hole in the base for the bottom set is 3/4 inch to 1 inch
from the edge and centered in the channel. Measure
your throat depth back from this hole to locate the
front vertical tube. The front face of the tube should
be at the exact distance you noted earlier to set the
throat depth. Use a small 1/2-inch piece of scrap tubing to mark the post and bolt-hole location.
Using a 1/2-inch tall piece allows your marker or
punch to reach the channel easily. The second vertical post is simply a stiffener for the frame, and its
position doesn’t matter much, so just make sure it’s
perfectly in line with the front set hole and the front
post. Once you have the holes located on the base
channel, drill them out with a pilot bit and use them
to transfer to the top tube after marking a centerline
on the top tube.
The holes for the vertical support post bolts
only go through the bottom of the top tube. The
front hole for the spring-loaded set needs to go all
the way through. Don’t drill this hole unless you have
the set on hand to make the proper size hole. A hole
that is too large will allow the set to wobble, and this
will open up opportunities to damage the material
Once you have all of your holes drilled to full size,
insert the front 7/16-inch bolt through the bottom of
the base channel, slide the front vertical post over the
bolt, then put the top tube in place. An extension magnet is useful here in getting the threads started
because access down inside the tube is obviously too
tight for fingers.
Once the nut is started on the threads, use a flat
screwdriver stuck down the tube to jam the nut in
place while you tighten the bolt end with a socket or
wrench. This is the difficult one, and once it’s done,
the second vertical tube can be put in place and the
process repeated. The nut on the rear bolt is much
easier to access to tighten it down, but it will still
need to be tightened from the bolt side (underside of
the C-channel) in the same fashion.
The sets can then be put in place, and there are
several options for the base set. I have one that sits
down on the base for dimpling skins, and another set
that sat on top of an extension so I could dimple
channels. The top tube set can either be spring
loaded or free falling. To make it spring loaded, simply add an adjustable collar and then install a spring
between it and the top tube. You can set it at whatever height desired.
Once materials are on hand, this C-frame can
be constructed in less than one hour. You may want
to take this even further and build a C-frame dimpling table, but that’s a project for another time.
Don’t forget to paint the C-frame to protect it from
Your One-Stop Prop Shop Only Sensenich Offers You the Choice: Wood, Metal, or Composite Adjustable
Wood and Metal
for Rotax 912,
propellers feature lightweight
metal-edge hollow blades
and easy, accurate, foolproof
Touch the stop
to the pin, tighten
the bolts, and it’s adjusted!
Lancaster, PA Plant City, FL