The fibre pulling machine had been showing some problems with reproducibility when last used by Alastair Heptonstal. We had a look at it and after checking the red to IR beam alignment (which is perfect) and some trivial re-alignment of the upper and lower clamps, it looks like the main problem is wear in the bearings on the motor of the spinning mirror. The symptom is that the red tracer beam draws out a sinusoidal like pattern rather than a straight line on the stock and that it moves around slowly (~ one to a few seconds timescale). Increasing the motor speed makes this worse, decreasing it makes it better. However, slowing the motor down means that the heating does not appear constant as far as the silica is concerned. We pulled and profiled fibres at fast and slow speeds and the slower speed ones were almost acceptable whereas the fast speed one was way off.
Doug Cook is going to order a replacement part and fit it when it arrives. With the new motor and standard speed (8.55V to the motor) the machine should be back to its old self.
Angus & Giles