7" f/12 R35 iStar Folded Refractor: New rotating focuser ring and baffle tube.

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 I decided to replace the cardboard focuser baffle tube with the aluminium. The plywood ring required replacement. So I cut out two squares of 10mm aluminium with the miter, circular saw. Then bored and turned them into matching, round rings in the lathe. 

The slight extra weight will aid the folded OTA's balance point. Which is presently very nose heavy, like many refractors.

Ring cut from 10mm sheet aluminium, faced and turned to size inside and out.

Counter-boring  the second side in my old S&B 'Sabel' lathe for the Vixen 2" focuser. I removed 5mm.

I had to use the 4 jaw chuck to have enough clearance for the depth of boring.

The rather tatty, old plywood ring with its aluminium copy alongside.The fixing holes have yet to be countersunk to remove the burrs.

The new ring clamped in place. I also cut two rings of PTFE/Teflon using sharpened workshop dividers. This saves wastage instead of sawing. One ring for each side of the backplate reduces friction between the all aluminium rubbing surfaces.

The focuser now rotates much more smoothly than it ever did with the plywood ring in place.

It is important that there is no flop or the baffle will fall off-center.

 The new focuser baffle tube fitted to the new ring. I laid a 60cm rule across the tops of the two folding mirrors to ensure safe clearance of the baffle tube from the optical path.

The inside of the 80mm alu. tubing is remarkably rough. Ideal for killing glancing reflections once it is coated in matt black paint. A thin, metal baffle will be cut to fit into/onto the end of the tube and all components painted matt black.

The larger of the two folding optical flat mirrors sits below. With its transparent food tub cover pressed over the collimation cell for protection. I left the label on to remind me to remove the cover.

With the temperature in the workshop hovering at +1C, 33F I had to bring the matt black painted baffle tube indoors to dry. The water-based, blackboard paint is supposed to take 48 hours to dry even at normal temperatures. The paint is very easy to use, goes on thickly and cleans off my hands very easily. Though I have now taken to routinely wearing surgical gloves for such tasks to avoid using harsh hand cleansers.

I spent a coupled of hours, wrapped up well, playing with collimation and finding the balance point of the folded refractor. First I removed the two solid stainless steel handles from the objective bayonet plate. This moved the balance more towards the focuser but not by as much as I had imagined.

Flashing a torch onto the various surfaces made it easier to identify which aperture I was trying to center during collimation. I am tempted to fit small hinges instead of securing bolts and rubber washers on the top, third point of the large, triangular, mirror collimation cells. At present the cells rise and fall slightly depending on the pressure on the springs on the other two points of the large triangles. Mirror height is important to collimation and I have slotted the mirror support bars to allow for this anyway. The folded refractor should eventually become a permanent feature on the big mounting. Repeated collimation should then not be necessary.

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