Before gluing the oak ring onto the base cherry ring
there is one last step. To remove any
problem with expansion and contraction due to humidity changes the disk needs
to float freely in the recess. If a
finish is put on the oak disk and the recess the disk won’t get securely glued
in place if I get a little sloppy with the glue when adding the oak ring. Here the left photo shows the recess for the
cherry ring with the finish applied.
Wipe-On polyurethane is used rather than my usual lacquer finish for reasons
I will get to when the finish is applied to the turned bowl.
Here is the disk with the finish applied, dry and ready
to be added.
Assembly is next with the left photo showing the cherry
base with its recess, the oak disk that goes in it and the oak ring that gets
glued on. On the right is after the oak
ring has been glued and clamped on. Note
how the 2” Fostner drill bit is being used to center the oak ring.
Laying out most all the pieces needed for the different
rings is next. I did spend some time
juggling the pieces to get the most efficient material use. I guess playing Tetris did have a good
use. The top photo shows how the main
plank gets divided up into pieces for eight different rings. Most of the pieces worked out so the plank
could be crosscut to a common length but one set of pieces didn’t so it got
separated into two dogleg pieces using the jig saw.
Next is to cut those pieces to width so they can be cut
into segments to make the rings. The
process in doing that is the same as already discussed. Here in the foreground is one set of segments
ready to have glue applied, one ring ready to be flattened and one ring clamped
while the glue dries. In the background
are blanks for other rings.
The rings are flattened and brought to final thickness
using the thickness sander. The top
photo shows the ring marked with pencil lines so when the piece is sanded I can
easily see those areas that are still low as they still have the pencil marks
on them. Once all the marks are gone the
surface is leveled. Same process is used
on the other side so I end up with flat parallel faces. In the bottom photo the two left rings are
sanded and ready to be glued onto the bowl stack. The right ring is clamped and waiting for the
glue to cure.
After letting the glue joint between the cherry base and
the first oak layer cure the oak layer can be turned round. The left photo has had a little done to knock
off the corners and the right photo is the turning in progress.
With the oak layer turned round I can use it to center
the next oak layer. In the left photo
after careful measuring the glued-up assembly is centered on the next layer and
the outline of the assembly marked on the to be added oak layer. The right closeup photo shows the pencil line
and a reference mark used for aligning the layers.
Once the glue is spread the pieces are aligned and
clamped together. Since the glue acts
like a lubricant it’s pretty common for the pieces to move as the clamps are
tightened so extra care has to be taken make sure they stay aligned.
For the next few layers, it’s the same process of turning
the previous layer round, using it to center the next layer and gluing that one
on. Earlier on I mentioned when
centering the layer there was some careful measuring to get it done. Here for the fifth layer, it seems like a
good time to go into a little more detail on how that’s done. The photo below shows after the layer stack
has been centered left to right with a couple of clamps used to hold it in position.
Next the same process is used to center the layer stack
top to bottom. That’s shown done in the
photo below. This process of centering
the bowl along one axis at a time speeds the centering up a lot since the first
two clamps hold it in place when you go to center the second axis. Otherwise, it can be a long process of
getting one axis right then accidently shifting it when making a change to the
other axis where you end up chasing the centering. Before calling it done the joints of the new
layer are checked to make sure they line up with the previous layer. If they don’t something is wrong.
Last is to mark a center line between two of the segment
edges then rotate the layer stack until the joint in the rounded layer lines up
with centerline. 
In order to give myself a limit to where the glue gets
applied the stack along with the new layer is clamped together, flipped over
and the inside outline of the new layer is traced onto the underlying
layer. Here is what the traced line
looks like so now I know where my glue application limit is.
The last step before gluing up is to do a little
preliminary turning to the inside of the bowl.
In this photo you can see how the layers are getting blended
together. Now this is in no way the
finished interior profile of the bowl but it is a start. Once the blending is done the next layer gets
glued on. I will get to smoothing the
outer layer later but now I need the layer steps there to provide me some place
for the clamps to go when adding layers.
After this layer there is only one more full thickness oak one to go
before there will be a shift in material and layer thickness.
Here the next layer has been added. One step not shown in the layer adding
process is to make sure the layer’s face has no runout or wobble along the
lath’s axis. Because the layers are
sanded smooth and parallel before gluing on, they are mostly true after being
glued on. Generally, it takes just some
final sanding using an oak scrap with sandpaper at the end for truing although
a little touchup with a scraper is sometimes needed. When sanding the oak sets on the lathe rest
with the sandpaper against the surface and the other end just touching the
face. Light sanding until the chalk is
gone gives me a flat smooth glue surface for the next ring.
Next Up – Thin Layers & Cutting Segments
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