How to Remove Nub Marks Without Stress Whitening

The nipper snips the part off the runner, and half the time it leaves two problems behind: a nub, the little stub of leftover gate, and worse, stress whitening, the pale crescent where the plastic got pinched pale. On a kit you plan to leave in bare color, that white scar is glaring, and chasing it badly can turn a two-minute cleanup into a scratched panel. Having catalogued 200-plus kits and tools across grades using our bench methodology, here is the reliable way to take a nub down to nothing without whitening the plastic around it.

Why nubs turn white

Stress whitening is mechanical, not cosmetic. When a blade crushes or pinches the plastic instead of slicing it, it stretches and fractures the material just under the surface, and those micro-fractures scatter light, which reads as a pale bloom. That is why a single hard cut flush against the part is the classic mistake: it pinches. The fix is a tool that slices and a technique that never crushes.

What you need

• A single-blade nipper. One flat back face, one beveled face; the flat side goes against the part so the edge slices the gate rather than pinching it. A value single-blade like the DSPIAE, around $40, or the endgame God Hand SPN-120, around $85, both cut clean. The full field is ranked in best nippers for Gunpla.
• A backup cutter for rough work. Keep a cheaper gateway nipper around $12 for thick runners so you never chip the good blade.
• A sanding-stick ladder. Foam sanding sticks in a range of grits, roughly 400 up to 2000 or higher, are what actually erase the last of a nub.
• A sharp hobby knife for shaving, and a cutting mat to work on.

Step 1: the two-stage cut

This is the whole game, and it is why a good nipper is worth the money.

1. Cut proud. Snip the part off the runner leaving a small nub, a millimeter or two, standing above the surface. You are not trying to cut flush yet. Cutting away from the part like this keeps all the pinching stress out in the waste gate, not on your model.
2. Flush-cut the nub. Now come back with the flat face of the single-blade against the part and slice the remaining nub nearly level. Because you are shaving a thin stub, not biting through the whole gate at the surface, the blade slices cleanly and leaves little or no whitening.

Two snips, zero stress marks. If you own only one nipper and must cut in a single pass, at least cut slightly proud and sand the rest; a single hard flush cut is what whitens plastic. The relationship between blade quality and how clean that cut comes out is broken down in God Hand vs DSPIAE nippers.

Step 2: the sanding ladder

Whatever nub remains, you climb it away with progressively finer grits.

1. Start around 400 to 600 grit to knock the nub flat. Keep the stick moving in one direction and check often; you are leveling the stub, not the panel around it.
2. Step up to 800, then 1000, then higher. Each grit removes the scratches the last one left, so the surface gets progressively smoother. Skipping straight to fine grit leaves the nub; skipping the fine grits leaves a dull scuff.
3. Finish fine. Going up to 2000 or beyond brings the spot back toward the plastic's original sheen. On foam sticks the backing conforms slightly to curved surfaces, which is why they blend better than a hard file on rounded armor.

As a first pass you can also shave the nub with a sharp knife held nearly flat, taking thin slices rather than digging in, then sand from a lower step of the ladder. The grits and files worth owning are compared in best sanding sticks and files for nubs.

Step 3: deal with the finish

Here is the part beginners miss. On bare colored plastic, sanding leaves a matte scuff that can look almost as obvious as the nub did, and any remaining whitening still shows. You have three honest options: sand up through the fine grits until the sheen returns and the whitening blends out, hit the spot with a touch of gloss or top coat to even it, or accept that you will paint or prime the model, in which case primer hides the scuff completely and you can stop fussing over a perfect bare finish. If you are painting anyway, sand only enough to level the nub and move on; if you are building straight out of the box in bare color, that is when the full grit ladder pays off.

Common mistakes

• One hard cut at the surface. The single biggest cause of whitening. Cut proud, then flush.
• A double-bevel cutter. If both faces of the blade are angled, it is a general-purpose cutter that pinches every gate. Single-blade is the fix.
• Stopping the grit ladder too early. A nub leveled at 400 grit is flat but ugly; climb the grits.
• Twisting the blade mid-cut or cutting thick sprue with your fine nipper, which chips the edge and then causes rough, whitening cuts.

The verdict

The nub problem has a two-part answer: a single-blade nipper and a two-stage cut for the removal, then a grit ladder for the cleanup. Cut proud, flush-cut with the flat face against the part, and sand from about 400 up through the fine grits, further if you are leaving the plastic bare. Buy the DSPIAE single-blade for the best balance of clean cuts and price, step up to the God Hand SPN-120 for the finest cut if you will keep a rough-work cutter beside it, and back either with a set of foam sanding sticks. See the sprue, gate, and nub in cross-section on the bench, and compare the tools on our best-of hub.