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FIGURE 13-41 The lens is placed in the lens holder on the mounting table so that the slot center is on the intersection of vertical and horizontal lines. The horizontal line running through the slot center overlaps the horizontal line on the table. This way the finished slot will be precisely vertical.
ADJUSTING THE DOUBLE-STRAP AREA
The way the straps are adjusted before mounting the lenses strongly influences the alignment of the assembled spectacles. For example, if the straps are bent forward, even though they are still parallel to one another, the temple will be spread too widely.
The nasal and temporal lens straps are bent to the correct angles, beginning with the nasal straps. Next the centerpiece on the lens is held so that the lens edge is between the two straps. This way it is possible to see if the “front” of the spectacles will align properly. When satisfied, the lens hole is aligned with the holes in the straps and a “tap” used to rethread the straps (Figure 13-54). (A tap is a lens threader mounted in a chuck handle.) Rethreading allows the screw to go through the straps at the proper angle. Next the temporal straps are done.
The shoe and spring section of the strap area contribute to the stability of the lens mounting. The shoe and spring should be touching the edge of the lens above and below the strap with moderate pressure. (To view this area of the frame, see Figure 13-3.) If necessary, the shoe is bent to establish proper tension against the lens edge.
FIGURE 13-42 The table is placed on the base of the stand and locked into position.
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FIGURE 13-43 A hole is drilled through the center of where the slot will be.
FIGURE 13-44 To make a slot, the locking mechanism is loosened to allow the drill to swing back and forth as it cuts the slot.
FIGURE 13-45 The drilling bit is pressed lightly into the surface and moved back and forth to remove plastic along the length of the slot. The process is repeated 15 or 20 times until the slot goes all the way through the lens.
FIGURE 13-46 A cone-shaped tool will safety bevel (chamfer) the lens slot and will keep the slot from chipping.
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FIGURE 13-47 The clip needs to be free of any dirt or oils before being put into the slot. Cleaning it with alcohol helps the lock-glue to adhere better as well.
FIGURE 13-48 Before applying lock glue, the fit of the clip in the slot is checked. If the tension is not correct, the clip needs to be widened or narrowed.
FIGURE 13-49 Clip width may be adjusted so that it has the correct amount of tension in the slot. Both sides of the clip must be parallel after adjustment.
The shoe should contact the lens all along the edge. To have this happen, the face of the straps must parallel the up and down plane of the spring/shoe portion of the assembly (Figure 13-55).
MODERATELY THICK LENS EDGES
If the lens edge is moderately thick, the location of the holes is marked, but the holes are not drilled yet. Instead the straps are adjusted to fit the edge of the lens
at the location of the proposed hole. If the straps need to be narrowed or widened, an old-fashioned strapping pliers is used (Figure 13-56). This widens or narrows the distance between the straps as shown in Figure 1357. The straps also should be shaped to conform to the curve of the lens, lying flat against it.
When in doubt as to how close to the edge the holes should be, the operator should remember that it may be better to have the hole too far in from the edge than too close to the edge. If the hole is too close to the edge,
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FIGURE 13-50 Applying “lock glue” to the inside of the slot and/or the clip before inserting the clip helps retain the clip in the lens.
FIGURE 13-51 The clip as it appears in the lens. Clips come in different lengths, depending upon the edge thickness of the prescription.
the lens will be loose. But if the hole is too far in from the edge of the lens, the front or back surface of the lens
under the strap can be filed. (See the next section.)
FIGURE 13-52 Computer-assisted drills are considerably Once the straps are adjusted, the new location for more expensive but are faster and require less training.
the hole is marked. That location will be closer to the lens edge than it would have been. Yet it will be at the same vertical height as it was before.
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FIGURE 13-53 One type of WECO edger drills the lenses immediately after they have been edged. For this feature to work, the locations of the drill holes, slots or notches are set up in the blocking process with the corresponding WECO blocker.
A B
C D
FIGURE 13-54 In this sequence, A shows straps that are improperly angled, causing the temple to open out too far. In B the straps are being reangled, and in C rethreaded, using a tap. When corrected as shown in D, the temple once more shows proper positioning. (From Brooks CW, Borish IM: System for ophthalmic dispensing, ed 2, Boston, 1996, Butterworth-Heinemann [Figure 8-67].)
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A 
B C
FIGURE 13-55 A, The straps are misrotated, causing the lens to be angled. B, The straps are re-angled using hollow snipe-nosed pliers. C, The straps are shown correctly positioned. (From Brooks CW, Borish IM: System for ophthalmic dispensing, ed 2, Boston, 1996, Butterworth-Heinemann [Figure 8-75].)
FIGURE 13-56 Strapping pliers are made to help in spreading or narrowing the distance between the double straps of an old-fashioned rimless mounting. (From Brooks CW, Borish IM: System for ophthalmic dispensing, ed 2, Boston, 1996, Butterworth-Heinemann [Figure 8-73].)
LENS TOO THICK FOR THE STRAPS
If the lens edge is too thick for the size of the straps, again, the location of the holes is marked. Their marked location is for vertical reference only.
Next the back surface of the lens is filed to thin the edge where the strap will grip the lens. On extremely thick lenses, it may be necessary to file some off the front surface, too. A rat-tail file is used to file the lens surface. When the lens edge is thin enough to accommodate the strap, the strap is adjusted to fit. The location of the new hole is marked and the lens is drilled.
BIBLIOGRAPHY
Air Titanium Optician’s Video, Frichsparken, Denmark, Lindberg Optic Design (undated).
DeFranco LM: Eight tips for processing rimless (or semirimless) eyewear, Eyecare Business, August 1999, pp 3637.
Field C: Processing drill-mounted eyewear, LabTalk 28(42):3234, 2000.
Geeren H: Werkstatt buch, Pforzheim, Germany, 1981, Verlag Neues Optikerjournal.
FIGURE 13-57 A strapping pliers can be used to either widen or narrow the distance between straps to accommodate varying lens thickness. (From Brooks CW, Borish IM: System for ophthalmic dispensing, ed 2, Boston, 1996, Butterworth-Heinemann [Figure 8-74].)
274
Herrick T: Three-piece mountings: when lenses are the frame, Lenses & Technology, April, 2000, pp 18-22.
How to assemble 1776 and other Balgrip mountings, Rochester, NY, Bausch & Lomb, (publication A-1907), undated.
C H A P T E R 1 3 D R I L L E D , S L O T T E D , A N D N O T C H E D M O U N T I N G S
Levoy BM: How to work with rimless, Optometric Weekly, February 17, 1977, pp 33-40.
Yoho A: Keeping the rimless lens tight, Eyecare Business, August 2000, p 34.
P r o f i c i e n c y Te s t Q u e s t i o n s
1.True or False? Polycarbonate is not well suited for any type of rimless eyewear because the material is so soft.
2.True or False? Using glass lenses in a rimless mounting, even when they are chemically hardened, is against FDA regulations.
3.Which of the following is not a good option for minimizing minus lens edges for rimless eyewear?
a.Use a lens with an ED at least 5 mm larger than the A dimension of the lens.
b.Use high-index material.
c.Polish the edges.
d.Use a small eyesize.
e.Use an AR coating.
f.All of the above are good options for minimizing minus lens edges for rimless eyewear.
4.To minimize and equalize plus lens edges for rimless eyewear, all but one of the following may help. Which one of the following will not help?
a.Choose a frame size such that A+DBL is close to the wearer’s PD.
b.Choose a shape with a narrow B dimension.
c.Choose a shape with an ED not much bigger than the A dimension.
d.All of the above will help minimize and equalize plus lens edge thickness.
e.None of the above will help minimize and equalize plus lens edge thickness.
5.For lenses of the same power, which of the following may be more difficult to mount in a rimless mounting?
a.One with a flat base curve
b.One with a steep base curve
c.One with an aspheric base curve
d.No difference exists in how easy or hard these lenses are to mount in a rimless frame
6.A drilling template describes which of the following?
a.A picture of the lens, including where the holes are to be drilled on the lens
b.Something that is shaped just like the lens. It is placed on the lens. Holes are drilled through the “holes” in the template and on through the lens.
7.A coquille describes which of the following?
a.The mounting assembly of a double-drilled mounting
b.A tool used to guide the drill through the lens, reducing chipping and spoiled lenses
c.A type of French monocle that is drill-mounted
d.The plastic display lens that comes in a frame
e.A flowerlike decorative piece that is drill-mounted to a spectacle lens
8.You must drill a lens for a semirimless mounting without the help of drill guides. Using only the frame, with which of the following would you begin?
a.The right lens
b.The left lens
c.The nasal hole
d.The temporal hole
e.Any lens or any hole; it will all end up the same anyway
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Nylon Cord and |
Other Groove |
Mountings
One method to keep frames and lenses together holds the lens in place with a nylon cord that
resides in a groove cut in the edge of the lens (Figure 14-1). Alternatively some frames have a rim that slips into the groove (Figure 14-2). When the frame rim slips into the groove, the groove must be wider than for nylon cords.
A nylon cord frame is also referred to by a number of names, including nylon supra, a string mount, Rimlon, Nylor, and suspension mounting.
Wearer Safety Issues
Wearer safety issues1 for grooved lenses are essentially the same as for rimless mountings and were discussed in Chapter 13. Reviewing these issues is recommended.
The issue of whether to use glass lenses in nylon cord frames is not as clear-cut as it is with drilled lenses. Most laboratories either do not put glass lenses in nylon cord frames, or if they do, they do so with reservations. The Optical Laboratories Association (OLA) addressed the issue in a 1993 technical paper. Even though a hardened glass lens will pass the required impact resistance test for a new lens in a nylon cord mounting, the edge of the lens is left unprotected. Putting the lenses on a rough surface or dropping them on a hard surface can
For more information, refer to Instruction for the automatic groove master, Los Angeles, Novamatic Systems (undated).
1The information in this section was taken from Bruneni JL: Ask the labs, glass lenses/nylon suspension mountings, (response by Dan Torgersen, technical director, Optical Laboratories Association), Eyecare Business, November 2000, p 36.
