Natural stones are classified by genesis, sedimentation and structure. For measuring equipment and on the precision sector, plutonic rock is preferred, as these materials offer a very dense and homogenous structure.

Compared to synthetic materials, natural products show a greater spread of properties. This spread is due, inter alia, to grain structure (size), microstructure and density.

Other stone types used today as material for precision machine manufacture:

–    Belfast (South Africa)
–    Diabas (Sweden)
–    Kuru Grey (Finland)
–    Bohus (Sweden)
–    Tarn (France)
–    Jinan Black (China)

– DIN 876 for flatness
– DIN 875 for rectangularity
– DIN 874 for parallelism

In our manufacturing process, we apply the general tolerances (precision measurement tolerances) of DIN ISO 2768. Irrelevant dimensions are approximations.

The accuracy of our products is due to consistent measurement conditions, i.e. a workpiece temperature between 19°C and 21°C for example, with admissible temperature variation of max. 0.1°C in 2 hours, and of +/- 0.5°C in 24 hours, and the machined workpiece evenly tempered through. A temperature variation between 0.2°C to 0.5°C is allowed, depending on the device’s specific grade. Consequently, our products are manufactured in air-conditioned rooms, allowing temperature instability of max. +/- 0.2°C during final machining and pre-delivery inspection.

For consistent, repeatable accuracy of measuring devices placed on auxiliary equipment, for example on one-leg supports, floor units etc., painstaking setup is an essential precondition.

Requirements for a Correct Setup:

The right distance to placed plate: We will at all times specify this distance, which depends on the manufacturing process.

– correct, tension-free setup:

1. assembly on three defined exterior spots     (see illustr.)
2. levelling on these three spots (horizontal    positioning)
3. all other support elements are just    manually positioned (tilt protection)


Standard structured varnish coating of the products in this catalogue is grey (RAL 7001).


Designs not included in this catalogue (special designs) must be listed separately in the purchase order.

DESIGN FEATURES

If a design is to benefit from a material’s favourable properties, it must suit the material. It must consider the raw material’s origin to be able to use its economic advantages. Whereas struts and thin-walled components are favoured for steel and cast designs, stone demands massive construction.

Initial product for a component is a cube or cubiform module (refer to small Abbildung on page 45), covered with a blast skin/crust that must be removed. Tempering is required for every further ablation. Consequently, thin-walled components or ribbed design are not recommendable from the economic viewpoint.

Presently, research focuses on the development of economic machining procedures. The target is the economically efficient manufacture of functional elements that can be directly co-moulded (e.g. when using certain casting materials).

Basically, there are two methods of joining natural stone components:

A: By screwing, i.e. by detachable bond

Threaded inserts (table 2) are glued into granite. A minimum distance - defined by amount and type of load - must be observed in bonding threaded inserts. Common reference value for the edge distance of the core drilling is one to one-and-a-half times the socket diameter.

B: By gluing, i.e. by permanent bond/only      destructively detachable. Methods are      surface and gap-gluing.

Surface gluing means the application of glue across the entire contact zone between components. By filling defined gaps, the glue is applied onto limited areas only. This method allows definition and co-ordination of the components’ positions.

Mixed systems are also common: Components are aligned and then screwed together. Gluing secures the components’ positions.

Sketch: Screwing principles for and
               onto granite


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