AO series 10 thumb wheel hard to rotate

[henryr]

It takes quite a bit of force to rotate the thumb wheel to adjust the interpupillary distance. Maybe the gibs need relubing. Are there any clear instructions, with photos, of disassembly to get to the gibs?

Thanks,
henryr

[CurlSnout]

I don't have step-by-step instructions, but this 'exploded-view' diagram (and parts list) might help. Left and right hand gibs are part #s 53 and 67, respectively.





Hi-Ho,

cs

[apochronaut]

It takes quite a bit of force to rotate the thumb wheel to adjust the interpupillary distance. Maybe the gibs need relubing. Are there any clear instructions, with photos, of disassembly to get to the gibs?

Thanks,
henryr

It is a fairly common problem with them , after 50 years or so. Some , not so. Either they have been relubed already, or AO changed to a different grease in the 70's sometime.
90% of it is in the sliding dovetail usually. Disassembly is best but annoying. The screws, # 45 in the exploded diagram must come out and are a really small hex. Can't exactly remember what size but they are often very snug and so the recess is easily rounded out .
I usually just open the interpupillary all the way and introduce a light oil at the dovetail seam. 2 drops each ,vtop and bottom, left and right : then rotate the wheel to close the distance fully and then back and forth. Usually this gets things going enough that the action is acceptable. All the other grease points in the mechanism are quite small and offer little resistance.
There is an arm that connects to the travelling telan lens in the bottom. That has a couple of hinge points but unless you are sure that is a problem, don't take the bottom off. It is tricky to put back together and working on it exposes the first surface mirror to damage.

Don't overlube with oil. If the 2 drops doesn't provide a fair increase in the freedom of movement then there may be another problem. Personally, I like the movement slightly stiff since I am the only user mostly. It stays put. I wouldn't go over 4 drops but the area you are lubricating is well away from optics.

[henryr]

Help...while it wasn't easy I got the two #45 top screws loose using a .05 allen wrench but I can't get the two screws on the bottom to move. Are there any tricks...maybe hit them with a heat gun? Or maybe a cotton Qtip with a bit of WD40 left resting on the screw?

[apochronaut]

That's why they have a tendency to round out.

[henryr]

Maybe this is a job for super glue. The .05 allen wrench fits very well so I'm thinking of super gluing it in the screw. Any other suggestions will be appreciated.

[PeteM]

A drop of penetrating oil (Kroil, etc.) and touching the end of a soldering pencil to the top of the screw - letting it cycle hot-cold a few times to let the oil penetrate over time might help. The fit of the hex wrench (and it's quality - hard enough not to round over) is key.

I'm not sure how much of a hex wrench rounding a screw head recess or the wrench itself is due to compressive vs. shear strength; but brass has about 5x the strength of super glue and steel even more. Glue might help an ill-fitting key stay put; but a tight fit should be better IMO.

Phil's suggestion of just working in a couple drops of light oil is worth a first try. Takes a while; but so does applying penetrating oil and then disassembling the slides.

[Greg Howald]

Please don't get super glue anywhere near a microscope. The stuff gasses off for 24 hours and sticks to glass very well. Bad news for optics when you realize you have to scrape the scum off. Speaking from a terrible experience.
Greg

[henryr]

So I've tried a few drops of Hoppes 9 and liquid wrench and a soldering iron and the screws are still tight. My last try is using DAP rapidfuse to glue the allen wrench to the screw and I can manage the outgassing with a small fan. But before I do that are there any other thoughts on getting those screws out?

[apochronaut]

I have cleaned more than 10 of those and only had to resort to using more than a few brain cells a few times. Usually, the passive oil introduction system works well enough if it is just a tight interpupillary adjustor but if the head needs cleaning anyway, you might as well go in. Using a quality well tempered allen key or allen type screwdriver is the first best option. They are usually more precise but those little allen screws only have so much shear resistance and they may have been threaded into a situation of slow galvanic corrosion, sulfitation or salinization for 50 years, so are pretty stuck. They also may have been subject to previous imprecise attempts to remove them. I encountered one in which the hex reliefs were round.

Applying a tiny amount of heat with a little jewellers torch with a fine tip might help or putting the flat of a healthy soldering iron across the top of the heads. I think they are chromed brass, so they transmit the heat quickly. I did have to resort to filing obverse flat sides on some and clamping on a pair of tiny needle nose clamping pliers. They don't take a lot of totque and several heads sheared off and had to be drilled and tapped for a larger screw. Those are truss head screws, so they are impossible to use vice grips on but precision filing does work.

[henryr]

Another option might be filing a slot in the head, for using a flat blade screwdriver, which I didn't try. What I did do was put the scope on its side and put a few drops of Hoppes #9 gun oil on the various outer edges of the dovetails, hoping the oil would penetrate and run down the mating surfaces. I left it for a few hours and then did the same on the other side. After several hours I turned the wheel back and forth a number of times and the movement became easier and smoother. And because the dovetail mating surfaces are at different angles I tilted the head, several times during the oiling, to position the targeted surfaces such that they would be inclined to allow the oil to run down the targeted surfaces. I did a couple of iterations over two days but very little oil was used. The needle applicator is very small so the drops are very small.

[henryr]

One thing I didn't mention is that after movement was working easily I left the scope on one side for about 6 hours and a very small amount of dark oil came out and I did the same for the other side with the same results. Based on this it seems the Hoppes#9 did work, a bit, like a penetrating oil.

[apochronaut]

glad it is working now.

[henryr]

I thought some photos, showing where I used Hoppes#9 gun oil, may help others with a similar sticking problem of slide parts #51 and #68.