A basic model isn’t meant to look finished; it can be bumpy, taped together, imperfect, and void of surface detail. Its function is to reveal issues that your flat sketch obscures. You want to use the model to determine if the product is too massive, too slender, too substantial, too angular, or uncomfortable to grip before investing effort in a more polished concept sketch.
Start by examining the model’s general scale. Something that appears proportionate in the perspective drawing can appear chunky once built on a table. Create a simple block of paper or foam board and disregard the fine points, such as panel lines, buttons, branding, and surface texture. Pick it up and rotate it, put it back down, and inspect it from the front, side, and top. Consider whether the overall size of the model seems appropriate for the product. A device for a desk might need a stable base. A handheld object may have too much bulk around a handle. A small packaging container may lack the necessary depth for the lid and body to feel functional.
Consider where the model touches your hand. Indicate where you touch and press with fingers, where your thumb rests, where pressure occurs, and where the model is put down; you can mark those places with a pencil on the model. If your hand keeps sliding to a location you didn’t expect, that’s a useful sign of feedback. If a button placement overlaps the natural location of your palm when holding, you can improve the drawing. If a panel line passes through a grip position, the product could feel uneasy or visually disorienting. Contact points can expose mistakes sooner than a more refined sketch.
Size should be checked separately, as novice designers often infer it based on its size on paper. A knob drawn as a reasonable size may turn out to be too narrow when cut into foam. A touch panel may appear large enough, until you compare it to your finger. A lid may appear clear, until the edge isn’t large enough to grasp it. Hold the model up against another similar object, such as a remote control, a bottle, a computer mouse, a power tool, or a kitchen appliance to get an idea for the thickness, reach, and size.
You can leave out detailed design work, but you can check the location of specific items in your model. You can use paper tape, small scraps of paper, or small pieces of card to represent a knob, a grip, an opening, a seam, the lower end, or an interface. Move these indicators around and see how it affects the design. Maybe moving a knob up just a bit means it can be pressed with less effort. Maybe moving the grip toward the back results in better balance. Maybe having a wider base will make the product look more stable. The benefit of a rough model is that everything is open for adjustment.
A model can be assessed by trying a simplified interaction. Pick it up off of a table. Carry it around. Activate a control. Imagine a lid opening. Replace it. Place it next to another object. Watch yourself for any hesitation. The place where you hesitate is often an indication of an issue with the design. The front may not be distinguishable. The hand holds may have no rounded edge. A surface may be too narrow to set the model down on. Such details point to the next set of modifications to make in the next design drawing.
After assessing the model, make one or two or three modifications in the concept drawing. Correct the model’s scale, fix the contact points, and make a part line or the interface area clearer. If you are able to ask yourself better questions, a simple cardboard or foam model is considered effective rather than making it look perfect. A cardboard model should remain straightforward so that you may build it, play with it, change it, and contrast it without having to feel invested in the first result.