The crank-shaft, piston and piston-rings
Many attempts have been made to obtain a built-up crank-shaft for small multi-cylinder motors, which could be machined in separate components each having one axis only, these components being susceptible of assembling to form a crank-shaft having any number of crank-throws, set at any desired angle to each other; also many special forms of lathes have been devised for crank-shaft turning, some of which have had considerable employment.
The Ford Company, however, adheres to the simplest form of integral four-throw crank-shaft, and uses lathes of ordinary construction for finishing the crank-shaft bearings and flange, and ordinary forms of grinding machines for finishing the crank-wrists, or "pins," as they are sometimes named. The Ford crank-shaft is therefore an integral dropforging , four throws, 2-inch crank radius, made of the highest grade of steel and heat-treated.
The Ford connecting rod is also a steel drop-forging, which has the piston pin fixed in the top eye, the crank-wrist eye being capped and babbitted , and the cap held on with two bolts. The babbitt bearing is broached, and thin brass liners, about 0.006-inch in thickness, are placed between the cap and the rod end, to permit wear take-up. The piston pin is cut off from steel-tube stock, centered, finished, and hardened and ground, fixed in the top rod-eye and rocking in bronze bushes in the piston-pin hole. It is common practice to give the piston pin as much diameter as may be and have it bear directly on the wall of the piston-pin hole, thus avoiding the piston-pin-hole bushes altogether, but the Ford piston pin is of comparatively small diameter and works in brass bushes, as before said.
The Ford piston is a very light and accurately formed gray-iron casting , finished all over outside and having three grooves cut in it to take gray-iron, eccentric piston rings, one ring in each groove. The piston rings are of gray iron, eccentric, finished all over, outside and inside. The gray-iron "pots," or flanged and cylindrical piston-ring blanks, weigh about 63^ pounds each as they come from the foundry and are expected to give 12 rings from each blank, or so-called "pot."
As is well known, three steel rings, cylindrical, not eccentric, can be placed in one single groove and make a perfectly tight packing having many advantages over the three eccentric rings in the way of lower cost, and giving more piston wearing surface; but the Ford engineers adhere to the usual eccentric gray-iron-ring practice, in spite of the cost and machining difficulties inseparable from that form of piston packing ring, which demands a great number of finishing operations.
The Crank Shaft
All cranks of any description whatever are difficult constructions , if a close degree of accuracy is expected. When it comes to an automobile crank-shaft, where lightness, strength, elasticity and accuracy of form are highly desirable , the four or six-throw crankshaft which fully meets the requirements of its employment becomes an extremely exacting production.
The Ford crank-shaft forms no exception to this rule. The steel stock must be the best known for the purpose. Then follows a host of problems in the way of heat-treating, straightening, centering and finishing , each one of these operations and their details demanding the very highest grade of metallurgical and mechanical skill, if the finished crankshaft is to have the strength, elasticity, and close approximations to accuracy of form and dimensions at every point which are so highly desirable, so fundamentally indispensable, that every crank-shaft maker roundly asserts the perfection of his output, although it is well known to all competent experts that very many crank-shafts for small internalcombustion motors are constantly being made which can lay no valid claim to high-grade construction from any view-point whatever.
The Ford crank-shaft is most scientifically constructed so far as selection of material, heat-treating and quenching are concerned. This much is fully proven by the very great trouble experienced in even slightly changing the form of the rough drop forging, before the crankshaft goes into the finishers' hands.
First there is the re-strike under a heavy steam hammer, in dies which are to crank-shaft form drawings; then, after snagging, comes the rough-straightening under a lighter steam hammer, then centering and finish-straightening with sledges and anvils, and many-times repeated gauging with the rough crank-shaft on centers, before the rough piece is in form for the first machine cut. The many separate operations required to finish the Ford crank-shaft drop forging, as received from outside suppliers, in order of sequence, are as follows:
Operations on Crank-Shaft
The operations in the Highland Park shops begin with four heattreat operations,—A, air heat; B, heat and quench; C, anneal; D, restrike . The heat-treating operations A, B and C are not here described. The story of the mechanical treatment of the Ford crank-shaft begins with operation D, re-strike.
As shown on page 198, the warm crank-shaft is laid in the lower half of a die of correct form and struck such blows as may be required with a 1,200-pound hammer having 36-inches fall. Three men are used in the re-strike gang, one hammer man and two tongs men, who lay the shaft in the lower half of the die. The production is about 200 re-strikes per hour, three men's time. Steam hammer by the Morgan Company. Operation E. Tumble. Two men and two tumbling barrels tumble about 100 crank-shafts per hour.
Operation F. Snag. Five men, using five emery-wheel stands, snag about 150 shafts per hour. The tumbling removes much of the scale produced by heating in presence of free oxygen, and the emery wheels leave the job in good shape for: Operation G. Rough-straighten. The rough-straightener uses flatslab stands, set with hardened-steel studs, which should touch the shafts at certain points.
In the picture shown on page 199 a rough-straightener has a crankshaft laid on the elevated gauge slab, and is looking through under the shaft, to see where it is away from the gauge pins. The 1,000 pound steam-hammer, 21-inches lift, is seen in the rear, with the hammer man at the levers. One hammer man and three gauge men make up the rough-straightening gang, and the output is about 150 crank-shafts rough-straightened per hour. Steam hammer by the Buffalo Foundry Company.
From the rough-straighten job the crank-shafts go to the machineshop finish-straighten gang, ten men all told—one centerer, seven finishstraighten gauge men, and three strikers, who use 18-pound sledges and strike the crank-shafts held on three anvils by the gauge men, as directed, often with a full-swing repeated in the same spot. The crankthrows often require opening, effected by standing the crank-throw on the anvil horn, and giving a full-swing 18-pound sledge blow on top of the crank-wrist. One would naturally expect to see one such blow open a throw of this slender crank-shaft half an inch or so; but no such result occurs, and often two or three full-swing blows of the sledge fall on the crank-wrist before the gauge man is suited. Indeed, it seems impossible that the Ford crank-shaft should show such indifference to heavy sledge blows as it certainly does show.
The illustration on page 200 shows a general view of finish-straightening , this page the crank-shaft centering, and page 202 a crank-shaft dead-centers gauging stand, showing the gauges used in finishstraightening the crank-shafts. After the hand-work operations described and illustrated, the crank-shaft finishing offers little of special interest, although every operation demands a well contrived fixture and accurate machine work. After centering, the first lathe cut is rough-turning the middle bearing . This is shown just below. Then follow in order the twentynine operations listed below: Turn center bearing. Reed lathe. The crank-shaft is supported on the lathe centers, and by a long sleeve-rest is fixed to the live spindle, which supports the crank-arm next to the center bearing, and gives steadiness to carry a big chip in rough-turning the center bearing. Five Reed lathes, one man to each, 25 center bearings turned by one man and lathe in one hour. Face the flange. Reed lathe and one man, 20 per hour. See page 203. Turn flange circumference. One Reed lathe, one man, 65 per hour.
Square down to center. One Reed lathe and one man, 65 per hour. "Re-center." Should read '' Deepen the center.'' The centers are not changed from first location. One Ford centering machine, one man, 125 per hour. Straighten. One man and one hand-operated screw-press, 65 per hour.
Drill and ream two 0.441 spotting -pin holes. These holes are diametrically opposite each other in the flange, same radius to centers, and serve to locate the crank-shaft for wrist - finishing by grinding. Only the crank-shaft bearings are turned with lathe tools. The wrists are finished wholly by rough-grinding and finish-grinding. One man with one two-spindle Cincinnati drill press drills and reams these two spot-holes in 40 crank flanges per hour.
Drill four fly-wheel bolt holes in flange; Cincinnati drill-press and one man, 100 per hour. Turn two end bearings. Reed lathe and one man, turn end bearings of 23 crank-shafts per hour. Rough-grind middle bearing. Landis grinder and one man, 40 per hour. Rough-grind flange bearing. Landis grinder and one man, 25 per hour. Rough-grind front-end bearing. Landis grinder and one man, 35 per hour.
Rough-grind wrists. Landis grinder and one man, 15 shafts per hour. Finish-turn flange. Reed lathe and one man, 25 per hour. Face ends of crank-shaft to over-all length. Reed lathe and one man, 50 per hour. Drill and ream one 1/2-inch starting pinhole, Cincinnati drilling machine and one man, 50 per hour. Mill key-way. Pratt and Whitney milling machine and one man, 125 per hour.
Hand-ream starting-pin hole and burr key-way, hand operations on bench, one man, 125 per hour. Balance; balance-disk stand and emery-wheel stand. One man, 40 per hour, close balancing. Finish-grind end wrists. Landis grinder and one man, 12 per hour. Shown below on this page. Finish-grind middle wrists. Landis grinder and one man, 12 per hour. Finish-straighten. Man, dead centers, and hand screw-press, 60 per hour. Finish-grind middle bearing. Landis grinder and one man, 35 per hour. Finish-grind flange bearing. Landis grinder and one man, 15 per hour. Finish-grind front-end bearing. Landis grinder and one man, 35 per hour. Finish-grind gear fit. Landis grinder and one man, 35 per hour. Finish-turn flange circumference . Reed lathe and one man, 100 per hour.
Burr. Twenty-seven per hour, one man on bench. This is the old style. Now, with new hand burring tool, one man burrs over 100 crankshafts per hour.
By the old method, with first-class vise hands using fine files of various shapes, one man could burr only a very few, not more than ten, crank-shafts per hour, and at that the job could not be any too well done, as some of the burrs were very difficult of access. The full capacity of this new burring tool, of which two views are shown opposite, is not yet certainly known. It was first placed in use about December 15, 1914, and effects a labor saving estimated at about $20.00 per day. Two widths of this hand burring tool will be used, one for each length of crank-shaft bearing. The up-turned toothed ends of the springs scrape the burrs off at one passage over.
Final operation. Polish the crank wrists. The crank-shaft is beltdriven on its own centers. Each crank wrist takes a special connectingrod end which closes a felt ring on the wrist, under light pressure. The free end of each rod is jointed to a vertical lever. The felt is not charged with any abrasive—simply rubs the wrist as the crank-shaft revolves. One of the wrist-polishing machines polishes the wrists of about 20 crank-shafts per hour.
The reader who follows this sketch of crank-shaft production attentively will fully understand that if the Ford crank-shafts are not well finished the faults cannot be charged to any lack of painstaking on the part of the machine-shop management.
The Ford Pistons
The Ford Model T piston is an extremely light gray-iron casting. The piston finishing is a simple job: the piston is first chucked, open and outward, in a turret machine of ordinary construction (Warner and Swasey, suppliers) and is then rough-bored and finish-bored with two tools in the turret and faced with cross-slide tools. This gives a substantial spotting surface for subsequent operations in piston-finishing. Next the piston-pin hole, about 15/i6 diameter, is drilled, bored and reamed; then the piston is rough-turned and finally completed by finish -turning.
If desired, the piston-pin hole could be made as much as l3/s inches diameter, could take a hollow piston pin 13A diameter, soft, which would give sufficient projected area to carry the piston pressure without displacing the film of lubricating oil lying between the pin and the walls of the piston-pin hole, and the entire piston and pin assembly weight could be brought below that of the present construction, which includes a hollow pin, hardened, and two bronze bushes forced into the pin holes in the pistons.
The use of a piston pin having sufficient projected area to prevent displacement of the oil film is not new. A good many years ago, in the shops of the first American automobile company to sell any considerable number of cars, I saw a motor, 4-inch diameter of pistons, pins 1% diameter , hollow and soft, pulled down after driving its car 5,000 miles on the road. Neither the piston-pin holes nor the piston pin itself showed any signs of wear, which was proof conclusive that the oil film had not been displaced, and this, too, in spite of certain proof that the job was not true, and that the piston-pin axis did not correspond with that of the pin holes in the piston. Of course, as every machine man well knows, it is far better to use a bearing of sufficient projected area to prevent oil-film displacement than to use a bearing of such small projected area as to make brass bushings and hardened rubbing surfaces necessary to successful working, because it is better to wear out the lubricating oil than to wear out the metal of the working parts.
The Ford engineers, however, elect to use a small-diameter hardenedsteel piston pin, and place bronze bushes in the piston-pin seats.
The foundry number of the pistons is 1-418. The foundry operat ions are, A, molding; B, tumbling; C, rough grinding; R P, chipping. The pistons are then sent to the machine shop for the following finishing operations:
Face and bore. Warner and Swasey turret machine, rough-bore and finish-bore open end of piston with two tools in the turret, then roughface and finish-face with two tools in the cross-slide. (See page 205.) Production, one screw machine and one man, 80 per hour. Drill, bore, and ream the piston-pin hole. Up to about a year ago these operations were performed on some single-operation tools.
Then the Ford Company installed three special machines by the New Britain Machine Tool Company, which are regarded as satisfactory, but have a combined capacity of only about 240 pistons per hour, 80 for one machine and one man, so that the old single-operation machines are yet used, though their work is the more costly. The special machine is illustrated on page 206.
In this adequate and well designed machine, which is automatic save for fixing and removing pistons on the four arms of the work-carrier, this fixture is automatically indexed to four positions by revolving the fixture on a horizontal axis placed lengthwise of the machine. At the right end this machine has three live spindles with independent feeds, one for drilling, one for boring, and one for reaming. The top of the four-arm indexing fixture turns toward the operator. Each arm face is offset the distance from the faced open-end of the piston to the center of the pin hole. The top of the fixture is the put-on-and-take-off station. As the fixture is indexed round, the piston first comes to the drilling station, and has the pin hole drilled. At the second station a second piston is drilled while the first pin hole is being bored. At the third station a third piston is being drilled while the second piston is being bored and the first piston is being reamed. The next movement of the fixture brings the first piston to top position, where the attendant removes it, and replaces it with another, and from thence on, so long as the attendant removes and replaces the pistons, all three operations of drilling, boring, and reaming piston-pin holes are in continuous progress, save for the time occupied by drawing the tools back and indexing the fixture from one position to the next following position.
Rough turn and groove. Vertical lathes with rocking tool carriers, by Foote-Burt. Set in banks of four-machines each, all four attended by one man. The piston is spotted on its open-end, and held by a pin in the pin hole and a tension eye-bar, shown at left, pulled down by the capstan wheel seen low down on base of the machine, a cam and a lever. Four of these well arranged machines and one man rough-turn 75 pistons in one hour. See page 207.
Press in bushings. Two brass bushings are forced into the piston-pin holes, one on each side of piston. One man and one Ferracute press place bushings in 300 pistons per hour.
The next two operations (formerly separated as K-6 and K-7) are now combined, and are performed on a line of sixteen new Reed-Prentice rocking-tool-carrier lathes. One man attends two of these fine tools. Production, one man and two of these lathes, 50 pistons finish turned per hour.
Ream bushings; this operation is worked on the motor-assembling job. The piston department work on the piston ends with operation 7, finish turn.
The Piston Packing Rings
The Ford gray-iron eccentric snap-rings, placed one snap-ring in each of three grooves in the pistons, are certainly a job. They are also certainly the most amazing example of subservience to vogue and prejudice that ever came under my observation. Cartwright, clergyman, of the time of James Watt, was the first one to devise a metallic piston-packing for steam engines. The Cartwright packing consists of three rings, cylindrical, in one groove; first a wide one, filling the groove inside, and outside of the inside ring two rings, each one half the width of the inside ring. This three-ring packing, 45-degree angle cuts, is tight, costs but little, needs but little expansion spring for smalldiameter cylinders, and is in every way so exactly right for its place that it came into immediate use and is, to-day, the standard packing for small steam engines.
Mr. Ford, who had an extended personal acquaintance with steam engines before he began with gas engines, must be fully aware of the Cartwright three-ring piston packing and its many virtues, and yet the Ford motors use eccentric snaprings , with holes straight through them, one ring in one groove, each ring tested to show 18 pounds of resistance to closing to cylinder-bore size. The " Reliance" of Detroit, used the Cartwright packing, three cylin drical rings in one groove, with entire mechanical success, but changed to eccentric snap-rings, one ring in a groove, because Reliance car purchasers preferred the eccentric snap-ring.
At the beginning of the American motor-car trade, American makers were beaten out of sight by the French and German automobile constructors , who had all the trade worth having, and presently the American builders joined in a cry of "Give the public what it wants" and with one accord began copying foreign practice, the snap-ring among other details.
I do not know whether Mr. Ford ever tried Cartwright packing in a gas-engine cylinder, but I am informed by the machine-shop head that no piston packed with three cylindrical rings in one groove has been tried in a Ford motor during the eleven years of his Ford Motor Company service.
The Piston-Ring "Pots"
These are gray-iron hollow cylinders, having a low flange at one end, from which the Ford eccentric snap-rings are laboriously carved. The twelve finished rings expected from one "pot" weigh about 17 ounces, or 15/i2 ounces each. Each pot as it comes from the foundry weighs about 6l/s pounds, or 104 ounces, from which 17 ounces of finished piston rings is expected to be produced—that is to say % of the pot stock is wasted.
The foundry supplies the machine shop with 13,000 pounds of ring pots per day, worth, at 2 1/2 cents per pound, $325 per day. The machine shop produces about 14,000 rings per day, 1 5/12 ounces
each, say 1,240 pounds of finished rings from 13,000 pounds of ring stock, 11,760 pounds of stock, worth $294 wasted for the pleasure of cutting it into chips and using snap-ring piston packing. That is to say, $325 worth of ring-stock is supplied to the machine shop, $294 of this value is wasted, and $31 of stock value utilized in the finished work.
These figures are not favorable to low-cost piston-ring production. The piston-rings finishing job works about twenty-two machine hands, and no less than fourteen inspectors are needed to make sure that the rings are suitable for their employment after they are finished.
The rough dimensions of the pot, a hollow gray-iron cylinder, flanged at one end, are as follows: diameter of hole, 3 1/2 inches, diameter of body, 4 inches, diameter of flange, 5 1/4 inches, thickness of flange, 1/2 inch. Length over all, 67/8 inches.
The operations on the piston rings are as follows: Face. The pot is chucked in a Reed lathe, flanged end out, is faced off, and the flange edge is cut to about a 20 degree angle, large diameter outside. This gives the holding surface for the Potter and Johnston automatic operation of boring, eccentric turning, marking thin point and cutting off. One Reed lathe and one man face 112 pots in one h(jur. See page 210.
Facing and beveling the pot flange. In specially designed Potter and Johnston automatic machines the pots are chucked by the flange on the face plate, cylindrical part of the pot in the air. See page 210. This tool has a frame, supporting a tool carriage which has an automatic feed and slides on top of the frame. This carriage carries a heavy
boring bar, cutter set in advance of the turning tool, which bores out the inside of the pot as the carriage is fed towards the head stock. The carriage also carries a cross-slide, moved by a crank action making even turns with the head-stock spindle, which moves the turning tool towards the work center and draws the tool away from the work center, both motions, once to every revolution of the pot. This gives the ring-blank its eccentricity.
The frame supports a headstock at the left-hand end, carrying a live spindle to which the pot is chucked, while a horizontal rock-shaft placed along the back side of the lathe carries a rocking tool-holder, automatically moved to cut the rings off successively as the carriage moves towards the head-stock, the rocking tool carrier having 13 parting tools fixed in it, the tools being set at different heights so as to cut the entire pot body into 12 separate eccentric rings by the combination of automatic agencies specified.
The illustration on page 211 gives an enlarged view of the carriage and the rocking tool carrier of this highly ingenious Potter and Johnston automatic piston-ring rough-turning and cutting-off machine, and shows the
rocking head of cutting-off tools, the front right two or three rings cut off and hanging on the boring bar, with the crank-moved eccentric turning action carried in a horizontal cylindrical cross-slide housing extending to the left. It is needful to know the exact thin point of the ring, and a spring striker, seen above the eccentric action slide, carries the center punch at its end and marks each ring at the thin point as the turning and cutting-off proceeds. Two machines and one man, 300 rings per hour rough-turned and cut off.
Straddle face the ring-sides. Pratt and Whitney machine, with expanding collet in five spindle, and ring receiver in hand-lever-moved tail-spindle. A notably clever machine design, shown on page 212. The workman places one ring in the tail-spindle receiver, pulls it over the collapsed expanding head-stock collet (which is milled on the
holding surfaces expands the arbor , withdraws the tail spindle, and then with two tools faces both sides of the ring at same time. One man and one machine, 300 rings faced on both sides per hour. The rings are not ground on the sides. "Break" slot. Cut the ring open at exact thin point, 45 degrees angle punch and die cut in Bliss press. See page 213. One man and one press, 1,062 rings per hour.
Mill slot. On small hand milling machine, having a mill of right width on the arbor in the live spindle, the rings are hand-lever clamped in a 45-degree angle receiving fixture and the "break" is widened to width of mill by handmovement of cross-slide. See page 213. This operation finishes the ring 45-degrees angle cut to final width. One man and one machine, 650 per hour.
Put on arbor, rough turn, take off arbor, put on arbor, finish turn, and take off arbor are sufficiently illustrated by page 214. When an eccentric snap-ring, rough turned, is pushed into a cylinder it does not touch the cylinder wall at all points. To obtain rings bearing at all points the rings are placed inside of receiving cylinders of tool steel, hardened and ground. The receiver stands on a flanged gray-iron base with top-end open, and first takes six rings, laid one on top of the other, thin sides and thick sides alternating. Next is placed a finished steel collar about Y2 inch thick, then on top of this collar, six more rings, similarly disposed.
Then the filled receiver goes to the arbor man, who passes a flanged arbor, fitting the receiver, through the inside rings, places a finished collar on top and screws a nut down on the collar, hard. Then the receiver and arbor go to the arbor-press man who presses the arbor out of the receiver, with the rings and collars firmly clamped in place by the arbor nut. Then the filled arbor goes to a hand on a Reed-Prentice lathe. The reader will understand that the ring's circumference is not, at this time, a true circle, but has high and low points, because an eccentric ring will not touch a confining cylinder at all points without special fitting. The lathe man now proceeds to rough-turn the rings with a cut just deep enough to clean their outside surfaces. One man and one Reed lathe, 12 rings on an arbor, 1,050 rings turned per hour. Next the rings are taken off the arbor and are then again packed in receivers, the same as before, and now stand very much less away from the containing cylinder than at first, but yet not touching all round. Once more the arbor is put through the rings, is pushed out of the receiver, goes to a lathesman, who takes the finishing cut over the rings, again barely enough to clean the surface.
The entire ring rough-turn and finish-turn gang, as shown in the illustration , can rough and finish-turn, with two Reed-Prentice lathes and two lathe hands, about 2,100 snap-rings per hour.
The fourteen inspectors on the ring job, two-thirds as many inspectors as there are workmen, inspect the rings constantly in course of finishing. The final inspection is for 18 pounds of ring resistance to closing to cylinder diameter. Several forms of closing-resistance testingmachines are used, the latest, in use but a short time.
The ring under test is seen close to right of the inspector's right hand, cut to front; the reader's left (workman's right) of the inspection machine , is fixed. The inspector lays the ring down flat on the testingmachine surface and pulls the ring towards him, left side of ring against the fixed abutment, ring passage resisted by a lever on right side, weighted to 18 pounds. When the ring resistance is 18 pounds the lever makes an electrical contact which rings a bell. If the inspector pulls the ring through with no ringing of the bell, the ring is a waster, and some lots of rings show 20 per cent of failures in standard pressureresistance . As a general rule, however, the failures do not go above about 5 per cent, of total number of rings subjected to test.