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Step 2Scrap some parts
- I've took off this nice (12 revolutions 100 positions each) knob from a salvaged resistors bank. It's actually inspired the design. I've drilled it's plastic top for the fixed shaft, because the height of the knob is not enough to contain the moving focusing shaft all the way it goes. Plus, it allows me to connect the flexible hand focuser in the future.
- The brass rod, which will serve as the new focusing shaft, was made of the variable resistor's shaft taken from the same resistors bank box. It's diameter is just perfect for this job. The especially nice fact is that the standard drill bit has the exact fit diameter (8/32in) too.
They are all of the same diameter for this size of variable resistors, though, just make sure it's long enough (about 40mm).
- I've cut it from the base flat. The size could be anything a bit longer than your scope's focusing shaft. But the longer, the better. It's easy to cut it later as necessary.
- then I've made a short thread on the factory end with hand tools to match some wide nut, I already had. The nut will be cut off of the hex side, polished on the other side and epoxy-glued to the shaft later, so the precision of the thread doesn't matter much. It's better to make it loose a bit, so you could precisely adjust the nut to the perpendicular position, while gluing or soldering it in place.
- next step is to drill the brass shaft along the main axis to make a good fit for the scope's focusing shaft. I had a smaller hole already in it, so it was easy to make it bigger.
- the last thing with the new shaft is to drill and tap the set-screw hole on the side of the brass shaft. It is better to assemble the focusing knob on the scope at this point and mark the lowest possible point for the set-screw beforehand.
- In order to do that, I had to enlarge the focusing shaft hole in the scope's back to fit the new shaft in it with some tension.
- The brass rod, which will serve as the new focusing shaft, was made of the variable resistor's shaft taken from the same resistors bank box. It's diameter is just perfect for this job. The especially nice fact is that the standard drill bit has the exact fit diameter (8/32in) too.
They are all of the same diameter for this size of variable resistors, though, just make sure it's long enough (about 40mm).
- I've cut it from the base flat. The size could be anything a bit longer than your scope's focusing shaft. But the longer, the better. It's easy to cut it later as necessary.
- then I've made a short thread on the factory end with hand tools to match some wide nut, I already had. The nut will be cut off of the hex side, polished on the other side and epoxy-glued to the shaft later, so the precision of the thread doesn't matter much. It's better to make it loose a bit, so you could precisely adjust the nut to the perpendicular position, while gluing or soldering it in place.
- next step is to drill the brass shaft along the main axis to make a good fit for the scope's focusing shaft. I had a smaller hole already in it, so it was easy to make it bigger.
- the last thing with the new shaft is to drill and tap the set-screw hole on the side of the brass shaft. It is better to assemble the focusing knob on the scope at this point and mark the lowest possible point for the set-screw beforehand.
- In order to do that, I had to enlarge the focusing shaft hole in the scope's back to fit the new shaft in it with some tension.
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