Edge grinding processing method of prism glass optical lenses

It is capable of edging lenses of various prismatic degrees according to prescription requirements, as well as lenses that have both prism degrees and require center shifting during processing. Be proficient in operating prototype machines and making prototypes by hand.

After measuring the processing center and processing reference line of the prism lens, make a template according to the frame. Then, place the template on the axis-fixing machine and position the lens above it. Ensure the reference line of the presbyopia lens coincides with the reference line of the template. The machining center should align with the center of the sample. For myopia lenses, the reference line should be 1.5~2mm above the sample's reference line. If the prescription has specific requirements, adjust the position of the processing center and the reference line accordingly, and then place the suction cup. Due to the thickness difference between the bottom and the tip of prism lenses, especially lenses with large prisms, the suction cup may shift when processed by an automatic edge grinding machine, affecting accuracy. Therefore, fixing the suction cup is crucial in processing prism lenses.

First, grind the lens into the geometric shape of the frame, a process called edging. Then, grind the edge of the lens to a specific angle, commonly known as "sharp edge." Generally, the groove depth of the frame is 0.5~1.0mm, so the height of the sharp edge should match the groove depth of the frame. The angle of the frame groove is 110°~120°, meaning the angle between the sharp edges of the lens must correspond. Additionally, for lenses with larger diopters and larger prisms, adjust the ratio of the edge positions of the sharp edges based on the frame style. Typical ratios are 6 inside, 4 outside, 7 inside, 3 outside, etc. After grinding, the lens needs chamfering. Finally, check the position of the optical center point, the direction of the cylinder axis, the direction of the prism bottom, any scratches on the lens, the condition of the peripheral corners, etc., to ensure they meet the requirements for fitting into the frame.

For frameless glasses, the varying thickness of the lens edges due to prisms necessitates careful attention to the angle when drilling. When notching half-frame glasses, use the thin direction as the reference direction and pay attention to the notch depth.

Precautions

The center shift of lenses containing prism power is based on the prism lens processing center, adjusted according to the frame size and interpupillary distance. For example, with an interpupillary distance of 60mm and a frame size of 52-16, the prismatic power lens moves the lens processing center inward by 4mm during edge grinding. This does not involve moving the optical center of the lens inward by 4mm. If the reference line needs vertical adjustment, move the processing center accordingly.

Related Information

1. Master the calculation of the minimum uncut diameter.

During the lens edging process, it is often necessary to shift the reference center or optical center of the lens to address discrepancies between the optical center positioning and the reference center distance of the frame, especially after adding prisms. Understanding these relationships is essential. Furthermore, knowledge of calculating the minimum uncut lens diameter (standard raw edge lens) is crucial. The formula is: Minimum uncut lens diameter = longest point on both sides of the geometric center of the frame (left or right) + twice the center shift amount + 2mm reserve. For example, if the longest length of a frame is 52mm and the optical center is displaced inward by 3mm, then 52 + 3×2 + 2 = 60mm. The minimum uncut lens diameter is 60mm. Consider an example with a prescription of -4.00DS2△ with the base facing outward. To achieve the prism effect, the longest part of the lens is 50mm. Determine the minimum uncut lens diameter. (1) Find the center shift formula: C = P / F (P = △, F = Diopter) 2 / 4 × 10 = 5(mm) inward shift.

(2) Minimum uncut lens diameter = 50 + 2×5 + 2 = 62mm.