Mr_Flibble
In Tabulas Argenteas Refero
The spring of the roller was wound about 7-1/2 turns by the way
Contax I ribbons
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Deklari
Well-known
My works at 8 turns. I have try 5, but at slow speed the top curtain really slowdown at the end.
Mr_Flibble
In Tabulas Argenteas Refero
Okay.
Drat, first ribbon that seemed to match the thickness of the original installed on the spring drum and threaded it through the clutch, but it feels like there's too much resistance feeding it through the clutch. A few other materials left to try.
Now, for the number of turns the ribbon is wound around the rollers on the spring drum. I take it that's about 1.5 to 2 turns? That leaves a gap size of at least the height of a film frame.
Drat, first ribbon that seemed to match the thickness of the original installed on the spring drum and threaded it through the clutch, but it feels like there's too much resistance feeding it through the clutch. A few other materials left to try.
Now, for the number of turns the ribbon is wound around the rollers on the spring drum. I take it that's about 1.5 to 2 turns? That leaves a gap size of at least the height of a film frame.
Deklari
Well-known
I did exact 2 turns.
Mr_Flibble
In Tabulas Argenteas Refero
Installed another ribbon (reminds me of Aki-Asahi in material an thickness) after testing the friction through the clutch.
With it in place the Sports group seems to run okay. the mid-speeds group seem a little slow, the slow speeds won't close.
Either I need to give the spring another half or full turn or I need to clean the rest of the mechanism and lubricate the gears and axles.
Here's a Short video of the shutter at 1/100th in the medium speeds group.
With it in place the Sports group seems to run okay. the mid-speeds group seem a little slow, the slow speeds won't close.
Either I need to give the spring another half or full turn or I need to clean the rest of the mechanism and lubricate the gears and axles.
Here's a Short video of the shutter at 1/100th in the medium speeds group.
Mr_Flibble
In Tabulas Argenteas Refero
Added another turn to the curtain drum spring. That appears to have improved all shutter speeds with the exception of 1/2s and Time. On those settings the curtain doesn't want to close properly.
Still, feeling well chuffed. First time I've done this type of repair on a Contax, never thought I'd be doing it on a Contax I at all.
Still, feeling well chuffed. First time I've done this type of repair on a Contax, never thought I'd be doing it on a Contax I at all.
Erik van Straten
Veteran
Well done, Rick, this really sounds great.
Maybe another turn will close the shutter at the slow speeds. The spring must generate enough tension to turn all the gears at this setting. Lubricating the gears with a very tiny amount of sewing machine oil will do no harm. Apply with a needle or your smallest screwdriver and wait a few days until the oil has settled down.
Good luck,
Erik.
Maybe another turn will close the shutter at the slow speeds. The spring must generate enough tension to turn all the gears at this setting. Lubricating the gears with a very tiny amount of sewing machine oil will do no harm. Apply with a needle or your smallest screwdriver and wait a few days until the oil has settled down.
Good luck,
Erik.
Mr_Flibble
In Tabulas Argenteas Refero
I've already done the oil trick. Will check again in the morning.
But I'm a little wary of removing the screws from the locking plate of the drum again to add another turn of tension to the spring. The aluminum of the shutter crate is rather soft as you said.
But I'm a little wary of removing the screws from the locking plate of the drum again to add another turn of tension to the spring. The aluminum of the shutter crate is rather soft as you said.
Erik van Straten
Veteran
Yes, it is. It is not made to try over and over again. Let's hope the oil does the trick.
Erik.
Dralowid
Michael
Rick, sounds like excellent progress, well done!
If you have it working within a useable range I'd leave well alone. As everyone says the metal is very soft, probably an equivalent of 'Zamak" or similar.
My Contax repair is, by comparison, unsatisfactory. I must have disturbed the gearing in some way and have decided to leave it until I feel emotionally stronger! 🙂
As remedial therapy I have been working on other devices to rebuild my confidence. Pentinas (x2) now functioning and now a Beaulieu to attend to. I do like cameras with larger screws that have properly threaded holes!
If you have it working within a useable range I'd leave well alone. As everyone says the metal is very soft, probably an equivalent of 'Zamak" or similar.
My Contax repair is, by comparison, unsatisfactory. I must have disturbed the gearing in some way and have decided to leave it until I feel emotionally stronger! 🙂
As remedial therapy I have been working on other devices to rebuild my confidence. Pentinas (x2) now functioning and now a Beaulieu to attend to. I do like cameras with larger screws that have properly threaded holes!
Mr_Flibble
In Tabulas Argenteas Refero
I don't think the problem is so much the spring tension as the the retarding mechanism that slows down the curtains on the longer times. Having added a touch of weapons-grade Teflon-carrying oil there has been some improvement, but 1/2s and Z don't want to cooperate.
1/2s and B (Z) will entail the most friction of all speeds, yes, as the first curtain clutches must, by definition, slide furthest along the ribbons as the curtain opens by itself, and the ribbon pulleys subsequently have to pull the ribbons through the clutches, in order to drag the second curtain shut. Assuming the clearance between the ribbons and the clutches is about right, and the mechanism is clean and lubricated, from my experience with the same situation with the II model, just a little more spring tension may be needed to persuade those speeds to complete. I've previously mentioned intermittent problems with those speeds capping off correctly, and/or capping off OK with the camera held normally (landscape) but failing to latch up fully if inverted with gravity pulling the curtains open, not shut. In each instance the remedy (having, as stated, ensured cleanliness and lubrication was OK) was an additional half a turn or so of spring tension (applied half a turn at a time). This may not be directly translatable to the specifics of the original shutter, not having worked on one of those myself, I can't say—nevertheless, FYI. Of course whether you want to chance manipulating the adjuster again given the fragility you mentioned is another matter. That some lubrication of the escapement has yielded some improvement may also suggest that this may be a part of the problem.
Cheers
Brett
Cheers
Brett
Erik van Straten
Veteran
Yes, we must not underestimate the working of gravity in those late Contax I models with brass shutter curtains. I've had the problem that the shutter worked fine in a vertical position, but failed to close in a horizontal position. I had to give the spring some extra tension. Then it closed perfectly. Unfortunately the shutter does not work at the highest speeds: the curtains then run closed.
Earlier models have aluminium curtains.
Erik.
Earlier models have aluminium curtains.
Erik.
Gben
Established
A first-class thread. I do not have much to add except early-on Micheal asked if anyone had watchmaking experience in regard to repairing springs and that would be myself.
When watchmaker straightens out the very fine balance spring in a mechanical watch, which may be as fine as a human hair, they use no heat but simply bend the spring back into the shape it needs to be in. Of course spring-steel can only be bent in one spot only so many times before it will break.
I was a student of an old watchmaker who learned his craft starting during WWII in Italy, later he went to more schooling in the USA and Switzerland. We used to have benches next to each other in his basement, I remember working on a small woman's watch movement that was probably from the early 1930s and I dropped the balance wheel with it's attached spring onto the floor and bent things up. I tried straightening the spring a bit but it looked like a bird's nest and I thought it was scrap and time to just get a replacement item. The old watchmaker, Ed, asked to take a look at it so I handed it to him and went about some other business. In just a few minutes he handed it back to me and it looked so perfect it was hard to believe, looking as if it had just left the factory because the spacing and roundness of the coils was perfect with no odd bends anywhere to be seen.
Not much help but it is possible to straighten small coil springs without heating them and to put them back into service, but of course you have to have the experience and tools, steady hands and sharp eyes. Ed was a sharp-shooter in WWII and did not need glasses until he was 70 years old.
Re-tempering a small spring at home is going to be very tricky as it has to be cooled down from a dull cherry heat at a certain speed to get it just the right hardness. Too fast a cool and it will be brittle and break in use, too slow a cool and it will be annealed and bend in use, so yes it is a craft in it's own and somewhere out there on a watchmaker's forum there is probably a thread like this with similar characters going back and forth about it.
Ed died a dozen years ago and I got out of playing with mechanical watches and many other things. I just feel burned-out after doing things like this most of my life. I have a few Contax cameras laying around and maybe if I get a bit organized and caught up on some important things I will take one apart and play with it. I am sure if I get stuck I will refer to this thread.
Keep up the great work guys.
When watchmaker straightens out the very fine balance spring in a mechanical watch, which may be as fine as a human hair, they use no heat but simply bend the spring back into the shape it needs to be in. Of course spring-steel can only be bent in one spot only so many times before it will break.
I was a student of an old watchmaker who learned his craft starting during WWII in Italy, later he went to more schooling in the USA and Switzerland. We used to have benches next to each other in his basement, I remember working on a small woman's watch movement that was probably from the early 1930s and I dropped the balance wheel with it's attached spring onto the floor and bent things up. I tried straightening the spring a bit but it looked like a bird's nest and I thought it was scrap and time to just get a replacement item. The old watchmaker, Ed, asked to take a look at it so I handed it to him and went about some other business. In just a few minutes he handed it back to me and it looked so perfect it was hard to believe, looking as if it had just left the factory because the spacing and roundness of the coils was perfect with no odd bends anywhere to be seen.
Not much help but it is possible to straighten small coil springs without heating them and to put them back into service, but of course you have to have the experience and tools, steady hands and sharp eyes. Ed was a sharp-shooter in WWII and did not need glasses until he was 70 years old.
Re-tempering a small spring at home is going to be very tricky as it has to be cooled down from a dull cherry heat at a certain speed to get it just the right hardness. Too fast a cool and it will be brittle and break in use, too slow a cool and it will be annealed and bend in use, so yes it is a craft in it's own and somewhere out there on a watchmaker's forum there is probably a thread like this with similar characters going back and forth about it.
Ed died a dozen years ago and I got out of playing with mechanical watches and many other things. I just feel burned-out after doing things like this most of my life. I have a few Contax cameras laying around and maybe if I get a bit organized and caught up on some important things I will take one apart and play with it. I am sure if I get stuck I will refer to this thread.
Keep up the great work guys.
Mr_Flibble
In Tabulas Argenteas Refero
Spent a few minutes adjusting the roller spring this evening.
Ended up giving it another full turn after testing it at half a turn first.
1/2s and Z are still a little hesitant on the last few millimeters of travel of the closing curtain. But at least it closes on its own now.
1/100th in the medium speeds group looks and feels much closer to the 1/100th in the sports group now. No way for me to tell without a proper shutter tester though.
Ended up giving it another full turn after testing it at half a turn first.
1/2s and Z are still a little hesitant on the last few millimeters of travel of the closing curtain. But at least it closes on its own now.
1/100th in the medium speeds group looks and feels much closer to the 1/100th in the sports group now. No way for me to tell without a proper shutter tester though.
Erik van Straten
Veteran
Rick, I think you have it now. I would close the camera to see if it still runs when closed. If it does, put a test film in it.
Erik.
Erik.
Gben
Established
Maybe someone has already thought of this, but with a ribbon that is thinner than standard, when the shutter is tripped and the ribbon is pulled and wound back up it will be moving slower than the standard thick ribbon because as the ribbon winds up in a coil the diameter of the coil of ribbon at any given point in the shutter travel will be smaller, so with each revolution it will be rolling up less ribbon than if it were standard thickness.
Maybe extra ribbon length would help if that extra length were reduntant except to be pre-wound and coiled up to make the coil of ribbon larger to start with at the instant the shutter is tripped.... Then the shutter speed would be higher as for each revolution of the coil it would be pulling it a longer distance.
Mr_Flibble
In Tabulas Argenteas Refero
I already had reassembled the camera. Adjusting the spring can be done by removing the two screws at the bottom of the frame mask/back cover of the shutter crate. That gives you enough clearance to turn the plate to change the tension.
So yeah, it's back together and it works.
It should get a fresh roll of film soon. Shame the RF is still dim after cleaning. Perhaps I'll change the beam splitter someday.
It's something thats crossed my mind, yes, and I agree with you that theoretically the thinner ribbon will make for a smaller diameter and hence, less rapid acceleration when the shutter is released, relatively speaking (comparing Eg. the same starting spring tension for a Contax with OEM ribbon, and another with AA ribbon). There's some tolerance for ribbon length at least in the subsequent II & III models. I used Rick Oleson's recommended ribbon length for the first two Contaxes I worked on which run well, even though I removed the ribbons from my second II intact and they measured a few mm shorter. But I installed new AA ribbons the same length as those I removed back into that camera, and I've been using it a lot, and its running very well. Purely on the basis of my own experience to date, I'm not sure if the ribbon thickness is as critical for curtain velocity as one might expect it ought to be, given the points you've mentioned. I'm not dismissing your comment by any means, because I've wondered about exactly the same point myself. Just saying that it may not necessarily be as problematic as one might expect. Of course, I am happy to be corrected by someone with more experience using different types of ribbons. After doing a great deal of research, all roads led to Aki Asahi for me--not perfect, in as much as they're not the same thickness as OEM--but can be made to work very well, and certainly seem to be the most durable, (my main concerns). Don't forget that there's also a relationship between the length of ribbon and how many turns of the tensioner are needed and possible (safe). There's a balancing act involved in making it all work well and absence of friction is probably much more critical than Eg ribbon thickness.
Cheers,
Brett
Gben
Established
Actually thinner ribbon would give a smaller diameter, more mechanical advantage and more acceleration as it rolled up but a lower top speed than thick ribbon would.
This would produce the exact effect that is being seen, where the low speeds that are governed would not be affected as much as the high speeds. If the Zeiss designers took this into account then the top speeds may not even be attainable with thin ribbon even with a perfectly and completely cleaned and lubed camera.
If the camera still has bearings with dirt and old lube in them on top of thinner ribbon than it is designed for then that would make the effect more pronounced because again the low speeds will be less affected but the high-speeds will be harder to reach because the frictional losses in a machine increase exponentially with speed.
Because the low speed is governed, the Contax that has the best chance to work at 1/500 and above will be one that has been completely taken apart, all clearances checked, all parts cleaned spotlessly, all lubricant replaced correctly and has the original diameter of the roll of ribbon when it is wound up at the end of the shutter travel.
