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Focusser 4
This final sequence shows where I change things again. As I have a small lathe I made a new focus housing, which was about 4mm shorter than the original, and also the diameter was matched to the bearing size. The hole in the scope is very oversized, so making the housing bigger does not cause any problems. The housing follows the original in that the flange is 1-1/2 inches in diameter. The bore is 1/2 inch + clearance, the smaller diameter is 23.25mm (matches the thrust washer, sorry for the mixed measurements) and the face to face length is 8mm (compared to the original of 12.8mm) I left a few score rings on the bore to hold grease better. The second image shows the full set of bearings and thrust washers, and that the recess is in the correct position.
There is a small recess in the end of the focus knob, that needs to be packed out, if this is not done then the thin edge of the knob could be damaged as the knob is tightened up on the brass thread. As this recess is where the nylon washers were located, packing the knob with the washers is the ideal solution. I needed to use two washers, as shown in the 4th image. Screw the silver knob onto the brass thread, and just tighten it enough to remove any play in the assembly. Only a very light touch is needed, as you are not crushing nylon washers, you have a nice set of hardened steel rollers to do the hard work now. The 5th image shows the completed assembly with the new housing.
The bearings, nut and thread were greased with a high quality Teflon enhanced grease. (The same as I use on the lathe lead-screws) and the assembly was refitted to the scope. All that you need to do is to locate the end of the threaded rod onto the pin, and apply a little grease. You then push the rod into the scope moving the mirror to the forward position as you do so. Replace the three cap head screws but do not fully tighten them. Wind the focus knob in and out a few times, and you will probably feel that the focus assembly shifts into the correct position. Then tighten the screws firmly.
The time taken to make this modification was not very long. I started at 13:30, and was finished by 16:00 and this included the machining and fitting of the new focus housing. Without the new housing the job would have taken well under an hour. The results - well as reported by others the focus is smooth and easy, and you can feel the difference in the weight of the mirror depending on the direction of travel.
