A Throttle Control Lever
                                  by
                              Ted Edwards
                            Ted_E@telus.net

Associated file: Throttle.jpg

My next door neighbour is building a small bi-plane and needs a control lever
for the throttle.  Some of the design and construction ideas may be of
interest to others.  He had already mounted an oak block on the fuselage with
a 1/4-28 bolt sticking out on which to mount the lever.

Ray laid out and cut out the desired shape of lever in 1/8" sheet aluminum
including a 3/4" hole for the mounting pivot.  A "washer" was then cut out,
1-1/2" OD by 3/4" ID and 1/8"+ thick, from a 1-1/2" diameter bar.  This was
welded to the handle to give a 1/4"+ thick area near the center.  This can
best be seen in photos 4, 5 and 6.

The handle was then mounted on an expanding mandrel set in the 3-jaw.  The
mandrel was brought up just snug and the handle pressed firmly against the
chuck jaws as seen in photo 4. The mandrel was then thoroughly tightened and
the handle faced off to the desired 0.250" thickness (photo 5).

The mounting base was turned from the same 1-1/2" bar.  A piece was cut off
long enough for a 1" diameter by 3/8" long section (to be used for holding the
part in later operations), a 1/8" thick flange, a 3/4" diameter by 1/8"
bearing area and a 0.560" diameter by 0.200" section (to be milled into a 1/2"
hex later) was turned.  (The set up for this later operation can be seen in
photo 1.)

The spin index sits on a block I made of just the right thickness to raise the
axis of the spin index to the axis of the lathe.  This made easy the task of
picking up the edge and offsetting 1/8" in toward the center.  Three holes
were drilled and countersunk for #5 flat head wood screws (photo 2).

The 1"D mounting portion now needed to be removed.  The spin index was used to
hold this awkward piece in the band saw (photo 3) and most of the unwanted
portion was cut off.  The workpiece went back into the lathe, held by the hex,
and the remnant of the mount gently faced off.

The cap needs to be restrained from rotating when the throttle is moved thus 
the hex.  The female hex in the cap was made by drilling a 1/2" hole and 
broaching with a piloted hex broach made from a piece of an old Alan wrench. 
The turned pilot undercuts the flat slightly to give a little rake to the 
points.  The broach can be seen with the rest of the parts in photo 6.

Two phenolic laminate friction washers were made from some 0.036" thick
material.  The OD was cut with a fly cutter (I don't have a 1-1/2" punch) and
the ID punched with a 3/4" Greenlee chasis punch.

The 1" diameter nylon friction adustment knob was knurled, drilled and tapped 
1/4-28 and cut to a 1" length.

The mounting mounting base will slip over the bolt in the fuselage and be
secured with the three #5 wood screws.  One fiber washer goes on next (photo
7), then the handle and cap (photo 8) and finaly, the knob.  The whole
assembly is shown on a piece of scrap plywood in photo 9.

The hexes slide freely along their axis but have very little rotational play.
Adjustment of the control friction is very smooth and easily ranges from very
free to plenty of stay-in-place.

A wodden ball will be epoxied onto the end of the lever (seen sticking up in 
photo 4).  A 3/16" hole will be drilled through the aluminum to lock the epoxy
in place.  The attachment for the control cable (at the opposite end) will be
left until the throttle travel at the carburator is known.