Darrell Feltmate wrote:
Hi John
Actually a 2" opening sounds huge and 4" depth short for ordinary hollowing
tools. I habitually use a 3/4" to 1" opening and 7" or 8" depth although I
have done deeper. Some times the simplest tools are the best. For endgrain I
like hook tools and for side grain like you are doing, scrapers or in other
words, typical inserted tip tools. A 3/16" HSS tool bit in a 1/2" to 3/4"
shaft is just fine. Take a look here
http://www.aroundthewoods.com/brace.shtml
the arm brace really makes a difference; and here for hollowing
http://aroundthewoods.com/hollow1.shtml including a couple of clips showing
the cutting tips at work.
I'm not a fan of the arm brace at all....
I do a fair bit of turning, and have built up tools that allow me to
safely go pretty deep, but just don't want to deal with the arm brace
types.
My rationale is that if I am using an arm brace, and there is actually
a catch, it will tend to be worse than if I'm holding normally. If I do
get a catch, I want to be able to release the tool if needed so I don't
get really hurt. The arm brace would only transfer the force and tend
to break an arm...
On the other hand, I love stabilized tools (where the force is taken by
the lathe bed or an outboard rig). In fact, some of my deep hollowing
tools allows me to reach over 3 feet into a vessel without any real
effort on my part. The tools have a tip that can handle a varity of
bits (from hook to disk to square machine tool bits in a variety of
shapes, both cutting and scraping tools), and the bodies are made of a
10 foot long section of thick wall 1 1/2" square steel tubing (each).
Support by the rest near the top edge of the vessel, and an outrigger
that supports it about five feet back (and also has a top bar that keeps
it from rising from the outrigger) transfers all of the downward force
to the rest, and all of the upwards force to the outrigger, so all I
need to do is concentrate on moving the tool back and forth and/or in
and out and not in actually holding it up or worrying about a catch.
The steel of the rest and a "slick plastic" surface on the outrigger
means it's easy to slide the tool back and forth or in and out. In
fact, with this setup I've never actually had a catch, as the cutting
part of the tool is always presented at the same angle and not allowed
to twist, which tends to be one of the typical mechanisms that cause
catches.
When I was freehanding deep vessels, on more than one occasion I got a
catch and was thankful I wasn't using a brace, as the catch only caused
me to lose grip on the tool, so all I needed to do to recover was step
back and hit the emergency stop of the lathe. No personal damage, and
(once you stop swearing and realize what could have happened) who cares
what happens to the wood if it saved your body from damage?
Now, given the desire to create really massive and/or long tools, I
wouldn't recommend anyone do really deep work without a stabilized rig,
but if you're doing relatively smaller work, you can do just fine with
longer than normal tools and common sense.
Sorby used to have a series of "texas tools" where the handle was nearly
two feet long and the steel part of the tool was 12 or 15" long. I got
the skew, plus 3/8 and 1/2" bowl gouges of this series. I've
successfully hollowed nearly 12 inches deep with the bowl gouges, and
really wish I'd bought at least another set while they were still
available. Since then, I've made a number of tools from 3/4 or 1 inch
round steel stock (24" or more long) and a couple with 3/4 x 1 inch
rectangular stock with correspondingly long handles. They tend to be
heavy, but the balance isn't bad at all, as I can fill the handles with
lead shot for the deep hollowing, and the extra mass helps keep them
from moving around. With 12 inches hanging past the rest, and nearly
three feet behind it, there's a great amount of leverage, and even an
interrupted cut or knots don't really make for a problem. I wouldn't
even think of trying to hollow 8" deep with a standard gouge (or hook or
scraper) because the leverage isn't anywhere as good. (8" deep, 14" of
handle behind the rest is less than 2:1, but one of the shop made tools
has 12" deep and 36" behind the rest for 3:1 leverage plus the mass of
the handle to help keep it from moving.) Physics is a wonderful thing
to get acquainted with again!
For the brave of heart, I've actually watched a couple of guys hollow
right up to the ferrule with a standard tool, but they had it in a death
grip that was very tiring, and took light cuts to begin with. As you
might guess, I wouldn't recommend it, but some people will try anything
(and a few will actually get away with it).
Good Luck, Be Safe!
--Rick