Chap. XX. Of the Drill-Boxes. 3 1 $ 



down by the Finger of the Player ; but the Drill- 

 fpring requiring to be of a vaftly greater Strength 

 than that, I made it of Steel, of the Breadth of half 

 an Inch, inftead of Brafs Wire : This performed very 

 well, and feveral Drills are yet extant, that have only 

 this Sort pf Springs : Yet I found there was great 

 Difficulty to fet the Legs at their due Diftance from 

 each other ; for their Seafoning would alter them 

 from what they were, whilft the Steel was foft : 

 They alfo took up too much Room in the upper 

 Part of the Mortife. Then, to remedy thefe Incon- 

 veniencies, I made it fingle, with only one Leg, 

 which by full Experience is found to be much better 

 than the double one ; it does not contain a Fourth 

 Part of the Metal, and is mod eafily made, requiring 

 none of that Trouble and Nicety that the double 

 Spring doth. I fhall therefore give a Defcription of 

 the fingle Spring only. 



B, the End of the Screw, which holds the Spring 

 to the Tongue, thro' a Hole near the upper End of 

 the Spring; D, the Middle, againft which the End 

 of the Setting- fcrew bears. 



Its Length is almoft the whole Length of the 

 Tongue ; the End E reaching very near to the 

 Jower End of the Tongue, and the End B is as near 

 the upper End of the Tongue ; as it can be placed 

 without touching the Cylinder of the Tongue. 



The Breadth is ufually about half an Inch ; the 

 Thicknefs muft be in proportion to its other Dimen- 

 sions, and according to the Degree of StifFnefs re- 

 quired. 



The longer it is, the thicker it muft be, to have 

 thft fame StifFnefs; but the broader it is, the thinner 

 it muft be of the fame Length; fo that it is hard 

 to determine its Thicknefs. It is made ftifFer or 

 ftronger by being cut fhorter ; it is made weaker, 

 or lefs ftiff, by filing or grinding it either thinner or 

 narrower, 



The 



