Cutting refers to using scissors or, more commonly, a hobby knife. It remove parts from a sheet of paper. As most papercraft modelers use a hobby knife, this tutorial will focus on this tool. Note, hobby knives are sharp and should be used with caution, especially with children in the area. When not in use, they should be stored in their original plastic case or other device.
Knife lifetimes vary by brand, but the tend to last roughly two months to four months, depending on frequency of use and surfaces cut. While knife edges can be sharpened to extend their lifetimes, this produces marginal results without a dedicated sharpening tool, either way, simply replacing the blade is the preferred. Hobby knives' blades are cheap, at less than five cents a blade, and are easily replaceable. To replace a knife's blade, unscrew the knurled (diamond pattern) grip until the blade can be pulled out with little force, and slide the new blade into the created opening until it will go no further. Re-tighten the grip, and pull and wiggle the blade to ensure its security. Blades should be replaced when they have dulled to the point of inability to cut paper without multiple passes or with extreme force. Blades dull due to shearing. Different amounts of shearing occur while cutting on different surfaces. Surfaces such as metal and wood cause the most shear, while cutting mats tend to have the least. Bent or curved blades must also be removed, as these can cause ripped paper, loss of control, and other consequences. New blades should be tested out, by making some cuts on scrap paper to get a feel for their abilities. During the first few cutting sessions, it is not uncommon to see small metal shavings. These are produced when the thinnest parts of the knife, along the edge and tip are trimmed off.
In order to have the maximum control over the knife, it is recommended to pull the knife toward ones dominant arm, turning paper to match a north-left to south-right angle (or north-right to south-left for left-handed cutters). Using a ruler as a guide for long, straight lines is preferred, however, there is no such guide for making rounded or other non straight parts. Rulers of six inches (15 cm) are the most handy, as they are easy to maneuver while still being long enough to suit most lengths. Larger models may require a 12 inch (30 cm) ruler, but these tend to be harder to maneuver. How to correctly hold the knife is paramount to control, as poor form may hurt ones hand and/or cause poor precision. There are several holds used for cutting.
- Pencil: Holding the knife like a pencil is most commonly used in free handed cutting, as this form allows one the most control. The muscles and coordination associated with writing are already developed and, therefore, are prime for cutting with.
- Thumb: Holding the knife with the thumb resting on top, this is similar to the pencil hold, however, the knife is angled upwards, with the thumb extended below the fingers. The knife rests on the lower joints of the index finger or in the same place as the pencil grip, while the thumb exerts force with either joint depending on angle. This hold is less coordinated and precise as the pencil, however, it can be used to cut upward without rotating the paper, or as relief for pain caused by holding the knife in the pencil too long. This hold is also often used when guided by a ruler.
- Scapel: The knife is held like a scapel, with the hand above the knife, and the thumb under. The index finger extends down the knife and provides force. This hold is fairly uncoordinated, and usually is used for very long, straight cuts, mostly aided with a ruler.
Exerting the force needed to cut paper with a knife requires a fair amount of tension and force from the hand, which can cause fatigue and pain. Alternating cutting and gluing is the best relief, but changing grip is also somewhat helpful.