With the Fostner bit modified and tuned up I can start using it. At 2 ½” in diameter it is pretty good sized and
stamped on the shank is a note that says, “480 Max. RPM.” That means the first step is to rearrange the
belts in my drill press to get at or below the
maximum recommended speed. I sure
don’t want to have it going to fast, overheat and ruin the cutting-edge
hardness.
With the speed turned down I chucked the newly tuned up
bit in the drill press and made a test hole in a scrap piece. Everything went well and after making the
test I used a fine tip marker to draw a line on the bit at the desired cutting
depth. Next is to carefully center the
bit on what will be the inside of the
bottom of the bowl then drill down to my depth line. Below shows the bit bottomed out in its hole
and then pulled out. The pulled-out
image clearly shows my depth mark.
Turning to the lathe I mounted the scroll chuck using
medium jaws, closed them down and was ready to clamp the blank in place.
For this operation the chuck jaws will fit inside the hole and as they are
expanded the serrated faces will bite into the drilled hole holding the blank
in place.
Here is what the blank looks like with it securely
clamped in place by the scroll chuck .
Next a live center is installed in the tail stock and ran
up against the face of the blank. I
probably could have skipped this step and started turning but having the live
center applying a little pressure to the blank to help push it against the
chuck jaws will help hold it in place
and give me a little additional piece of mind.
Once I had a bowl in progress break loose climb up my arm then go flying
across the room. Let me tell you once is
more than enough.
The turning could now start in earnest. First step is to true up the outside edge of
the blank then flatten the face toward the live center. With that done I marked out a 4¼” circle for
the “foot” of the finished piece. It
will also act as an attachment point when the blank is flipped so the inside
can be turned. From there I can start thinning the outer edge
to create a gentle curve from the edge to the foot. Below shows the nearly finished arc and the
foot. Since I do not want to lose much
in the way of thickness and only want a small profile the foot is not too tall,
only about 3/16”. The foot is not done
and will not be finished until near the end.
Those with sharp eyes will note the change to the live center from a
flat pressure plate to one with a cup and point.
Moving to the inside face of the blank I trued up about
an inch in from the outer edge. This
makes this face parallel to the just
turned bottom of the bowl and will work as a reference face later on.
Last bit of work is to make a small 15/16” diameter
recess in the center of the foot for the flat plate insert in the live
center. I need this or at least think I
will need it when I do the final bit of turning after both halves are glued
together. Naturally I don’t have a
Fostner that size. My choices were 7/8”
and 1”.
Because I think I want a snug fit the 1” was too big and therefore not
suitable. That left me with using the 7/8” bit to make a shallow hole, left photo below. A little delicate work with the parting tool
gave me the additional 1/32” radius cut.
The below right photo shows the flat plate held in place with just a
friction fit.
Switching out the jaws on the scroll chuck is next. The jaws now on it are my medium sized set
and I needed to go to the large diameter set to grab the 4¼” foot that had just
been turned. This is what that set looks like on the chuck and ready to
go. Note that the inner face which is
what I will be using is smooth unlike the ribbed set I had on before. The smooth jaw faces should dramatically
reduce the marring of the gripped surface.
That’s not really a problem with the ribbed set as the entire 2½”
mounting hole will shortly be completely removed.
The photo below shows the chuck with its large jaws
clamped on the outside of the blank using the
4¼” foot.
Moving in to a close up of chuck’s jaws and how it is
clamped onto the foot. If you look
closely you can see that the jaws are tapered
on both the inside and outside faces.
This taper provides a more secure grip and reduces the chance that the
blank will come lose. Remember the
thickness of this foot is only about 3/16” which is not a lot.
About an hour later the majority of the shaping is done
and all that is left of the 2½” drilled hole is a little nub that will be soon removed. The narrow flat face along the outer rim is
the mating surface between the two halves where they will be glued together.
After more refinement of the interior face I finally have
matched its curve to the curve of the outside face giving me a consistent wall
thickness of a little under 3/8”. A little sanding and this half can be set
aside for a while so I can get started on the top half, next post.
Next up – Completing Phase 1 Turning
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