Capabilities and Tolerances
The size capability and tolerance to which a specification can be held are influenced by the cutting and edging process. The above listed size and tolerance capabilities are a guideline only. These tolerances are used as defaults for the listed sizes and shapes. Tighter tolerances may be available upon request.
|Edge Type||Raw Edge||Hand Edge||CNC Edge||Water Jet|
|Rectangle||Min||5mm||+/- .2mm||Min||10mm||+/- .2mm||Min||25mm||+/- .1mm||Min||25mm||+/- .25mm|
|Max||1000mm||+/- .5MM||Max||1000mm||+/- .5mm||Max||500mm||+/- .2mm||Max||350mm||+/- .25mm|
|Diameter||Min||7mm||+/- .2mm||Min||25mm||+/- .2mm||Min||25mm||+/- .1mm||Min||25mm||+/- .25mm|
|Max||500mm||+/- .5MM||Max||500mm||+/- .5mm||Max||300mm||+/- .2mm||Max||350mm||+/- .25mm|
|Custom||Min||5mm||+/- .2mm||Min||TBD||TBD||Min||25mm||+/- .1mm||Min||25mm||+/- .25mm|
Coresix maintains a variety of equipment and processes which are capable of fabricating glass from and to a wide range of thickness. Though we have limitations within certain processes, the versitility of our equiment allows us to be creative in meeting extreme specifications. The chart to the right is provided as a general guideline for some standard operations.
The glass materials with which we work most often have a wide variety of thickness tolerance (+/-) and total thickness variation (TTV) or parallelism which can be discussed upon request. Coresix can generally improve upon these characteristics through a lapping and polishing process. Though we are capable of tolerances to +/- 10μm, TTV of within a part to 2μm and TTV from part to part of <5μm, actual capabilities will vary and should be established per part requirements.
|Scribe & Break||.050mm||12.0mm|
|Lap & Polish||.350mm||100.omm|
For full details on the process, click on the keyword…
This is a common way of interpreting the results of an interferometer as described the the "fringes" definition above. Counting the fringes from left to right, then top to bottom, the larger number is the "power". Subtract the smaller number from the larger number to get the irregularity. The final number being the size of the aperture, the spec then reads P/I/A. For the example below, the flatness is 8/5/4 (8 fringes power, 5 fringes. As expressed over a defined aperture (ex. 12/12/4 = 12 fringes of power and 12 fringes of irregularity over a four-inch aperture) is measured in newton rings on an interferometer.
Measured by interferometer, a fringe is a distortion in the surface relative to an optical plane (1 fringe = ½ wave)Using an interferometer with a monochromatic light source, the object part is measured against an optical flat. As light reflects in the gap between the object and the optical flat, the light will interfere with itself creating light and dark fringes or bands. As commonly measured on a helium neon laser at a waavelength of 632.8nm, each fringe is equal to .316 microns. These fringes can be counted to express flatness over a given area or evaluated as a contour map and interpreted for shape and flatness
Fringes (Power and Irregularity
Is a measurement of the small-scale variations in the height of a physical surface. A common measure of surface roughness is the rms (root-mean-square) height of the surface bumps.
Scratch and Dig - (MIL Spec XX)
Definition: The first number represents the maximum allowable scratch width in microns (20/10 = no scratches greater than 20um wide allowed). The second number represents the maximum allowable dig in 10's of microns as measured LxW/2 (20/10 = no digs greater than 100um allowed).
Typical Scratch and Dig Specifications:
120/80 Defects are clearly visible in normal room lighting. This is generally a commercial specification for glass that will be exposed to further wear.
80/50 Defects are discrete but visible in normal room lighting. This specification is typical for commercial and non critical optical applications.
60/40 Defects are visible under fluorescent lighting (1.5K Lux). This specification is common for non-magnified optical applications.
40/20 Defects difficult to detect under fluorescent light and may require low-intensity halogen lamp (5K Lux). Typical optical applications.
20/10 Defects require Hi-Intensity halogen lighting to identify (10K Lux). Common specification for critical optical applications.
10/5 Defects require Hi-Intensity halogen lighting to identify (15K Lux or greater). Common specification for the most critical optical applications.
A scratch and dig spec can be written and inspection standard developed around any known requirements. The sample specifications listed above are intended to provide a general guideline and encompass the most commonly used values.
Intensity Definition: Coresix uses a standard "K Lux" to describe the required light intensity for a given inspection criterion. Any existing or known light intensity such as foot candle, wattage, etc. can generally be converted to a K Lux standard. Once the standard is defined, the specification states "no defects visible with the unaided eye" under the specified light intensity, in the specified position and within the specified inspection time.
Typical Light Intensity Specification
1.5K Lux Typically used to identify scratches beyond 60um wide and digs greater than 400um for low-end optical or high end industrial applications.
5K Lux Typically used to identify scratches beyond 40um wide and digs greater than 200um for common optical applications.
10K Lux Typically used to identify scratches beyond 20um wide and digs greater than 100um for high end optical applications.
15K - 50K Lux Various collumated lighting used to identify defects to 1um for critical optical applications.
Position Definition: The angle, distance and/or orientation of the glass being inspected to the light source.
Angle: The angle at which the part is held to the light source can influence the visibility of a defect. The specified angle may be driven by the final application(coatings to be applied, angle to be viewed, etc.) or to achieve maximum effectiveness. Unless otherwise specified, the angle will be defined by the standard to orientation.
Orientation: The orientation of the part to the light source can influence the visibility of a defect. The specified orientation may be driven by the final application or to achieve maximum effectiveness. Unless otherwise specified, the standard orientation of inspection will be transmissive.
Distance: The distance of the glass from the light source is generally defined by the specified light intensity. However, under certain conditions it may be necessary to specify distance in conjunction with light intensity. If no specification is provided, distance from the light source will be defined by the specified light intensity.
Time: The longer an inspector looks at a glass component under any condition, the more likely he or she is to identify defects. For production efficiencythe specification is designed to identify the necessary cosmetic quality level in a minimal inspection time. Our standard inspection time averages 5-10 seconds per part.
Parallel simply means that the distances between two surfaces, in this case the front and back planes of the glass component, are constant. If the surfaces were to extend theoretically to infinity, they would never converge.
In the world of glass components, perfect parallelism does not exist. Therefore, it is necessary to set required limits and measure for accuracy. Parallelism, also referred to as “wedge”, for glass components can be defined in several ways:
Transmitted Wavefront Error (TWE) is the degree of deviation seen in the wavefront when a beam is transmitted through an optical component. Although wedge/parallelism, power and irregularity all have the potential to contribute to total TWE, most definitions of TWE include only the irregularity component. For most components, Coresix can achieve ¼ wave per inch TWE.
Total Thickness Variation (TTV) is the difference between the minimum and maximum values of thickness over the clear aperture of the component. We determine this value using a scan pattern with a dual head laser accurate to 0.1µm and can achieve TTV’s of <1µm.
Arcs (Minutes and Seconds) A minute of arc (arcminute) is a unit of angular measurement equal to 1/60th of one degree. An arcsecond amounts to 1/60th of an arcminute. So, one arcsecond is equal to 1/3600 degrees of a full circle. Arcminutes and Arcseconds can be converted to degrees of deviation from perfect parallelism, both expressing the same measurement.