How to Remove Nubs on Gunpla: A Step-by-Step Guide to Clean Builds

Originally published December 2024. Updated April 2026.

Ever wonder why those builds on Instagram look silky smooth while yours is covered in little bumps and white marks from cutting parts off the runner? Let's be honest - those competition-level builds represent days, weeks, sometimes months of cleaning, modifying, painting, more cleaning, more modifying, more painting, and finally a $1,500 camera setup to make it all look even better. But here's the thing: if you strip away the painting, the modification, and the expensive photography, the gap between your build and theirs starts with something surprisingly simple - how you handle your nubs.

Learning how to remove nubs from Gunpla cleanly is the single most important skill you'll develop as a builder. It's not hard. It just takes the right tools, the right technique, and a little patience.

What Are Nubs (and Why Should You Care)?

Nubs are the small bits of plastic left on a part after you cut it from the runner - the plastic frame that holds all the parts in a Gunpla kit. During injection molding, liquid plastic flows through channels called gates to fill the mold cavities that form each part. When you clip a part off the runner, you're cutting through those gates, and the leftover plastic at the cut point is your nub.

If you leave nubs on your parts, two things happen. First, the kit looks rough. Nubs show up as bumps, ridges, or discolored spots that catch light and draw the eye to exactly the wrong places. Second, and this is the one beginners don't expect, nubs can actually prevent parts from fitting together properly. A nub on a peg or connection point means the part won't seat flush, which leads to gaps, loose joints, and a kit that feels fragile where it shouldn't.

Even if you're building straight out of the box with no painting or customization, clean nub removal makes a noticeable difference in how the finished kit looks and holds together.

Tools You'll Need

You don't need much to get started with gunpla nub removal, but the tools you use matter more than you'd think.

Nippers (side cutters) are your primary tool for getting parts off the runner. Any plastic hobby nipper will work when you're starting out. As you get more experienced, you'll probably hear about single-blade nippers like the GodHand Ultimate Nipper, which make cleaner cuts and leave less material behind. They're nice to have but absolutely not required for good results.

A hobby knife (X-Acto or similar) is what you'll use to trim nub remnants down close to the surface of the part. Keep fresh blades on hand - a dull hobby knife is both dangerous and ineffective. You'll be pressing harder to cut through plastic, which means less control and a higher chance of slipping.

Sanding sticks or sandpaper in multiple grits handle the final smoothing. You'll want a range: something in the 400-600 grit range for initial material removal, 800-1000 for smoothing, and 1500-2000+ for polishing if you want a really clean finish. Sanding sticks (foam-backed sanding tools) are easier to handle than loose sandpaper for most Gunpla work because they conform slightly to curved surfaces and give you more control on small parts.

That's the core kit. A cutting mat to protect your desk is smart. Some builders also like glass nail files for quick nub cleanup, and if you plan to paint later, you'll eventually want sanding and polishing supplies in higher grits.

Step 1: Cut the Part Off the Runner (Leave Room)

This is where most nub problems start - and where you can prevent most of them.

When you cut a part from the runner, don't cut flush against the part. Cut a few millimeters away from it, closer to the runner than the part itself. You want to leave a visible chunk of gate material still attached to your part.

Why? Two reasons. First, cutting flush puts mechanical stress directly on the part's surface, which causes stress marks - those white or discolored spots that appear where the plastic has been stretched or compressed. Stress marks are especially visible on dark plastic (Bandai's dark blue is notorious for this) and once they're there, the only way to fully eliminate them is painting. Second, and this is one beginners learn the hard way, cutting flush makes it far too easy to overcut and clip into the actual part itself. Once you've gouged into the part's surface, there's no easy fix.

Cutting away from the part gives you a controlled amount of material to work with in the next steps instead of hoping you got it right in one shot.

Hold the runner steady while you cut, and support the part so the weight of the runner doesn't bend or snap it at the gate. This is especially important on thin or delicate pieces.

Step 2: Make a Second Cut Closer to the Part

Now that the part is free from the runner, you've got a nub stub sticking out. Use your nippers to make a second, more precise cut closer to the part's surface. You still don't want to cut perfectly flush - leave just a tiny bit of nub material, maybe half a millimeter.

The goal here is to get the nub small enough that your hobby knife or sandpaper can handle the rest. Trying to nip it completely flush in one shot almost always causes stress marks, even with high-end nippers.

If you have single-blade nippers, this second cut is where they really shine. The cleaner cut leaves less material to clean up afterward. With standard double-blade nippers, just take your time and position the flat side of the blade against the part's surface for the cleanest possible cut.

Step 3: Trim with a Hobby Knife

With the nub trimmed down to a small bump, it's time for the hobby knife. This step is about shaving that last bit of material down to (or very near) the surface of the part.

The technique that works best for most builders: hold the blade nearly flat against the part's surface and use a slicing or shaving motion rather than pushing straight down. You're trying to peel thin layers off the nub, not chop through it. You want the blade to glide along the surface, taking a little material with each pass.

A few things that will save you grief here. Always cut away from your fingers. This sounds obvious, but when you're focused on a tiny nub on a small part, it's easy to lose track of where the blade is headed. Offering your own blood to the Gunpla gods is not recommended. Also, make several light passes rather than one aggressive cut. Pushing too hard stresses the plastic (hello, stress marks) and risks gouging into the part itself.

For curved surfaces, angle the blade to follow the contour and work from both sides of the nub toward the center. On flat surfaces, keep the blade parallel to the surface and take thin, even passes.

One more thing: avoid scraping. Some guides recommend using the blade edge to scrape across the nub, but this is hard to control and can leave uneven marks or dig into the surrounding plastic. Cutting and shaving works better.

Step 4: Sand and Polish

After the hobby knife, you'll often be left with a surface that's close but not quite flush - maybe a slight ridge, some knife marks, or a texture difference where the nub used to be. Sanding fixes all of this.

Start with a lower grit (around 400-600) to knock down any remaining raised material. Use light pressure and let the abrasive do the work. Heavy pressure just digs grooves into the plastic. If you're new to sanding Gunpla parts, err on the side of too gentle rather than too aggressive - you can always sand more, but you can't un-sand.

Move to medium grits (800-1000) to smooth out the scratches left by the coarser grit. Every grit level removes the scratch pattern of the previous one and replaces it with finer scratches.

Finish with high grits (1500-2000 and above) if you want the surface to match the surrounding plastic's sheen. For unpainted builds, getting the sanded area to visually disappear is the goal. A matte top coat applied later will also help hide any remaining surface differences.

For sanding direction, work in one consistent direction or use small circular motions. Avoid sanding in just one straight line back and forth, as this can create visible scratch patterns. On flat surfaces, sanding in multiple directions helps blend the area evenly.

Sanding sticks are generally easier to use than loose sandpaper for Gunpla because they give you more control and keep the abrasive flat against the surface. If you're using sandpaper, try wrapping it around something flat and firm (a popsicle stick, a small block of wood, or even a thick piece of plastic card) so it doesn't flex and dish out the surface unevenly.

For a detailed breakdown of grits, techniques, and when to use what, check out our full sanding and polishing guide.

Dealing with Stress Marks

Stress marks are those white or lighter-colored spots that appear on plastic when it's been mechanically stressed - usually from cutting too close, applying too much force with dull nippers, or bending the plastic at the gate. They're the bane of nub removal, and they happen to everyone.

The best approach is prevention: use the two-cut method described above, keep your nippers sharp, and never try to cut flush on the first pass. Darker plastic colors show stress marks more than lighter ones. White and light gray parts are the most forgiving, while dark blue, black, and red will show every stressed spot.

If you do get a stress mark, here's what you can do. Light stress marks can sometimes be reduced by rubbing the area firmly with your fingernail. Yes, your actual biological fingernail. It sounds like folk wisdom from a 2008 forum post, but the friction and pressure can partially re-seat the disturbed plastic, and it still works. Sanding through the stressed area and polishing back up helps in some cases too, especially if the mark is shallow.

For stubborn stress marks on an unpainted build, a matte top coat will reduce their visibility significantly. The matte finish diffuses light instead of reflecting it, which makes the color difference much less obvious. If you're painting the kit, proper sanding and primer will cover stress marks completely.

There's also a more advanced technique where you dissolve same-colored runner plastic in plastic cement to create a color-matched filler, then apply it directly to the stress mark. It's effective but requires some practice, so we'll cover that in a future article on advanced finishing techniques.

Special Considerations for Clear Parts

Clear and transparent parts need extra care during nub removal. The same cutting and sanding process applies, but with more caution at every step.

Cut even further from the part on your first cut. The pressure from nippers can create micro-fractures or "fogging" in clear plastic that shows up as a cloudy white spot - and on a clear piece, that's visible from every angle.

That said, before you go down the rabbit hole of making a clear part absolutely flawless, check whether the nub will actually be visible after assembly. A lot of clear parts - cockpit canopies, visor lenses, beam saber blades - have nub locations that end up hidden by surrounding armor or frame pieces. If the nub won't be visible once the kit is assembled, you just need it clean enough to be flush and not interfere with fit. Save the perfectionist energy for the spots people will actually see.

When you do need a clean finish on a visible clear part, you'll need to go higher in grits than you would on solid-color plastic. Sand up through 2000 grit and beyond, then use a plastic polishing compound to restore full clarity. It's more work, but the results are worth it on parts like exposed eye pieces or canopies that are front and center on the finished kit.

Undergates: Don't Overthink These

You'll notice that some kits - especially newer releases - have gates that connect to the underside or inner surface of parts rather than the edges. These are called undergates, and they're specifically designed so that any leftover nub mark is hidden once the part is assembled.

With undergates, you don't need to go through the full sand-and-polish routine. Clip the nub, trim it flush or close to flush with your knife, and move on. As long as the nub is removed cleanly enough that it doesn't interfere with assembly, you're done. The whole point of an undergate is that it won't be visible on the finished kit, so there's no reason to spend five minutes perfecting a surface nobody will ever see.

The same logic applies to regular gates on surfaces that will be completely covered by other parts. Check your instructions - if a piece is sandwiched between two other parts or sits against a frame, a quick cleanup is all it needs.

Common Mistakes to Avoid

Cutting flush on the first pass. This is the number one mistake. Always use two cuts minimum. The time you save trying to do it in one cut, you'll spend three times over trying to fix the stress mark - or worse, the gouge where you overcut into the part.

Using dull blades. A dull hobby knife requires more pressure, which means less control and more stress on the plastic. Swap blades frequently - they're cheap, and a fresh blade cuts cleaner and safer.

Skipping grits when sanding. Jumping from 400 grit straight to 2000 doesn't work. Each grit level exists to remove the scratch pattern from the previous one. Skip steps and you'll be left with visible scratches that no amount of fine-grit polishing will remove.

Ignoring nubs on hidden surfaces. You'd be surprised how often a nub on a "hidden" surface actually prevents a part from fitting properly. Even if it won't be visible, check that nubs on connection points and peg surfaces are cleaned up.

Putting It All Together

Nub removal is one of those skills that feels slow and tedious at first but becomes nearly automatic with practice. Your first few kits might take longer because you're being careful (which is the right approach), but by kit number five or six, you'll have a rhythm. The two-cut method, a few passes with the hobby knife, quick progression through your sanding sticks - the whole process starts taking seconds per part instead of minutes.

If you're just getting started with Gunpla, understanding nub removal alongside how to read instruction symbols and choosing the right grade for your skill level will set you up for clean builds from the start. And once you've got nub removal down, the next steps - panel lining and top coating - will take your builds from clean to genuinely impressive.