This tool system is
a refinement of many other hollow form boring systems.
It will allow you to have more control, consequently more
fun and take the stress out of hollow form turning.
It can be seen by viewing Hollow
Forms - The Easy Way with Lyle Jamieson, a 90-minute
video/DVD covering the set-up and use techniques for both
the boring bar and laser systems produced by Phil Pratt is
system has three components:
- The Boring Bar system
- The Backrest system
- The Laser Measuring system
the boring bar has a dual function. It has a hole in
both ends for the swivel tip cutter assembly. This gives
you a straight boring bar on one end and a bent type boring
bar on the other end. Just flip the bar end to end.
90 degree rule must be kept in mind when you set up the system.
Never allow the cutting tip to cut at an angle of more than
90 degrees as it touches the wood. If more than a 90
degree cut is made you are no longer scraping and you will
get a catch. To set the cutting edge angle to less than
90 degrees, place a straight edge of some kind on the top
of the swivel tip holder and sight back along the boring bar
to the support handle. The tip should be parallel to
the floor so that the tool cutting on the side of the vessel
will not violate the 90 degree rule.
When you have set the tool tip at the proper position, go
back and grind a flat spot for all the set screws. First,
for the 3/8 tip assembly rod, and second for the boring bar
at the stabilizer handle coupling. At the other end,
grind flat spots for both tip assembly and handle set screws.
The flat spots will help you set up the tip angle in the same
place each time you move it and it is also a safety feature
so the set screws don't slip with the twisting forces of the
Use the swivel tip
holder to position the cutting tip so that it points in the
direction you wish to cut, straight ahead for cutting into
the bottom of the hollow form or twisted to the side to cut
the side on the vessel. To make a cut set the cutting
tip at the centerline of the hollow form. How do you
find the centerline when you are peering into a vessel and
your view is blocked by the boring bar? With the lathe
off, score a line with the cutter tip from side to side on
the bottom inside of your form. Take the boring bar
out and look with a light at the line. Move the front
tool rest up or down until the line is right on center.
I always bore a pilot hole to the proper depth with a forestner
bit prior to starting my hollowing.
The stabilizing handle
holds the boring bar in position. Again, this is set up to
never violate the 90 degree rule. The welded handle
is not a precision instrument, it does not have to be.
The front tool rest will adjust to put the tip on centerline.
The handle does not take the stresses of the cut, the forces
produced are down on the front tool rest. The handle
only stabilizes the position of the cutting tip. The
handle does not have to be perfectly straight or perfectly
flat. The system works because the cutting tip is positioned
in the correct position to cut safely and easily. The
rectangular support of the boring bar handle will prevent
any twisting. The system removes any twisting force
common to bent tools not supported in this manner. You
no longer need to place your tool rest way back behind the
bent portion of your Stewart Bent tool (if you have one).
Slide the tool rest right up as close to the wood as you can.
The new tool handle will keep it from twisting or jumping.
second component is a second backrest. The most abuse
the backrest will take is you leaning on it. It too
does not have to be high tech. Keep it simple.
The impact of the cutting force is absorbed by the front tool
rest. The backrest should be positioned at centerline
height. When the boring bar handle is set on top of
this new backrest it will be positioned a very little bit
above centerline. This will set up a very slight downward
slope to the cutting tip. This position will put the
cutting tip at the cutting angle of less then 90 degrees.
Again, protection from getting a catch. The backrest
should not have height adjustment. The front tool rest
will give you the critical height adjustments to put the cutting
edge right on center. You'll find that this eliminates
the nub or center cone-shaped protrusion in the bottom of
your hollow form.
fingertip control that you achieve with this tool system allows
thinner forms and smooth inside surfaces even when doing a
piece with voids. It is extremely easy to use, but there
is an adjustment time needed for your body to get the "feel"
of the new system. When in use the new tool stays in
the backrest. The tool tip adjustments are done easily
with the tool supported on both tool rests. The same
is true when you are sharpening, leaving the boring bar and
handle cradled in the backrest.
I have made David Ellsworth-type tools out of 3/8-inch steel
rod - one bent and one straight. Now they fit right
into the boring bar for doing smaller pieces with a very small
entry hole. You can fabricate other bars to fit into
the 3/4-inch handle.
laser measuring system is the third component. This
is a whole new ballgame, see the laser page for details.
turning deeper vessels I have designed a jumbo bar that is
1 1/8-inch diameter with a bent swivel tip assembly.
The jumbo bar can be used with the standard support handle
and backrest. Vibration is the enemy! If vibration
occurs a larger diameter boring bar is the solution.
Don't push the limits of any boring bar to the vibration point.
set up and use techniques in my DVD, HOLLOW FORMS-The
Easy Way 90 minutes long produced and edited
by Phil Pratt, gives much more detailed help for both boring
bar, backrest and laser systems.
Order Tools contact me at:
accepting credit card orders
more white knuckling it. No more sitting on top of your
lathe. No more fear of catches. This
takes both the mental and physical stresses out of hollow
form turning. Have fun!