Building Mecha Kits: Nib and Stress Marks

Fadila Soehedi
Mecha Model Guide for Beginners, Derick Siu

I have been building models kits for years, mostly consisting of the mecha (robot) types. These are plastic figures you build from the "ground up". Being only provided with small plastic pieces and instructions, building can be a challenging yet rewarding experience (a little like LEGO's).

Half of the pieces provided in an average master grade level kit

Getting into the hobby can be fairly difficult as you need to be patient, careful, and precise with the plastic that you build with. The plastic is extremely fragile, you can quickly snap, scratch or bend the pieces you have. Since there are no extra pieces provided, the only way you can replace these parts is by buying another kit or buying parts from Japanese Ebay sellers. Either way, its fairly expensive.

Locations of nib marks are circled on this
Gundam's arm

Now if you use the right tools, you can get around these issues and build a very pretty little robot. Although tools can significantly help with the building process, a large amount of builders use them incorrectly and may not have the correct ones. The most common issue with newer builders is that they leave nib or stress marks and a LOT of them. "Nib marks are small, white indentations in the plastic left when cutting pieces out of their runners, these marks can be very unsettling and can have a negative affect on the presentation of the finished model." (Siu 48)

Nib marks and stress marks are most commonly left by simply cutting out the plastic with clippers or cutters positioned in a way where they are cutting as close to the piece as possible on the gate. Some people try to get rid of this by sanding or cutting the mark only to realize that they created or made a bigger stress mark on the piece by trying to level out the plastic. The size and appeal of the piece will be significantly reduced.

Diagram of a still-attached piece
(to help with explanation on the right)

There is a handful of methods that help avoid this but I will be discussing the one I use. In his book, Derick Siu states, "In order to avoid nib marks, you must cut the gate as close to the runner as possible, not the piece. Now, you'll be left with a chunk of the gate on the piece. From here, you cut away the excess plastic from the gate little by little and slowly with a clipper and razor blade. The idea is to cut until you leave a thin layer of gate and cut that last." (Siu 26) The logic behind it is that the less volume of the gate you cut, the less strain/stress is produced on the plastic, therefore preventing the white strain marks to appear after the cutting. With the mark gone, the plastic will look much smoother and will feel better on the model.

Comparison of the locations of contact that have been cut on these similar heads.
The left was incorrectly treated, the right was cut correctly.

Comparison of contact points on the back of the heads

Throughout my years of building, I realized my mistakes and have tried to improve with my building. Only recently have I been utilizing a razor blade for cutting and the difference in cuts are phenomenal. Although it takes more time, the technique that uses both the cutter and razor blade is much preferred. Each piece needs about 5-10 minutes of work and can really make your fingers sore but the final product is all worth it!

To other model kit builders (who are less likely to see this), what methods do you use for avoiding nib marks? Do you sand down the gate or cut it like I do? If you use neither, please tell me how you do it!
As for those people new to the concept of model kits, what do you think about it? Would you consider trying the hobby?

Siu, Derick, Mecha Model Guide for Beginners (Volume 1), CreateSpace Independent Publishing
    Platform; 1st edition, 2013