Before turning the actual knobs, I did a test using a
smooth surface on the tuned knob to see if that would provide enough grip to
tighten things down and to no real surprise it didn’t. A couple of different treatments to the
knob’s surface were tried and the one that worked the best is similar to a
knurled finish only at a larger scale.
The test pieces and the finished knob (on the right) with its six
rounded lengthwise notches is shown below.
Now the threaded rod can be glued into the knob blank
using a 2-part epoxy. A toothpick places
a little epoxy in the hole then the rod gets run in. The hex and wing nut let me use a wrench to
run the rod to the proper depth by measuring what’s exposed using the dial
caliper.
After letting the epoxy cure overnight, the threaded part
of the knob is run into a jig mounted in the lathe. Since the hole the rod goes into is threaded
when the rod is fully run in it is held tight in the jig.
Next the square blank is turned round to the proper
diameter, trimmed to the finish length and the outside edge rounded. With that done the layout for the lengthwise
notches for the surface treatment can be laid out using the reference lines
on the jig. They were added to the jig
using an indexing feature on the lathe that can lay out a variety of evenly spaced lines
around a turning.
Cutting the slots were as I suspected not an easy
task. On the first test piece I tried to
cut a couple of them freehand with a round file. That took quite a bit of time and was not
very good so that method was eliminated.
I thought about building a jig and cutting them on the router table but
don’t have a round end bit that small, it could have to be ordered but it’s
pretty pricy so that got eliminated.
Next, I tried using a small carbide burr in the Dremel tool making the
cuts freehand and it did do a good job cutting but I didn’t do so well guiding
it freehand. What worked is a jig that
holds the knob in the right place and guides the Dremel tool in a straight line. The top photo below shows the final setup and
the bottom photo is the burr.
Here is a look on how the jig works. With the knob locked in the jig the Dremel
tool rides along the top of the vice while the shaft of the burr rides along
the spacer to make a smooth cut. All I
have to do is control the depth of the cut by making multiple shallow cuts
until the desired depth is reached. The
bottom photo shows a completed notch and the short spacer that holds the knob
away from the vertical part of the jig clamped in the vice. 
After all the notches are cut the knob is removed from
the jig where the just cut rough edges get cleaned up and smoothed using a very
small round file. From there the knob is
remounted back in the lathe but this time it’s held away from the jig itself so
the sharp back edge can be rounded slightly.
After all I don’t want to cut myself when tightening the knob down. The last little bit is to sand with the lathe
spinning both forward and reverse with 220 and 320 grit paper for a smooth
surface. Forward softens one edge of the
notches while reverse softens the other edge.
There is one last set of holes to drill before I do the
final sanding and then start the finishing process. They are for two bolts that act as guide rods
while also capturing the leveling bars to the base. The bolts go in a threaded hole in the base plate
and are locked in place using epoxy, Loc-Tight or super glue
(cyanoacrylate). The drawing below shows
where they go.
These holes have to line up with the holes in the
leveling bars so accurately locating them and setting up stop blocks is a good idea. The photo on the left shows the center finder
being used to set the stop blocks and the right photo shows one of the holes
drilled.
Threads are added using a ¼”-20 tap to match the
threads on the bolts. The tap is made for
metal but can be used in wood and since the wood is a lot softer than steel, I
can use the drill to run the tap in. The
bottom photo shows the hole after the threads have been cut. This completes 99% of the woodworking so now
it’s time to clean up the shop so the finishing can start.
The finish is a sprayed lacquer and I have decided to spray
all the parts. Because of the difference
in the various component sizes two different spraying methods are used. The small parts like the knobs and the wheels
get sprayed with the airbrush. The
remaining larger parts have their finish applied with the High Volume Low
Pressure (HVLP) sprayer. Here is the
mixing setup with all the various fluids and containers needed for spraying.
The photos below show how most of the pieces are hung so
all sides can be sprayed at once. There
are two exceptions. One being the sled
base on the left side in the background of the left photo. It is set on a rotating base so it can be
spun around to make all sides easy to get to. The other is the knobs most clearly seen in the lower right of the right
photo that are screwed into a scrap piece of plywood. To keep the finish off the threaded rod part
of the knob assembly that area is masked off.
After the first coat has dried for a few hours they all
get wet sanded with water and a 2800 grit sanding pad. That’s followed by a second coat, an overnight cure and the finish wet sanding.
This sanding starts with a 3200 grit and works up to 8000. Below are all the completed parts ready for
assembly.
One component not yet addressed but shown in the above
photo is the self-stick 80-grit sandpaper strips. They go on top of the leveler bar as shown in
the drawing below and will help grip the board that’s being flattened. I cut them from a
12”x18” sheet made for a floor sander using a template and sharp knife. To assure a good bond once stuck in place
they are clamped together overnight (right photo).
Next Up – Final Assembly & How to Use
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