Perfectly spherical steel shells for wood bowl coring lathe
 

Guys, I am building a coring lathe to cut bowl cores from half a log
section. That's right, I am primarily a wood turner, but I built both my
lathes from scratch, so I am somewhat metal capable.

The coring lathe will take a log half section and secure it with a
faceplate. Then the largest coring cutter that will fit the log half will
pivot into the faceplate side of the log and cut the corners, etc. away,
leaving the outside of the largest bowl. Then the next coring cutter will
pivot into the log half and remove the largest bowl. And so on down to the
smallest bowl.

To support the cutters, I need perfect (essentially, plus/minus 0.0625 would
be ok) spherical sections. In a perfect world, the largest section would
have a 12" inside radius, the next a 10.5" radius, the next a 9.0" radius,
then an 7.5", 6.0", 4.5" and finally an 3.25" radius. Wall thickness
needs to be 0.250".

I could do without the smallest radius cutter, if necessary, as it makes the
smallest (and less valuable) bowl.

Imagine an orange, with the peeling sliced top to bottom say, 8 times. Take
one half of the peeling and that is what the cutter will look like.

Anyone have any ideas as to an economical (scrapyard prices preferred)
source for such items?

Best regards,
James Johnson

Please reply directly to me.

Perfectly spherical steel shells for wood bowl coring lathe
 

JR Johnson wrote:
Guys, I am building a coring lathe to cut bowl cores from half a log
section. That's right, I am primarily a wood turner, but I built both my
lathes from scratch, so I am somewhat metal capable.

The coring lathe will take a log half section and secure it with a
faceplate. Then the largest coring cutter that will fit the log half will
pivot into the faceplate side of the log and cut the corners, etc. away,
leaving the outside of the largest bowl. Then the next coring cutter will
pivot into the log half and remove the largest bowl. And so on down to the
smallest bowl.

To support the cutters, I need perfect (essentially, plus/minus 0.0625 would
be ok) spherical sections. In a perfect world, the largest section would
have a 12" inside radius, the next a 10.5" radius, the next a 9.0" radius,
then an 7.5", 6.0", 4.5" and finally an 3.25" radius. Wall thickness
needs to be 0.250".

What's wrong with simply using a bar bent into a circle?
Remove some metal at the appropriate edges to thin it while retaining
the stiffness.

First drill/cut out a 2" or so conical plug inside the 3.25" bowl.
Now, place a couple of bearings on a really, really thick bit of metal
supporting a sickle-shaped cutter in the hole.
The sickle shaped bar with cutter on the end is then advanced into the
work to cut a hemisphere.

Perfectly spherical steel shells for wood bowl coring lathe
 

In article , JR Johnson
wrote:

Guys, I am building a coring lathe to cut bowl cores from half a log
section. That's right, I am primarily a wood turner, but I built both my
lathes from scratch, so I am somewhat metal capable.

The coring lathe will take a log half section and secure it with a
faceplate. Then the largest coring cutter that will fit the log half will
pivot into the faceplate side of the log and cut the corners, etc. away,
leaving the outside of the largest bowl. Then the next coring cutter will
pivot into the log half and remove the largest bowl. And so on down to the
smallest bowl.

To support the cutters, I need perfect (essentially, plus/minus 0.0625 would
be ok) spherical sections. In a perfect world, the largest section would
have a 12" inside radius, the next a 10.5" radius, the next a 9.0" radius,
then an 7.5", 6.0", 4.5" and finally an 3.25" radius. Wall thickness
needs to be 0.250".

I could do without the smallest radius cutter, if necessary, as it makes the
smallest (and less valuable) bowl.

Imagine an orange, with the peeling sliced top to bottom say, 8 times. Take
one half of the peeling and that is what the cutter will look like.

Anyone have any ideas as to an economical (scrapyard prices preferred)
source for such items?

Best regards,
James Johnson

Please reply directly to me.




Any decent metal spinning shop can make them for you, but the spinning
forms will be pricey.

Perfectly spherical steel shells for wood bowl coring lathe
 

"Ian Stirling" wrote: What's wrong with simply using a bar bent into a
circle? (clip)
^^^^^^^^^^^
These are available on the market. Check with Craft Supplies, Packard, or
any other vendor selling wood lathe tools. The cover a wide price range,
depending on the diameter of the wood being handled, and the number of
coring radii provided.

Of course, if you built your own lathe, you may also prefer to build your
own coring system, but you do not need to re-invent the wheel. BTW, none of
them use spherical shaped cutters--it ain't necessary, as Ian pointed out.

Perfectly spherical steel shells for wood bowl coring lathe
 

||Imagine an orange, with the peeling sliced top to bottom say, 8 times. Take
||one half of the peeling and that is what the cutter will look like.

Don't you mean 1/4 of the peeling (90 degrees of arc)?
Texas Parts Guy

Perfectly spherical steel shells for wood bowl coring lathe
 

"JR Johnson" wrote in message ...
Guys, I am building a coring lathe to cut bowl cores from half a log
section. That's right, I am primarily a wood turner, but I built both my
lathes from scratch, so I am somewhat metal capable.

The coring lathe will take a log half section and secure it with a
faceplate. Then the largest coring cutter that will fit the log half will
pivot into the faceplate side of the log and cut the corners, etc. away,
leaving the outside of the largest bowl. Then the next coring cutter will
pivot into the log half and remove the largest bowl. And so on down to the
smallest bowl.

To support the cutters, I need perfect (essentially, plus/minus 0.0625 would
be ok) spherical sections. In a perfect world, the largest section would
have a 12" inside radius, the next a 10.5" radius, the next a 9.0" radius,
then an 7.5", 6.0", 4.5" and finally an 3.25" radius. Wall thickness
needs to be 0.250".

I could do without the smallest radius cutter, if necessary, as it makes the
smallest (and less valuable) bowl.

Imagine an orange, with the peeling sliced top to bottom say, 8 times. Take
one half of the peeling and that is what the cutter will look like.

Anyone have any ideas as to an economical (scrapyard prices preferred)
source for such items?

Best regards,
James Johnson

Please reply directly to me.


There was an article a number of years ago in Fine Woodworking mag
about a machine that did this very thing, I believe the company was
making wooden salad bowls. IIRC, the machine was quite old.

I remember thinking at the time the arms supporting the cutters were
not as a beefy as you might expect they'd have to be.

Maybe someone has an index to back issues? A picture is worth a
thousand or more words.

Perfectly spherical steel shells for wood bowl coring lathe
 

First of all, I have all copies of Fine Woodworking, including the issue
with the coring lathe. Secondly, I own (and use) both the McNaughton System
and a home made system for coring bowls. The problem (one of) with the
commercially available systems is that you have to reduce the half log to a
hemisphere, then reverse it on the lathe and core out the largest bowl.
Then take the core, reverse it again, turn a tenon, take it off, reverse it
back onto the lathe, cut the next core. Do this for each bowl. Takes a lot
of time, and the cutters are kinda flimsy when they extend out over the
support by 14-15" (measured along the curve).

The machine in FWW was over 100 years old, used !/4 arc cutters (same as I
am looking for) and still works fine. But they have one guy whose full time
job is to sharpen the cutters and maintain the machine. I don't anticipate
making that many bowls, but I sure hate how long it takes me to make 3 or 4
bowls blanks currently.

Thanks for all the replies.

Regards, James

Perfectly spherical steel shells for wood bowl coring lathe
 

Soren Berger recommends using leaf springs -

"Ian Stirling" wrote in message
...
JR Johnson wrote:
Guys, I am building a coring lathe to cut bowl cores from half a log
section. That's right, I am primarily a wood turner, but I built both
my
lathes from scratch, so I am somewhat metal capable.

Perfectly spherical steel shells for wood bowl coring lathe
 

Here's a link that has a more efficient method of using the McNaughton
System: http://www.chesapeakewoodturners.com/fcapril2002.pdf

Automobile leaf springs would be a good cheap source of material.
Regular hot rolled bar isn't very expensive either. If these are too
narrow, just weld several together. You will need to anneal the
springs first, by heating to red hot and allowing to cool slowly. Bend
the bar to the radius desired, then use a hand held angle grinder to
finish forming to the spherical shape. It shouldn't be too hard to
hold the tolerance you are looking for.

I think 1/4 arc is overkill, but you can get this by welding in braces
instead of using solid plate. Just bend the braces to the correct
radius first.

p.s. You can also get 30% more bowls from each log by only allowing
10% thickness for each bowl. The 12" bowl thickness is about right,
but each of the smaller bowls can be quite a bit thinner and still
have enough meat to allow for shrinkage.

"JR Johnson" wrote in message ...
First of all, I have all copies of Fine Woodworking, including the issue
with the coring lathe. Secondly, I own (and use) both the McNaughton System
and a home made system for coring bowls. The problem (one of) with the
commercially available systems is that you have to reduce the half log to a
hemisphere, then reverse it on the lathe and core out the largest bowl.
Then take the core, reverse it again, turn a tenon, take it off, reverse it
back onto the lathe, cut the next core. Do this for each bowl. Takes a lot
of time, and the cutters are kinda flimsy when they extend out over the
support by 14-15" (measured along the curve).

The machine in FWW was over 100 years old, used !/4 arc cutters (same as I
am looking for) and still works fine. But they have one guy whose full time
job is to sharpen the cutters and maintain the machine. I don't anticipate
making that many bowls, but I sure hate how long it takes me to make 3 or 4
bowls blanks currently.

Thanks for all the replies.

Regards, James