O-rings and washers

[Ben the Ignorant]

Hi!

Here are some tips you can achieve with rings of various materials; they are some of the most simple and cheap DIY's. I don't know if I can write between pics so I numbered them, and will comment them one by one from the top of the page.

1. Sky-Watcher tripods have a gap that I always fill eventhough I'm a visualist. An astroimager friend had filled the legs with concrete, very good, but forgot this, so his mount could play during an exposure and ruin it. As a principle I don't let mechanisms play.

2. That pesky what's-its-name plastic thingy can break if you tighten the bolt too hard, and replacement is impossible to find, so I limit the bolt's range with O-rings and/or washers. A guy in the field did just that harsh tightening to my mount, thinking he was doing good, but he broke nothing due to this precaution.

3. Limiting the range of finder screws prevent it from straying much away from the ideal setting, and make it more stable. Set the thickness of the rings' pile so the screw is tight at the right spot.

4. and 5. My old Celestron tangent arm had a little backlash; I suppressed it with an O-ring on each side. The rubber is pressed hard against the metal to remove play, but doesn't bind like metal against metal would (and it's silent). Lubricated a few times over the years and the puny rubber ring never broke; smoother feel, too.

6. This completes the anti-backlash job. The factory horseshoe spring washer left some play; I filled the gap with a homemade washer cut from those tear-proof blister packagings. Been there for years and never complained. That material is very tenacious, easily workable with blades and sandpaper, and lubes well.

7. Just for a better feel I insert O-rings there, the lever is no longer loose.

8. Visual backs on Schmidt-Cass have a large gap between the two parts. I filled it with a copper wire; even when you remove the visual back from the scope the wire stays in place by magic. The core of a TV cable sanded down a tiny bit gave the right gauge. The two components remain centered, now.

9. and 10. This solar filter has to fit two scopes with different dewshield profiles, so I had to craft it a little strange. O-rings grip well, but a rubber band that I keep tucked at the rear of the dewshield holds the filter much safer.

11. This is only for looks. I don't like components that stray from their spot, so I keep the dob's tension spring in place with rubber rings. It might be prudent to keep the leverage close to the trunion, imagine if the traction point was very far away from it, the plastic trunion might suffer. Won't experiment to find out how true this is.

12. I balanced the dob's tube, so much less tension is needed in the spring. I could have put any circular steel ring there, but this elliptical one has no extra belly so it doesn't look like it was an add-on. Put only a few ungainly little things on your scope, and it soon looks too obvious that they are mods.

13. An eyepiece hitting the rack makes a loud ringing noise that's amplified by the resonance in the wooden rocker (looks like a guitar amp's cabinet, uh?) and the steel tube (looks like the guitarist came with his drummer). Rings of felts dampen the sound, but not enough yet. There is also foamy material between the rack and rocker, but still too much gong effect.

14. A loose findershoe screw on a tall dob would let that hard an heavy object fall; I don't finf that safety rubber band paranoid. First I put flesh-colored regular rubber bands, but their color is horrible on a scope; fortunately I found dark blue rubber bands.

15. I have no use for the rotating focuser lock, and its metal tip pushes against metal, not good, so I keep it in place but neutralize it with a piling of washers.

16. The single factory O-ring doesn't limit play enough, adding a few more till they push against the lens cell reduces play.

17. The tension screw on this focuser makes the motion noticeably harder if you simply brush it, but a couple O-rings prevent that.

18. Losing the right setting here is very annoying because the right interplay between the two screws is not easy to find, but again, the right piling up of O-rings and/or washers maintains it.

These mods are discreet and very cheap, hope they will help.

[Dave Lloyd]

Do you own an o ring company?. Seriously there are some good ideas here. I bought a big set of various o rings for a pond pump seal I didn't know the size of so I've got plenty lying around. I'll have a go at some of these.

[Ben the Ignorant]

Same for me, I've bought them without knowing what they would be for, because a box of 125 costed very little. Used a few, kept the others idle in their box until I scratched my head about where to use them in telescopes.

By the way, the diagonal in my old Celestron Schmidt-Cass had thin aluminum walls, and the screw was steel or brass, but harder than aluminum. I had the bad habit of tightening it too hard, eventually ruining the thread in the diagonal. Drilled and tapped another hole but not pretty, and ended up loose, too, because hard metal against soft metal eats up soft metal. Fortunately, now diagonals have sturdier walls and an aluminum screw but since it costs pennies and it's barely visible, I insert rings and/or washers to make overtightening impossible.

This is a good measure for scopes that will be used by people who're not familiar.

[Ben the Ignorant]

I forgot this: my Schmidt-Cass had a large (half a millimeter) gap between the plate and the secondary cell, it could move around, forget about centered optics. So I took this waffled, firm but compressible sheet of plastic, and made a centering ring with it. Star test and planetary detail improved. The sheet made the bottom of a bakery bag rigid; I kept it because of its texture, and eventually found a use for it.

I blackened the mirror's and plate's sides while I was at it.