Re: Sanding round prop spars

From: Don Slusarczyk <don_at_slusarczyk.com>
Date: Thu, 24 Oct 2013 07:55:31 -0400

The method I use was told to me by Jerry Nolin way back when in regards
to making EZB prop spars (when they were~1.2gr so more like F1L) but the
method I use for other events with round spars. It is easiest to start
off with a tapered square spar but does not have to be. Then I sand the
corners a little using the V technique described below. The goal is to
get the spar to be able to roll easy on a flat surface. Then to do the
rounding and sizing you roll the spar between two sanding blocks. I use
two blocks about 4" wide and about 8" long. I typically use 220 grit
sand paper. The sand paper needs to be glued to the sanding block. The
one block I lay on the table and hold so it does not slide then lay one
side if the spar on the block and use the other block on top of the spar
then with almost no pressure (the weight of the sanding block) roll the
spar between the two blocks using a circular motion. A side to side
motion will not work, it must be circular. At the beginning you will
hear noise as the spar rotates on the corners, after a few motions the
sound goes away as the spar has been rounded. Also the spar may slide
out from the blocks when doing this so you just move them back to the
middle and keep going. Then to fine tune the taper you can move the
block closer to where you want to sand more off or apply pressure to the
block on one side more than the other. You can use a narrower block or
rotate the block so you are using only the 4" wide section so the
sanding is localized. The technique is more difficult to describe than
it is to actually do. You can make a nice rounded spar in about a minute
for each side of a prop. I have even started with 1/16 sq and then
rounded the whole spar then worked on one side at a time to get the one
side tapered then work on the other side so you end up with a one piece
prop spar tapered on both side. You want to keep track of how many
sanding motions you do so you don't over sand one side, or keep a
caliper handy. It is like making a glider wing or similar, 10 rotations
on one side then 10 on the other spar to be even. You can also make a
secondary block of say 320 grit to fine tune the taper but you will need
the 220 grit or even 150 to get the initial spar rounded, using too fine
a paper initially will take forever to round and use.

Don



> I have just made a set myself for F1D. Spars were sanded to a square
> cross section. Corners were sanded off by hand to make it roughly
> octagonal and the process completed by spinning the spar in one hand
> and using fine garnet paper folded into a 'V' to simulate a lathe
> function. The thin part at the tip requires the lightest of
> compression to avoid twisting of the wood. A micrometer provides the
> necessary checks. for roundness etc.
>
> No jigs required!
>
> Bob
>
Received on Thu Oct 24 2013 - 04:53:36 CEST