AO 10/20 phase condenser needing repair

[dtsh]

In a recent trade I managed to acquire some spare AO phase parts for series 10 and 20 scopes, but some of the parts are damaged or missing pieces. In some of my discussions with other members here, I know that some of you also have damaged phase condensers so my intent is to try and document what we can figure out and see how many of these damaged units we can put back into service.

Previously I only had one working AO10 phase turret (Cat.1240) which I was not willing to risk damaging, but now that I have some which are already damaged I am no longer restrained from dismantling. I have been told some have phase condensers where the hex key socket of the alignment screws are wallowed out making adjusting the annuli annoying on a good day. I know there are some other units out there with similar issues so this seemed like the best place to start.

I removed one of the alignment set screws from the worst of the condensers and measured it, I've been as careful in my measurements as I can using a common Starrett No.230 micrometer which has seen a fair amount of use, though I think it's accuracy is probably still higher than mine.

The easy measurements first, the screw is 0.3165" long (8.034mm), and accuracy in this dimension is not terribly important so long as it's +/- 0.05" or so, maybe even more. A more critical measurement is the thread major diameter of 0.098"(just barely under, perhaps 0.0978) which correlates well to a #3 machine screw's max and min diameters of 0.0983 - 0.0938".

The number of threads per inch however, is harder to measure as my Starrett No.40 thread itch gauge only goes down to 40tpi, meaning I need to measure it some other way and here is where we enter the realm of guesswork and estimation. Due to a variety of reasons I am unable to make a reliable measurment of the threads per inch, but after repeated attempts I think it's 48tpi. My reasoning is that I get approximately 0.228" crest to crest, over 11 turns of thread using a flat anvil micrometer, which is not an accurate tool for the task. But doing the math of 11/0.228 x x/1.0 = 48.245 which is pretty close to 48. It so happens that a fine thread #3 set screw is....48tpi.

The second part of this are the wrenches. Both sets I have seem to be within the realm of acceptable and fit into

The stock wrenches appear to be 3/64 hex key based on the two sets I have.
I have some ideas about replacing old wrenches with new ones, but first off I need to see if I can find set screws that fit the condenser as that will define what socket size the wrench needs to be; with luck it'll be 3/64

Anyone else been down this road ahead of me with more accurate measurements?

Failing all else I can always fall back to my original plan of stripping the worst condenser to repair the other two.

[PeteM]

I'm pretty sure that the setscrews take a pair of 0.050 hex wrenches. Recollection is that your 3-48 assessment is right, but less sure of that.

You might want to try a long 3-48 screw or tap (assuming that's right) and run it through the threads just to make sure they're clear of gunk?

[dtsh]

I'm pretty sure that the setscrews take a pair of 0.050 hex wrenches. Recollection is that your 3-48 assessment is right, but less sure of that.

You might want to try a long 3-48 screw or tap (assuming that's right) and run it through the threads just to make sure they're clear of gunk?

Looks like there's about 0.003" between 3/64 and 0.050, but 0.050 looks like the normal nomenclature for such a size; just another reason to love imperial/US Customary.

If I think it's 3-48 and you think it's 3-48, I'll gamble a few dollars and see if we're right.

[apochronaut]

I bought a bunch of screws from China about 4 years ago for 2 or 3 bucks. I think I have about 50 of them here. I could not get the round head version ; had to settle for the pointed tip but they work well. One could always put a dab of silver solder on the end. How many do you need? Pete is correct on the hex if I recall: .50.

[DrPhoxinus]

I am one those who has what must be rounded out sockets.

Instructions and pictures would be great help

Phase isn’t usable on the AO 10 right now

[dtsh]

I bought a bunch of screws from China about 4 years ago for 2 or 3 bucks. I think I have about 50 of them here. I could not get the round head version ; had to settle for the pointed tip but they work well. One could always put a dab of silver solder on the end. How many do you need? Pete is correct on the hex if I recall: .50.

Ammusingly, I don't think I need any. I am certain to have one condenser of the 3 that's incomplete, as one is missing most of the annuli and the condeser lens (Cat.1242) plus I only have 2 full sets of objectives. As I pick over this incomplete one I'll get the info I need to tackle to the two working ones to ensure they're both working 100%. My hope is to document some of this as I've had conversations with others who have broken ones, but didn't know where to start to get them fixed. If my experimenting on this spare Cat.1240 body can help get more working again, I'll consider it a win and worth the effort.

[DrPhoxinus]

Dtsh,

You are a saint in the AO pantheon

Thanks

[apochronaut]

The screws are purposely sacrificial. Much easier and cheaper to replace than the captive wrenches , which are pretty hard. Any of those systems are a minimum of 35 years old, most around 50. The lubricant on the adjustment screws gets hard and the screws become tighter to turn and eventually the softer metal of the screws deforms and the hex rounds out.

You will have to remove the 4 top slot head screws and separate the body to replace them.. You want to then lift out the carrousel but once the body is separated pay attention to the stop latch. It is accuated by a riny axled wheel that rotates in a spring loaded claw. Deflecting that claw allows the carrousel to lift out free of the latch. Remove and tuck that wheel away. Very hard to replace.

You will need to remove only the diaphragms affected by bad screws. You can lift out the leaf springs and the diaphragm housing related to the offending screws ,keeping them as sets. Follow the screw tunnels through to the diaphragm ports, to determine which ones match. It is a little unobvious.

When the screws are in place and adjusted they are closer to the end than the beginning, so to get them out, usually driving them all the way through is the easiest. ...which means you need to get a little thin oil on the threads. Almost always with the old grease limbered up, even a rounded out screw can be driven through but not often with a hex wrench. I have had much better success using the largest torx or slot screwdriver you can get in there. A little tap into the rounded out socket and usually the screw can be moved forward. Get the old grease loosened up first, though.

Once the old screw is out of the bore, a new one can be threaded in from the outside with the hex wrench. You have to deal wth that old grease first. Pipe cleaners work.

[zzffnn]

dtsh:

0.050” Allen key works perfectly on my cat # 1240 phase condenser. I tested it for you just now and adjusted both screws.

This matches PS Neely’s description. Not everything on that web page of Neely’s is correct, but the 0.050” Allen key is correct.

This is off topic:
The wrong part of Neely’s page, that I know from my own testing, is: LOMO 40x NA 0.75 water immersion objective does NOT image well on AO10; it produces an acceptable image but the image has quite some spherical aberration; one with good eye sight has to use nicely mounted diatoms in darkfield to see it clearly, but once you see the fog / haze caused by SA, you will not forget it. In comparison, AO10 infinity 50x NA 0.85 oil iris objective with water immersion (with cover slip) actually produced visibly better (and pretty decent by itself) image than the LOMO. I remember apochronaut said NA 0.85 version of the 50x does not work as well as the NA 0.80 version in water immersion; I can imagine that the NA 0.80 version must produce very good image that way, since the NA 0.85 version’s image looks quite decent as it is.

Apochronaut,

Please send me two screws, thank you very much. Right now I am using Allen keys.

[PeteM]

With respect to pointed rather than rounded ends on the setscrews - it's easy to chuck a conical-end setscrew in a small drill and run it against a deburring wheel or even a bit of sandpaper to round it off.

[apochronaut]

I rounded them off on coarse emery.

[dtsh]

Not that I didn't believe, but have confirmed the alignment setscrews are #3-48

[dtsh]

Looking at a wrench, mic'ing the OD of the threads gives me 0.275 and the thread pitch gauge gives me 32tpi, which doesn't look good for an easy find. 1/4" is 0.25" and the next normal size up is 5/16 with a nominal size of 0.3125, so unless I'm missing something, this is a non-standard sized part. Not a show stoppper, but it'll take some figuring. The closest match would be a 35/128 bolt, but I don't think such a thing exists; it's also a really close match for an M7-0.8 bolt, but that's also a tad weird.

Anyone else figure this one out before? A set of wrenches I do need(*) so it looks like unless I've missed something, I may be mangling some threads on the lathe.
Since this thread has been woefully lacking in images, here's one that isn't likely useful.

AO10_phase_wrench.jpg (158.2 KiB) Viewed 2780 times

*) need is not the right word, why does a condenser without annuli or a condenser top need wrenches?

[PeteM]

I'd be inclined to use a pair of 0.50 hex wrenches - tiny ones with screwdriver handles are readily available. They're actually easier to use than the push in wrenches with the push-back springs that get stuck.

If you want to make something up yourself along the lines of the original, Schrader valves are 32 tpi, slightly larger diameter, and have taps available.

[apochronaut]

Looking at a wrench, mic'ing the OD of the threads gives me 0.275 and the thread pitch gauge gives me 32tpi, which doesn't look good for an easy find. 1/4" is 0.25" and the next normal size up is 5/16 with a nominal size of 0.3125, so unless I'm missing something, this is a non-standard sized part. Not a show stoppper, but it'll take some figuring. The closest match would be a 35/128 bolt, but I don't think such a thing exists; it's also a really close match for an M7-0.8 bolt, but that's also a tad weird.

Anyone else figure this one out before? A set of wrenches I do need(*) so it looks like unless I've missed something, I may be mangling some threads on the lathe.
Since this thread has been woefully lacking in images, here's one that isn't likely useful.
AO10_phase_wrench.jpg


*) need is not the right word, why does a condenser without annuli or a condenser top need wrenches?

The o.e.m. wrenches for the earlier systems were just the inner part of that. Once you get used to using them you barely miss the captive feature and the screwdtiver handle hex wrenches work as well.

[dtsh]

I'd be inclined to use a pair of 0.50 hex wrenches - tiny ones with screwdriver handles are readily available. They're actually easier to use than the push in wrenches with the push-back springs that get stuck.

If you want to make something up yourself along the lines of the original, Schrader valves are 32 tpi, slightly larger diameter, and have taps available.

As a person with too much on my bench, I like the fact that the wrenches are captured as it's much harder for me to then lose them; misplacing items is a super power of mine. I'll have to fetch a valve from the garage tomorrow and see how well that fits, thank you for the suggestion. A die would be handier than turning such short thread on my ancient lathe, for such a short length I typically turn the head manually which takes a lot of time. If I can find a workable die at a reasonable price that might be an option. I don't think an adjustable split die would allow for enough deviation to get either up to or down to 0.275 from either 0.250 or 0.305. I may give it a shot on the lathe if I have any aluminum scraps of an appropriate size, worst case scenario is I waste some time and turn scrap into smaller scrap.

[dtsh]

A schraeder seems a tad too large, so I think that's out of the running.
I've got too many projects to get to the lathe (for starters, there's a car in front of it that needs to be fixed first), so it will be a while before I attempt anything there. In the meantime, I've begun modelling the wrench parts in freecad. Prior to this I had never attempted to make threads in it, but after a couple of iterations I now have a working thread that fits the condenser turret. I might have some 0.050 allen wrenches out in the shop, will need to rummage about and see if I can find them (if they exist).