Main tube Pt.3 Objective cell adapter [counter cell.]

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A single front ring will be bored larger to fit the rear of the objective cell at 168mm. This will help to support the weight of the heavy cell and objective glass. As well as sealing it more effectively to the main tube. 

With the bore being very slightly larger than the tubing flange I can glue the front ring to the others to make a more solid unit. If the bore were any smaller it would catch on the flange as the adapter was slid backwards off the tube. Which would trap the adapter on the front of the telescope. I might want to work on the adapter for some reason in the future. So it would be easier If I didn't need to destroy the adapter just to remove it from the main tube.

The three rings can be turned smoothly on the outside. Once they are glued together while being aligned and clamped together on the telescope tube. The images show progress producing two tightly fitting, adapter rings on the lathe. They were too large for the 4-jaw chuck. So I had to screw them, from the back, to my largest faceplate. I doubt they need to be quite so tight. So I will sand them to tidy them up.

Whoops! Re-measuring the flange made it larger than the rear cell diameter. The front ring will have to be screwed to the rear rings. Or, I file [or grind] the tube flange smaller. This would allow the three rings to be glued solidly together but still removable from the tail end of the tube. I want to smooth the exteriors to match each other once glued together. To look like a solid object once painted. I must remember to cross the surface grain of all three rings to avoid warping over time.

Sunday 26th. Another grey day. Third [front] ring completed to fit over the rear of the 168mm iStar 150mm objective cell. The two front rings have been eased by sanding and then glued together while fitted onto the tube.

Yet to decide whether I want to reduce the tube flange slightly and glue the front ring to the other two. Or screw the front ring to the other two with machine screws. There is only a few millimeters difference in diameter between the flange and ring. So it's not much work. I'll think about it over lunch. Sudden sunshine at 13.30!

I have decided to reduce the tube flange to allow the three rings to be slid all the way onto the tube from the eyepiece end. An angle grinder and ear defenders are all you need to disturb the peace on a Sunday afternoon! Besides, it will drown out the neighbours dog! 😎

Monday 27th. 41F. Another grey day with occasional rain. After overnight clamping I smoothed and sanded the rear pair of  adapter rings. Then glued the front, cell support ring to the other two. The full ring is presently sitting under the woodburning stove to speed drying while well covered in spring clamps. It's only 43F in the workshop now so a bit chilly for wood glue. I also reduced the small flange on the end of the main tube. The angle grinder was wonderfully noisy! Then I filed and sanded the sharp edges away.

I have had the idea of bolting the three, plywood rings together precisely where the collimation "push" screws will press. Then the M5 screws will have something hard to push against without denting the plywood. M6 hex socket heads will allow the M5 to reach the bottoms of the sockets.

When the glue is dry I'll spot through the six, collimation screw holes in the objective cell to mark the adapter ring ready for drilling. I need to get some more M5 T-nuts for the collimation "pull" screws.I can use flanged, M6 furniture nuts for the ring clamping [together] screws.

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