Popular Science Monthly 



771 



|*^*j To be drilled 

 in one only 



Simple Die Casting for the 

 Home Shop 



A SIMPLE and easily made mold for the 

 use of the home mechanic is shown in 

 the illustration. It consists of a length of 

 tubing of any convenient material, cut 

 longitudinally into two equal parts. Steel 

 caps fit close over both ends of the two 

 parts of the tubes, holding them firmly to- 

 gether and in line. In use, one-half of the 

 shell is first ,.. 



filled with plas- 

 ter of Paris, a 

 block of wood 

 being used at 

 each end to re- 

 tain the plas- 

 ter. The pat- 

 tern, having 

 been oiled with 

 lard, or with 

 graphite-filled oil, is embedded 

 halfway in the plaster. After 

 the plaster is set, the surface 

 of the first half of the shell is 

 carefully wiped over with 

 graphite, and then the second 

 half is filled in the same way. 

 The parts thus placed to- 

 gether are all capped and put 

 away to set. 



When the plaster has set 

 and become dry the caps are removed, the 

 tube taken apart, and the pattern removed. 

 The core A is now set and the pouring gate 

 B and riser C are cut in the plaster. The 

 parts are then put together and the caps re- 

 placed. The mold is then ready. 



The great advantage of this mold is that 

 its alinement is positive and automatic. 

 This mold is intended for white metal, 

 pewter and metals fusing at low tempera- 

 tures. The drawing shows how the gates 

 and risers should be located with reference 

 to the pattern in all castings. If the mold 

 is well dusted with graphite before each 

 cast, and a proper number of cores supplied, 

 a number of castings can be made from it. 



This mold is especially adapted for mak- 

 ing metal patterns to take the place of 

 wood. — J. B. Murphy. 



Painting on Cemented or 

 Concrete Surfaces 



r HEN 



WHEN paint is applied directly 

 cemented surfaces the free lime 



to 

 in 



the cement will saponify the oil of the 

 paint and destroy its integrity so that 

 finally the paint will peel off. After such 

 a surface has been exposed to the elements 

 for about a year, paint may be applied 

 with little danger of deterioration. But 

 I this is not sure. 



both ends to^?= :::= p^^ 

 tit caps 



i.x\ 



! 



J_ L L 



Mold made in 

 plaster to shape 

 metal castings 



Expansion Shield for Screws Made 

 of Sheet Lead 



AVERY good expansion shield is made 

 from sheet lead rolled up to such a 

 size as to snugly fit the hole. 



One of the 

 early processes 

 for neutralizing 

 the free lime 

 was by the use 

 of dilute muri- 

 atic acid of 7 

 or 8 per cent of 

 concentration 

 mixed with 

 water. But it 

 was soon found 

 that the acid 

 used to neutral- 

 ize the lime 

 converted it into calcium chloride, 

 injuring the cement surface so that 

 it crumbled or pitted badly. An- 

 other and better method of pre- 

 paring the surface consists in the 

 application of carbonate of am- 

 monia, io lb. to 45 gal. of water. Insoluble 

 calcium carbonate was formed and a large 

 amount of ammonia was liberated. This 

 preparation does not injure the surface of 

 the cement. When used on a mortar plas- 

 ter containing lime, as in building a stucco 

 house, it is better to apply two weak 

 solutions of this kind, rather than one 

 strong solution. 



But the best treatment is with zinc 

 sulphate, used with water of equal weight. 

 This wash is put on with a brush having 

 stiff bristles. The chemical effect is in 

 changing the caustic lime into calcium 

 sulphate or gypsum, and zinc oxide is 

 formed in the pores of the cement. This 

 treatment has no injurious effect on the 

 cement surface; on the contrary it makes 

 it fit to take and hold the paint. This 

 method of preparing cement for paint has 

 been well tried out and is reliable. 



The following formula for painting on 

 concrete or cement may safely be followed: 

 For the first or priming coat, after the sur- 

 face has been sized with the zinc sulphate 

 solution and is dry, mix ioo lb. pure car- 



