Final sanding of the top of the base using 220 grit
sanding paper is next. That’s followed
by gluing and clamping the dowel in place in the photos below.
After the glue cures the dowels which are just a tad long
are sanded flush with the base. The
large disk sander with a guide to keep the base square with the disk is
used. That’s followed by sanding the
sides and ends down to 220.
With the dowels flushed to the sides and all sides finish
sanded the brass insert can be epoxied in place. A small amount of the epoxy is spread on the
sides of the hole in the base. The
insert is run in with the ground off end put in first until it bottoms
out. That’s done using a short bit of threaded
rod that has a couple of jam nuts on it chucked up in a drill.
Below in profile you can see how the insert sticks up
above the top of the base and that’s why earlier a countersink was added to the
underside of the top. Without it the top
wouldn’t be able to clamp down on the sandpaper holding it in place.
While the epoxy cures the 3-layer top stack gets its top
edges and corners rounded over for a softer feel in the router with a 1/8”
radius bit. The corners get done first
because they are end grain which is prone to chipping when the router bit exits
the cut. That’s solved by using a scrap
backup piece. Another consideration is
that the pieces will be on their narrow edge when routing and could be prone to
tipping which is solved by clamping it to a wide block for stability. Clamping to the wider block also helps guide
the piece across the router bit as the opening in the fence is wider than the
piece. I did add a second larger push
block to the right to provide some additional stability for peace of mind. It worked well on the single prototype so
when routing the rest they all got clamped together and routed in one
pass. The setup below shows everything
ready to go. The long edges are easy to
route using a push block to keep my fingers away from the bit. Once routed all the surfaces get sanded.
When I did the prototype the knob that clamps the
sandpaper in place is domed as in the photo below on the left. It was acceptable but I wanted a shape that
provided a better grip and felt good in palm of my hand and didn’t want any sharp
edges. Lots of ideas came to mind but
all had one or more flaws. A shape
that did occur to me in the middle of the night is similar to what’s called an
Acorn nut shown on the right. With that
shape in mind, it’s back to the prototype stage figuring out how to make a
domed hexagon. Once I got a finished
prototype it’s time to make five more.
The process starts by laying out a 1 5/8” diameter for
the knob with a compass. Here are the
oak, cherry and walnut blanks to be used.
Next, it’s over to the bandsaw to cut the rough knob
blanks out. The bandsaw has a ½” wide
blade on it which is too wide to make a 1 5/8” diameter cut. If I changed it out to a ¼” one there would
be a lot less burning and a smoother cut since a ¼” blade can cut a tighter
radius. However, it takes a while to change
the blade and adjust the six blade guides.
Besides these are all going to be turned round on the lathe so it’s not
a big deal.
After rough cutting the blanks out on the bandsaw a 7/32”
hole 5/8” deep is drilled for threaded rod.
The 7/32” diameter is a little odd size but it is just slightly less
than the diameter of the ¼” threaded rod. I do that so some shallow threads get cut
into the knob when doing the initial install of the rod. That’s done by using the drill press, rotated
by hand, to make sure the rod is square and true to the underside of the knob. That's so when it gets tightened the knob lays flat against the top of the sanding
block.
Sizing a section of threaded rod that will get epoxied in
the knob is next. The procedure is a
little more involved than just using a bolt cutter or hack saw to cut the rod
to length. Either one of those damages
the threads at the cut making it hard to start in the brass insert and I want
the rod to easily start and have no sharp edges at the cut. The photo below shows the threaded rod
clamped in place with a piece of tape marked with the 1¾” length needed. On the left is a ¼-20 die that will be used
to chase the threads after the cut.
Also, in the background you can see three finished pieces ready to be
epoxied in place.
This is after the rod has been cut and you can see the
resulting burr on both pieces. From here
the long rod is removed from the clamp, the rough end ground smooth and the die
spun off the rod to reform the threads.
Last, the short section of rod to be used gets its end cleaned up by
grinding the rough end smooth then running the die from the good end to reform
the threads.
Next the sized threaded rod is epoxied in the cap place
making sure 1 1/16” of rod is exposed. A
pair of jamb nuts and a wrench lets me run them in.
After the epoxy cures overnight the cap assembly is
threaded in a lathe fixture made specifically for this purpose and a nut is put
on the threaded rod from the inside locking the assembly in place. The top photo shows the rough blank mounted
and the bottom one it turned down to a cylinder. The left white line is where the dome part of
the knob starts and the right line is the overall height.
In checking there was a problem with one knob where the
end of the blank was not square with the threaded rod. No idea why but it did need to be trued up so
it will lay flat on the sanding block’s body when tightened. Fortunately, it was not hard. Below shows the lathe setup. From the left a drill chuck clamps onto the
threads but not so tight that it deforms them.
Next is a couple of jamb nuts on the threaded rod that are tight to the
jaws of the chuck. To the right of the
knob is the lathe’s tail stock. It has a
live center mounted in it that applies pressure against the knob which gets
transmitted to the jamb nuts providing enough friction against the chuck that
the face can be turned true. That’s as
long as the tools are sharp and a light touch is used.
Next Up – Completing Knobs, Danish Oil Finish & Done
No comments:
Post a Comment