CHAPTER XIX. STEAM TILT-HAMMER — PATENT OF 1784 PARALLEL MOTION COUNTER-THROTTLE-VALVE LOCOGOVERNOR MOTIVE STEAM-CARRIAGES - - A FAVOURITE employment of Mr. Watt in the workshops at Soho in the latter months of 1783 and earlier ones of 1784, was to teach his steam-engine, now become nearly as docile as it was powerful, to work a tilt-hammer for forging iron and making steel. So far back as 3 May, 1777, he had informed Mr. Boulton that "[John] Wilkinson is going to work "in the forge way, and wants an engine to raise a stamp of "15 cwt. thirty or forty times in a minute. I have set Webb "to work to try it with the little engine and a stamp-hammer "of 60 lbs. weight. Many of these battering rams will be "wanted if they answer." During his long absence, and constant occupation in Cornwall, this labour seems to have been intermitted; and we do not find it resumed in earnest till November, 1782. Then "the rotative motion and mill "part answered to every expectation, but the hammer-frame "and anvil-block were not sufficiently secured, which, how66 ever, I have given orders for doing. And as the engine has a great overplus of power, I mean to increase the weight of "the hammer to about 1 cwt., and to cause it to make 250 or 300 strokes per minute, by diminishing the height it "rises to 9 or 10 inches. The present facts are, cylinder, 15 "inches diameter, and 4 feet stroke, 25 strokes per minute; "hammer makes 6 blows per stroke of the engine; fly under "5 cwt., and 7 feet diameter; hammer 120 lbs., and 18 inches "wide; it strikes a good blow, and forges iron very well. "The camms were wood, and were cut all to pieces by the "anvil-block sinking. I have ordered steel ones to be made, 66 66 "which I expect will stand it."* 66 66 66 66 66 66 66 On the 30th of November he says," I saw the tilt go admirably from 16 to 24 strokes per minute, and it could have gone much faster, but our "men could not work the iron under it. Joseph said that yesterday they made it go 28 strokes per minute, which is "much more than the engine should do by my calculations; "but in the midst of our glory, the hammer helve broke: it appears to have been rotten. The steel camms answer very "well, and the whole will answer better when made to have a less lift and more strokes, as it will then answer for a "common tilt for steel; at present the blow is so strong, that "we dare not attempt to hack a piece of iron under 1 inch square, otherwise it knocks it to pieces. By the help of some more weight on the outer end of the beam, it goes so "regular that you cannot tell when the engine is going out "or when coming in." On the 12th of December,—“ I went "out to Soho yesterday forenoon, hoping the engine would "be ready for trial, but it was not. In the evening they wrought it 2 hours, 240 blows per minute, rise of hammer "8 inches." On the 13th,-" We have tried our little tiltingforge hammer at Soho, with success. The following are "some of the particulars :-cylinder 15 inches diameter, 4 "feet stroke, strokes per minute 20. The hammer-head, “120 lbs. weight, rises 8 inches, strikes 240 blows per minute. "The machine goes quite regular, and can be managed as "easily as a water-mill. It requires a very small quantity "of steam, not above half the contents of the cylinder per "stroke. The power employed is not more than of what "would be required to raise the quantity of water which "would enable a water-wheel to work the same hammer with "the same velocity." Next month, they were "making an"other to work a hammer of 700 lbs., which will soon be at "work." This was for Mr. John Wilkinson at Bradley, and, on the 27th of April, 1783, Mr. Watt writes, "We have had a "trial of our new forge-engine at Bradley; cylinder 42 inches "diameter, 6 feet stroke. Makes from 15 to 50 (even 60 66 *To Mr. Boulton, 28 November, 1782. "strokes per minute) at pleasure, works a hammer of 71⁄2 cwt. "raised 2 feet high, which makes 6 strokes per stroke of the "engine, and has struck 300 blows per minute; we are, how"ever, going to make it strike only 4 blows per stroke of "the engine, because we want the latter to go 20 strokes per 66 minute, and they want only 90 blows of the hammer in "that time; but will increase the weight of the hammer to "10 cwt. N.B. The engine is to work two hammers, but is capable of working four hammers, of 7 cwt. each." 66 In a letter written on the previous day, he had said, with excusable pride, "I believe it is a thing never done before, "to make a hammer of that weight make 300 blows per "minute; and, in fact, it is more a matter to brag of than 66 for any other use, as the rate wanted is from 90 to 100 "blows, being as quick as the workmen can manage the iron "under it." This most valuable application of steam-power was, accordingly, reserved for insertion in yet another patent, which Mr. Watt took out on the 28th of April, 1784. The relative specification, enrolled on the 25th of August in that year, may probably be viewed as second in importance to none of those prepared by Mr. Watt subsequent to that of the Separate Condenser in 1769; as, besides many improvements now of minor consequence, such as steam-wheels, balancing of pumprods, communication of motion from the same engine to two separate primary axes, and apparatus for opening the regulating valves with rapidity, it contains various methods of converting a circular or angular motion into a perpendicular or rectilineal motion,-one of those methods being the wellknown and much-admired Parallel Motion;-a method of working a tilt-hammer for forging iron, making steel, &c., by steam;-and the application of the steam-engine to give motion to wheel carriages for carrying persons or goods. Of the last-mentioned invention, and of its inventor's views of the subject of locomotion by steam, in general, we shall presently treat. Of the invention of the Parallel Motion,—a beautiful mechanical puzzle which different philosophers have attempted to explain in various ways, but which has uni formly commanded the admiration of all who either comprehend the principles on which it acts, or behold the smoothness, orderly power, and "sweet simplicity" of its movements, -we find the following account in a letter from Mr. Watt to his son, already cited:* 66 "The idea originated in this manner. On finding double "chains, or racks and sectors, very inconvenient for communicating the motion of the piston-rod to the angular motion "of the working-beam, I set to work to try if I could not "contrive some means of performing the same from motions "turning upon centres, and after some time it occurred to 66 me that AB, CD, being two equal radii revolving on the "centres B and C, and connected together by a rod AD, in "moving through arches of certain lengths, the variations "from the straight line would be nearly equal and opposite, " and that the point E would describe a line nearly straight, " and that if for convenience the radius CD was only half of "AB, by moving the point E nearer to D, the same would "take place; and from this the construction, afterwards called "the parallel motion, was derived. * Though I am not "over anxious after fame, yet I am more proud of the parallel "motion than of any other mechanical invention I have ever "made." In Mr. Watt's Appendix to 'Robison on Steam and Steamengines,' he mentions that "the invention was made in the "latter end of 1783.” The manner in which we find the contrivance of this admirable piece of mechanism first recorded in his correspond * Mr. Watt to Mr. James Watt, 10th November, 1808. 66 66 ence, six months later than the date thus assigned to it by Mr. Watt, is interesting:-"I have started a new hare. I "have got a glimpse of a method of causing a piston-rod to move up and down perpendicularly, by only fixing it to a piece of iron upon the beam, without chains, or perpen"dicular guides, or untowardly frictions, arch-heads, or other "pieces of clumsiness; by which contrivance, if it answers fully to expectation, about five feet in the height of the [engine-]house may be saved in 8-feet strokes, which I "look upon as a capital saving; and it will answer for double engines as well as for single ones. I have only tried it in a slight model yet, so cannot build upon it, though I think it 66 66 66 66 a very probable thing to succeed, and one of the most inge"nious simple pieces of mechanism I have contrived, but I "beg nothing may be said on it till I specify."* And again, on the 11th of July:-" I have made a very large model of "the new substitute for racks and sectors, which seems to "bid fair to answer. The rod goes up and down, quite in a "perpendicular line, without racks, chains, or guides. It is "a perpendicular motion derived from a combination of "motions about centres, very simple, has very little friction, "has nothing standing higher than the back of the beam, " and requires the centre of the beam to be only half the "stroke of the engine higher than the top of the piston-rod "when at lowest, and has no inclination to pull the piston-rod "either one way or another except straight up and down. It "has rather more power at beginning and end of the stroke "than in the middle,-I think about one-sixth; which I "believe will do no hurt in rotative motions, and little in any "case. Beams mounted in this way need no arches; and the "whole iron-work will not, I think, be more than chains, 66 martingales, and their appendages, if quite so much. How"ever, don't pride yourself on it; it is not fairly tried yet, "and may have unknown faults. Where it is used, the "beams will be best above the centre of motion, which will "answer double engines very well, and may in most cases be *To Mr. Boulton, 30 June, 1784. U |