What we have now looks somewhat akin to an expensive wood carvers mallet so its time to crack on and start giving the aluminium ‘bar’ a recognisable shape.
Having now machined the ‘electronics’ or cable end we now turn our attention to the ‘globe’ end.
This is considerably more complex from a machining perspective and the allowable tolerances are very tight indeed.
It’s quite fascinating seeing a rod become a contoured head which Bert made look all too easy. I’m glad I wasn’t doing this part for the aluminium merchants would have been very happy indeed! Sales would have been rather brisk I think 
The challenge is the inside machining with very narrow steps and ridges, the purpose of which are to:
- Locate the (originally 5mm float glass … more on that later…)
- To position the all important ‘O-ring’
- To control how much the ‘O-ring’ can be compressed (by the front bezel).
- To manage the degree to which the ‘O-ring’ can deform when subjected to water pressure
- And finally to locate and provide an anchor for the front bezel itself.
First of all once the external contour was done we set about boring out the front face:
The clamping arrangement to the left I’m informed is called a ‘steady’ which is required to help maintain ‘true running’ when it comes to some of the finer control work later on in the machining process.
At this point the basic hollow is in place:
And next comes the initial sizing of the various ‘lands ‘ onto which the other elements will rest:
In the next post i’ll explain the contours in terms of what goes where…