Scale Modeling Techniques, Tips and Tutorials
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Filling Seams and Sanding Scale Model Aircraft

Removing the seams and joint lines is necessary when building model airplanes. Many assemblies often result in unnatural gaps or cracks in the fitting. Among the most common problem areas are the wing roots and the mating lines between both sides of the fuselage. To produce an authentic looking aircraft model, I recommend the following technique.

To begin, you will need various grades of sandpaper, including 600ALO, 400ALO, 320SIL and 150SIL. Other necessary tools include; a sharp hobby knife, a paintbrush and a container with a small amount of water. We will also cover the use of model putty and Tenax-7R, a fast-dry formula used for welding plastic scale model parts.

I should remind the reader that when building model airplanes using hazardous materials, it is very important to have plenty of ventilation around the working space. You should also pay close attention to all the warnings that come with each chemical, usually found on the product container.

This technique will be illustrated using the fuselage parts of the aircraft model. You can begin by welding the left and right sides using Tenax-7R. With medium pressure, hold both sides of the fuselage together and simply touch the entire seam using a paintbrush. Once you have completed the application, gradually increase your hold pressure over the next 10 seconds until you have a firm bond. Tenax-7R will actually fuse the plastic scale model by slightly melting the parts together. Allow about 5 minutes for the weld to dry and lightly scrape off any excess chemical using a hobby knife.

Should there be any imperfections on the aircraft model, such as gaps, pits or scratches, you can apply model putty (filling material) using a toothpick. Be very careful not to smudge or place it on areas where it is not necessary as excess putty will go a long way in hiding surface details such as rivets and panel lines. If possible, mask off the crack or opening to be filled using tape. Then, apply a thin coat of putty and allow about 30 minutes for drying time. Once the putty has dried completely, sand the area down to the level of the tape using 600 ALO sanding paper. If the gap has not filled, or if the putty has dried and contracted to a groove between the parts, re-apply more putty and repeat the dry time and sanding process. Once you have a level surface, remove the tape and begin fine sanding your work.

As one of the most important steps in building model airplanes, the sanding process should be very meticulous. You can begin sanding the aircraft model using 600 ALO paper to go over all the areas where putty and Tenax-7R was used. Be extra cautious not to sand off too much, as you may end up losing some of the finer surface details. You can then dip a paintbrush in water, and moisten the entire sanded area. Once again, using 600 ALO paper, wet sand the area until it begins to look smooth. For an accurate sanding job, this process should always be done under a strong light so that rough areas can easily be spotted. Before moving forward, clean your aircraft model using water and dry it with a rag or paper towel.

Once the plastic scale model has dried completely, do a thorough check for rough patches and use 400 ALO or 320 SIL paper to repeat the process, sanding and wet sanding the working area. You can complete this technique using a fine 150 SIL sanding paper. This final sheet will leave your aircraft model looking smooth and natural, without any visible blemishes. This step does not require wet sanding. Simply run your 150 SIL paper over the entire sanded area. Once this is complete, your aircraft model is ready for painting.

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