Hello,
I have a large walnut bowl blank (actually two). They are around 18"
in diameter and I suspect weigh about 45-50 lbs apiece. I have a PM
3520 and an 8" Oneway faceplate, and a SuperNova with the power jaws
(3"). I am a little nervous about turning something this large, but I
want to! I usually put the face plate on the top of the bowl and cut
the outside and the fixing for the chuck and then turn it around and
cut out the inner portion of the bowl. I will use the tail stock as
much as possible.
Any other considerations I am not thinking about? I have a new Sorby
bowl gouge and a wolverine jig. I want this to be pretty, so any help
you can offer I'd appreciate.

When I get these I also have two large Aromatic Cedar (17") and four
17" Maple blanks waiting. All these are green.

Thanks for your help.

RP

Subject: 1st Attempt at large bowl turning
From: (RP Edington)
Date: Wed, Oct 22, 2003 8:25 PM
Message-id:

Hello,
I have a large walnut bowl blank (actually two). They are around 18"
in diameter and I suspect weigh about 45-50 lbs apiece. I have a PM
3520 and an 8" Oneway faceplate, and a SuperNova with the power jaws
(3"). I am a little nervous about turning something this large, but I
want to! I usually put the face plate on the top of the bowl and cut
the outside and the fixing for the chuck and then turn it around and
cut out the inner portion of the bowl. I will use the tail stock as
much as possible.
Any other considerations I am not thinking about? I have a new Sorby
bowl gouge and a wolverine jig. I want this to be pretty, so any help
you can offer I'd appreciate.

When I get these I also have two large Aromatic Cedar (17") and four
17" Maple blanks waiting. All these are green.

Thanks for your help.

RP






Hello RP,

Your Powermatic has variable speed, so first thing is start at zero and slowly
ramp up the speed until the lathe begins to vibrate, then back it off until the
vibration stops. Start cutting at this speed. When you've removed some wood the
balance of the piece should improve, so slowly try turning up the speed again
until it vibrates and again back off till it stops and proceed. There is a safe
speed rule that Dale Nish always uses. Multiply the diameter of the wood times
the rpm of the lathe, and the number you come up with should be between 6000
and 9000 (example: a 6" bowl X 1500 rpm = 9000, so the maximum safe speed for a
6" bowl is 1500 rpm.)
An 18" bowl should be turned no faster than 500 rpm (9000 divided by 18 = 500).

Never use drywall screws for a faceplate. They are too brittle and can snap
under load. Instead use sheet metal screws, or even better use SPAX screws that
have a deep thread and are serrated near the tip.
Take it slow and don't take large cuts and you should be fine.
Let us know how you did,


-Jim Gott-
San Jose, CA

The tools and equipment sound OK.

Consider which is more important, big or pretty. Be willing to make a
pretty 14" bowl instead of wood-saving 18" bowl. You will be happier in
the long run.

Big pieces that are out of balance can be miserable to get roughed into
shape and balance starting at 120 RPM. Every minute spent with a
chainsaw or bandsaw before the blank goes on the lathe will pay you back
later.

Good luck,
David

RP Edington wrote:
Hello,
I have a large walnut bowl blank (actually two). They are around 18"
in diameter and I suspect weigh about 45-50 lbs apiece. I have a PM
3520 and an 8" Oneway faceplate, and a SuperNova with the power jaws
(3"). I am a little nervous about turning something this large, but I
want to! I usually put the face plate on the top of the bowl and cut
the outside and the fixing for the chuck and then turn it around and
cut out the inner portion of the bowl. I will use the tail stock as
much as possible.
Any other considerations I am not thinking about? I have a new Sorby
bowl gouge and a wolverine jig. I want this to be pretty, so any help
you can offer I'd appreciate.

When I get these I also have two large Aromatic Cedar (17") and four
17" Maple blanks waiting. All these are green.

Thanks for your help.

RP

--
http://www.wademade.net

I like to start between centers, making use of a pin chuck or pin jaws.
Others claim they need the "artistic freedom" to reselect their axis after
preliminary turning, and so use their spur center. A Google search shows a
number of these to be the same who tell horror stories about blanks
departing the lathe at speed. I have cut and split a few hundred cords of
wood, so I can tell with reasonable certainty what is available in the log.
When I make the preliminary cuts I reveal more, and can examine still more
as I begin to rough on the bandsaw. Aside from modifying the original
concept of the piece to avoid a bark pocket that went too deep, that
suffices, and I've _never_ lost a piece held with pin and tailstock. Also,
I have never made _the_ piece, and probably never will. Each is yet
another, and if it's not perfect in my mind, the next will be better.

You can get pin jaws for your Nova, and they give you a few other creative
options as well.

I don't know about variable speed, having only four on Ol' Blue, but if it
bounces, I also believe slowing can help. Other options include removing
some wood with a gouge, scrub plane or forstner bit to equalize the weight.
It does, of course limit you, as wood so removed cannot be returned. If you
have a real pin chuck http://personalpages.tds.net/~upgeorge/index.html you
can mount a plywood disk with holes to bolt counterweights into ahead of
your piece. Be sure to use fiberlock nuts or add some CA to keep them from
unwinding. I suppose the Cole jaws and long bolts available for your Nova
would work as well.

Last advice is to say don't cut the edge of the bowl, cut the bottom up. If
you have the nose of the gouge alternating between wood and air, you're much
safer if the gouge is supported firmly and close to the piece on the
toolrest, versus some mixed strong arm/hip rest method.


"RP Edington" wrote in message
om...
Hello,
I have a large walnut bowl blank (actually two). They are around 18"
in diameter and I suspect weigh about 45-50 lbs apiece. I have a PM
3520 and an 8" Oneway faceplate, and a SuperNova with the power jaws
(3"). I am a little nervous about turning something this large, but I
want to! I usually put the face plate on the top of the bowl and cut
the outside and the fixing for the chuck and then turn it around and
cut out the inner portion of the bowl. I will use the tail stock as
much as possible.
Any other considerations I am not thinking about? I have a new Sorby
bowl gouge and a wolverine jig. I want this to be pretty, so any help
you can offer I'd appreciate.

When I get these I also have two large Aromatic Cedar (17") and four
17" Maple blanks waiting. All these are green.

RP,

You've already got some good tips. I have a 3520 and use pieces like that
regularly. I have had pieces that I already chainsawed round, that I had to
take back off the lathe and remove minor corners that were hitting the lathe
bed. The 3520 is up to the job.

Use decent screws for the faceplate, such as stainless. I now use a bunch
of 1 1/4 screws. I used to use longer ones but it easy to snap the heads
when you use a 1/2" drill to drive them in like me. Using the drill with a
nut driver is a big time saver.

Like the others said, make it as round of a blank as possible with a
chainsaw or bandsaw. Take light roughing cuts at a slow RPM until it is
round. Use the tailstock, and regularly check it to ensure it is tight.

Even after it is round, keep the RPMs fairly low. Big bowls have a lot of
kinetic energy. Have fun.

Jeff Jilg
Austin, TX




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Hi RP, Your query elicited some good advice from two excellent turners,
and you obviously are no slouch either. Beginners should heed their
advice and follow your plan. David's caution re not letting the blank's
size dictate the form should be emphasized. This advice is hard to
follow with expensive or even 'road kill' wood. As with other turning
admonitions like the bother of persistent resharpening of tools, it is
important for turning 'pretty'.
I've made a lot of ordinary NIP pieces by trying to get the largest
possible instead of wasting (a misnomer) wood by adjusting to get a
smaller but nicer piece.

Remember the potential toxicity for flora & fauna by the walnut
shavings. Also, for security use a face plate instead of a scroll chuck.
No doubt about Jim's advice that you should back off from vibration
speed when roughing big blanks. I might mention that going a little
beyond vibration speed on a _balanced blank can often safely smooth
things out. Please share the story of your life with big bowls. Arch

Fortiter,