It has been some time since I had done a major lathe specific
project so I decided to do another
largish segmented bowl. The difference
this time is it will have a complex feature ring. The last large-scale turning was a segmented
bowl about 18” or 19" in diameter done in 2018.
It was made out of cherry and walnut.
Below on the left is it right after completion. The photo on the right was just taken about
five years later. It’s interesting on
how the wood changes color as it ages with the cherry getting darker and the
walnut getting lighter.
My first step is to come up with the main feature ring
and the minor feature ring then draw it up.
Once that was done working out the overall shape and proportions came
next. In the center below the shape of
the bowl and the feature rings are shown.
To either side are the bowl’s profiles.
The left one is the concept section while the one on the right has a more
refined section in green with the outer and inner buffer areas shown in gray. These buffer areas allow me to make subtle
changes to the profile as the turning progresses. 
The main feature ring consists of four identical layers
where each layer is made from twelve segments and each of the segments has two
pieces. One made from a light wood and
one from a dark wood. All told there are
96 individual pieces in these feature rings.
The drawing below shows what a single segment looks like.
Since all those
pieces are identically shaped, I will be building a jig or two to make the
blanks the segments are cut from. Below is the drawing for the first jig. Due to the direction the grain needs to run
the pieces can’t be cut out of one long piece but that’s all going to get
explained later when the jig is used.
The jigs will be made from some almost 30-year-old
completely dried construction 2x4’s and 2x6’s.
While they are now dry and stable as they were drying, they twisted and
cupped. Using the Planer Sled to hold
them stable it’s pretty easy to get the first reference surface flat. Here one of the 2x6’s is set in the sled
ready to run through the planer.
A few passes through the planer and I have a nice
straight flat reference surface to work with.
That’s shown in the photo below.
From here all that’s required is to put the reference face down in the
planer then mill the second face so it ends up parallel with first face.
For the feature ring the most important part of the first
jig is making the tapered piece at the correct angle so that’s what I will start
with. This piece gets rough cut with the
bandsaw. That starts by setting the
angle needed which is 13.45 degrees. In
the photos below you can see the bandsaw setup to make the angled cut. The angle gets measured with an electronic
gauge.
Taking one of the flattened trued up 2x4’s that had a
good straight edge the table saw is used to rip the other edge parallel to
it. The blank is then flipped over and a
skim cut to the first edge cleans it up giving me a flat, true blank with
square parallel edges. The blank is then
ripped with the bandsaw giving me the two pieces below.
While the bandsaw makes a pretty good cut it is still too
rough and uneven for me to be able to depend on it to provide a consistent
accurate reference surface in the jig.
The photo below shows what I mean.
Smoothing out the minor irregularities is not as simple
as hitting it with a hand sander as I need a flat surface all in the same plane
at the right angle. To create the smooth
surface the two just bandsawn pieces are put back together with the original
outer faces next to each other held together with double face tape. That puts the bandsawn faces to the outside
with the angles canceling each other out resulting in the sawn faces parallel
to each other. That’s shown in the left
photo below with the electronic gauge set on the cut surface reading zero
degrees or level. This means that I can
run the assembly through the thickness sander to flatten and smooth out the
opposing faces. The problem is because
the surfaces are rough the angle changes as the surfaces are smoothed. The fix for that is to find out which edge
needs to be raised to correct the angle and add shims along that edge. It took a little trial and error to get the
correct shim thickness shown in the right photo which ended up being a playing
card plus two layers of masking tape.
Setting the gauge on the offset gave me an accurate reading of the
adjusted angle. Once the top piece angle
is right the assembly gets flipped over, the shims removed and the other face
made parallel giving me two angled pieces with the correct angle.
Assembling the jig is next. One of the just finished angled pieces gets a
square edge cut then screwed to a plywood base flush with the base’s edge. The other angled piece gets ripped down so
it’s just a little wider than the basee. I did that to give me a little lip to grab
onto when the jig is run through the thickness sander. One other detail is the way the two angled
pieces come together. The piece on the
right has a square edge and the one on the right has its angled edge. I could have put the right piece in with its
matching angled edge to make a nice tight joint but wanted to leave the gap so
there was a space (red arrow) for sawdust to go so it does not get trapped
throwing the jig’s accuracy off as it’s run through the thickness sander. That’s all done below along with a
greyed-out test piece with the pencil line on its end showing the finished
piece’s final thickness.
The finishing piece on the jig is an end plate to keep
the angled blank in place while the jig is being run through the thickness
sander. Note that all the jig’s pieces
are screwed on and not glued. That’s so
if I need to make changes to the jig it will be easy to do. Below is the completed jig and an angled test
part sanded to its final shape.
Next Up – Gluing Jig, Sample Testing & Material
Selection
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