Machining Makes Headlines
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New Tool Forms have been Evolved to Cope with Demands of Higher Cutting Speeds. Novel MeiLds have been Devised for Reclaiming Damaged Tools. A U.§e has been Found for H.E.
in the Machine Shop
FOR the milling of steel a range of inserted blade milling cutters has been developed. The cutters ars. available in four sizes-2-in. with three blades, and 3-in., 4-in. and 5-in., each having four blades. All sizes employ the same standard, interchangeable and renewable tips. Two sets of the blades are furnished with each cutter head.
Another interesting milling cutter is the heavy-duty face cutter employing a special locking principle for interchangeable blades, which are 1 in. in diameter and will take cuts up to in. The cutter body is supplied in diameters from 6 ins. to 8 ins. inclusive for shell-end arbor mounting, and diameters of 9 ins, and larger for spindle mounting. They can be obtained with negative cutting angles.
Two new types of tipped tool, particularly designed for machining steel, have been placed on the market, and comprise a cutting tip of Stellite 98M2 cobalt-base alloy, brazed or buttwelded to a tough steel shank, with correct clearance and lead angles for turning steel. They are advised for work demanding tools with a large cross-section or those that are bent or offset, and are ground with a 15-degree side-cutting-edge angle, a 7-degree relief angle, and a 7-degree side relief angle. They have flat tops, and users grind their own rake angles for each specific operation.
Drills That Break in Their Holes The removal of drills that have broken' in the holes is always an irritating and laborious process. An electrolytic method has now been evolved, by means of which the embedded portion of the tool is disintegrated and dissolved. The solutions used contain inhibitors that prevent electrolytic attack on non-ferrous metals and alloys, so that the dimensions and shape of the hole remain unimpaired after the fractured drill has been withdrawn, and drilling can be
resumed. A specially designed electronic unit working on 110 volts ac. controls the process.
A portable testing machine has been designed for testing brazed joints, spot weld's, standard round or flat bars and springs, in order to ascertain their comparative strengths. The appliance has seven intermediate and interchangeable indicators up to 10,000 lb„ and the testpiece can be quickly inserted and removed Although the normal machine is operated by hand, an electric driving motor can be supplied.
" Pentrating "finish is being increasingly applied to small engine parts. It makes use of a salt mixture to achieve controlled oxidation and gives a lustrous black finish to the surface of the metal, increases its durability, and heightens anti-frictional and anti-rust properties.
In this process the parts are first dipped in a mixture of alkaline cleansing agent and water at a temperature of approximately 80 degrees C. After 15725 mins. immersion, all oil and grease are eliminated. The parts are then transferred to a second tank containing hot water, in which they are twice manually rinsed to remove vestiges of the cleanser. A third bath contains the " Pentrate " solution, heated to 140-145 degrees C. In this the parts are immerseci for 25 mine., after which they pass to a fourth tank containing a further quantity of the solution, this
tine at 150 degrees C, A further 25 mine. immersion .is followed by a rinse in cold water obtained in a fifth
tank. This rinse occupies a further 25 mins. and the liquid is air-agitated to ensure removal of the solution. Last comes a bath of soluble oil and hot water at 82 degrees C., in which the part s are once more 'immersed for 25 mins. This coats them with an oil film. They are then drained and cooled on racks, placed in trays, and coated with a rust-preventive solution. The specific virtue of the process lies in the low temperatures used, which render warping of the parts impossible.
A special alkaline zinc-plating solution has been esaolved for producing
satin-bright to bright deposits. The extent of the brilliance of finish produced is governed by the particular working conditions. A series of lead solutions has also been introduced. A non7organic coating for metal in a wide range of colours is another finishing process recently introduced, and is termed Poroseal. It is not a paint, but may be employed in a single or double coating on sheet steel and malleable or cast iron by either spraying or immersion. The coating is extremely resistant to corrosion, acids, solvents, high temperature, and abrasion, and is non-toxic, homogeneous, and without odour.
Reference has already been made in this account to an electrolytic process for removing broken drills from holes. Another new method developed for this purpose involves the use of dynamite, which is particularly useful in removing fractured portions of drills from deep holes. The explosive is packed into the hole and a detonator inserted; less than a thimbleful of the charge is employed. The drills are liberated by blast pressure, which travels down the flutes of the drill to the bottom of the hole, and then, unable to proceed farther, turns upon itself and blows out the embedded driltportion. No damage to the drilled part has been experienced. Where the drill has fractured level with the metal surface, the difficulty is overcome by fashioning a putty dam lj ins, in height above the hole, in which to insert dynamite, fuse, and detonator.
A blind rivet has been designed capable of application in virtually any position for riveting. It is made up of three parts, a steel, cadmium-plated, recessed head screw inserted into the hollow shank of an extremely strong aluminium alloy rivet, and a knurled nut of cluralumin threaded on the end of the screw. Rivet sleeve and nut are both standardized. Several forms of heads are obtainable.
Negative-rake milling is becoming highly popular in certain machine shops. Experience appears to have proved that lower speeds than originally advocated (between 700 ft. and 800 ft. per minute), together with higher feed rates and consequent higher chip loads are necessary to give the most economical tool life. Double negative angles of 10 degrees are suggested for both cast irons and steels in order to produce the most satisfactory • results: On the other hand, it should be noted that some experienced users of milling cutters for highly alloyed steels disagree entirely with negative rake milling, which is necessary only with tungsten-carbide cutters, because at the moment the necessary high tensile strength is not obtainable. Once this position is remedied, negative rake milling will cease to be advocated, they contend,
For gear-tooth grinding operations, where the cut depth required is greater than may be taken with a single adjustment of the cutting feed, an automatic adjustment has been -developed; this advances the feed after each complete 'cycle of the gear. Manual advancement of the cutting feed is no longer necessary, and it, therefore, becomes feasible for a single worker to maintain three gear grinders simultaneously in operation.
Radiography in Simplified Form
Of great interest is the electronic search ray, which is claimed to provide a safe, simple, readily operable X-ray apparatus. for the instantaneous fluoroscopic and radiographic examination of parts and finished products of light alloys and many other materials, and for package inspection. It is obtainable with accessories, enabling radiographic examination covering a maximum area of 11 ft. by 14 ft. to be made, using standard 12-in, by 14-in. X-ray film or paper.
Another most inviting development is the furnace-atmosphere indicator, which is based on the thermal conductivity method of analysis. It is said that the best possible atmosphere for a specific job may be ascertained and afterwards reproduced for any similar operation by regulating the air-fuel ratio to produce the same indicator reading. The indicator is ia continuous operation throughout the whole heating cycle, so that the operator can detect any alteration of importance in the furnace.atrnosphere that may occur as a result of fluctuations in the gas supply.
When parts are chromium-plated or selectively hardened, use is generally made of a masking lacquer, which prevents certain areas from being affected. Removal of this lacquer is often troublesome, and for this reason many readers will welcome, a new material which makes this operation rapid and simple, every trace of the lacqher being eliminated, even when in,ternaI. As the new stripper is non-acidic, it does not attack the finish of the parts in those areas that have not been lacquered, and it has no deleterious effect on the
operator. It comprises a blend of various solvents and must be confined' to lacquer removal. It_is not a thinning medium. It can, however, also be employed to remove coatings applied as protective agents on plating racks.
Ferro-Gas Welding and Cutting By means of the new '' Ferro-Gas " -method, household-type gas may be employed for welding, brazing, descal-1 ing, billet-dressing, steel-cutting, and similar operations in which acetylene gas .alone ceuld previously' be used.
A new handling appliance magnetic. ally picks up metallic, objects from floors. A magnet energized by, a fourcylindered motor is driven about the plantpicking up steel parings. nails, etc. In one works, four days' use of this device added nearly two tons of metal to the firm's scrap heap.
An ordinary lathe can be converted into a turret lathe by means of a recently invented tool post, built in two sizes to take six or eight tools. It may be inserted into existing tool-post slots and is provided with setscrews for tools, but none of the holes for tools is drilled. These are bored and reamed after the tool post has been locked in position on the lathe carriage. One or two taper pins serve to secure the cross-carriage in a central position, so that the post may be restored to its correct position if it be desired to remove it. It is stated that this post converts the normal lathe into a multiple-purpose machine able to execute work at present done on turret lathes
or special machines. , A new high-speed-steel metal saw allows accurate slotting and cutting off • to be carried out in milling machines. The new saw is made 0.062 .in, thick on the tooth edge and 0.052 in. at the mandrel. Each tooth has a relief clearance ground at the back to the depth of the gullet, and this gives adequate clearance where tolerances as close as 0.0002 in. have to be maintained. The saws are manufactured in 3-in., 4-in., 5-in., 6-in. and 8-in, diameters, for the majority of standard milling machine arbors.
Dies of tool-steel composition made by powder metallurgy are now in successful commercial use. Their cost exceeds that of ordinary powder metallurgical parts, but is much less than that of the dies they replace.
A new proprietary solution for loosening rusted-in screws, etc., seeps into the smallest openings, • and unfreezes stuck or seized parts. It has been proved .to penetrate orifices as small as a millionth of an inch, and not only saves time by increasing the
speed with which parts can be freed, but often prevents the scrapping of parts that appear impossible to separate.
A new, coated, high-tensile, bronze electrode has been brought out. This is a shielded-arc electrode, but may also be employed as a filler-rod in carbon-arc welding. It gives deposits of high strength and hot ductility, together with great corrosion resistance, It may be employed in welding the majority of bronzes, malleable and cast irons and steels. It has also specific uses for which it is particularly designed, e.g., the welding of manganese bronze for parts demanding treat strength, ductility, and resistance to corrosion; it Can also be employed for welding unlike metals, e.g., cast iron to' brass, steel to malleable iron, or to unite any two metals that can be welded with aluminium bronze, Internal Finishing of Hollow Valves Internal combustion -,engine valve stems have to withstand heavy axial stresses by reason of the severe hammering that takes place at high operating speeds. Hollow valves in particular are affected in this way, and it is for this reason highly desirable that their inner surfaces should have maximum continuity, so as to prevent as far as pisssible the occurrence of cracks caused by fatigue.
An improved method of polishing the interior of poppet valves has been designed, and by its means the dangerous circumferential scratches and tool marks are removed. A stronger valve stem is thus obtained without its being necessary to increase the thickness of the walls of the stem to guard against fatigue.