TURNING OUT BOMB CASES

Southland Times, Issue 24596, 19 November 1941, Page 4

TURNING OUT BOMB CASES

CITY WORKSHOPS BUSY

IMPORTANT CONTRIBUTION TO WAR EFFORT

Day by day in engineering shops throughout New Zealand the work of making munitions of war continues, unnoticed for the most part by the general public. Many of these shops are quite small. Most have been altered and fitted out with new machines —metaphorically speaking, to turn out swords instead of plough-shares. Two Invercargill firms are malting munitions. In their case the sword of the metaphor is bomb-cases for Stokes trench mortars—weapons which are still among the most destructive in modern warfare. They are not actually making the bombs, although they are doing a large part of the work. They are finishing off the cases from rough castings supplied from Dunedin. The cases go elsewhere to be tested and, if passed, to be filled with high explosive. Although a bomb is only a metal case filled with high explosive it is the product of several highly technical engineering processes that demand a great degree of skill. Symmetry is essential. IMPORTANCE OF UNIFORMITY The case must be of uniform thickness all the way round. That is because when the explosion occurs the case must split up into as many fragments of steel as possible if it is to wreak the greatest damage. Uneven thickness "of the casing would limit the number of particles into which it splits. A visit a reporter paid to a local workshop revealed that the job of making a properly finished case from the rough casting involves 10 processes, most of which require the use of lathes. The various machines have been hired from garages all over Southland and from Balclutha.

Cast by means of iron chills, a difficult process that maintains uniformity of shape and makes for rapid work, the castings in the rough have a central core which is smoothed and bored in subsequent processes. First, a hack-saw machine is used to trim the tail of the casing. Next the tail is bored, being centred concentric with the interior so that uniformity in thickness will be secured in the operations that follow. ROUGHING UP EXTERIOR The fuse end or mouth is then bored and the next operation is to rough up the exterior. .A lathe is used that takes a cut of 3-16 of an inch in the remarkably short time of one minute 10 seconds. A 10 horsepower- motor is required to drive the lathe. The cutting tool is tungsten-carbide tipped—a tip that is said to be only 10 per cent less hard than diamond. I Following operations deepen the core, finish the exterior, bore the mouth, | turn and screw the tail, and thread the mouth. In the tenth stage the band that fits the bomb is ground and the case is stamped with the maker’s name and the date. On completion of this operation the case is finished so far as the Invercargill workshop is concerned. An Army inspector checks the dimensions and the. case is sent away to be subjected to pressure and hydraulic tests and later to be filled with explosive. UP TO SCHEDULE That is a short description of the work that is going on day after day. One firm alone has an order for 20,000 cases and production is up to schedule. Already they have manufactured several thousand. One shift a day only is being worked as the supply of rough castings is not sufficient to keep the finishing machines running at maximum capacity.

Proof has been given that the Invercargill workshops are turning out a highly satisfactory article. An expert has already pronounced them as being equal to anything made anywhere in the world. The men employed are craftsmen of skill aind experience. They have to be, in view of the exacting tests which the cases have to pass. Perfection is their aim. They are making bombs that are probably the most effective of the kind ever invented. It is possible to fire them so quickly that during the last war the Germans nicknamed the Stokes mortar the English sausage gun. The time may come when “sausages” made in Invercargill will play a part in the defence of the Empire.