Calculating drilling parameters for different lens curvatures is a precise process that ensures a rimless frame sits correctly on the wearer’s face. The core challenge is that the demo lens used for fitting often has a different curve than your actual prescription lens.📐 The Core Problem: Curve MismatchWhen a rimless frame is fitted, it’s usually done with a demo lens. However, your actual prescription lens may have a different surface curve (how domed the front is). If you drill a hole perpendicular to the demo lens and use the same angle on the actual lens, the frame’s endpiece and temples may not align properly, affecting fit and the temple opening angle .🧮
How the System Calculates the Correct AngleModern lens processing machines solve this with a geometric calculation. The operator selects a drilling mode, typically one of these three :
1. First Drilling: The hole angle is normal (perpendicular) to the demo lens surface.
2. Second Drilling: The hole angle is normal to the actual lens surface.
3. Third Drilling: The hole angle is arbitrarily set by the operator.The most complex calculation happens in the First Drilling mode. The system uses the following data to find the correct hole position and angle on your actual lens :· Demo Lens Data: The system needs the surface curve (or radius of curvature) and the exact hole position coordinates from the demo lens .· Actual Lens Data: It also needs the surface curve of your actual prescription lens .📉 The Calculation in ActionUsing these inputs, the software performs a geometric correction. It calculates a correction amount (ΔW) to shift the hole position on the actual lens. This shift compensates for the difference in curvature between the demo and actual lenses .The goal is to find the correct hole angle and hole position on the actual lens so that when the frame is assembled, the endpiece fits the lens edge perfectly and the temple angle remains correct for the wearer’s face .📏 Practical Considerations· Perpendicularity: The system can adjust the lens tilt so the drill enters perpendicular to the refractive surface, which is often desired for a stable fit .· Data Transfer: In practice, manufacturers like Silhouette provide drilling coordinate files (often downloadable) that give exact measurements for automated machines or printable templates for manual drilling, which account for these curve variations .In short, the calculation is a geometric correction. It uses the curve values of both the demo and actual lenses to determine a corrected hole position and angle, ensuring the rimless frame fits properly regardless of the prescription’s curvature.