Metal Working Tools 43 



measurement with the inside callipers, a slight lateral play being 

 allowed in measuring for a working fit, whereas a driving fit 

 will necessitate the callipers being only just movable in and out 

 of the hole, of course without " spring." The measurements 

 so obtained are then transferred accurately to the outside 

 callipers, and used as a gauge. 



Files. Large files are not likely to be needed in our 

 work, hence a 10" flat file (rough) will be sufficient for the 

 heavy work required, and smaller ones may well be 



1. An 8" half round bastard file. 



2. An 8" hand file (or pottance file), second cut, safe-edge. 



3. An assortment of six small key files (Adams, page 120, 



No. i set). 



No. 2 will be found the most useful of the group, as the 

 safe-edge permits its use up to a corner. 



Files cut by abrasion, and are named in accordance with 

 the coarseness of the teeth. Rough, bastard, second cut, 

 medium, smooth, super (or dead smooth), being the usual 

 terms. Examination of files will be the best way of becoming 

 familiar with these grades. 



An ordinary file cuts on the forward stroke only, and should 

 be held with the handle in the palm of the hand, in order that 

 the full force of the stroke may be communicated to the tool. 

 Handles should therefore be selected of such size and shape 

 as will permit this. Frequently one sees chisel handles sup- 

 plied on files, but tool handles are by no means interchange- 

 able in this way. An uncomfortable handle prevents good 

 work with any tool, and in the case of files this is particularly 

 noticeable. 



New files should be used on brass ; indeed a new file is 

 almost necessary for this material, but, when worn out for 

 brass, it will still cut cast iron well, consequently it is well to 

 keep a mental record of the history of one's files. 



Filing should only be attempted when the object is suffi- 

 ciently tightly held in a vice to permit the full force of a stroke 

 being made, but instrument makers are frequently called upon 

 to use the file in awkward and constrained positions, con- 

 sequently no general rules can be given. It should, however, 



