.
I wish he would post more often to rcw.

BTW Mac, why is it that telemarketing calls altho cut short, cause worse
warps and cracks than a call from a friend or re a sale at a gallery??


Turn to Safety, Arch
Fortiter



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