2.1 Selected Form Elements

Basic Technical Terms and Definitions

In the exercises, the CAD system Siemens NX is used to create various elements and parts that are well known to some. But many do not know what they represent and what they are used for. Therefore, some of the elements used in the exercises are listed below with a brief explanation.

• Shaft: A shaft is a machine element for transmitting torque. It is used in all areas of mechanical engineering: e. g. as a smooth shaft in gear construction or as crankshafts in motors for converting linear movements into rotational movements and vice versa.

• Axis: An axis is geometrically similar to a smooth shaft, but it does not transmit torque. Axles are used to support and store other parts such as rollers or wheels. They can be fixed or rotating. Example: Deflection rollers on pulley blocks run on axles.

• Boreholes: Holes are divided into through holes and blind holes. Through holes run through the entire workpiece, i. e. the drill bit exits at the bottom of the workpiece. Blind holes, on the other hand, are only inserted into the workpiece up to a certain depth, which results in the so-called drill cone, i. e. the conical "bottom" of the blind hole.

Both hole types are shown in the picture above. The middle hole is a countersunk hole. It is used to countersink the head of the screw completely into the workpiece in case of a screw connection. In the following some examples of bolted connections of two workpieces are shown, where the mentioned hole types occur.

• Rounding: Roundings are usually attached to shafts that have heels with different diameters distributed over their length. They are located where the shaft diameter changes "abruptly". Roundings usually have manufacturing reasons, i. e. machining the shaft is easier. However, they also offer advantages in terms of the strength of the shaft, as the stress distribution in the shaft is better.

• Undercut: With undercuts, the turning tool can run out freely during the production of turned parts. Undercuts ensure an exact attachment of adjacent components and you reduce the notch effect by avoiding a sharp-edged transition. They are standardized according to DIN 509 (see chapter "3.3. undercuts according to DIN 509: Form E and F").

• Chamfer: Chamfers are bevelled surfaces (usually at an angle of 45°) created by machining an edge. Most parts that are machined and later come into contact with people are chamfered to avoid sharp edges and injuries and to remove the burr, and/or to enable installing of gears or bearings.

• Slot: A slot is an oblong guide or fitting recess, usually with a rectangular cross-section, which occurs in shafts, beams, plates, etc. The groove not only guides a part into its seating position, it also often forms a positive connection. The most frequently used slots in mechanical engineering include the keyway (in shafts), the T-slot (e. g. in machine tables) and the annular groove (on shafts or axles).

• Rib: Ribs are used to reinforce and strengthen flat components. They are usually attached to the respective part in the form of additional bracing or are directly included e.g. for castings by the mould. Ribs offer some advantages in casting: they take up loads and thus prevent component deformation, cast cores can often be saved by ripping (lower costs) and when cooling the parts, they keep distortion to a minimum.

• Flange: A flange is an element that is always used where parts have to be connected which, due to their geometry, do not offer any space or "point of contact", e. g. for screws or similar things (example: pipe ends). Flanges are disc-shaped or plate shaped components which are fastened to the ends of the parts to be joined, e. g. by welding. Only through a flange the space for e. g. a screw connection is created.