Setting the base ring aside I stated working on the
sacrificial sandwich that acts as the transition from the cast iron face plate
to the actual bowl. It is made from two
layers, a piece of 5/8” plywood glued to a ¾” piece of particle board. The plywood layer is screwed to the cast iron
face plate which is why I used plywood as it holds screws better than particle
board. One thing I do not want to happen
is for the screws to work lose and potentially let go allowing the in-progress
bowl to launch itself at me. I had a
bowl break free once and that made for a very bad day. Here the photo shows the two layers glued and
screwed together. The screws will be
removed once the glue sets overnight.
Once the glue cures the sandwich is run through the
thickness sander to make sure the faces are parallel. The bottom ring of the bowl will get glued to
the particle board layer. When it comes
time to separate or part off the bowl I will be turning through it. Since the screws only go into the plywood it
will be easy for me to not hit one accidently.
Hitting a hardened steel screw with a lathe tool is not a good idea. Next the sandwich is centered and securely
screwed to the face plate with a whole bunch of screws, 15 to be exact.
This assembly is then mounted on the lathe and each layer
is turned to a true circle. Next an MDF
reference block in the center of the bottom ring is attached using double face
tape. I used the ring joints to mark it
to give me my center then measured the particle board diameter and drew a
couple of concentric circles on the ring face.
One the diameter of the particle board and a second just a sixteenth or
so larger. These will allow me to center
the bottom ring on the particle board when gluing the two together.
A layer of glue is spread on the base layer then the face
plate assembly is carefully centered on the pencil rings. Eight clamps hold things in place, but I have
to be careful when tightening them as the glue acts as a lubricant which allows
the pieces to slip around and out of alignment.
It just takes some time keeping an eye on things and making small
adjustments as the clamps are tightened.
Once the glue had cured I mounted the assembly on the
lathe and was ready to go. The photo on
the left is taken from the lathe headstock side while the right one is from the
face where rings will be added and the turning will take place.
Below the left photo is a little closer look before I
started turning and the right one is after I have knocked off all the corners
and trued up the ring.
Next up is the second ring. I am fortunate to have a pretty good stack of
thoroughly dried lumber. Some is rough
sawn, some is surfaced on the two wide sides and some also has one edge ripped
straight. Well, sometimes it is
straight. Unfortunately, a fair amount
of the lumber I will be using for this project does not have a straight edge to
reference off of. This piece of walnut
is a case in point as while it was flat and not warped both long edges were
nowhere near straight. They were way too
far out to even think about using the hand plane to clean up. The solution is to take an 8’ level and use
the straight edge to mark a reference line.
I then carefully cut along the line using the band saw getting close to
straight and then clean up with my long hand plane. Last, as shown below is to clamp the level to
the rip fence on the saw to give me a long surface for the walnut piece to
register against. Flipping the board
over after each pass ended up giving me straight parallel edges to work from.
To make the second ring and all the subsequent rings
except for last one I need 12 cherry pieces and 6 walnut ones all the same
size. The process is the same as what I
went through to make the bottom layer with one important difference. I do not have a cut slot on one edge. Not having that slot allows me to make more
efficient use of my wood as there is not a specific Inner or Outer Face. In the images below, you can see what I mean. The top photo shows the cuts required for the
bottom layer where each segment has to begin with a new edge so the slot is
always on the inside. The bottom photo
is for the second layer whose segments can be cut in a continuous string with
no waste.
Once I get the 12 cherry and 6 walnut pieces cut I can
clamp them together to do a test fit to check for gaps or any other
problems. In this case everything looks
good. Last is to chalk the sides that
face up so I make sure none of them get reversed in the controlled chaos of
gluing the ring together
After letting the glue cure overnight as before I ran the
ring through the thickness sander to flatten.
Next is to center the ring on the stack.
That’s done by aligning the joints with the previous layer and very
carefully measuring the distance between the edge of the to-be glued layer and
the turned edge of the previous layer.
If nothing is in error when that distance is the same all around all the
joints should align. If they don’t then
there is a problem somewhere. Here you
can see everything is good. Last is to
draw a pencil line around the first layer on the new layer.
The glued-up bowl stack is removed and alignment marks
are drawn on the new layer. The marks
cross the just made pencil line and are centered on the segments. I make two arcs using a compass working from
each joint. Any error will show up as a
gap between or overlapped lines.
Glue-up is next.
Note that there are alignment blocks held on by orange bodied F
clamps. They are set on the centering
circle and keep the two pieces in place while torqueing the grey BESSY clamps
down. Because the glue acts like a
lubricant between the gluing pieces without the blocks they will slide around
as the clamps are tightened. Without
them it’s a real pain to try and keep both parts aligned. Once the glue has taken an initial tack the
blocks can be removed and the glue allowed to cure. Looking close you can see how the joints
between layers are offset by half.
Next up – Rings & More Rings
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