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