This article first appeared in Practical Engineering 1940 Vol1 No5. The contents of the article are accurate as of 1940. This article describes new Tools brought to the Engineering market at the time.
New Van Dorn Grinder
The new Van Dorn tungsten carbide portable tool-grinding and lapping machine is a recent introduction by Alfred Herbert, Ltd. Cutting tools tipped with Ardoloy or other hard-metal tips require special equipment for regrinding and maintenance. Cutting edges should be sharp but smooth, and the frequent use of a diamond impregnated grinding and lapping wheel will keep the tools in good condition.
The installation of this machine in various parts of the shops where hard-metal tipped tools are used, prevents loss of time in returning tools to the stores for re-sharpening purposes. It can be used to advantage by the machine operator, who can, without loss of time, re-condition his tools and so maintain production.
The machine consists of a heavy, vibration-less constant-speed motor mounted on a base plate. The motor, which is universally wound and therefore suitable for either direct or alternating current, can be supplied in 110, 200/220 or 230/250 volts. The motor speed is 7,500 r.p.m. This gives the correct surface, speed for the wheel supplied, which is a Norton diamond cup wheel 150 grain. Wheels of finer grain, i.e., 220 or 320, can be fitted, if required.An adjustable tool rest is fitted which can be easily removed, if desired. When using this rest care must be taken to adjust it to the correct angle to coincide with the clearance angle of the tool to be ground, as it is essential that the tool be held flat against the wheel face, otherwise undue wear of the diamond wheel will result. The use of a coolant or cutting lubricant is unnecessary. The cutting surface of the wheel can be easily cleaned and restored to its original sharpness by dressing lightly with a piece of pumice or a fine and soft crystolon stick.
The Schrader Blow Gun
In time of war, when production in nearly all factories is being speeded up towards its peak, compressed air plays an important part in facilitating the despatch of work through the shops. Not the least important amongst its jobs, is the cleaning of the dust and swarf which gathers on machine tools and workbenches. Frequently a blow valve is actuated by a cam or a ram on the machine itself. There are, however, circumstances where this method cannot be employed by reason of the construction of the machine or the work involved. In such cases, it may be that it facilitates the operation to direct the air blast by hand.
It is in these circumstances that the Schrader blow gun is designed to give maximum ease of operation, and the direct action of the push-button control ensures a powerful air blast. With its aid a blast of air can be directed towards any part of the machine desired, or the finished work.
The Schrader Blow Gun No. 7,184 is very sturdily built in cast bronze and specially designed for one-handed operation. The internal mechanism consists of a plunger unit, moulded rubber washer, and deflator and spring. The gun is constructed for very hard wear, and the integral parts are easily replaceable in the event of a part becoming damaged. The nozzle of the gun is also detachable, allowing for alternative fitments for special work.
In itself, the blowgun forms a complete seal on the airline and no leakage of air occurs when it is connected. Hose couplings or tail-pieces can be supplied to fit all sizes of hose and flexible tubing.
Complete details of Schrader Blow Guns can be obtained on application to Messrs. A. Schrader's Son Division of Scovill Manufacturing Company, 829, Tyburn Road, Erdington, Birmingham 24.
"Bur-Free" Nibbling Machine
An extended and improved range of patent nibbling machines is now being manufactured by J. B. Stone and Co., Ltd., of 135, Finsbury Pavement, London, E.C.2. Known as the "Bur-free "—signifying work done free from burr—these machines are specially designed to cut sheet metal to any shape, and, as they leave a comparatively smooth edge, little finishing is required. These machines, it is claimed, are extremely economical in use and simple to operate. Where it is required to reproduce up to several hundreds of the same part, and where it would obviously be uneconomical to make press tools, the "Bur-free" nibbling machine has been found particularly suitable. All cost of tooling is saved, and the fact that they work to a template eliminates on the part of the operator any tendency to inaccuracies. They have been found extremely useful in experimental work.
All the machines can be obtained in fully motorised form, and, with the exception of the smallest unit, known as No. 0, they can be arranged for line-shaft drive. Where motorised, the price of the machines includes belt guards, V-ropes and full electrical equipment. All machines are equipped with circle cutting attachments.
No. 0 machine is designed for bench work and is capable of cutting mild steel from 1/32in. to 3/32in. thick. It is equipped with integral motor drive and has a gap of 7-1/2ins, which is ample for the class of work for which the machine is designed.
No. 1 machine is designed for cutting thicker metals, 1/16in.- to 3/16in. in mild steel, and has the added advantage of being able to deal with stainless steel from 1/32in. to 3/32in. This machine, which has a gap of 12in., incorporates a variable stroke, which permits the use of the same thickness of template throughout the capacity of the machine, e.g., should it be required to cut a particular design of mild steel 3/16in. thick, and should it subsequently be required to cut a similar pattern from mild steel 1-16in. thick the same template would serve both cases by merely altering the stroke. The stroke can be adjusted to short, medium or long.
No. 1A machine is designed to deal with the same thicknesses of material as No. 1, but has a still wider range, as it has a gap of 30in., which is sufficiently large to meet all possible requirements. The machine is equipped with special c rests so that large sheets of metal can be easily handled.
No. 2 machine is the heaviest machine of the "Burfree" range, and is primarily designed to cut mild steel from 1/8in. to 5/16in. thick, and stainless steel from 3/32in. to 1/8in. thick. The outstanding feature of this machine is its ability to deal with stainless steel up to a thickness of 1in. The gap of this machine is 12in.
The Salford Hardness Tester
Many methods exist for measuring the hardness of metals, but all are unsuitable for measuring very thin metal sheets or foils. Hardness-testing instruments usually work on the well-known principle that a steel ball of certain dimensions makes, under a certain load, an impression giving the number corresponding to the particular hardness.
The usual type of instrument working on this principle makes an impression approximately 0.05 mm. (.00197in.) deep, and since the depth of the impression for measuring the hardness of the metal should not be more than l-10th of the thickness of the metal itself, it will be seen that this method is suitable only for sheet metals which are thicker than 0.5 mm. (.0197 in.).
This new instrument has been specially designed to measure very thin metal sheets or foils, and makes an impression of only 2 or 3 thousandths of a millimetre (.00008in. to .00012in.), and it is therefore suitable for hardness measurements on thin sheets and foils of the order of 2 or 3 hundredths of a millimetre in thickness.
The instrument comprises a micrometer of the electrical induction type, of which the movements are indicated on the scale of a galvanometer. A load applied through a spindle to a steel ball 1/16in. in diameter, makes the impression on the metal being tested. Movement of the spindle causes a movement of an iron core between two electro-magnets which are parts of a Wheatstone bridge. This movement produces a change of inductance of the electro-magnets, un balancing the bridge system, and giving a reading of an indicating instrument in the bridge circuit.
The Wheatstone bridge operates from the standard 230 volts 50 cycles supply, and a special compensating circuit employing inductances and condensers ensures that the accuracy of the instrument is unaffected by fluctuations of mains voltage.
The galvanometer is calibrated both in millimetres and directly in the Rockwell hardness scale, so that the instrument gives a direct indication of the hardness of the material being tested. Since the instrument makes use of a steel ball of 1/16in. diameter, the load for making the impression is very small, approximately 100 grammes in weight. Also, as the ratio between the diameter of the steel ball and the load is very unusual, it is necessary to calibrate this instrument with metal sheets of known hardness.
The accuracy of the instrument is not so great as that of hardness-measuring instruments which operate with bigger loads and bigger impressions, but in most cases it will be sufficient, and is in any case a very good means of making comparisons. The accuracy varies between 2 to 5 Rockwell degrees. A calibration curve is supplied with each instrument, enabling easy comparison to be made between the Rockwell and Brinell hardness degrees.
The Salford hardness tester is useful not only to foil makers, but also in any case where the hardness of thin metal sheets is of interest.
Normally the instrument has the Rockwell 15 T scale which is suitable for soft metals like aluminium. The instruments can also be supplied for measuring the hardness of other metals.