Rock Section Cutting Apparatu.'^. 67 



with sliL'iiii|- and griudiny discs of 8in. diameter and less. Both 

 experience and experiment had satisfied me. that, given an 

 accurately made motoi'-driven machine, slicins; and grinding 

 discs lOin. in diameter might safely be speeded up to 1000 

 revolutions per minute, with a proi)ortinnate increase in effi- 

 ciency. This c-onclusion, the results obtained have fully sus- 

 tained. 



Again, all the machines of English design and make, so 

 far as my experience of them goes, are only provided Avith one 

 revolving spindle or mandrel, which is invariably made to 

 pass through the centre of l)oth slicing and grinding discs, 

 thus greatly limiting the efficiency of the latter. The single 

 spindle also entails fret]uent changes from slicer to grinder ; 

 and further changes of the grinding laps, according to the 

 differing grades f)f abrasives used; two of which, at least are 

 always required. These frequent changes, of course, involve a 

 considerable loss of time. 



A further important defect — and this applies to both 

 English and German machines — ^is that they have a far too 

 limited top or bench space, hence both slicer and grinder are 

 inconveniently crowded together, seriously hampering free- 

 dom of movement in both slicing and grinding operations. 

 This crow'ding together of rapidly moving parts is also nearly 

 always associated with inadequate protection to bearings and 

 screws, etc., against the intrusion of emery or carborundum, 

 the presence of which even for a short time is rery destructive 

 as well as difficult to remove. 



In the machine I have constructed — and to which I may now 

 l)riefly refer — I have endeaA'-oured to fully provide against the 

 several shortcomings I have named. The machine is speeded 

 to run at close upon a thousand revolutions joer minute. The 

 slicing discs and grinding lajDS are lOin. in diameter. The 

 latter are mounted like the face plate of a lathe ; they run 

 dead true, and have a. clear surface for all operations. The 

 laps and slicer are each separately mounted, with ample space 

 for free movement, as well as with efficient guards, both with 

 respect to ilic operator's clothes, the bearings and other moving 

 ]iaris: the necessity for such protection is obvious. 



