Centre punches

The centre punch is used to provide a centre location for dividers and tranunels when scribing circles or arcs, or to show permanentiy the position of a scribed line by a row of centre dots. The centre dot is also used as a start for small diameter drills. 

Centre punches are made from high carbon steel, hardened and tempered with the point ground at 30° when used to provide a centre location for dividers and at 90° for other purposes. 

State tuvo uses ot a centre punch when maildng out... 

Unless the workpiece is held in a drill jig, the position of holes on a workpiece must be marked out. When the position of a hole is determined, its centre is indicated by means of a centre dot, using a centre punch. This centre dot is used to line up the drill and as a means of starting the drill in the correct position. The workpiece is set on the worktable, carefully positioned under the drill, using the centre dot, and clamped In position as shown in Fig. 8.19. Two clamps are usually required, one at each side of the component. 

State two uses of a centre punch when marking out. 

There are several mechanisms by which wow can occur. One cause is a variation of rotational speed of the recording medium during either recording or playback. A further cause is eccentricity in the recording or playback process for disc and cylinder recordings, for example a hole which is not punched perfectly at the centre of a gramophone disc. Lastly it is possible for magnetic tape and optical film to become... 

Colored Stars may be mode by using any of tho receipts for colored fires, with a solution of isinglass, ounce camphor, ounce and alcohol, J ounce. Make into cylindrical cakes of the requisite size, punch a hole in the centre of each, roll in gunpowder, and dry in tho sun. 

It should be noted that this discussion assumes that only one punch is actively applying the force to the powder mass while the other is stationary and passive. This is true in the case of an excentric press, but with a rotary tablet press, both punches move and hence both exert forces on the powder bed. The force distribution so obtained is thus different from that shown in Fig. 7, and results in two low density zones near the faces of the tablet and a high density zone in approximately the centre of the powder mass. 

Filling and injection stroke Plunge-in stroke top-punch Tablet th ickness in lower dead centre Return-expansion of pressed article... 

Different methods can be applied to impose a bending moment on a sheet metal blank (Lange 1985). The most common techniques consist of positioning the sheet to be formed with the bend line coinciding with the centre line of a V-die and pressing a punch tool in the orthogonal direction (Fig. 1 right). The force... 

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