Monday, November 3, 2014

Back to Basics 2: Getting Rid of Nubs

Nubs - those unsightly bits of protruding plastic on a part that has liberated from it's sprue - are an inevitability. The best a manufacturer can do is to undergate (to design a sprue in such a way that the gates will have minimum effect on a kit's appearance once assembled), but even then they still need to be cleaned off. Luckily this isn't difficult to do in most cases. Here's what you'll need:

1. Hobby Knife
2. Waterproof sandpaper in increasing grits (ex. 600 grit, 800 grit, 1000 grit, 1200 grit...)
3. Wash basin with water
4. Old soft-bristle toothbrush
5. Nail buffer (optional)
6. Paper towels


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Use the hobby knife to shave of the nub a little bit at a time. I prefer a short bladed knife because it feels more stable. You can place the part down on a flat surface such as a cutting mat and slice the nub off downwards, similar to how you would cut a vegetable...


You can also hold the part firmly with one hand and use the other hand to slice the nub. You can slice moving the knife away from you - this is safer but offers less control - or you can move the knife towards you, similar to how you would peel an apple.  This offers a bit more control, but you need to take extra care to avoid cutting yourself. If this is the only way to get at a nub, I suggest wrapping your knife hand thumb with some masking tape, or put a band-aid on it, just so the blade doesn't come in contact with your skin. Also, rest your elbows on your work table for added stability.


Shave down the nub as cleanly as you can, but be careful not to dig into the actual surface of the part.
You may also skip the knife altogether and go straight to the sandpaper if the nub is small enough.


Either way, you will have to smooth out the surface. Take some sandpaper and dip it in water, then sand the nub away. Start with a lower grit then work your way up to higher grits, smoothing out the scratches.


If you're planning to paint, you can finish at 1000 grit (this will be explained in a separate guide on surface preparation). If you aren't, you can sand up to 2000 grit or more, and use a nail buffer to polish the part and bring back the natural shine of the plastic.

By the time you're done, your parts will be covered in sanding debris. Use a soft bristle brush to clean them off in a basin of water with a drop of dish washing liquid. This will also get rid of any oil or residue left behind from the molding process.

TIPS:

  • You can make sanding sponges by sticking your sandpaper onto double sided foam tape (also called mounting tape) and cutting it to your preferred size.
  • Sanding sponges are recommended for rounded surfaces because there is less risk of flattening the surface while sanding.
  • You can make sanding sticks by gluing the sandpaper onto popsicle sticks.
  • Sanding sticks are stiff and are best suited for sanding flat areas and help preserve the sharpness of edges.
  • Sandpaper gets mucked up easily. Rinse it off in a basin of water to maximize it's effectiveness.

If you have any suggestions, or know any alternative methods for dealing with nubs, feel free to use the comments section below.

Stay tuned for the next post in this series! Until next time, keep building plamo!

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