80 W. R. TRAVISS ON AN EXPANDING STOP FOR 



spirit-flame or a gas-flame turned down to a small blue light. 

 Take the sheaves with the pins in one by one, try how little 

 salamrnoniac you can use, and when the sheave is getting of a 

 reddish colour, not red-hot, touch it with the tip of one of the 

 thin, hair-like strips of solder. If overdone, brush off the excess 

 with the feather, and with a little practice this can be done very 

 neatly (Fig. 4). Next nip oft' each pin close to the top so that 

 there is now one headless pin pointing up and one down. Take a 

 piece of metal of the O04 gauge, drill a hole in it, and clamp it 

 in the vice. Let the hole be made to just free the pins. Now 

 put each pin through this hole, nip off close to the brass, and with 

 a small, fine, smooth file take off the sharp edge left by the nippers. 

 If a slight burr is raised on the pin, it can easily be forced out 

 with a sharp point. It must on no account be pulled through, or 

 the sheave will be bent, and it is most important that it should 

 be quite flat with a pin on each side. Having made a dozen or 

 more in this way, we can now go on to the next step. 



If a sheave is made to pivot in the plate used as a template 

 (Fig. 2) at A, and moved round it from B to D, the pin B, when 

 at E, will be at the nearest point to the centre, and the dis- 

 tance from C to E will be the length of the slot (to be presently 

 described) for the upper plate. Now take a disc of O04 brass, 

 and using Fig. 1 as template, mark off all the holes round the 

 edge at regular intervals ; then scribe a circle from the centre to 

 E, Fig. 2, and draw radii from the centre to each hole as accur- 

 ately as possible. Drill holes at C and E that will just allow the 

 pin to pass and no more. Drill a series of such holes along the 

 line of the radius from C to E as close together as possible, and 

 then, with a very fine needle file, break through the metal between, 

 so as to convert the line of holes into a slot, Fig. 5. Two or three 

 files may be required before the plate is completed, unless they 

 are very carefully used, as the tips break very easily. The slot is 

 finally smoothed out with the flat part of the file. When all the 

 slots are cut, see that a pin passes freely up and down them. 

 The action of one sheave can now be shown by passing a pin 

 through the centre, having one sheave in Fig. 1, and then putting 

 the plate, Fig. 5, on the top ; holding the lower one between the 

 fingers of one hand and twisting with two fingers of the other, it 

 will be seen whether it clears the slot at E. The reason for a 

 limit to the number of sheaves and the distance at which the arc 



