|
Phil practiced dentistry for 29 years. He retired 22 years ago. He restored
classic cars for several years after retirement and took up wood turning about
14 years ago, about the same time Kirk DeHeer started turning. He first saw a
stone turning demonstrated by Lee Carter at the Utah Symposium several years
ago.
About Talc (or soapstone)
Talc is a very soft stone (Blackwell hardness of 1). It occurs in many places
in the world but the nearest quarrie to us is in Montana. Talc is used
industrially in many applications but largely in cosmetics and skin powders.
These users prefer white talc so colored talc is often regarded as
unacceptable; however, it is excellent for turning. Talc can be cut with
high-speed steel turning tools and standard bandsaw blades. It is very easily
scratched so in finishing stages it might best be handled with cotton or vinyl
gloves.
If talc is turned at low speeds (< 500 RPM) it is less likely to create dust.
The dust is also heavy enough that it settles quickly rather than clouding the
air. Alabaster is more prone to dusting. A dust mask is still a good idea for
safety. Talc pieces often contain fissures that can result in disintegration at
higher speeds unless stabilized by filling the fissures with thin C/A glue.
Thus a face mask is also a wise precaution. Because of its softness and absence
of fibers talc is less demanding of tool sharpness than wood; however, sanding
is critical to achieve a good finish. More of the turner’s time will be spent
in sanding and polishing than in tooling the stone.
Preparing the Stone
Talc generally comes in chunks. Phil inspects the raw chunk to determine how
best to saw the stone to minimize waste. He uses a bandsaw to make an initial
cut to provide a flat base from which other cuts can be made. He can then cut
the large chunk into smaller blocks. Most of his stone turnings are quite
small. In this demo he began with a blank about 2½" square by 2½"
long. He also uses the bandsaw to cut the blank into a rough cylinder. It is
important that the base of the blank be flat and smooth. He glues a
waste-block disk (¾" flat stock) on the face of a 3" face plate with C/A
glue. He then glues the flat base of the stone blank onto the waste block with
C/A glue taking some care to center the stone blank as well as he can. When the
glue is well set the assembly is ready to mount on the lathe.
Turning the Exterior
Phil uses the Henry Taylor mini tools for shaping cuts. His favorite tool is
the ¼" gouge but he also made use of the parting tool and the skew. The
design he chose to demonstrate was a miniature pedestal bowl. The 2¼"
diameter bowl sat on a cove-cut pedestal with a stem diameter of ¾" and
a flared base diameter of 1" to 1¼". The waist of the bowl was at the
2/3 point of the total height of the piece. The lip of the bowl was beaded and
a narrow flat fillet separated the bottom of the bowl from the upper flare of
the cove-cut stem. He mounted the face plate and stone on the lathe and ran the
lathe at about 400 RPM with the outboard face of the stone blank supported by a
live center in the tailstock. He used the ¼" gouge to turn the blank to
a cylinder and then began rough forming the base and stem of the piece. The
base was oriented at the tailstock side of the blank. He reduced the diameter
of the base to about 1¼" and gradually defined the cove of the stem
and the round curve of the bowl. He used a skew to cut the fillet at the bottom
of the bowl. After moving the tail stock out of the way, he turned the bottom
of the base to a slightly concave profile and then cut a flat square groove
into the base to provide detail and a band in which to scribe his name later.
This 3/16" wide groove was cut with a square end scraper (or parting tool).
With the profile of the piece established he began finishing the exterior with
240 grit sandpaper progressing through 600 grit. As he identified fissures or
defects he filled them with C/A glue and retreated to 240 grit paper as needed
to eliminate the flaws. Final sanding was done with 1200 grit wet/dry abrasive
paper with liberal use of water to lubricate and clean the surface. Phil began
the polishing process with EEE Ultrashine abrasive wax which he applied fairly
liberally with a cloth with the lathe stopped. He then buffed the entire
surface with the rag while the lathe turned. Phil pointed out that as you buff
the EEE its abrasive particles break down to provide finer and finer grit.
After the buffing he wiped the surface with a clean cloth and then applied
friction polish with the lathe turning. This sequence produced a smooth and
glossy surface.
With the exterior turned and polished, he removed the stone piece from the
waste block. He used a thin parting tool to cut through the wood of the waste
block without marring the glued face of the stone.
Turning the Interior
To hollow the interior of the bowl it is necessary to reverse-chuck the stone
piece. He trued up the face of the waste block and then used a caliper to
transfer the diameter of the base of the piece onto the dressed surface of the
waste block. He used a skew to cut a shallow, flat recess into the waste block.
The recess must be flat to mate well with the bottom face of the base. The
diameter of the recess should not be too tight, but it should not be so large
that it makes centering the base in the recess difficult.
Phil normally mounts the stone base in the shallow recess and holds it in place
with the live center to check to ensure the piece is centered on the lathe
axis. When he is satisfied with the alignment he uses a hot-glue gun to apply
hot-glue strips from the stone base onto the waste block in four positions
around the circumference of the base. At that juncture he would leave the piece
on the lathe for some time to allow the glue to cool and harden. However, in
this demo he tried to accelerate the cooling by daubing water (and ice) on the
glue beads. This proved to be unsuccessful and the glue didn't harden enough to
allow hollowing the bowl.
He described the procedure he normally uses from this point. He uses the gouge
to begin the hollowing process then goes to a hooked hollowing tool, such as
the Kelton, to complete the hollowing. He recommends leaving a wall thickness
of about ¼". The same sequence of sanding and polishing steps is
used on the interior as was described above for the exterior surface. He then
applies wax while still on the lathe.
Removing the finished turning from the waste block demands some care because of
the ease of scratching the stone surface. He demonstrated how he uses a pallet
knife to detach the glue from the waste block leaving the glue attached to the
completed stone turning. The finished stone with the glue still attached was
carefully removed from the waste block. He used needle-nose pliers to pull the
glue beads off the stone without ever touching the stone itself with the
pliers. After the glue is removed another coat of wax is applied and hand
polished.
Phil used a sharp pointed awl to scribe his name in the flat groove on the
bottom of the base.
|
