742 CASE-HARDENING 



tho frame of the bod plate, with his right foot on the board a and his hands on the 

 steering wheels ; on releasing the pressure of the foot tho vertical slide descends by 

 its unbalanced weight until the tracer h comes in contact with the pattern ; tho cut- 

 ters m, m, are made to revolve by steam-power at tho rate of seven thousand times 

 per minute, and are so shaped as to cut like a revolving gouge, so that they instantly 

 cut away all tho superfluous material they come in contact with ; and, by tho time the 

 tracer has been brought over every part of the pattern, tho pieces h, i, j, k will have 

 become exact copies of it. 



So far as panel carving is concerned the whole machine has been described ; but it 

 is requisite to elaborate its construction a little more for the purpose of carving on 

 tho round, and copying subjects which require the blocks to bo cut into in all possible 

 directions. Various modifications have boon used, but we shall only explain that 

 which we think best adapted to ornamental carving. It is not requisite that we 

 should go into the various applications of this machine, to tho manufacture of printing 

 blocks, ships' blocks, gunstocks, letter cutting, tool handling, cabinet shaping, &c. &c., 

 all of which have been shown from time to time to be within its power ; nor is it 

 requisite to describe more recent inventions founded on it, as they will more properly 

 come under other heads. 



When the machine is intended to copy any form which can be carved by hand, tho 

 floating table is differently constructed, but all other parts remain as before. In the 

 floating table used for this purpose, there is an opening in tho centre of the table, and a 

 turning plate, which is mounted a few inches above the level of the table, to turn in 

 bearings in standards. Underneath the turning plate, and forming a part of it, there 

 is an arc of rather more than half a circle, having its centre in the axis on which the 

 plate turns, and this arc is cogged on its edge to fit tho threads of the tangent screw 

 on the axis of the wheel, so that by turning this wheel, and dropping its detent into 

 any cog, the workman can fix the plate at any angle with the horizon. There are 

 three chucks fitted into sockets of the turn plate, and these are similarly divided on 

 their edges by holes or cogs, into which detents fall, so as to secure them steadily in 

 any required position. 



In going through the process the workman will, of course, attack the work when it 

 is placed in a favourable position for the tools to reach a largo portion of its surface : 

 and having completed as much as possible on that face, he would turn all the chucks 

 through the same number of divisions ; the pattern and work will still have the same 

 relative position to each other as before, but an entirely new face of both will be pre- 

 sented to the tools ; this will be carved in like manner, and then another similar 

 change made, and so on until all has been completed which can be reached without 

 changing the angular position of the turning plate. This can be done by the wheel, 

 and when a sufficient number of these changes have been gone through, the work will 

 bo complete on every face, although the block may have required to be pierced through 

 in fifty different directions. T. B. J. 



Notwithstanding the remarkable ingenuity displayed in tho construction of this 

 carving machine, it has not been so largely used as might have been expected. In all 

 cases where repetitions are required its advantages are obvious, yet prejudice appears 

 to have stood in the way of its general adoption. 



CASCAXiHO. After tho first washing of sand for gold there is a deposit loft, and 

 this, in Brazil, is called Cascalho. The name is also given to the alluvial soil in which 

 Brazil diamonds are found. 



CASCARILI.A BARK. (Spanish, Cascara, bark.) The bark of Croton eleuthcria 

 and C. cascarilla, both of which shrubs grow in the West Indies. The bark possessing 

 tonic properties is used medicinally. 



CASE-HARDENING is the name of tho process by which iron tools, keys, &c., 

 have their surfaces converted into steel. 



Steel when very hard is brittle, and iron alone is for many purposes, as for fine 

 keys, far too soft. It is therefore an important desideratum to combine tho hardness 

 of a steely surface with the toughness of an iron body. These requisites are united 

 by the process of case-hardening, which does not differ from the making of steel, 

 except in the shorter duration of tho process. The property of hardening is not 

 possessed by pure malleable iron ; but by a partial process of cementation the iron is 

 converted externally into steel, and is subsequently hardened to that particular 

 depth. Tools, utensils, or ornaments, intended to bo polished, are first manufactured 

 in iron, and nearly finished, after which they are put into an iron box, together with 

 vegetable or animal charcoal in powder, and cemented for a certain time. This 

 treatment converts tho external part into a coating of steel, which is usually very 

 thin, because tho time allowed for the cementation is much shorter than when tho 

 whole mass is to bo converted into steel. Immersion of the heated pieces in water 

 hardens the surface, which is afterwards polished by the usual methods. 





