-1^ MACHINE P! \M> DU 



that ot the smooth mil, are .-ailed 



tl><- i "*<wof the f..rmer 



li surface of a tc* 



\\heel l.y ;i plan.- |.er|>eiidiml:ir to it- I UFOfe, and is 



Called \V e may also say that the pitrh cutk is 



the edge of the pitch surface. The j.itdi cin ! is ^ii'iilly 



traced on the side of a t. .<.tln d \\heel.aml is rather m-an-r the 

 points of tho trrtli than (he roots. 



Pitch / T"th. The distant- fn.ni tli. mitre of one tooth 

 to the centre of the next, or from the front of one to the fn .nt 

 of the next, measured at the i>it<-l< <-nrle, is called th< /,itrl, <>f 

 the teeth. If D be the diameter of the pitch circle of a wheel, 

 n the iiuiuliiT of teeth, and p the pitch of tin t,th, then 

 Dx 3-1416 = nxj>. 



By the diameter of a wheel is meant the diameter of its 

 pitch circle. 



Form and Proportions of Teeth. The ordinary form of 

 wheel teeth is shown in rig. 44. The curves of the teeth should 

 be cycloidal curves, although they are generally drawn in as 

 arcs of circles. It does not fall within the scope of this work 

 to discuss the correct forms of wheel teeth. The student \\ ill 

 find the theory of the teeth of wheels clearly and fully ex- 

 plained inGoodeve's ' Elements of Mechanism, and in I'nwin's 

 Ma.-hine Design.' l 



The following proportions for the teeth of ordinary toothed 

 wheels may I*' taken as representing average practice : 



h of teeth . . . -/r-arcaft/-ni-_ -H 



Thickness of tooth , -be* ; 



NS idth of space . . . -j&~ 



1 See also ' A Manual of Machine Drawing and Design,* by D. A I , vs 

 and A. W. Bevis. 



