How to Remove Nub Marks from Model Kits: Sanding and Polishing Techniques

If you've ever built a model kit, you know the frustration of nub marks – those unsightly remnants left where parts were attached to the sprue. They can ruin the clean look of an otherwise perfect build. Fortunately, removing them is a skill that any modeler can master with the right techniques and a bit of practice.

In this guide, we'll walk you through the process of sanding and polishing to effectively remove nub marks, leaving your Gunpla and other model kits looking factory-fresh. Whether you're a beginner or a seasoned builder, these tips will help you achieve a professional finish.

Understanding Nub Marks

Nub marks occur when you cut a part from the sprue, leaving a small protrusion of plastic. This is especially common on Bandai model kits, where the gates are often thick and visible. The mark can be a simple bump or, in worse cases, a stress mark – a whitish discoloration caused by the cutting process.

To effectively remove nub marks, you need to understand the type of plastic you're working with. Most Gunpla kits use ABS or PS plastic, which respond well to sanding. However, some third-party kits may use different materials, so it's always a good idea to test on a hidden area first.

• Nub marks are inevitable, but they can be minimized with proper cutting and sanding.
• Stress marks are often more visible on darker plastics.

Tools You'll Need for Nub Removal

Having the right tools makes all the difference. For basic nub removal, you'll need a pair of sharp hobby nippers, a hobby knife, and a set of sanding sponges or files. Sanding sponges are particularly useful because they conform to curved surfaces, making them ideal for Gunpla parts.

For polishing, you'll want a set of polishing cloths or compounds. Many modelers also use a glass file, which can quickly remove nubs with minimal effort. If you're looking to upgrade your toolkit, consider investing in quality tools from brands like GodHand or Tamiya.

• Use a sharp nipper to cut the part away from the sprue, leaving a small nub to sand.
• A hobby knife can help shave down the nub before sanding.

Step-by-Step Sanding Techniques

Start by cutting the part from the sprue with a nipper, leaving about 1mm of the nub. Then, use a hobby knife to carefully shave the nub down as close to the surface as possible without cutting into the part itself. This reduces the amount of sanding needed.

Next, begin sanding with a coarse grit, such as 400, to remove the remaining nub. Work in a circular motion, applying even pressure. Gradually move to finer grits – 600, 800, 1000 – to smooth the surface. Always sand in one direction to avoid creating uneven spots.

• Always sand in a well-lit area to see the nub clearly.
• For curved surfaces, use a flexible sanding sponge.

Polishing for a Glossy Finish

After sanding, the area may look dull compared to the surrounding plastic. To restore the original gloss, you'll need to polish the surface. Use a polishing compound or a fine polishing cloth, and rub the area in small circles. This will bring back the shine and blend the sanded area with the rest of the part.

For an even better result, you can apply a clear coat over the entire part. This not only protects the surface but also gives it a uniform finish. Many modelers prefer to polish before applying any paints or topcoats to ensure a smooth base.

• Polishing compounds come in different grades – start with a medium grade and finish with a fine one.
• Microfiber cloths work great for the final buffing step.

Advanced Tips for Perfect Nub Removal

For stubborn nub marks or stress marks, you can use a technique called 'wet sanding.' Dip the sandpaper in water before sanding – this lubricates the surface and prevents the plastic from heating up, which can cause further stress marks. It also helps to wash away plastic dust, giving you a clearer view of your progress.

Another pro tip is to use a glass file, which can remove nubs in just a few strokes. These tools are incredibly effective and leave a smooth surface that requires minimal polishing. If you're building a kit with visible nubs, such as the Premium Bandai HG 1/144 GINGA HYOURYUU VIFAM – FAM-RV-S1 ROUND, these techniques will help you achieve a clean build.

• Wet sanding is excellent for preventing stress marks.
• Glass files are a worthwhile investment for serious modelers.

Common Mistakes to Avoid

One of the most common mistakes is sanding too aggressively, which can remove too much plastic and leave a dip in the part. Always start with a coarse grit and work your way up gradually. Another mistake is skipping the polishing step – without it, the sanded area will remain dull and noticeable.

Also, be careful not to cut too deep with your hobby knife. It's better to leave a small nub and sand it down than to risk damaging the part. Remember, patience is key – rushing through the process will only lead to unsatisfactory results.

• Test your sanding technique on a spare runner first.
• If you do sand too much, you can fill the dip with putty and re-sand.

Mastering nub removal is a fundamental skill that will elevate the quality of your model kits. With the right tools and techniques, you can achieve a clean, professional finish that makes your builds stand out. So grab your sanding sponges and start practicing – your next Gunpla will thank you!