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SPECIAL TOOLS ABRASIVES
Abrasion, more often called 'sanding' by those who don't make much use of machine tools - is the means by which we reduce the thickness of the surface whose form we wish to alter; material is abraded away in a controlled, precise manner; with each stroke of the file, sanding block or Flexi-File we alter the shape of the work, leaving in our wake a powdery trail of substrate dust mixed with lost abrasion particles. Cutting typically divides one material into two materials, each of which is a significant fraction of the former whole. Abrasion, on the other hand, is a cutting action that removes very small amounts of material the abraded material representing a very small fraction of the whole. With classic sandpaper your dealing with thousands of tiny knife like particles adhered to a flexible (sometimes stiff) backing; paper with glue bound graduals of sand, flint, garnet, emery, aluminum oxide; oxides of Tin, Iron, Chromium and Manganese; diamond, or silicon carbide to name a few of the commercially available abrasive materials. Abrasives are secured to paper, flexible plastic sheets, canvas, leather, to wheels; embedded within the matrix of cut-off wheels; or are suspend in oil, water, fat, or are applied directly in powder form and worked with a cloth this is called polishing.
Many of today's paper backed abrasives are suitable for wet sanding.
Abrasion is a process of reduction. As counterpoint, sculpting, as I apply the term here, is a process of addition and reduction:
One sculpts with wood, expanded foam, hard plastic, metal, Bondo, clay, putty, primer, and even adhesives.
Abrasion tools can be as course and mean as a sheet of #32 Garnet paper, capable of taking big ugly heaping chunks of material away with
each pass. Yet, other abrasion tools can be as subtle as a beautiful woman's breath in your ear: the finest of polishing rouges used to give a mirror like reflection on a gloss finish, for example. Abrasives, their
selection and use, are one of the first things you better understand and employ if your work is to be anything worth looking at!
Sandpaper is defined by a number a number that loosely translates to the mesh spacing of the sieves used to separate abrasive grain sizes
during manufacture. #100 grit sandpaper is very course (course to those who assemble kits and build models, though considered a finishing grit to Carpenter's). The higher the grit number, the finer the sandpaper.
Typically, a Model Builder will use descending grades of sandpaper as he works a surface: #100 grit for basic shaping. #240 to remove the
major scaring of the course #100, then down to #400 where you're ready for primer, #600 to sand the primer, and paint the colors. If you're after a gloss coat: lay down a heavy clear coat, then a light wet-sanding
with used #600, followed by a heavy wet-sanding with #2400, then on to buffing with abrasive pastes.
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The re-contouring of the upper hulls bow started with the build-up of two-part polyurethane fillers - that's fabrication by addition.
However, each time material was added, that operation was followed by abrasion - fabrication through controlled reduction, using file and sanding blocks. Later, still making use of abrasives, the FS-1 models bright
yellow surface was given a glass-like sheen with very fine sanding paper and a lot of hand polishing.
Wet Sanding
Most of the time it's enough to simply use the sandpaper dry. However, when you do a massive amount of sanding, particularly with the finer grits (anything under #400), where the grit particles are closer together and more susceptible to clogging, the introduction of water works to 'lubricate' the grit (making the sandpaper last a bit longer before 'dulling') increasing the cutting action. Wet sandings biggest asset is the waters action of washing away the abraded material and loose grit that would otherwise clog the sandpaper. Experience will tell you when to dry-sand and when to wet-sand.
Specialized Sanding Tools
Examination of the photo shows the many types of sanding tools that can be made with traditional sanding paper. Glued to sticks, backed by flat blocks, glued around a semi-circular block, tightly wound into a cylinder or attached to a stick and handle for getting into deep wells. I use CA adhesive mostly to glue sandpaper to small backing items. However, for the larger backing forms (sanding wheels and sanding blocks) I use 3M contact-cement, available in the spray-can.
Sandpaper is a very versatile tool in the hands of an imaginative craftsman. All of the sandpaper I purchase is industrial grade stuff, most
of it suitable for either dry or wet sanding.
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Wooden sanding blocks are the traditional way to back sandpaper when sanding flat or simple convex curved areas (a simple curve is a surface
that bends in only one plane). Soft foam backing blocks are used when you sand over or into complex (convex and concave) curved surfaces.
A fantastic tool that has come on the scene in the last decade is the semi-stiff sanding sticks offered by Flexi-file. Their Flex-Pad
sanding sticks - an abrasive glued to a soft flexible pad which in turn is adhered to a stiff plastic stick - perform most functions of a traditional sanding block, but have enough 'give' at the abrasives edges to
permit precise sanding within tight radius fillets, holes, and deep wells. Flex-Pad is available at most of the better hobby-shops. You can get the Flex-Pads in a variety of grits.
Oh
here's a tip: You can purchase much larger Flex-Pad like abrasive sticks at make-up/beauty and nail styling supply houses in town.
Typically, these stores will sell the abrasive sticks in packs of ten or more at a good discount. But beware, not all the grit numbers listed on these products (if they are listed at all) will equate with the grit
numbers you may have become familiar with. Don't know where these outlets are? Thumb through your local Yellow Pages listings or ask someone who works at a nail-boutique where they get their supplies.
If you can find an outlet, and they'll sell to you, look through the inventory: beauty supply houses have a lot of neat stuff that will find
immediate use by the kit-assembling/model building craftsman. Keep in mind that some of these outfits are exclusively wholesalers to the trade; so don't get your nuts in a bunch if they refuse to sell to just any
schmuck who wanders in off the street. Plan B is to sweet-talk one of the little gals at the nail-boutique to pick some abrasive sticks up for you. Hey!
Nothing ventured, nothing gained, pal.
Onto page 4
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