When I started back with DE shaving, I bought a Merkur 34C and used it every day for six months. Four months ago, I bought a Rockwell 6S and have used it nearly every day since, and like it much more than the Merkur and every other razor I have tried. But why? The designs are very similar. I usually use plate 3 on the Rockwell, which is similar in aggressiveness to the 34C. But imho, there are two crucial design differences, which I've tried to show in the comparison photos below.
First, the supporting rails on the base plate are spaced further apart on the Rockwell. This means the point at which the blade is clamped to the razor head is closer to the blade edge, i.e., the clamp distance is less. Second, the Rockwell cap has a greater curvature, or a smaller radius of curvature, which means the blade is bent or curved more sharply when loaded.
What both these design features do is make the blade more rigidly held in the Rockwell, and less prone to chatter or flexing. Clamp distance is a crucial parameter for rigidity, imho, and shorter clamp distance means more rigidity, other things being equal. Greater blade curvature also results in less flex as the already flexed blade acts as a spring and pushes with more force against the cap. Designs with less blade curvature need to compensate with less clamp distance to maintain rigidity. Of course, greater curvature has an impact on blade angle, but that can be compensated for with other parameters.
My theory is, the Merkur, like the vintage Gillettes, was designed for the thicker gauge, stiffer, less flexible blades that were standard in the olden days. Rockwell has made some subtle but very useful modifications for the thinner more flexible modern blades.
First, the supporting rails on the base plate are spaced further apart on the Rockwell. This means the point at which the blade is clamped to the razor head is closer to the blade edge, i.e., the clamp distance is less. Second, the Rockwell cap has a greater curvature, or a smaller radius of curvature, which means the blade is bent or curved more sharply when loaded.
What both these design features do is make the blade more rigidly held in the Rockwell, and less prone to chatter or flexing. Clamp distance is a crucial parameter for rigidity, imho, and shorter clamp distance means more rigidity, other things being equal. Greater blade curvature also results in less flex as the already flexed blade acts as a spring and pushes with more force against the cap. Designs with less blade curvature need to compensate with less clamp distance to maintain rigidity. Of course, greater curvature has an impact on blade angle, but that can be compensated for with other parameters.
My theory is, the Merkur, like the vintage Gillettes, was designed for the thicker gauge, stiffer, less flexible blades that were standard in the olden days. Rockwell has made some subtle but very useful modifications for the thinner more flexible modern blades.