W. E. Dalby 43 



screws may be screwed into the timber, the heads of these screws 

 being specially formed, the screw at C with a conical hole, the screw 

 at B with a V-slot, and the screw at A with a plane head. 



The reference plane will stand at a fixed distance from the plane of 

 the machine defined by the hole-slot-and-plane clamping except for 

 the negligibly small error produced by warping and shrinking in the 

 distances of Z from the clamping points. This error is minimised by 

 selecting Z as close to the conical hole as possible. 



3. General Description of a Eecorder. 



The particular form which the profile recorder takes depends upon 

 the purpose for which it is required and upon the sizes of the samples 

 which are to be tested. 



Apparatus may be designed for drawing the profile curves of the 

 largest planks or for studying samples of moderate size or for measuring 

 the shape of the blades of an aircraft propeller. 



One type (Mark 2) is shown by the photographs Figs. 4 and 5. 

 This apparatus takes samples 30^" by 6" and any thickness up to 1|". 

 Variations in the shape of the surface are shown twice the actual size 

 in the record. This multiplication of the surface variations can be 

 carried to any extent desired but the scale once settled remains constant 

 for any particular machine. 



Referring to Fig. 4 the timber sample T is clamped down by the 

 clamps A, B and C to the corresponding studs below it. The drawing 

 paper on which the records are to be taken is pinned down to the drawing 

 board at D. The angle iron framework is self-contained and supports 

 on the one side the timber sample and on the other side the drawing 

 board. 



Lying on the bottom bars of the framework is a guide frame GG 

 consisting of two parallel rods secured in end pieces. It will be seen 

 that this frame can be lifted from its position and can then be placed 

 in another position defined by any one of four pairs of V-notches cut 

 in the lower bars of the framework. These notches are pitched 1 inch 

 apart. 



The stock of the machine is supported by the guide frame. It is 

 shown separately in Fig. 5. Its base is made of cast iron and it is 

 grooved to slide along the guide bars GG seen in Fig. 4. It is pushed 

 along them by hand when a profile curve is being drawn. 



The stock carries an exploring roller R on the end of an arm and a 



