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sanding |
shop talk
Steve Condon
The fine (and coarse) art
of sanding and shaping
The following is part one of a two-part
series of insights on what I believe to be the most important and versatile tools in model
building — sandpaper and other shaping tools. In this first part, I will describe the
variety of sanding and shaping tools that can be made or purchased and some of their uses.
In part two I will go in-depth on sanding and shaping tricks and techniques. If you have a
sanding trick or technique that you would like to share with Gull Wings readers, please
submit it to me for inclusion in next month’s article.
Whether you're removing the flash from the
seam of your beautiful all-glass molded model, or roughing-out an all-wood fuselage, using
the proper tool will make the job easier and the result more desirable.
Sanding blocks:
The sanding block is a tool common to most
every modeler's shop. How many do you have? How many do you use? I have found, over the
past 30-odd years of model building, that you can't have too many sizes and varieties of
sanding blocks. Some may only see occasional use, but when you are at a critical stage of
a project and you're thinking, "what can I use to sand in that tight little
spot?" they earn their keep.
Sizes and varieties:
The leading edge block. My favorite
block for this purpose is a piece of 2" square aluminum stock 24" long that a
friend of mine gave me. I use adhesive backed sandpaper (the gray stuff made by 3M) that's
41/2" wide and put 100 grit on two sides and 220 grit on the other two. Having both
grits on the same block saves a bit of time when shaping leading edges and other surfaces
that require a long, straight block.. My favorite
block for this purpose is a piece of 2" square aluminum stock 24" long that a
friend of mine gave me. I use adhesive backed sandpaper (the gray stuff made by 3M) that's
41/2" wide and put 100 grit on two sides and 220 grit on the other two. Having both
grits on the same block saves a bit of time when shaping leading edges and other surfaces
that require a long, straight block.
The all-around block. I liked using
the aluminum stock block so much that I got another piece 9" long (the width of a
sheet of sandpaper) to use with other grits. I must admit, however, that I prefer the
adhesive-backed paper to bonding other types of paper to the block with spray adhesive. I
bought three rolls (available at Tool Mart or other tool specialty stores) of 80, 100 and
220 grit about three years ago and I still have a lot left. The rolls were around $10
each. On this block I have the 80 and 100 grits and find it useful for many rough sanding
applications. Another good base for this type of block is a 1" thick piece of
hardwood at least 2" wide and 9 to 11" long. I liked using
the aluminum stock block so much that I got another piece 9" long (the width of a
sheet of sandpaper) to use with other grits. I must admit, however, that I prefer the
adhesive-backed paper to bonding other types of paper to the block with spray adhesive. I
bought three rolls (available at Tool Mart or other tool specialty stores) of 80, 100 and
220 grit about three years ago and I still have a lot left. The rolls were around $10
each. On this block I have the 80 and 100 grits and find it useful for many rough sanding
applications. Another good base for this type of block is a 1" thick piece of
hardwood at least 2" wide and 9 to 11" long.
The all-important small block. One day
I was building a hand-launch model and realized that I needed a small block to sand
something down inside the fuselage. At that time I found myself sidetracked into making a
half dozen sanding blocks out of a piece of pine and putting a variety of sandpaper grits
on them . Most of these blocks are 1" wide, 3/4" thick and about 4" long.
Another two are 3/4" wide, 3/8" thick and 8" long. I have found these to be
very valuable blocks for sanding small areas or in tight quarters. One day
I was building a hand-launch model and realized that I needed a small block to sand
something down inside the fuselage. At that time I found myself sidetracked into making a
half dozen sanding blocks out of a piece of pine and putting a variety of sandpaper grits
on them . Most of these blocks are 1" wide, 3/4" thick and about 4" long.
Another two are 3/4" wide, 3/8" thick and 8" long. I have found these to be
very valuable blocks for sanding small areas or in tight quarters.
Rubber sanding pads. For wet
sanding, finish sanding or for shaping any curved surface, an automotive color-sanding pad
works very well. If you've never seen one, they're made of 1/4" thick semi-porous
rubber and are 2 1/2" by 5 1/2" (the perfect size to wrap a half sheet of
sandpaper around). It has a series of holes in it and one side has nubs on it to aid in
"cutting" while the other side is smooth for finish sanding. This type of pad
can be purchased at any automotive paint store. For sanding wood or glass fuses, wing
surfaces and small parts with curved surfaces, nothing works better. For wet
sanding, finish sanding or for shaping any curved surface, an automotive color-sanding pad
works very well. If you've never seen one, they're made of 1/4" thick semi-porous
rubber and are 2 1/2" by 5 1/2" (the perfect size to wrap a half sheet of
sandpaper around). It has a series of holes in it and one side has nubs on it to aid in
"cutting" while the other side is smooth for finish sanding. This type of pad
can be purchased at any automotive paint store. For sanding wood or glass fuses, wing
surfaces and small parts with curved surfaces, nothing works better.
Power tools:
Sometimes it is simply necessary for
"more power!" When you have a lot of material to remove or you just want to
expedite the job, power tools are the way to go. A word of caution though, don't try
taking too much of a short cut with your power sander. If you need to bring
something into a precise tolerance, use your power sander to get it close, then finish it
with a block or other precise hand tool. Like my dad always says: "Do it right the
first time!" He's an engineer and was always amazed that there never seemed to be
enough time to do it right the first time, but their was always time to do it right the
second time. The moral is to take your time and get it right.
Belt/Disc sanders.This is probably the
favorite and most used tool in my shop. I have a bench-top combination 4" belt and
8" disc sander that I bought through the Penn State Tools catalog a long time ago for
about $120. I don't see how I ever got by without it! It has a table with it that you can
switch between the disc and belt, but I seem to leave it on the disc at all times. I keep
the belt in the horizontal position so I can hold small parts in my hand and work them
over the belt. There is even a fence you can put across the belt so you won't launch your
work across the shop. I generally don't use it since I find it cramps the
"freeform" style of sanding--and, yes, I occasionally launch pieces of work
across my shop! My shop teacher would surely cringe.
Orbital sanders. Nowadays you can buy
a palm orbital sander for a reasonable price. Makita, DeWalt, Porter Cable and Black &
Decker all make nice ones. The ones with the dust collector are more desirable, not
because they suck-up some of the dust, but because they keep dust from being trapped
between the paper and work and eventually clogging the paper. These tools work well for
sanding the surfaces of many things, including wood-skinned wings. Here again, don't get
carried away! These things can remove material fast and get you in trouble. I know a guy
who got so into making his Obechi wings smooth and ripple free that he unknowingly thinned
the sheeting about 75%. He made a beautiful model, but removed much of the strength of the
wing. And then one day on a healthy winch launch — BANG! Toothpicks of very nicely
sanded Obechi drifted down from 400 feet to cover the field.
Drum Sanders. Another set of tools
that I use every once in a while, but am thankful I have, is the various sizes of drum
sanders that fit in my drill press. They're made of hard rubber and come in a number of
diameters. Pre-formed sanding drums of various grits slide over and are held in place by a
nut which expands the rubber slightly. I bought a variety pack of these at Tool Mart for
less than twenty bucks--including a bunch of drums. When you must have a precise concave
curve, the drum sander does the job. Another set of tools
that I use every once in a while, but am thankful I have, is the various sizes of drum
sanders that fit in my drill press. They're made of hard rubber and come in a number of
diameters. Pre-formed sanding drums of various grits slide over and are held in place by a
nut which expands the rubber slightly. I bought a variety pack of these at Tool Mart for
less than twenty bucks--including a bunch of drums. When you must have a precise concave
curve, the drum sander does the job.
The Dremel Moto Tool. The
versatileDremel Moto Tool and Mini-Mite are great power tools for shaping and removing
material in curved or tight spaces. I find that the little drum sander works very well for
shaping the pieces of a fiberglass fuselage around the canopy, wing saddle, servo tray and
other spots. If you need to make a curved slot in your fin for the rear rod of a
full-flying stab, a moto tool works great. I'll describe a simple jig for doing this in
next month's column. I have found it to be a good investment to buy some carbide bits for
my Moto tool. They cost about $8 each, but cut through most things like warm butter.. The
versatileDremel Moto Tool and Mini-Mite are great power tools for shaping and removing
material in curved or tight spaces. I find that the little drum sander works very well for
shaping the pieces of a fiberglass fuselage around the canopy, wing saddle, servo tray and
other spots. If you need to make a curved slot in your fin for the rear rod of a
full-flying stab, a moto tool works great. I'll describe a simple jig for doing this in
next month's column. I have found it to be a good investment to buy some carbide bits for
my Moto tool. They cost about $8 each, but cut through most things like warm butter.
Sanding alternatives
The block plane. A little block plane
is the first thing I use for rough-shaping a spruce leading edge. With practice (and a
sharp plane), you can get an almost perfect leading edge shape that requires very little
sanding. It is important to test the setting of the blade before just digging-in. Planes
also work well to do the initial knockdown of the corners of a wood fuse. A little block plane
is the first thing I use for rough-shaping a spruce leading edge. With practice (and a
sharp plane), you can get an almost perfect leading edge shape that requires very little
sanding. It is important to test the setting of the blade before just digging-in. Planes
also work well to do the initial knockdown of the corners of a wood fuse.
Rasps. These are very coarse
tools that generally only get used for a short time on the initial shaping. A Sureform
rasp works well to remove big flashing from molded fiberglass parts.. These are very coarse
tools that generally only get used for a short time on the initial shaping. A Sureform
rasp works well to remove big flashing from molded fiberglass parts.
Files. Certainly one of the most used
tools in my shop area variety of files: Certainly one of the most used
tools in my shop area variety of files:
Needle files are great little tools
for fine shaping of everything from servo tray cutouts to precision holes for incidence
pins and the like. You can buy them in a set that generally includes 10 to 12 shapes. I
use these all the time. If you want to find them inexpensively, go to the swap meet or try
the tool vendors at the IMS show. I found a medium size set at the swap meet that I use
more and more. are great little tools
for fine shaping of everything from servo tray cutouts to precision holes for incidence
pins and the like. You can buy them in a set that generally includes 10 to 12 shapes. I
use these all the time. If you want to find them inexpensively, go to the swap meet or try
the tool vendors at the IMS show. I found a medium size set at the swap meet that I use
more and more.
Combination or Bastard Files
are
great for many modeling jobs. They make an easy tool for precisely shaving down the seams
on molded airplanes. are
great for many modeling jobs. They make an easy tool for precisely shaving down the seams
on molded airplanes.
A mill file works perfect when you
need a precisely flat trim job on surfaces that include mixed materials (like where a
brass tube comes through the surface of a fiberglass fuselage)
Scrapers
Last but not least, the cabinet scraper is a tool that comes in handy occasionally. This is nothing more than a piece of steel
with a burr on one edge. This is another good one for removing material from a leading
edge before sanding. Scrapers can be purchased at tool stores for a few bucks or you could
make one with a small piece of steel. Use a file to pull a uniform burr on one or two of
the edges. Be careful not to cut yourself on it!
That's it for ‘shop talk this month.
Again, if you have any sanding or shaping tricks that you would like to share, please
write it down and e-mail or otherwise send it to me.
The fine (and course) art
of sanding and shaping — II
Last month we discussed a variety of
different sanding and shaping tools and their best applications. In this month’s
column I want to share some tricks and techniques for making the most of those tools.
Block sanding techniques
Probably everyone has used sanding blocks
at one time or another for building a model. The basics, of course, are that you generally
want to sand with the grain, unless you just want to remove a lot of material in the
"roughing" stage.
If you're doing something long like a
leading edge, be sure to start at one end with part of the block off the workpiece and
move the entire length of the workpiece. A very common mistake on a leading edge is to do
shorter strokes spending more time on the center portion and then ending-up with a curved
leading edge. To avoid this, do long end-to-end strokes and stop frequently to make sure
it's still straight. Good overhead lighting is helpful for easy inspections.
If you're going for a precision finish,
such as to angle a root rib perfectly straight/flat to butt-up against the fuse, it is a
must to have the sandpaper glued to the block. Again, the adhesive-backed sandpaper that
is sold in rolls is an easy way to quickly attach the paper to a block. You may get away
with a loose piece wrapped around the block, but it is more difficult to make an accurate
"cut."
On this type of operation I like to place
the work on a bench surface. If you're sanding a delicate wing, put a towel folded
lengthwise on the work surface to avoid denting or scratching the wing. It is best to hold
the work firmly so you can get the proper leverage. New sandpaper is also helpful to make
an accurate cut possible. I generally prefer short, slow passes with a firm grip on both
the block and the work to ensure that I'm not rocking the block in any way to end-up with
a curve where I need it straight. It is also helpful to have a light pencil line to sand
to so you know exactly where you need to stop. If you do this, decide if you want to stop
short of the line, or "eat the line." I prefer to use a drafting pencil for a
thin line and then sand through half of it
Planing Techniques
One of the best tools for making accurate
cuts (especially on wood leading edges) is a block plane. Two things that are essential to
planing success are the proper setting of the blade (DON'T try to take too big of a cut!),
and the sharpness of the blade --the sharper, the better. If you don't have a sharpening
stone, now would be a good time to buy one. Planing with a dull blade is like trying to
slice a tomato with a dull knife--you smash it instead of slicing it. A good sharp edge
makes a huge difference.
As for technique, it is proper to hold the
plane at about a 30-degree angle to the direction of movement. Tip: test the depth of the
cut on a piece of scrap first! If you are planing a spruce leading edge on a balsa or
obechi sheeted wing, a good safety measure is to place a piece of 1" masking tape on
the sheeting about 1/16" back from the leading edge stock. This way if you
accidentally angle the plane too much toward the wing surface, you hit the tape and not
your sheeting (unless you are trying to take too big of a bite). The blue painter's
masking tape works very well for this since the adhesive is not so strong as top pull-up
any grain when you remove it.
Orbital sanders
I think the important thing to remember
with orbital sanders is not to over-do it. If you plan to have a natural wood finish, keep
in mind that orbital sanders tend to leave small "swirls" in the grain that
don't really show-up until you put the finish on. In this case, using 220 or 320 as the
coarsest cut will make the swirls less noticeable. For doing the rough curves or rounding
the corners of a wood fuse, an orbital sander with something like 60 or 80 grit gets you
there in no time. Again, don't over-do it!
Moto-tools
Ever wonder how the "pros" get
such a neat slot for the bell-crank in a fiberglass fin for a full-flying stabilator?. In
last month's column I mentioned a trick for making this slot using a moto-tool. Well, this
is how I do it.
On models like an F3B Eagle or anything
else with a full-flying stab, once the pivot tube is installed, the tricky part is to cut
a smooth slot in the right place. All you have to do is take a piece of 1/4" ply and
drill a hole the same exact diameter as the front rod for your stab. It is best if the
hole is slightly undersized so the rod fits tight enough that it won't fall out. Then,
carefully measure the distance between the centers of the two rods. Drill a hole at that
exact spot in your 1/4" ply (it helps to use an awl to poke a little pilot hole) the
same diameter as the shaft of the cutting tool (or even a drill bit) for making the slot.
I have found it helpful to mark the top and bottom of where I want the slot by putting
pieces of masking tape on the fin at the extremes of elevator throw. After you are
satisfied with where you'll be stopping, slip the pivot rod into the piece of ply, the
cutter into the ply, and then place the whole assembly over the fin with the rod through
the pivot tube.
Do a few test passes with the power off to
get the motion figured-out. You will want to be sure the fuse is stable so nothing will
move when you start cutting. Another precaution to take at this time is to make sure the
bellcrank on the inside of the fin is out of the way of the cutting tool! Not taking these
precautions could result in a very ugly situation.
When satisfied that you are ready to
proceed, turn on the moto-tool and carefully plunge the cutter into the fin a small
distance from one end of the prescribed arch. It is important that you keep the moto-tool
at a 900 angle to the fin during the cutting process. Move from the starting
point to one end and then back to the other end stopping precisely at the tape you've put
on the fin. Flip it over and repeat the process. Test fit your stab and make sure both
slots start and stop in the same spot on both sides. "Clean-up" the slots as
necessary and you are finished.
That's it for ‘shop talk this
month. Next month, I'll be sharing some tips on the application of epoxy resin for
bonding, finish and filling.
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