Hollowing the bowl out begins by trimming the top of the
bowl almost to its final location. I had
left a little extra on both the top and bottom to give myself some room for
error during the outside turning. Once
that’s done the ¼” wall thickness gets marked in pencil and the actual
hollowing can begin. Shown here is early
on with only about half an inch in depth removed and the wall thickness just a
shade thick. You can still see just the
tiniest bit of the pencil line on the inside of the rim. As I near the bottom of the center hole it
gets drilled ½” or so deeper and the hollowing process continues with me
checking the wall thickness frequently. 
Progress continues until the desired depth is reached all
the while frequently checking the wall thickness with an outside caliper. When done the inside surface of the bowl
needs to be free of any ribs or humps, just a smooth continuous curve from rim
to bottom. With that done the rim gets
rounded then both the inside and outside are finish sanded up through 320 grit
sandpaper.
Last bit of work at this stage is to cut off the bowl
from the sacrificial base and that’s done in two steps. First is using the parting tool a cut is made
until there is only about a 1” diameter piece between the bowl and the
sacrificial base. This is then cut off
using the back saw shown while the lathe turns at a slow speed. The red arrow points to the 1” piece that was
mentioned earlier.
Last is to clean up the just cut base. To do that the 4-jaw chuck gets a different
set of jaws installed. These are pretty
large and imaginatively called jumbo jaws.
They have adjustable rubber bumpers to hold different size bowls in
place and as you can see it is capable of holding much larger bowls. Now there a restriction and some precautions
to be taken when using this jaw set.
First, the instructions list a not to exceed speed of 600 RPM’s which is
about half the speed I have been turning the bowls at. Second, is to remember that this set of jaws
uses rubber bumpers to hold the bowl in place rather than a set of steel jaws
so the grip is going to be a lot less.
Last is when tightening these jaws down because the walls on the bowl
are only ¼” thick and while I have not tried it, I do have a concern that too
tight could crack the bowl. To work
around these constraints, I use freshly sharpened tools, a slower speed and a
light touch with the end result shown.
Here in the top photo, you can see the small, medium and
large maple bowls. The bottom photo shows them
stacked. That’s three down and nine to
go. From here on my plans are to only
show any differences in turning or when doing the feature elements of the
bowls.
The next set to work on is the cherry. One interesting aspect of this set is when
hollowing out the bowl I cut through the layers that make up the feature ring
and got these results part way through the three layers of the top feature.
All went well with the cherry set until I checked the
depth of the large bowl I had hollowed out because I want to see how much there
was for me to smooth out and cup the bottom after the sacrificial foot got cut
off. Much to my surprise and chagrin the
bowl depth was about ½” too shallow. Not
a small error that I could let go and a potential disaster. With the sacrificial food cut off there is no
way to mount the bowl in the lathe to turn the inside of the bowl to its proper
depth. After an appropriate number of
bad words I decided to make a new sacrificial foot then glue it on (red
arrow). Gluing the new foot in place
using the lathe tailstock to center it should keep the bowl and new foot’s
center lines aligned. This way I can cut
a new tenon concentric to the bowl, remount it in the 4-jaw chuck and finish
the hollowing. Fortunately, when cutting
the old foot off I had left the bowl about 1/16” in long at the base. This means that when the time comes, I should
be able to cut off the new sacrificial foot and finish up with the bottom
ending where planned.
Below the top left photo is after I cut the tenon that
will go into the 4-jaw chuck so I can deepen the bowl’s interior. The bottom left photo shows the jaws changed
on the chuck with the piece flipped around and mounted in the chuck. The open end is now ready for me to cut it
down to its proper depth. Once that’s
done the bowl is parted off shown in the bottom right photo. From this point on the bottom is finished
just like the previous bowls.
Here are the finished cherry bowls. In the photo you can see how the use of
layers allows the feature ring to be seen inside and outside the bowl.
With half of the bowls turned and ready to finish I
decided to clean the lathe area up a bit.
Here is the pile of shavings from the first six bowls. It filled more than one 13-gallon kitchen
garbage bag.
Starting on the next group I decided to try a different
method of aligning the turning block with lathe’s central axis. Where before I had used the corners as an
alignment method this time, I used a dial indicator using it to make sure the
face of the turning block is 90 degrees to the lathe’s axis. Process is to eyeball block square then
measure to see how much wobble is in the face.
Corrections are made until the wobble is down to a couple of
thousandths. The point of the live
center in the tail stock is then run up against the block giving me a set point
so the block can easily be reset to be in line with the lathe’s centerline and
the turning can begin as before.
Next Up – Adding Copper Band to Walnut Bowls & Spraying Lacquer
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