Last update: 02.09.2019
Standards & norms
8.

Tolerances for standardised requirements

The basic principles for tolerances are specified in the applicable standards. However, these standards are not always sufficient in actual practice. This chapter therefore describes those applications that are listed in the standards where they are not clearly defined or are not specified at all.

The basic principles for tolerances are specified in the applicable standards. However, these standards are not always sufficient in actual practice. This chapter therefore describes those applications that are listed in the standards where they are not clearly defined or are not specified at all, and breaks them down into two categories:

  • Standard tolerances - Standard tolerances are tolerances that can be ensured during the normal course of production
  • Special tolerances - Special tolerances can be realised during production with additional precautionary measures and must be agreed upon on a case-by-case basis

Base glass

EN 572 is a normative standard for base glass.
The standard specifies the deviation limits for nominal thicknesses for various glass products. Furthermore, requirements for quality as well as optical and visible flaws in basic glass products are defined in this standard.
The following tolerances of the nominal thickness apply:

Deviation limits for glass thickness


No differentiations are made between standard and special tolerances when considering the deviation limits.

 

Cutting

EN 572 and general length dimensions also apply, in all cases ± 0.2 mm/m edge length.

 

General

The angular break must be taken into consideration! This type of break depends on glass thickness and the quality of the base glass.

Overbreak


These factors must be taken into consideration when providing information on tolerances, i. e. glass dimensions may change with a raised edge by twice the value of the angular break.
As for non-rectangular elements, the following tolerances shown in Table 2a can apply to the given angles (similar to cutback). The geometry of the elements remains the same.

Angular break values

 

Possible break-off for float glass

Cutback

 

Acute angle of tempered glass, laminated safety glass, IGU-cutback (zone not to be assessed)

Due to manufacturing reasons, the glass manufacturer reserves the right to cut back, according to Table 2b. If such a cutback is not performed, the measurements listed in Table 2b are considered zones that are not to be assessed. In this case, unevenness at the edges (e.g. upper breaks) and on the surface may occur and are not a reason for complaint.

If the angle is > 25°, the cutback equals the break-off. The tolerances listed in Edge processing chapter, Table 6 should not be added to the tolerances mentioned above in Tables 2a and 2b.
 

Cutback

Length, width and perpendicularity

Based on the nominal dimensions of the length H and width W, the glass pane should fit into a rectangle that has been enlarged in size by the upper deviation limit and reduced in size by the lower deviation limit.
The sides of this rectangle should be parallel to each other and share a common middle point (see fig. 4). The rectangles also describe the limits of perpendicularity. The deviation limits for the nominal dimensions of length (H) and width (W) are ± 5 mm.
 

Angularity

Processing

The tolerances depend on the respective type of edge processing. In addition, EN 14179 and national requirements, such as DIN 1249, Part 11 in Germany, also apply.

 

Edge processing qualities

Special rectangle deviations

 

Standard tolerances

Edge processing is divided into bordered, ground, smooth ground and polished. Therefore, there are two tolerance categories:

•    The tolerance with angular break indicated in “cutting“ applies to bordered edges.
•    The following table applies to smooth ground / polished edges.

Standard rectangle deviationsEdge processing

The diagonal deviation is derived from w2 + h2 Example:

glass pane     w · h = 1,000 x 3,000 mm

therefore:    plus dimension:    √1,52 + 2,02 = +2,5 mm
minus dimension:     √1,52 + 2,52 = -2,9 mm;
therefore:    diagonal deviation:     + 2,5 / - 3,0 mm

 

Special tolerances

The tolerances listed in Table 4 can be realised with an increased effort. This special effort is necessary because the first glass pane must be measured exactly. Unground glass panes should be recut in this respect.

 

Special shapes

The following table applies to 15 and 19 mm glass:

Special shapes

 

Edge processing 

Edge processing

 

Processing (cut-outs, notches)

Processing can involve corner cut-outs, surface cut-outs and edge cut-outs in a glass pane. Positions and dimensions of processing should, where not standardised, be agreed to suit each production situation. As for corner and edge cut-outs, the minimum radius of the processing tool should be considered. The hole position and/or position tolerances of different kinds of processing are the same as the edge processing tolerances.

Corner cut-off, seamed < 100 mm x 100 mm

Standard deviation ± 4 mm

Corner cut-out, seamed 

Standard deviation ± 4 mm to position/deviations

Edge cut-out, seamed

Standard deviation for manual processing – cut-out dimensions

Edge cut-out deviation

Standard deviation for CNC processing – cut-out dimensions

Important: 
minimum dimension with internal radii: 15 mm

Edge cut-out deviation CNC

Corner cut-off, smooth ground

Standard deviation ± 2 mm (Edge cut-off < 100 mm x 100 mm otherwise special shape)

Special deviation ± 1.5 mm Production performed in CNC processing centre

                      
Corner cut-off, polished - CNC processing centre

 

Standard

Standard deviation ± 2 mm
(Edge cut-off < 100 mm x 100 mm, 
otherwise special shape)

Special shape

 

Special deviation

Deviation ± 1.5 mm

 

Corner cut-out, smooth ground 

 

Standard

Depending on the glass thickness, minimum distance with internal radii:
≤  10 mm: R 10 
≤  12 mm: R 15 
Deviation of size ± 2 mm
Deviation of position ± 3 mm

 

Special deviation

Minimum dimension with internal radii: 17.5 mm, deviation 1.5 mm. 
Special processing is performed in the CNC processing centre.

 

Corner cut-out, polished - CNC processing centre

Minimum dimension with internal radii: 17.5 mm

Standard

Deviation ± 2 mm

Special deviation

Deviation ± 1.5 mm

 

Edge cut-out, smooth ground or polished - CNC processing centre

Standard deviation

Minimum dimension with internal radii: 17.5 mm

Edge cut-out deviation CNC

Special deviation

Minimum dimension with internal radii: 17.5 mm,
Deviation ± 1.5 mm

 

Drillings

The drilling positions and/or position tolerances correspond to the edge processing tolerances.

 

Diameters of drilled holes

The diameters Ø of drilled holes should not be smaller than the glass thickness. Please enquire separately from the manufacturer regarding small diameters of drilled holes.

 

Limitation and position of the drilled hole

The position of the drilling (edge of the hole) relative to the glass edge, glass corner and next drilling depends on:

•    glass thickness (t)
•    diameter of the drilling 
•    shape of the glass pane 
•    number of drillings


 

Position of hole relative to edgePosition of holes

Limitation and position of the drilled hole

 

Deviations in drilling positions

Deviations in the position of individual drillings equal those of width (W) and length (H) from Table 11.

Deviations in drilling positions


The position of the holes is measured in perpendicular coordinates (X & Y-axis) from the reference point to the centre of the hole. The reference point is generally an existing corner or an assumed fixed point. The position of the holes (X, Y) is (x ± t, y ± t), where x & y are the required distances and t is the deviation.

Deviations in drilling positions

 

Drilled hole positions

Drilled hole positions

 

Drilled countersung hole diameters

Diameter:
≤  30 mm: ± 1 mm
>  30 mm: ± 2 mm
 

Countersunk hole deviation

 

Drilled countersunk holes in laminated safety glass

The cylindrical drilled hole of the opposite glass pane must have a 4 mm larger diameter compared to the core diameter of the drilled countersunk hole.


 

Drilled countersunk holes X

 

 

 

 

min. glass thickness

 

Drilled countersunk holes

 

Tempered glass, tempered heat-soaked glass and heat-strengthened glass

Following standards apply:
EN 12150-1/-2 for tempered glass
EN 14179 for heat-soaked tempered glass
EN 1863 for heat-strengthened glass
 

 

General distortion – uncoated float glass

The induced stress conditions can produce an overall bow.
Standard 0.3 % of the measured length. To be measured at the edges and diagonal, where none of the measured values may exceed 0.3 % of the measured length. With square formats with side ratios between 1:1 and 1:1.3 and with glass thicknesses ≤ 6 mm, the deviation from the straightness is larger compared to narrow rectangular formats due to the toughening process.
 

General distortion

Local distortion (roller waves) – uncoated float glass

Glass that is passed horizontally through an oven may contain a very slight surface distortion (wave) caused by contact with the rollers. The reason for this is softening of the glass at the end of the heating cycle. 


 

Local distortionLocal distortion

 

Standard 0.3 mm over a distance of 300 mm of the measured length. The measurement must be performed in a min. distance of 25 mm to the edge.

 

Recommended minimum glass thickness depending on the glass dimensions

Due to the thermal tempering process, we recommend the following size-dependent minimum glass thicknesses. In this context, application requirements are not considered.
 

Minimum glass thickness

Insulating glass units (IGU)

Following standards apply:
EN 1279-1 ... -6 (insulating glass)
EN 1096-1 (coated glass) 
supplemented by national requirements.

Edge seal

The structure of the edge seal corresponds to the system specifications of the manufacturer. The maximum deviation of the edge seal width is ± 2.5 mm.
 

Thickness tolerances in the edge area of the insulating glass unit

The actual thickness should be measured at each corner and near the midpoints of the edges between the outer glass surfaces. The measured values should be determined to an accuracy of 0.1 mm. The measured thickness values may not deviate from the nominal thickness specified by the manufacturer of the insulating glass units by more than the deviations specified in Table 13. The thickness tolerances of insulating glass units with multiple pane cavities are ensured by adhering to the following rules:


a)    determine the tolerances of every single glass/cavity/glass formation according to Table 13
b)    calculate the squares of these values
c)    sum the square values
d)    take the square root of this sum

Thickness tolerances


Dimension tolerance / offset

The dimension tolerances are calculated from the tolerances of the primary products used in insulating glass units plus the possible offset dimensions from insulating glass unit assembly.

Dimensions tolerances

 

Laminated safety glass

Laminated safety glass consists of two or more glass panes that are connected to form an inseparable unit by means of one or several polyvinyl butyral (PVB) films. A distinction is made between glass with a PVB film thickness of 0.38 mm and glass with a PVB film thickness of at least 0.76 mm.

Dimensional tolerances

The tolerances generally comply with EN ISO 12 543.
Laminated safety glass is distinguished according to its structure: laminated safety glass 0.38 PVB, laminated safety glass from 0.76 PVB, laminated safety glass with sound protection film (sound control laminated safety glass) and laminated safety glass with coloured film (PVB).
The respective dimensional tolerances of the semi-finished products used in the laminated safety glass element apply, and additionally the permissible displacement tolerances as shown in Tables 16 and 17.

Limit sizes for dimensions

 

Example:
Laminated safety glass made of 6 mm tempered glass / 0.76 PVB / 6 mm heat-strengthened glass; polished edges. Deviation of the single pane: ± 1.5 mm, additional offset tolerance: ± 2.0 mm.
The permissible offset tolerance adds up to ± 3.5 mm

 

Displacement tolerance (offset)

The individual panes might be displaced during the laminating process for manufacturing reasons. 

The cutting tolerances are added to the displacement tolerances. The longest edge of the element is used in tables 16 and 17. 
Offset

 

Permissible maximum dimensions

 

Thickness tolerance

The thickness deviation of laminated safety glass should not exceed the sum of the individual glass panes, which is specified in the standards for basic glass (EN 572). The tolerance limit of the intermediate layer must not be taken into account if the thickness of the intermediate layer is < 2 mm. For intermediate layers ≥ 2 mm a deviation of ≤ 0.2 mm is taken into account.