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Tech Tips

What Dentistry Can Do for the Modeller

Part 1: Filling

n by Frank Spahr


Being a dentist by profession, and modeller by interest, I have been using some tools and materials from dental supply that I think might be interesting for other readers of these pages.

What can dentistry do for the modeller? Quite a lot, actually, apart from dental prophylaxis and therapy :-). When you see what dental technicians do at work, the similarities with our hobby are evident. Many techniques easily blend into our modelling work. For some, you'll only need some basic materials, for others, the aid of a dentist or a dental technician.

Using Dental Wax as Filler

One of the jobs that I wholeheartedly dislike is filling gaps. I am always in imminent danger of smearing the putty over all those beautiful details (here comes my favorite term recessed panel lines), and I positively hate sanding. It vividly reminds me of the monstrous resin tooth we had to make quite early in dental school, a tooth 9 cm long and 3 wide and deep, and I can tell you, that meant lots of sanding.

As long as the filler is not required to improve the model's structural stability and it need not be applied over wide areas, dental casting wax is a very suitable and time-saving alternative. Nowadays, most filling means closing comparatively small gaps, most often at the wing roots of aircraft models, and this is where wax is the winning alternative.

Excessive filling done with dental wax is evident on the belly of 
Gromit's figure
.
 

Dental technicians use a number of different waxes for various purposes. For plastic models, we need a wax that has a comparatively high melting point and is rather hard, so that it can be scraped to a certain form. These demands are met by casting and aesthetic dental waxes, normally used to produce models of inlays, crowns and bridges that are used as masters for casting in metal. The required narrow range of tolerance in this process ensures that dental waxes used are of high quality. You can buy them in smaller or bigger sticks as well as in various colors, including red, green, yellow and blue. I use Schuler's Ästhetikwachs, which is ivory colored.

Tools and accessories

Some special tools will be required to use the wax. As a heat source you will need a small spirit burner. On the German modelling scene, electric wax heaters are currently available, but I find them a bit oversized and much too expensive for my purposes.

You will also need two tools. First a waxing tool - I recommend a cheap copycat of the PK Thomascolor #1 applicator (it's always gold in color) or another of similar shape. When buying one, take the #1 rather than #2 - it is smaller and more versatile.

The other accessory required is a small waxing knife, similar to the laboratory technician's common Le Cron knife, but smaller and sharper.

Apart from these, you will only need an old paintbrush, some Kleenex tissues, Q-Tips and white spirit.

Here are all the necessary tools. 
From top to bottom: Spirit burner, Le Cron knife and wax applicator.

Applying the wax

With the heated applicator, take a portion of wax and apply it to the model. Repeat that until you have filled a bit in excess. Allow the wax to cool down for a while. Now remove the excess wax with the knife, then smoothen and polish the surface with Kleenex and white spirit.

Of course, every new technique takes some practice to perfect. Make your first attempts on a piece of scrap plastic and try to find out how much heat is required, and how to handle the applicator with the wax on it. You positively don't need to heat your tool red-hot, which is contraproductive in several ways. Equally important is the temperature on application: too cold means that the wax will not leave the applicator's tip at all or so hesitatingly that it will settle down on the plastic in a single blob. Too hot means that you might damage the plastic with the overheated tool. 

Heated wax applied to the seam
 

Generally, stay rather on the cooler side, since you can always touch the wax with the freshly heated instrument, melting it again and allowing capillary forces to do their work. They are your real helpers with wax. The properly heated medium will be literally drawn even into the smallest crevices. This feature is  especially useful in areas where it is difficult to apply conventional putty.

Another big advantage is that you can correct nearly anything. You can scrape away the wax without doing damage to any model detail, quite different from using putty. You can reapply, scrape, smoothen and redo as long as you like.

To smoothen the filled area, use the waxing knife. When using Le Cron knife, be aware of its curvature. Try to avoid scratching deep into the filled area. Work from various angles in order to avoid producing grooves and scratches.

Finally, use a rather coarse brush to clean the waxing debris and always clean the surface with white spirit to assure paint adherence later on. Areas filled with wax can be painted regularly, but they may need an extra coat of primer. Ready!

Seams cleaned up with the knife and ready for painting.
 

The filled seams may not be exposed to heat and physical stress. Casting wax melts somewhere between 50-60 ºC, but softens earlier. A conventionally puttied area will have roughly the same strength as the rest of the model, but waxed areas are considerably weaker! Beware of flashlights on modelling contests...

To illustrate the technique, I liberally used wax on my Wallace and Gromit model, as seen in the pics.

The wax applicators are also beautifully suited when making antennae and rigging. I like the wires as thin as possible and consequently use only stretched sprue of an appropriate diameter. It can be easily attached with cyanoacrylate glue in a slack position so that it hangs somewhat. Tightening is achieved by carefully holding a heated wax applicator in the vicinity of  the sprue until it tightens out on its own. It takes several attempts and a learning phase until this works, but in my eyes, it pays off greatly.

n


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