Control Line Aerobatics - 2011/03

IT’S TIME TO get back to our discussion of properly setting up and
equipping a shop to build a CL Aerobatics (Stunt)—or any other type
of—model. Before beginning I’d like to extend a “Thank you” to all
who have written, called, and/or e-mailed me about the “shop setup”
series.
In all the years that I’ve been writing columns, no other subject
that I’ve covered has been as well received as this one. It seems that
many want and enjoy tips on shop setup and tools.
I left off in the September 2010 column with a discussion of
sanding tools. I promised then that I would tell you what I feel are the
best and most useful kind available. No more suspense; it’s Perma-
Grit!
What is Perma-Grit? It’s a line of sanding, filing, and grinding
implements that feature bits of tungsten welded to metal plates, sticks,
and grinding bits. The tools are indispensible for quality, efficient, and
effortless model building.
I purchase all of my Perma-Grit products from Bob Violett Models
(BVM). The Web site shows all of that brand of tools that BVM
carries.
There are so many different and unusual Perma-Grit tools that a
complete discussion of them here would be impossible. Instead I’ll
give you the skinny on my favorite instruments in the company’s line
and tell you why they are just that.
Without a doubt, the Perma-Grit tool I use most in my shop is the
22-inch-long Sanding Block (item SB-560). It features two Perma-Grit
sanding strips: one Fine Grit side and one Coarse Grit side.
The sanding strips are adhered to a precision aluminum extrusion
that measures 2 inches wide by 19/16 inches high by 22 inches long.
The same height and width extrusion is available in two shorter
lengths, and one of those features wedge-shaped ends to allow easy
access into tight areas.
I use the 22-inch-long Sanding Block for many modeling jobs. It’s
great for truing the LEs and TEs on freshly covered foam-core wings
and works well when shaping foam fuselage top and bottom bucks
that will be used for making molded shells. However, my favorite use
for this tool is truing the edges of balsa sheeting pieces that have been
edge-trimmed with a knife.
To achieve a perfect square edge that will fit together with no gaps
and will butt-glue accurately, set the Sanding Block on its side (the
extrusion that the bar is based on is so accurate that it presents a square
side no matter which edge it is laid on). Position it against the edge of
a piece of 3/4-inch-thick chipboard or plywood.
Lay a trimmed balsa sheet on the chipboard, against the fine-side
edge of the Sanding Block. Then use a Great
Planes aluminum sanding bar fitted with 80-
grit sandpaper to hold the balsa sheet down
against the chipboard and the edge against
the Sanding Block. Push the balsa sheet fore
and aft against the bar until the edge is trued.
I’ve included a photo of this process that
(I hope) will explain it better. With the edges
trued in this manner, you can achieve a fit
that is airtight, requires little glue, and won’t
show later when you apply the finish to the
model.
Another pesky job is smoothly blending a
soft balsa surface into a hard surface, such as
plywood, without having a lump or
depression where the dissimilar materials
meet. On a CL Stunt model this would
include blending the fuselage sides into the
top block and the cowl block where they
meet the spinner. There are usually plywood
doublers beneath the balsa fuselage sides,
Sanding tools that should be in your shop
[[email protected]]
Control Line Aerobatics Bob Hunt
Perma-Grit offers a wide variety of extremely useful hand tools that can ease your
model-building chores. Once you get one, you might want them all!
Blending hard materials smoothly into soft materials—such as
shaping the front of a fuselage to flow into the spinner—can be
challenging. The Perma-Grit Flat Full Length Hand Tool makes
this chore painless.
The Perma-Grit 22-inch-long Sanding Block can be used, as
shown, to true the edges of balsa sheets, allowing them to be
edge-glued accurately with no gaps. A Great Planes aluminum
sanding block is shown being used as a gripper/pusher.
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and they need to be blended in a compound
curve to flow smoothly into the spinner.
Several Perma-Grit tools make this job
easy, such as the Flat Full Length Hand
Tools (items F-100, F101, and F-102). Each
measures 9 x 11/2 inches and comes in three
grits. These instruments provide precise
sanding and are extremely easy to control, to
accomplish the required blending of soft
materials to hard.
I’ve included a photo that shows the nose
of a typical CL Stunt model that was sanded
to shape using a Flat Full Length Hand Tool.
This job used to be a nightmare for me;
now, with the help of Perma-Grit, it’s easy!
I have a complete set of Perma-Grit
Hand Tools that came in a pouch. I don’t see
that grouping on the BVM Web site, but all
of the implements in the set that I have are
available separately, so you can choose
which ones will work best for your
aeromodeling applications. I’ll bet that when
you get one, you’ll soon order all of them!
These tools are available in a variety of
shapes, including several constant-diameter
rounds, angles, concaves, and half rounds.
I’m including a photo of the pieces that came
in my set.
Another great Perma-Grit offering is the
Flexible Strip (items FXT-103 and FXT-
104). The two types are essentially the same
sandpaper pieces that are adhered to the
extruded sanding bars, but they are sold
separately. These strips can be used in the
manner of the Flat Full Length Hand Tool
for deft shaping, and they can be cut with tin
snips to any size or length you desire.
I have cut a 3/4-inch-wide piece off of one
of the strips and use it as a tool with which to
open hinge slots to a perfect size, to allow
the hinge to slide in without spreading the
wood on either side. It has made hinging
painless!
An indispensible Perma-Grit item is the
Needle File set (item NF-1). These tools
come with comfortable handles and are great
for working in small areas and with materials
with which regular needle files have trouble.
There is also a huge selection of Perma-
Grit Rotary Files (grinding bits). My favorite
is the 10mm Diameter Ball (item RF-8c),
which is wonderful for hogging out the
majority of balsa when hollowing a cowl
block or carved-balsa wingtip blocks. Other
rotary tools include a selection of Cutting
Disks.
A Perma-Grit video is available that
explains each tool and suggests many ways
to effectively use it on balsa, plywood, and
composites. It also shows how to clean and
care for your Perma-Grit tools. Do yourself a
favor and get a copy of this DVD before you
start using your purchases.
This line of tools truly needs to be in
every modeler’s shop. These implements are
not inexpensive, but they are priceless!
Till next time, build and fly Stunt! MA
Sources:
BVM
(407) 327-6333
www.bvmjets.com
Precision Aerobatics Model Pilots
Association
www.control-line.org