22.03.19 Collimatable focuser backplate assembly.

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A helpful, local engineering company ran their bandsaw through a length of 180mm Ø [7"] aluminium bar. They produced a range of slices in several different thicknesses for me. After having the [scrap] bar for years I can finally use some of it in the lathe. It would have taken weeks to saw through such a large diameter with a hacksaw and completely impossible to part off in my lathe.

I spent a couple of hours truing up a 20mm thick, sawn disk for the new backplate in the 4-jaw chuck. The plan is to thin and recess the disk, to lighten it and counterbore it to fit a sunken base ring. Four [eight] push-pull screws will be arranged on a radius for fine collimation outside the focuser base. I must await the arrival of another component before I can proceed.

I have ordered a threaded and anodized, aluminium ring to be made by Teleskop-Express custom machining services. This is to fit the focuser base because I have doubts as to the wisdom of my trying to produce such a fine, large diameter thread: 5.125" x 24TPI.

The cost of the custom ring was only about half the asking prices of the standard base adapters offered by the US manufacturer of the focuser. I couldn't bring myself to spend that much on their simple CNC'd components and none of them suited my construction plans anyway.

I have been using a secondhand Vixen 2" focuser, without fine focusing, for more years than I care to remember. It came already modified and attached to an old and very secondhand, shortened, 6" f/8 Celestron refractor. Which is now my H-alpha PST modified telescope. Waste not, want not.

Trying to focus the sun's image from the Neximage5 on the end of the 7" f/12 iStar has been extremely frustrating. So I am buying my first, decent, brand new focuser in nearly 60 years of telescope making on a shoestring. And I still feel guilty at the expense! That's a 2" Baader, Click-lock, eyepiece adapter for those hoping for a clue. 😏

Click on any image for an enlargement.

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