With the outside of the bowl turned to its final shape
it’s time to start on the inside. This
starts by taking the blank out of the lathe and flipping it end for end so the
base is now at the headstock end. I
didn’t mention the scored line near the bottom before but that’s where the
bottom of the bowl will be.
Marking the bowls ¼” wall thickness is next to give me a
starting guide. Also, a hole is drilled
just short of the depth I need to hollow out to. Since I had the Fostner bit already in the
chuck that’s what got used.
Here the bowl is a bit over half turned. The red arrow points to a pencil line partway
down the inside of the bowl. That’s my
reference mark showing from there to the lip of the bowl is the correct
thickness with everything on down too thick.
From here it’s removing material and checking the wall thickness along
with the depth until done.
Once the interior of the bowl is turned to size it gets
sanded then removed from the 4-jaw chuck and the jaws get changed out once
again. This time a set of Jumbo jaws get
installed and the bowl gets mounted top edge in. As the bowl’s walls are only ¼” thick the
jaws get lightly tightened down to prevent the walls from being damaged. To provide some stability the tail stock gets
a live center brought up and a little pressure applied to hold the bowl in
place. Now I can clean up most of the
base then cut the foot off.
Last is to finish turning and cleaning the base up. Here on the top left is after the foot was
cut off and on the top right is the finished base. The bottom two images show different views of
the bowl.
With an actual mid-size bowl done I measured its real
volume which was 1 cup with the calculated volume of .953 cups, close enough
for our purposes. The drawing below
shows the comparison between all three different sizes that I will be making.
With the woods selected, the prototype finished along with the overall shape and stepped sizes set it’s time to do some testing of the various types of feature accents we discussed. Those include the following where each of the items are about ½” or so down from the top of the bowl:
- A copper band around the bowl.
- Six equally spaced round aluminum or brass dots inlayed into the wood.
- Six equally spaced square walnut pegs set into the wood deep enough so that when the bowl is turned, they will be visible on the inside of the bowl.
- A turquoise ban inlayed around the bowl.
- A band of brass shavings inlayed around the bowl set in a clear epoxy.
- A series of three grooves burned into the bowl at the top and one at the bottom.
- A feature ring consisting of three thin wood layers with the top and bottom matching and a contrasting center layer.
Now there were some early tests that got quickly
discarded for one reason or another. One
example was the idea to use lead free solder to fill either square or round
holes. The photo below shows that
test. One problem was that the melting
point of the solder was pretty close to the burning point of the wood and it
ended up charring the edge of the holes.
Also, there was enough surface tension in the molten metal that the
square corners didn’t get filled. 
Making a decision on which features to use is next. During our discussions one was a clear
choice, that of the turquoise inlay probably in oak as a nod to where we live
in the Southwest. Beyond that it was
pretty open so I started with four promising possibilities. The copper band, brass and aluminum dots and
square walnut pegs. Taking some scrap
oak a block was laminated up and turned to a cylinder using the same process as
the cedar prototype giving me a blank canvas to work with. At this point a major part of the testing was
to see if I could actually make what I had designed. The brass and aluminum inlay dots had me
concerned because with the bowl walls a ¼” thick I really only had 1/8” depth
to work with. Laying out the dots was
the first problem since they needed to be equally spaced with the mounting hole
drilled perpendicular to the center of the cylinder. In the end this is the setup I used to
accomplish that.
Cutting the dots, fastening them securely in place then
bringing them flush to the wood turned out to be challenging but doable. Both the copper band and walnut square inlays
were easier than I thought. The photo
below shows the results from this first bit of testing. 
In a video call with my son, we discussed which options
might look the best with which woods.
Using photos of three different woods and some time with Photoshop, I
put together these possibilities. More
discussion ended up with selecting the copper/walnut for sure. The burned lines in maple are a strong
contender with the square walnut inlay and aluminum dots rejected.
Next alternates for the oak and turquoise were discussed
as there were three different color mixes available with a fourth option of
contrasting layers thrown in for good measure.
The choice was the top right image. 
Besides the oak choices there were eight others for the
maple and cherry. Those are shown below
along with the walnut and copper version we had selected. The cherry bowl generated the most versions
and we ended up with five different possibilities.
I am not going to bore you with the discussions on how
the final designs were selected but here are the final four choices. In a curious twist the aluminum and brass
options that were the most difficult to do in testing got eliminated for
aesthetic reasons.
The last decision to make was regarding the spacing from
the top for the various feature rings. I
thought constant spacing of the top and bottom decorative rings might look out
of proportion with the different sized bowls.
To my surprise after doing some drawings the bottom inlay at the same
height looked fine while the top inlay did not.
In the drawing the bowls on left have the same spacing while the bowls
on the right vary by less than a tenth of an inch. Not much but it does make a difference since it’s
the details that count.
Next Up – Sacrificial Bases, Walnut & Cherry Blanks plus Making Veneer
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