39 



THE DALBY PROFILE RECORDER. 



By W. E. DALBY, M. Inst. C.E., F.R.S. 



Professor of Engineering, City and Guilds Engineering College. 



(With 7 Text-figures.) 



1. Introduction. 



A SHORT time ago Professor Groom asked me if a method coukl be 

 devised to enable him to measure the shape of the surface of a timber 

 sample with reasonable speed and accuracy so that measurements taken 

 from time to time could be compared in order to study questions relating 

 to the warping of timber. 



In response to this request I designed a machine by means of which 

 the shape of the surface could be explored and recorded automatically 

 without the necessity of taking a single measurement directly. 



The result of the exploration of the surface by the machine is a 

 drawing showing the shape of the surface along parallel lines spaced 

 at definite distances apart. 



Such a drawing is seen in Fig. 1. It is the result of exploring an 

 artificially prepared surface of a piece of pine along five parallel lines. 

 The surface was made specially irregular in order to illustrate the 

 working of the machine. 



The five datum lines numbered respectively 1 to 5 and the corre- 

 sponding profile curves were drawn in 3 minutes. The datum lines are 

 spaced 1 inch apart and the length of the record is about 2 feet. The 

 size of the sample used in the particular machine in which the record 

 was drawn is 30| inches long and 6 inches wide. 



The curves on the drawing are really the profiles of five equidistant 

 sections of the timber sample taken normally to a reference plane. 

 The profiles recorded show the variations of shape to twice the actual 

 size for convenience of measurement. The machine can be designed 

 to give the record the actual size or any multiple of it. 



2. The Reference Plane. 



The machine is so designed that the datum lines in the record 

 correspond to lines lying in a common plane in the timber sample. 



