The lathe test indicator, fig. 232, is for use in setting central any point or hole in a piece of work to be operated upon in a lathe or upon a lathe face-plate. It may also be used for testing lathe centres, shafting, or other work held between lathe centres, the inside or outside of cylinders, pulleys, etc., and all work of a similar class. The tool is of such size as to be held conveniently in the tool post of a lathe; the bar is drop-forged and formed at the end to receive an universal joint for supporting the finger. A clamp nut is provided for clamping the joint when it is desired to have only a vertical movement to the finger, as in testing pieces held between lathe centres. The bushing which holds the finger is split, thus allowing the finger to be adjusted to any-required length, and clamped in position. The finger holder is provided with two fingers; either one of these may be quickly attached; one finger is ground to an angle of 60 deg. and the other is bent for inside and outside testing. A spiral spring is provided for holding the finger against the work with an even pressure.

Fig. 232.

Fig. 233.

An improved instrument known as a centre-tester, fig. 233, is of a special design for use in adjusting and locating central any point or hole in a piece of work, which is to be operated upon, in a chuck or upon a face-plate. The tester is shown fixed in a tool post ready for use; a steel bead (not shown) is carried on the needle, it slips over the point of same, when used for inside work. The instrument is joined to a tool post shank by a flexible steel ribbon, with sufficient spring to properly hold the needle in contact with the work. The ball through which the indicating needle passes is pivoted to form an universal joint, but may be instantly converted into a single joint for a tilting motion, by tightening the knurled nut.

Fig. 234.

Fig. 235.

Another test indicator, fig. 234, is especially serviceable to those who have the erecting or inspecting of high-class machines, as it is possible by its use to readily determine the degree of inaccuracy of a surface on the top, bottom, or side of a piece of work, or to easily ascertain the amount of end movement, for example, of a spindle, or the extent to which it runs out of truth. The illustrations, figs. 235, 236, 237, and 238, show a few of the many applications of the test indicator. The upright post or stand may be clamped at any point upon the base by the thumb nut, and the sleeve which carries the arm may be fastened at any height on the post, or turned around the post to bring the arm on either side. The arm turns in the sleeve, and may be set at any angle relative to the base; it may be converted so that the point brought in contact with the work will be downward rather than in the position shown in fig. 234, or

Fig. 236.

Fig. 237.

Fig. 238 it can be removed from the post and used independently. A split block and an angular post are furnished with this test indicator, for use in the tool-post of a lathe. The movement of the point that bears against the work is magnified a number of times by the length of the index finger, and can be easily read upon the scale. The finger can be adjusted and brought to zero by the knurled screw shown. It is enclosed and protected from injury, and stops are provided for use on the underside of the base against perpendicular or angular surfaces; the length of the base is 8 in., the height of the post 9 in., and the graduations read to thousandths of an inch.

One method of setting for boring two holes at a definite distance from centre to centre is represented at fig. 239. For example, the holes required to be bored in a steel die A are between their centres. This method is frequently used in first-class workshops, but although very useful under certain conditions, it is not a sure or reliable method. The least speck of dirt between the faces of P and A 2 will alter the measurement, besides special packing pieces being required for every different measurement.

Fig. 239.

1/2 in. diameter, and their centres 1 in. apart. F P1 represents a lathe face-plate, upon which is fixed the steel die; this is shown set in the position required for the first hole to be bored. S is an iron plate to prevent the die A 1 from dropping. Another small iron stop plate S 1, is to prevent the die A 1 from dipping sideways. The small iron straps or plates and bolts for holding the die upon the face plate are not shown. The setting of the die would be done with the assistance of the special centre tester as represented at figs. 232 and 233. Having bored the first hole, the die is moved along the stop-plate S a sufficient distance to allow the packing piece P to be introduced; this piece is filed up to measure exactly 1 in., and consequently the two holes in the die will be exactly 1 in.

Another method of setting for boring holes is seen at fig. 240, and may be depended on to give absolutely accurate results. Referring to the figure it will be see that the die has been fixed by the aid of a centre tester, and the stop plate S brought up to the die, and the first hole bored. We will now trace the means by which the new position is found. Referring to the section it will be noticed that a standard 1/2 in. plug gauge B has been inserted into the first hole. 17wp

Fig. 210.

This 1/2 in. plug must necessarily be a good fit. A second plug A, which may be any diameter (in present instance 5/16 in.), is made in the form of a lathe centre, and is fixed into the barrel of the movable headstock of the lathe. It will be readily seen that by means of these two plugs it is easy to so fix the die A 2 upon-the face-plate as to enable holes to be bored at any required centre. Taking the example of the 1/2 in. holes of 1 in. centres, here we have 1 in. centres plus half 5/16 in., plus half 1/2 in. = 1.406 in. Therefore, when the micrometer gauge just passes over the plugs, then the die is set for holes at 1 in. centres. One practical application of the method represented at fig. 240 was boring the two holes in the standard die or cutting-out bed, fig. 91.

Another method by which two or more holes may be drilled at any centres is shown at fig. 241. In this case the centres are fixed by means of steel bushes and packing pieces. To make the method readily understood, we may for simplicity still keep to the steel die having holes 1/2 in. diameter, and 1 in. centres. X is a piece of steel measuring 5 1/2 in. in length, 2 in. wide, and 1 in. thick. This has a slot 4 in. long and 1 in. wide running along the centre. Into this slot two steel bushes 1 in. diameter and 1 1/4in. long are introduced, the bushes having 1/2 in. holes bored through them, and they are hardened and ground perfectly true.

Fig. 242.

Then when these two bushes are brought together their centres will be exactly 1 in. apart, and since they are firmly fixed together by means of packing pieces and set pin, the whole arrangement becomes at once a simple form of drilling jig. The packing pieces being .250 in., .375 in., and .5 in. thick, when placed between the pair of steel bushes the centres of these bushes will be l.250in., 1.375 in., and 1 .5 in. apart respectively.

At fig. 241 Z is a section showing the method by which No. 2 hole is drilled. The die D I is coupled to the drilling jig by means of a steel plug S P, and a 1/2 in. twist drill is passed down the second bush, and its point penetrates the die a short distance, sketch D 2, fig. 242. The next step is to pass a 3/8 in. or7/16 in. twist drill through the die-(see D 3)-then finally pass the 1/2 in. twist through the bush and die (sketch D 4). This system has been adopted for making a variety of tools and jigs for drilling and piercing, and has been found useful and reliable.

The sketches, figs. 243, 244, 245, indicate the usual method by which a piece of work to be bored is fixed upon the face-plate by bolts and strapping plates. These sketches further show the principle of the centre tester. Referring to fig. 243, the steel die A is fixed upon the face-plate F P ready (in this instance) to have a hole bored in it. The die A is held by S and S1. There are two wood packing pieces W P between the straps and the face-plate. No stop plates are required on this work, since there is only one hole to be bored; but there are instances where it may sometimes be advisable to use one or more stop plates, so as to prevent the work being accidentally moved whilst boring-as for example, when heavy l>oring cuts are being taken, or when a piece of work is of delicate strength and peculiar shape. In instances of this kind the stop plates, besides holding the work steady, also drive it in a similar manner to that that the driving peg drives a lathe carrier when a shaft is being turned.

Fig. 243.

The old method of setting work true upon a face-plate was to describe a large circle upon the surface, as at 0, fig. 243. A pointed piece of steel was then fixed in the toolbox, the point being brought close up to the c rcle whilst the lathe was in motion, thus indicating if the circle 0 ran true. This large circle is not necessary if a centre tester is used. It will be noticed that a smaller circle N is shown, which has been described from the centre dot C upon the die A, and is equal in diameter to the hole that is to be bored. At figs. 244 and 245 a ring R is seen, into which the steel rod a, having both ends pointed, is fixed, and another rod b, having one end drawn out to a long taper terminating at a point. These two rods a and b are in perfect alignment; one end of rod a is held in the centre dot c of the die, whilst the other end is placed into another centre hole d of the holder B. This apparatus demonstrates the principle of the delicate special centre-testing instruments described in figs. 232 and 233. As may be judged from the sketches shown at figs. 244 and 245, this is an apparatus that can be made in any ordinary tool-room, and, though of rougher character than fig. 233, it is very useful. The position of centre hole d, at fig. 24 4, would be determined by placing it against the lathe centre. B is fixed into the tool holder by the clamp plates D and D1. In fig. 245 it will be seen that the length of rod a is 2 in., whilst the distance from d to the extreme end of rod b is 10 in., or a ratio of 5 to 1. So that, when testing a piece of work for being set true, should the centre dot c run out of true 1/32 in, the extreme end of rod 6 would run out of true 5/32 in., thereby magnifying the inaccuracy. From this it will be readily understood that the centre tester is of great assistance when setting work.

Fig 244.

Fig. 245.