This blog series is going to cover another lathe
project. I plan on making a large
diameter hollow form. Typically, you
turn a solid block of wood round then working from one end hollow out the
center. So, if you want a small opening
at the top then the removal of all the material from the inside has to come out
of that small hole. However, that’s not
the way I plan on doing this project.
The short sequence for the way I am going to do it is to:
- Take two pieces, a top and bottom then on the lathe rough turn the outside of each one.
- Next, turn the inside part of the top half and bottom half.
- Stain and finish the inside of each half.
- Glue the two halves together.
- Final turn the outside then finish it.
There are a lot more steps than this but it’s a good
overview.
I had done a small-scale prototype some time ago so had
an approximate design done. With that in
mind I start by selecting the material.
When I built the combination Dining/Gaming table for my son I had some
6/4 or just under 1½” rough sawn red oak cutoffs. They had been laying around for the better
part of a couple of years and were roughly the right size for the project. Here are the three pieces I started
with. Not so good looking and a couple
were cupped really badly with just a little twist to complicate things. Oh yes, the ends were split and cracked too.
Below is a photo of the best-looking piece which will be
used for the top half with the prototype setting on it.
To get the bottom half I needed to recut, flatten and
glue these two ugly boards together.
Taking the left-hand piece, I marked out where I needed
to make the cut to get the majority of the cup removed. Fortunately, the cupping was not even across
the board but much more sever towards one side.
Cutting to an approximate length also helped get rid of some of the
twist and the end splits too. Here you
can see how much it helped in removing the cup.
Also, if you take a look at either edge of the cut-out piece you can see
where the surface has been smoothed out for about an inch. That is where I used a hand plane to take out
the twist so there is a flat surface when it gets run through the thickness
sander to flatten. Since the pieces are
so rough and cupped, I used a 36-grit belt.
Not quite as rough as a gravel road but pretty close.
Here are the pieces now just over 1 3/16”
thick flattened, squared up and marked with the bowl blank diameter. The two pieces on the right are matched so
the grain flows from one to another and should be nearly invisible when glued
up.
The glue up is pretty simple as shown here just one joint
with four clamps to keep everything aligned.
Once the glue had cured, I checked for flatness made a
couple of small adjustments and redrew the bowl blanks on each piece.
To speed the process of turning the blanks round I used
the bandsaw to cut the blanks close to final size.
The next step is to drill a 2 ½” diameter hole on the
inside of the blank for mounting in the scroll chuck. That is not an arbitrary number it is based
on matching the arc of the chuck’s jaws to a specific diameter circle. That way you get maximum surface contact
between the jaws and the piece of wood which makes the mounting more
secure. Having a 1 ¼” thick, 11 ½”
diameter piece of oak come flying off the lathe at me is not my idea of a good
time. Anyway, when I went to get the
drill bit, boy was I surprised as my set did not have one that size. Closest was a 2 3/8”
one which is too small for the oak blank to even mount on the chuck. I know I tried it with a piece of scrap. Much to my disappointment a Fostner bit that
size was not available locally so I ordered one on-line which ground the
project to a halt until the bit arrived.
About a week or so later thanks to the internet and
Amazon the new 2 ½” bit arrived. This is
what it looked like after cleaning the protective oil off all ready to use, or
not.
After inspecting the bit, I found it needed some
modification before it was usable for my purpose. There are two things that need to be
done. First, in the photo below you can see
the center point is pretty good size. It
is about 5/16” above the cutting edge on either side which for most
applications is OK but here since the bottom of the drilled hole is going to be
pretty close to the bottom of the bowl it needed to be shortened. I sure did not want to have it come through
the bottom and needed to be able to later turn the divot it leaves out. This may not make a lot of sense now but it
will later on. Second, the long
horizontal cutting edges need to be cleaned up so the little chips and nicks
are gone then sharpened as right now they leave a little to be desired.
This is after about an hour of grinding, hand filing and
honing. The center point is 1/8”
shorter and the long cutting edges have been honed using a diamond file. There are still a few nicks on the leading
cutting edge but it is way better and a whole lot sharper.
With the bit ready I can finally start making some
shavings.
Next up – Turning the Bottom Half
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