Fig. 252.

The old system of stripping, which is even now practised to a certain extent, is to have a slot cast through the back of the press in single-sided presses, and in double-sided presses a slot cast through each side of the press-frame casting. This slot is of sufficient width and depth to receive a hexagonal-headed bolt, and allow of the bolt being raised up and down for adjustment. A wrought-iron angle forging is fastened to the press-frame by means of the bolt and a strap plate, the bolt passing through the angle-iron and the slot in the press-frame. The angle-iron can either be made to act as a stripper, or some other form of stripper may be mounted and securely fastened to it. An angle-iron stripper will be seen at fig. 252. This angle-plate method of stripping is a rough-and ready one, and is used with some success for rough sheet-iron work. It cannot, however, be recommended with safety for general work for several reasons.

Firstly, this stripper arrangement depends too much upon the ability and expertness of the tool-setter. Secondly, this stripper is apt to be used for too many kinds of work. Thirdly, as the stripper is held against the face of the press-frame by a bolt, there is considerable leverage upon the angle-iron, which springs the whole stripper arrangement.

In many instances a tool-setter will take advantage of this springing action for the purpose of throwing the work from the tools, and it is done in the following manner: After a blank is pierced, the punch on the return stroke carries the blank up to the stripper, and this in turn forces the stripper to spring upwards, and directly the blank is removed from the punch the pressure is released from the stripper, which now returns to its normal position, and thereby throws the blank some distance from the tools. This fact will demonstrate that a fair amount of springing action occurs with this type of stripper, which is detrimental to both work and tools.

The reason why the angle-iron type of stripper, fig. 252, is used so extensively is that it can be used for various sizes of work, even though there may be a large clearance between the piercing punch and stripper hole, which may cause the blank to be bent or otherwise distorted during the process of stripping.

Suppose twenty sets of tools, all differing, are to be used in a particular power or screw press; one angle-plate stripper can be used for the twenty sets of tools by using various iron-plates (see fig. 252), where the additional stripper-plate S P is attached to the angle-plate stripper A IS. The only instance where this type of stripper has been known to work successfully was when the angle-plate forging was planed square, and had a rib upon the back, as fig. 252 at R, to fit the slot in the press-frame. Also when used on a doubleaided press, and two separate and well-made angle-plates have been fixed, one on either side of the press-frame, set level with each other, and planed upon the top (see fig. 253 at T), to receive various special stripper-plate forgings, which have in turn been planed, bored, and turned perfectly square and true, as at F. It is, however, seldom that one can meet with strippers of this type made and finished in the manner they should be if good work is to result.

Fig. 253.

From what has here been mentioned in reference to the angle plate type of stripper, it will be readily understood that, when possible, it is advisable to dispense with it, and substitute a more reliable form.

An excellent combined stripper-plate and metal-guide is shown at figs. 103, 104, and 105, arranged to be fixed to the die bolster, and intended for cutting chain-link blanks. In this case the stripper is raised and lowered by means of lock-nuts, and the two small bars across the underside of the stripper-plate are placed at a sufficient distance apart to admit the steel strip from which the blanks are to be cut. When a set of tools are fitted up in the manner shown at figs. 103, 104, and 105, the punch may be removed from the press after a batch of blanks have been cut, and punch, die, bolster, and stripper all stored away together ready for immediate future use.

The proper method is to provide every bolster with its own stripper or strippers, which should be made suitable for the various sets of tools. It is necessary that the bolster be planed on the top, and have suitable holes drilled and tapped to receive the stripper holding-down pins. A stripper may either be fixed in this manner, or it may be attached as shown at figs. 103, 104, and 105.

Fig. 254.

A stripper to work efficiently must be set at right angles to the side of a punch, and absolutely level with the top of the die, and the hole in the stripper should be of sufficient size to comfortably pass the punch. When a punch is raised up it should, after piercing a blank, bring the whole surface of the blank into contact with the under side of the stripper (see fig. 254); the blank will then be removed from the punch with an easy sliding action, and without placing any side strain upon the punch, as would happen if the stripper were set as shown at fig. 255. It will readily be 18wp seen in this figure that the slipper-plate S P is not set level; consequently the blank touches at a and is off at b. When tools are set in this careless manner trouble will arise. Owing to the improper use of strippers and tools it is not unusual for much time to be wasted.

It is interesting to trace the proper method of setting the tools seen at figs. 102 to 105.

Firstly, the punch should be firmly fixed into the press-ram by means of the Bet-pin in the ram, the pin preferably being screwed up by a steel box-spanner, since it gives a better purchase than can be obtained by an ordinary spanner. Secondly, after fixing the bed into the centre of the bolster, bring the latter under the punch, which carefully lower into the bed. Place the bolster holding-down pins into position, and lightly nip them down; raise the punch and again carefully lower it into the bed, making quite certain that it does not come in contact with the cutting edge of the bed. Next screw down both holding-down pins, proceeding a little at a time-first one pin, then the other. Thirdly, place the stripper in position on the bolster, the guide-bars resting upon the top of the bed. Place a piece of metal upon the bed, and cut one blank; the punch should then be raised up until the metal strip touches the under side of the stripper, which may now be set level with the metal strip. If instead of the stripper being fixed by lock-nuts it had been fastened upon the top-surface of the bolster, it would not have been necessary to test for being level. The idea of using the lock-nuts in the tools, fig. 104, is to enable beds of various thicknesses to be used, without the necessity of packing pieces. Now, suppose the tools which may have been working a few hours require grinding and re-setting, the bed-key can be driven out, tig. 102, and replaced after the bed has been ground, enabling the tools to be re-set in considerably less time than had the bolster been loosened.

Fig. 255.

When cutting blanks from sheet-metal without the assistance of feed-rolls, it is usual to fix a stop-peg in the bed to enable the operator to bring the metal in the proper position to cover the hole in the bed. Were it not for this peg, it would be practically impossible for an operator to leave a uniform amount of scrap metal between each pair of blanks. A bolster B and a bed D are shown at fig. 256, fitted with the stop-peg P, the end E of the metal M being brought up against the stop-peg whilst the first blank is cut Previous to the second blank being cut, it will be necessary to lift the metal over the peg P, so that it comes into the hole made by the cutting of the first blank; this places the metal M in the proper position ready for the second blank to be cut The bed is here seen fixed in position by the key K, and the stripper-plate S is secured upon the bolster casting at A. Fig. 257 is a plan of the stripper-plate, and it will be noticed that the hole in the stripper-plate is slightly larger than the hole in the cutting bed.

Fig. 256.

Fig. 257.

Fig. 258.

Fro. 259.

Fig. 260.

The tools, fig. 258, are for piercing a round hole in the blanks that have been previously cut by the tools, figs. 256 and 257. Referring to fig. 258, a guide plate G P is fixed upon the piercing die, to ensure the metal-blank M B being pierced centrally.

The stripper S is fastened at A, and this part of the bolster casting is raised up a sufficient height to allow proper freedom of space between the stripper and guide plates. A plan of the piercing tools is shown at fig 259 from which the position of the stripper and guide plates will

Fig. 261.

Fig. 260 represents another type of bolster to receive a similar pair of piercing tools to those at figs. 258 and 259 the difference being, that whereas in fig. 260 the stripper Plate is fastened to the bolster at A, and the guide-plate is fastened on to the bolster at H, in figs. 258 and 259 the guide-plate is fastened on to the bed itself.

Another design of bolster and tools is shown at fig. 261. This set of tools is arranged for piercing the same blank as the tools, figs. 258, 259, and 260 were, but in the case of fig. 261 both the bolster and the bed are cylindrical in form.

The stripper-plate S P is secured to the raised portion A of the bolster-casting B, whilst the guide-plate GP is fastened to the top of the bolster at T1T1. Three set-pins, a, a1, a2, are intended to enable the tool-setter to move the bed about until it is set in the proper relative position with the guide-plate, to ensure that the blanks shall be pierced centrally.