Steven Tribe
2-Jul-2011, 03:52
Up to now, I have always been able to find old waterhouse stops that could be modified to fit lenses which needed them.
But now I have a Euryscope VIIa, 8 which needed some and nothing was available.
All the brass/bronze plates I had were a little on the thick size so I looked around for alternatives.
Some years ago, I built a massive square trough for my wife's hobby - basketry. The willow has to be soaked for weeks to be flexible. This was built in building quality zinc - obviously with some metal additives to stop oxidation.
So I used the remaining material to attempt some waterhoiuse stop manufacture.
This quality zinc was easy to cut, drill and file - without getting bent at the edges.
It was much easier to work with compared with aluminium of the same thickness.
It appears to bond well to mat black enamel.
Now I was working without a dummy stop, so I have a few comments that might be useful for others:
Cut blanks with the right width.
Check these fit.
Do not worry about the vertical position of the hole - my experience is that this is best adjusted after the hole has been made.
Make a central vertical mark with a sharp hobby knife.
Drill out the various holes in the blanks - making about 1-2mm undersize. The hole will not be completely round with ordinary drill tools.
File the holes (chain saw file?) and make completely round using appropriate wet/dry wrapped round a finger or round object. A slight bevel towards the front of the lens can easily be added.
Make ink marks on the largest new stop that correspond to the "framing" ring diameter in the stop frame.
Remove gradually material at the two corners at the end of the largest stop until the two marks can be seen to just touch the top and bottom.
Repeat for the stop blanks. Do not use the first as a template for the others as the angle of cut of the edges and the precise width of the individual stops will have surprisingly large effects on an exact central position.
I also discovered that you should not rely on the engraved F value for calculating the exact iris diameter without stops. This Euryscope says F18 - but the basic iris diameter corresponds to F16 - there must have been a large waterhouse stop which corresponded to the F.18.
As the strength of this material obviously less than brass, I have made the stops so that there is quite a large area at the top to grab hold of.
But now I have a Euryscope VIIa, 8 which needed some and nothing was available.
All the brass/bronze plates I had were a little on the thick size so I looked around for alternatives.
Some years ago, I built a massive square trough for my wife's hobby - basketry. The willow has to be soaked for weeks to be flexible. This was built in building quality zinc - obviously with some metal additives to stop oxidation.
So I used the remaining material to attempt some waterhoiuse stop manufacture.
This quality zinc was easy to cut, drill and file - without getting bent at the edges.
It was much easier to work with compared with aluminium of the same thickness.
It appears to bond well to mat black enamel.
Now I was working without a dummy stop, so I have a few comments that might be useful for others:
Cut blanks with the right width.
Check these fit.
Do not worry about the vertical position of the hole - my experience is that this is best adjusted after the hole has been made.
Make a central vertical mark with a sharp hobby knife.
Drill out the various holes in the blanks - making about 1-2mm undersize. The hole will not be completely round with ordinary drill tools.
File the holes (chain saw file?) and make completely round using appropriate wet/dry wrapped round a finger or round object. A slight bevel towards the front of the lens can easily be added.
Make ink marks on the largest new stop that correspond to the "framing" ring diameter in the stop frame.
Remove gradually material at the two corners at the end of the largest stop until the two marks can be seen to just touch the top and bottom.
Repeat for the stop blanks. Do not use the first as a template for the others as the angle of cut of the edges and the precise width of the individual stops will have surprisingly large effects on an exact central position.
I also discovered that you should not rely on the engraved F value for calculating the exact iris diameter without stops. This Euryscope says F18 - but the basic iris diameter corresponds to F16 - there must have been a large waterhouse stop which corresponded to the F.18.
As the strength of this material obviously less than brass, I have made the stops so that there is quite a large area at the top to grab hold of.