HAZARDOUS MATERIAL REMOVAL

Last modified: Saturday, January 6, 2001 6:20 PM

Sanding's no fun. Wives don't like to be handled by husbands whose arms are covered with a white fuzzy dust or plastic chunks. That, and the other techniques which remove material from your pattern are among the most unglamourous aspects of modeling (there's a glamorous side to this kind of modeling?)-- The processes are usually tedious, messy, and potentially dangerous. Yet, they're unavoidable and an integral part of the hobby. Major remodeling has two complimentary aspects which shape the pattern-- you add material, and you remove material. In both cases, your goal is to shape the material and ultimately give it a surface "finish", or texture.

Elsewhere in the web site, I discuss some materials for the additive process-- clays, putties. You glop these on, give them a rough shape and fine tune them as much as possible. In this first stage of sculpting, both aspects are integrated in the process, since the material is malleable. However, once the material is hardened- through baking or curing- the processes become more distinct.

Unless you're really good, the results of your first stage shaping probably won't be good enough. Sanding will show you that curves and flat surfaces aren't as uniform as you had thought. Lines might not be as sharp as they should be, or perhaps surface detail isn't as defined as you'd like. This leads to the observation about the general process of shaping: organic/expressive forms are easier to produce in soft materials, whereas precision/mechanical forms are easier to produce in hard materials.

This is a somewhat intuitive observation: if you want a crisp line in clay, it's going to be sharper if you cut it in hard clay than if you impress it in soft clay-- the soft clay surrounding the impression will tend to deform with the pressure. That's true of sculpting detail in general-- stiff clays work best for fine detail. Note that it isn't necessarily going to be easier to cut the line in hard clay since if you freehand the cut, the line may drift and the cut depth will vary. But the edges will be sharp and crisp. If you don't have the machining tools that allow you to cut a line with mechanical precision, you can use a combination of the two processes to "fake it": impress the line in soft clay, bake it, and sharpen the edges in the hard clay by cutting or sanding the surface.


TOOLS

Because it's such broad territory, there are a number of tools which can be used in the subtractive processes. They all work by using their abrasive qualities to remove material.

Engraving and Detail: Exacto blades, scribing tools, pin vise drills, files, & the Dremel Mototool. The manual tools are more controllable for minute detail work. However, an engraving or tiny cutting bit on a Mototool is indispensible for freehanding relief cuts in a tiny area very quickly.

General Shaping and Contouring: sandpaper, steel wool, the Mototool and various types of motorized sanders.

Finishing: Since finishes can range from intentionally rough to glass-like, you can take this as far as you want to. The rough finishes are the easiest of course, and for matte finishes, you may not have to go above 400 grit sandpaper. For higher gloss finishes, you can use a variety of superfine grit sandpapers, plus rubbing and polishing compounds. (Specific products are mentioned in my angst-filled Tamiya Motorcycle article.)


SAFETY

One very important and unfortunate aspect of removing material is that it creates a mess. Sanding resin, epoxy putty and clay creates very fine particles which become airborne and find their way into your lungs. They're not good for you. Needless to say, if you value your health, you'll prevent this from happening by wearing a facemask respirator with the appropriate filtering qualities. What doesn't end up in your lungs will end up everywhere else, creating a nasty cleaning nightmare if you do it indoors. Ideally, you should use some type of sanding box (like a spray painting booth) which contains and evacuates the particles from your immediate area (and into the great outdoors for the general population to enjoy). I occasionally use a vacuum cleaner hose secured nearby to help suck away dust particles as I work when doing really nasty power grinding (don't think it's too good for the vacuum cleaner though). If you're using wet/dry sandpaper, it's a good idea to use it wet-- besides producing very good results, it also keeps the soggy particles from becoming airborne.


TOOL REVIEW: DREMEL CONTOUR SANDER

(07/99) This is a fairly new tool from Dremel, and appears to be marketed at the mainstream Do-it-Yourselfer interested in woodwork for things like sanding the dowels in chairs. It's a handheld A/C motorized tool, similar in size to their Mototool, and is intended to spare you the trouble of hand sanding contoured areas.

The "business end" is a 2-inch long slot at the front, into which you can slip rubber forms, molded into different shapes-- concave, convex & blade-edged. The contours have different radii, and an optional set of forms is available in case the one you need isn't included in the standard package. Additionally, a flat almond-shaped plate is provided for non-contoured, and detail sanding.

Naturally, this is designed to use Dremel's special sandpaper-- the contour forms are fitted with a tube-shaped piece of sandpaper, and the plate is backed with velcro to fit special almond-shaped sandpaper. The refill packs aren't cheap either. The good news is that you can cut regular sandpaper to wrap around the contour forms; the bad news is that you can't easily convert regular sandpaper to fit the plate.

The sanding motion is short front-to-back strokes (versus orbital), and the speed is continuously variable from 4000 to 8500 strokes per minute. It's pretty quiet at the low speed, but noisier than their mototool at full tilt, no doubt due to the more complicated reciprocating mechanism. I probably don't use it in the way they intended-- instead of swapping out contour forms, I stick with a thin one and do contouring by manipulating the tool, using different areas of the surface. It's fairly light, quiet, and easy to use in fairly small areas. The on/off switch on top seems a little too far forward, but that's probably the best place they could put it. I'm also not fond of where it exhausts hot air-- it's exactly where I want to grip the tool.

I don't know if I can strongly recommend this tool for this particular hobby use, unless you've got money to burn and are a gadget freak (It's about 70-100 bucks). It's not a "must-have" tool. It's faster than doing it by hand, and you can focus it's power on problem areas more intensely. But finish level sanding isn't unbearable by hand (machine sanding isn't what I'd call fun either) , and your hand has a better ability to adapt to contours. Tools like this tend to produce undesirable flat areas more easily because they do the job more quickly, and you don't have that direct tactile feedback. Another thing is that the machine is heavier than a piece of sandpaper, so it's doubtful that you're sparing yourself that kind of fatigue. However, for small hobby use, it's a better choice than a heavier and awkward-to-handle orbital palm sander.