The last several days have been spending time in the garage on the lathe making these fittings for the scope.
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Both these fittings are shown upside down to make the threads visible. On the left is an adapter sleeve which is placed over the base illuminator opening. A telescope eyepiece filter is screwed into the top. Before this was made, the eyepiece filter was resting on top of the upper lens in the illuminator, not the best arrangement.
On the right is a threaded plug that goes into the vertical tube port on the trinocular head. Before this was made, was leaving the tube screwed in with a plastic cap on top to keep dust out of the prisms in the head. Now the tube only needs to be mounted when doing photography.
The filter sleeve on top of the illuminator:
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The vertical tube port plug installed on the trinocular head:
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Noticed something interesting about the threads on the telescope filters. They are made in Korea for 1-1/4 inch telescope eyepieces made in China. I figured the threads would probably be metric. After not being able to get a close fit with metric thread pitch gauges, went to the U.S. thread pitch gauges. Got a very close but not exact fit with 40 threads per inch. Did some checking and discovered 40 TPI is very close to a .65mm metric thread, but that gauge leaf was not in the metric thread pitch set. I guess that thread pitch is not commonly used. Anyway, it was a fortunate coincidence, because my lathe cannot cut metric threads without buying additional gears to mount on the quadrant in the head.
And this time was careful to fasten the compound rest at the correct 29 degree angle, so the threads came out a lot better looking, but not perfect. Still a bit ragged in places. Anyway, the parts fit smoothly without binding or excessive looseness.