13 



SECTION II 



1. MACHINE FOR PULLING MICRONEEDLES AND MICROPIPSTTES 



In designing a machine for this work a study was first made of the hand movement a 

 of an expert in making needles and pipettes. The essential movements seemed to be 

 a removal of the glass from the heater at the correct temperature followed by a 

 rather quick horizontal pull-out. 



In the machine as designed, a parallel motion was devised which, when the glass 

 becomes plastic enough to stretch under a light pull, lifts the glass up and out 

 of the heater and, at the same time, increases the pull by an increase of leverage. . 

 The result is a rapid pull-out at the correct instant. 



The machine as shown in figure 9 is in its final position after pulling two 

 needles, and one needle (a) is still held in the machine by the clamp (b) though 

 the locking nut (c) has been unscrewed, ( much more than is necessary to release 

 the latch (d) ). It is obvious from the drawing that the clamps (b) remain always 

 parallel to the base due to the hinged side bars (e) but perhaps it is not so clear 

 that the alignment rod (f ) passes with a sliding fit through the cross bars (g) of 

 the clamps (b) so that the two clamps must move up and down together, always re- 

 maining in alignment with each other. To "set" the machine the clamps are pressed 

 down until, by turning the knurled knob (h), the retaining bar (i) may be swung 

 over the alignment rod (f). The clamps are then opened and a glass rod or capillary 

 of double length is dropped bietween the guides (j). This rod or capillary will rest 

 on the leather pads (k) and .vhen the clamps are closed anfi latched will be held 

 firmly by the rubber pads (l). The retaining bar (i) may now be swung off, without 

 changing the position of the machine, though the glass will no?/ be under the tension 

 of the springs (m). In this position the glass rod or capillary will pass through 

 the heater (n) and upon switching on the current the glass will become softened. It 

 will pull out, first slowly and then, as the clamps rise, the action will become 

 rapid ending with a quick pull-out, and two needles or pipettes will be pointed and 

 ready for bending. 



Thi6 machine has a number of elements which can be adjusted to give any form of needle 

 or pipette point desired. This is necessary as different types of points are often 

 required, but no change in adjustment is usually necessary for glass of different 



diameters. 



The heating element is a platinum wire in a T-shaped holder of mica. A resistance 

 must be used in series with the heater with a snap switch to turn the current on and 

 off. If the platinum wire is too small it may burn out. At least size #26 should be 

 used. The best form of the wire is shown in the diagram. The width of the heater 

 determines the length of glass softened and so controls the length of the tapering 

 shank of the point. With the form shown this will be about correct, but the shank 

 oan be lengthened by spreading the loops of the wire if desirable. The temperature 

 of the heater depends upon the current which flows and this can be adjusted by the 

 series resistance to give a safe temperature which will not burn out the platinum. 



