How to Make a Phonograph.
By Shelford Bidwell, M.A., LL.B.
I SHALL assume that readers are acquainted with the nature and principle of the instrument. The most important part of it is the cylinder. This, in my phonograph, is a hollow brass casting, 4 1/2 inches long and 4 1/2 inches in diameter. It is mounted upon an iron spindle, 3/4 inch in diameter and 16 inches long, at one end of which is a winch handle. Upon that part of the spindle which lies between the handle and the cylinder a screw is cut, having eight threads to the inch. The other end of the spindle is left plain. The cylinder having been turned perfectly true, a screw is cut upon its surface of exactly the
same pitch as the screw upon the spindle — i.e., eight threads to the inch. Tbe depth of the spiral groove thus formed is 1-16 inch, and its breadth is 1-16 inch. It is better to cut it square, and not V -shaped. Two brass bearings for the spindle are made of the following dimensions— length, 2 1/2 inches ; thickness, 1 1/2 inch ; height, 1 1/2 inch. One of these has an inside screw corresponding to the screw upon the spindle. Each bearing has two holes for screwing it to the support, as may be seen in Fig 1. which is engraved from a photograph of the instrument. The cylinder, spindle, and bearings being completed, ten pieces of wood must be prepared as follows : — A is 12 inches x 9 1/2 inches x 1 1/2 inch.B is 3 inches x 3 inches x 1 1/2 inch. C is similar to B. D is 5 1/2 inches x 5 1/2 inches x 1/2 inch, and has a circular hole, 2 1/2 inches in diameter, cut in its centre. E is similar to D. F is 5 1/2 inches x 5 1/2 inches x 1/2 inch, and has a hole, 1 inch in diameter, in its centre. G is 5 1/2 inches x 2 1/2 inches x 1/2 inch.H is similar to G. I is 8 inches x 2 1/2 inches x 1/2 inch. K is similar to I. B and C are the upright supports for the bearings, one of them being shown in Fig. 1. The position of the others is indicated by the letters corresponding to them in Figs. 2and 3. The uprights B and C are fixed near to the ends of the baseboard, A, by means of 2 1/2 inch screws. D and F are screwed together (see Fig. 1.), and the two are then fixed perpendicularly upon G. G is joined to I by a pair of hinges. The two ends of I are screwed to the baseboard, but the holes in I are 1/2in. larger in diameter than the screws which pass throuh them. The heads of the screws are effectively enlarged by iron washers 3/4 in. in outside diameter. The object in this arrangement is to allow a certain amount of play in the board, I, for purposes of adjustment. When properly adjusted the screws may be tightened, and the board firmly fixed in position. E is attached perpendicularly to H, and made right with two small triangular pieces, which are not shown in any figure. H is hinged to K, and K is fixed to the base in exactly the same manner as I.
Through the middle of I is passed a brass-screw bolt, the square head of which is fixed in I. The screw goes through an elongated hole in G, and is fitted with a round milled brass nut. It is well to place a washer under the nut. Screw-bolts of this description are used for fixing the expanding bodies of ordinary photographic cameras, and may be had of any optician. H and K are fitted with asimilar bolt. Two rather stiff pieces of steel spring are attached to the ends of I, and extend for a little distance underneath G. These springs tend to separate Gand I, or rather to cause G to turn backwards, like the lid of a box when opened. One of the springs may be seen in Fig. 1. The nut, of course, works against the springs. When the nut is screwed up tight G and I approach, and may be made almost to touch each other. When the nut is loosened the spring causes G torise. Very delicate adjustment is thus rendered possible. H and K are fitted with similar springs for a similar purpose. We come now to the diaphragms and points. The diaphragm which receives the voice is fixed over the circular hole in D, as shown in Fig. 2. It consists of a circular plate of very thin iron 4 inches in diameter. Ferrotype plate will answer the purpose very well, but thin charcoaliron is better. It is, however, possible to have the iron too
thin. I should say that about two-thirds the thickness of an ordinary ferrotype plate is the best. The point is made from a knitting-needle about 1-20th of an inch in diameter, which must be very hard — one which can be bent is of no use. The original point had better be broken off, and a new one ground upon an oilstone. For this purpose the needle is held at an angle of about 30 degrees with the stone, and is constantly turned round. The point, having been made tolerably sharp, is polished and cut off with a file. The part so cut off is 3-16ths of an inch long. This has now to be attached perpendicularly, to the centre of the diaphragm, and the method of doing so is as follow : — The diaphragm is laid upon a sheet of glass, and a little spot in its centre— about 1/2 in. in diameter — is scraped clean with a knife. This must be done carefully and gently, or a bulge will be produced. The fragment of knitting-needle is then taken up with pliers, and its blunt end, having been moistened with soldering fluid, is held above the flame of a spirit-lamp, and touched with a piece of tinfoil. With a little manipulation a small bead or globule of tin may thus be made to adhere to the end. The scraped spot on the diaphragm is now moistened with soldering fluid, and the diaphragm is supported at some distance above a small spirit flame. The ring of a retort stand forms a convenient support. The butt end of the point, with tin globule attached, is then applied to the scraped spot with pliers. In a few seconds the globule melts, when the lamp is instantly removed, and the point manipulated with the pliers, so as to be perfectly upright when the tin hardens, which will take place in a few seconds more. The point will then be found to be firmly attached. The diaphragm and point must, after this operation, be thoroughly washed with soap and water, and slightly oiled — otherwise they will rust. The only precaution to be observed is to apply no more heat than is just necessary for melting the tin. Too much heat will warp the disc and, if it is a ferrotype, blister the japan. The soldiering fluid consists of equal parts of hydrochloric acid and water, in which is dissolved as much zinc as possible. A pile of books will be found useful for steadying the arm while manipulating the point. The diaphragm is fixed in its place by means of a brass flange (like a camera flange), 4 inch in outside diameter, with a 2 3/4 inch opening. Four screws are used. The second diaphragm is made of parchment paper, like that used for covering jam-pots. It is 4 inch in diameter, and is gummed over the cylinder (see Fig. 2). When the gum is dry the diaphragm is moistened, and again allowed to dry, when it will be found to be as tight as a drum. The second point is exactly like the first, though it may with advantage be a trifle sharper. It is not attached directly to the paper diaphragm, but to a steel spring, which may be seen in Figs. 2 and 3. This is a piece of main spring 5-16 inch wide and 2 1/2 inches long. It is fixed above the hole in E by means of two strips of brass, as shown in Figure 3, and is just so much bent that the end of it, when free, is 3/8 inch distant from the plane of E. The power of this spring may, however, be varied within considerable
limits without appreciable difference in its performance. The point is fixed to the spring in the same manner as to the iron disc, but the same care as to over-heating is not requisite, and the operation is consequently easier. Before the spring is screwed in its place a loop of sewing silk is attached to the centre of paper diaphragm by means of a piece of court plaister 1/4 inch square (see Fig. 4, where A is the piece of plaister, B the loop). The length of the loop must be such that when it is drawn over the spring just above the point, the end of the spring may be nearly in the plane of E. The spring is thus caused to draw the paper drum even tighter than before, and its inner surface is rendered slightlyconvex. Another flange carrying a short rim or spout is now screwed round the paper drum. A paper resonator is made to slip over the short rim or spout. It is a cone made of two or three thicknesses of stout drawing paper. Its length is 18 inches ; diameter at small end 24 inches, and at large end 7 inches. The resonator greatly reinforces the sound when the phonograph is speaking. A wooden mouthpiece like those used for speaking-tubes is inserted into the hole, F (see Figs. 1 and 2.) The instrument is now complete, but it will require care- ful adjustment before it can be used. In the first place the screws which attach I to the base must be loosened, the milled nut on F screwed up tight, and the piece, I, shifted about until the point on the iron disc is exactly in the middle of one of the grooves on the cylinder, and barely touches the bottom of it. Then the screws must be tightened, and this part of the apparatus is finally adjusted. The same process is repeated on the other side, but in this case the adjustment is not quite final, as will hereafter be seen. The next thing is to procure suitable tinfoil. This should be rather stout — about 15 square feet to the pound — and should be cut into pieces 141/2 inches by 4 1/2 inches. Before putting a tinfoil upon the cylinder the two nuts are removed and the diaphragms turned back out of the way. A little gum brushed along one end of the tinfoil will be sufficient to keep it firmly in its place; the join must be carefully smoothed. Tne diaphragms are then turned back to their places, and the nuts screwed on. The nut on G is screwed up just far enough to cause the point on the iron diaphragm to touch the tinfoil very lightly. The handle is then turned about a quarter of a revolution, causing the point to make a short scratch on the tinfoil. The nut on G is thereupon loosened withdrawing the point from the tinfoil, and the nut on B. being screwed up, another turn is given to the handle. If the scratch thus produced exactly coincides with the former one well and good ; if not, the screws attaching K to the base must be loosened, and K shifted about until absolute coincidence is attained. The utmost accuracy on this point is essential.The instrument may now be considered fit for use. Loosen the nut on H, so that the point of the spring may be well away from tbe tinfoil and screw up tho nut on G, so far that the point on the iron diaphragm may score a well-defined furrow on the tinfoil when the handle is turned. Turn the handle with as great regularity as possible, at the rate of about one turn per second, or a little slower. Speak loudly and distinctly into the mouthpiece, putting the mouth as near as possible to it, without actually touching. When you have finished, withdraw the point by loosening the nut, turn the handle backwards until the cylinder is in its original position, and screw up the second nut until the
second point presses but steadily upon the bottom of the furrow. Then put on the paper resonator, and turn the handle at the same speed as before. If the adjustments are perfect, the result will be astonishing. I will conclude with a few general remarks and hints. It will be observed that this instrument has two diaphragms, whereas Edison's latest have only one, which does both the receiving and the speaking. I have made many experiments with the object of dispensing with one of the diaphragms, but I have never, under any circumstances,obtained so good results with one as with two. Mr. Preece told the Physical Society that the employment of only one was a ' retrograde step.' Reason and experience led me to concur in his opinion. I do not believe that iron and parchment-paper are the best possible materials for the diaphragms, though they are better than any others which I have hitherto tried. The great fault in the iron appears to lie in its tendency to resound forcibly to certain overtones in certain vowel sounds. I have tried to overcome this by coating the diaphragm with indiarubber, but with no great success. I think, however, that a ring of indiarabber between the diaphragm and the flange has an undoubted effect in diminishing the nuisance. The steel spring is subjected to independent vibrations of a similar nature. These may be damped by causing a piece of soft indiarabber to press lightly upon it at a point about 1/2 inch below the lower strip of brass. I have also found it an advantage to wrap indiarabber round the top of the spring before screwing it on. I believe that the mouthpiece of a telephone would give better results than that of a speaking tube. A long resonat- ing mouthpiece like that which Edison first used is worse than useless. The point on the steel spring should be made to turn very slightly upwards instead of being perpendicular. In the latter case it is liable to produce a squeak something like that of a slatepencil when drawn upwards across a slate. If the points are to sharp, they will cut and scrape the tinfoil : if too blunt, the articulation will be muffled. After the points have traversed the cylinder 200 or 300 times, they will require sharpening. This can be done with a small oilstone, without removing them. In conclusion, I may mention for the encouragement of
those who wish to make a phonograph, that the performance of the instrument here described is at least equal to that of any which has hitherto been exhibited in London.— Mechanic.
Shelford Bidwell, inventor, late 19th century.
 Scientific. (1878, July 6). The Sydney Mail and New South Wales Advertiser (NSW : 1871 - 1912), p. 16. Retrieved October 17, 2015, from http://nla.gov.au/nla.news-article162694127
I hope that you have enjoyed this very detailed scientific article written by my distant cousin Shelford Bidwell.
Sharing The Passion In Family History
I hope that you have enjoyed this very detailed scientific article written by my distant cousin Shelford Bidwell.
Sharing The Passion In Family History
© Science Museum / Science & Society Picture Library
A Bit About Shelford BIDWELL
Bidwell anticipated what would later become television. Inspired by experiments with the photophone, Bidwell went on to attempt the 'telegraphic transmision of pictures of natural objects'. The photophone, invented by Alexander Graham Bell (1847-1922) in 1880, worked by transmitting sound on a beam of light. Bidwell used the principle of the Bakewell or D'Arlincourt copying telegraph, 'in which the variations of the current necesary to produce the design are effected by the action of light on a selenium cell'. Bidwell was President of the Physical Society from 1897 to 1899.
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