How to Clean and Re-Grease a Stiff TeleVue Ranger or TV-60 Helical Focuser
Tele Vueís multi-use small refractors, the Ranger and TV-60, have a unique drawtube-plus-helical focusing mechanism. This works well when new, but the brass helical fine-focus ring almost always becomes stiff after a few yearsí use. In extreme cases, the helical focuser can seize up completely.
The good news is that the focuser (probably) isnít broken or worn out, itís just that the grease has dried out and become too sticky and viscous. To fix it, you just have to dissemble and clean it, then re-grease.
Itís a straightforward job that takes perhaps an hour, but you have to be careful and work cleanly to avoid getting grease on parts that wonít appreciate it. Also, some of the parts are tiny: be careful not to lose them!
What You Need
∑ A rag and white spirit or equivalent for removing grease
∑ A 1/16 Allen key
∑ a 7/64 Allen key
∑ Light automotive grease (I believe special focuser grease is available, but I havenít tried it).
How To Do It
Note: Each step refers to the image(s) above it
Step 1: Remove the nylon thumb screws in the end of the focuser tube that hold the eyepiece or diagonal. You have to do this to disassemble the focuser.
Step 2: loosen the two tiny grub screws that hold the end-ring for the focuser in place. To do this, use a 1/16 Allen key. These are tiny screws - put them in a little zip lock bag so you donít lose Ďem.
Step 3: Unscrew the focuser end cap and remove it.
Step 4: Remove the thin plastic washer/shim from the end of the brass focuser ring.
Step 5: Unthread the brass focuser ring that has the helical groove inside it.
Step 6: Remove the thin plastic washer/shim from the other end of the brass focuser ring.
Step 7: Use a 7/64 Allen key to undo the small bolt in the slot that guides the inner focuser drawtube. Again, carefully put it aside.
Step 8: Pull the inner focuser drawtube out from the end of the main drawtube.
Step 9: Clean everything thoroughly to remove the old grease. Do this with a rag and white spirit, then hot water, detergent and a toothbrush. Dry everything thoroughly.
Step 10: Re-grease sparingly with light automotive grease and re-assemble. Adjust the stiffness of the helical focus with the tension on the outer ring. Once youíve got it right, the grub screws are meant to hold the ring at that tension, but tighten them carefully to avoid moving the ring as you do it and inadvertently changing the tension.
The focuser should now move freely and smoothly.
Note that I did this with a Ranger, but the same process should work for a TV-60 focuser: