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Winfried
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, March 12, 2004 - 02:32 pm: | 
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I recently bought an old french Kinax 6x9 folding camera. When it arrived, it was impossible to move the aperture lever, and the cocking lever of the shutter was also completely blocked.
It finally turned out that the actuating rings for the aperture blades and the shutter blades were stuck although there was no visible corrosion. They could not even be put back itno place after lifting them - they simply were too tight.
After disassembling the shutter completely and grinding the inner circumference of both rings with sanding paper I managed to get both parts running again (this phrase reads in a few seconds but it is not very easy to re-assemble a nine-leaf aperture especially if one of the blade pins breaks off during that procedure...).
Both the aperture housing (on the collar of which the aperture ring is riding) and the shutter bottom plate are made of die-cast material (aluminium or zinc alloy). Even a couple of pivots and pins are just cast into shape, the desingers obviously wanted to save a lot of costs for machining and drilling of the usually quite complex shutter bottom plate.
My theory is that these parts have changed their dimensions slightly over the decades so that the fit of both rings changed from snug fit to tight fit. The rings which seemed to be too tight are made from stamped metal sheet (brass or steel), and they show no signs of corrosion. Anyone around having experience with the long-term behaviour of precision die-cast materials? |
rick oleson
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, March 12, 2004 - 03:20 pm: |
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i'm not aware of an explanation for this, I don't know of metals growing over time.
However, i have encountered a similar phenomenon with a DOC shutter on an old waltax folding camera (early zenobia). nothing moved freely in the thing, though like you i saw no corrosion but moving parts had interference fits. i'd swear that the thing never worked when it was new, but if so why hadn't it ever been thrown in the trash for 50 years? a nearly identical zenobia, maybe a year or two newer, works beautifully.
 = |
Winfried
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, March 12, 2004 - 04:15 pm: |
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I have read in a Leica newsgroup that the die-cast bodies of the Leica C and later models will shrink over time and such will get out of focus, but from my (not very deep) knowledge of metallurgy I think this is rather an urban legend.
My thoughts about this shutter was just a vague theory, since I can't find any other explanation. Later models of the Kinax cameras seem to have machined shutter bottoms and housings. |
David Ritchie
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Votes: 0 (Vote!) | | Posted on Friday, March 12, 2004 - 05:19 pm: |
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I, like Winfried, am not an expert on metallurgy, but I do know that auto carburetors, which are also cast do shrink over time. As I remember, the holes get larger. Somewhere along the line, shrinkage stops or slows down. If you get a well done rebuilt carburetor, the holes have been drilled out to a standard oversize and appropriate shafts etc installed. Shrinkage is not a myth. |
Bill Salati
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, March 12, 2004 - 06:38 pm: |
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I have some die cast model train engines and cars from the 1950s. Some parts have warped, others have crumbled, many are fine. I think it depends on the quality of the alloy. |
David Nebenzahl
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, March 12, 2004 - 08:13 pm: |
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I think those last two bits of anecdotal evidence--carburetors (or carburettors if you prefer) and model railroad locos--are outliers and not really relevant here. Carburetors work in a hot environment, and some model railroad castings are notoriously crappy ("white metal" and all that). I find it very hard to believe that any decent camera casting would change its shape that drastically, but that doesn't help to explain Winfried's puzzling problem, does it? |
Winfried
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 13, 2004 - 03:47 am: |
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To give some more hints, the ring which actuates the shutter blades was so tight I had to use some force to remove it from its seat (and some patience to straighten it again). It was not possible to get it back into its seat without using brute force.
The shutters used on the Kinax (simply named IPO, after the company which made these cameras) did not have a bad reputation. IPO was one of the many post-war start ups in the french camera industry. The shutters claim to reach 1/350 sec without any booster springs. The Kinax with the shutter in question seems to be a very early model, with a Berthiot Flor f/4.5 105mm lens (similar to a Tessar, it performs quite well in the 75mm version on my Semflex TLR). Later models were equipped with Berthiot Special triplet lenses (also a good performer) and Angenieux U1 lenses (one of my Kinax has an Angenieux X1 lens to which I could not find any reference, but it seems to be an export model with a distance scale in feet).
I have 6x9 folders from several french manufacturers, and the later Kinax models can easily compete with 6x9 Zeiss Ikontas in quality. I am mentioning this to show that it is unlikely that the shutter is a crappy design.
However, after re-sanding the inner circumferences of both rings mentioned, re-soldering a pin to the shutter blade (you will have to grind off the black 'coating' of the blades and use plumbers solder), and puzzling the speed escapement back together (I took off the wrong screw and it fell apart) the shutter is getting back to life again. |
charlie stobbs
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 13, 2004 - 06:37 am: |
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If anything shrinks, the holes will shrink also. |
Winfried
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 13, 2004 - 09:27 am: |
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I know, on college I had classes in mechanical engineering and learnt that due to heat expansion ALL dimensions of an object will get bigger, which means that ALL dimensions including hole diameters will get smaller during contraction.
That's why I am a bit puzzled by my observations on this shutter, it seems as if the material has expanded which is contrary to the rumours I have heard about die cast materials.
As mentioned, there are no or only little traces of corrosion inside the shutter (minor traces of rust on some steel bolts and parts). In most cases the corrosion products have a lower specific weight, or, in other words, a bigger volume than the original material which causes rusty screws to stick. But the die-cast parts seem to be clean and there are no whitish traces on it as you sometimes seem on die-cast non-plated aluminium parts of cameras. |
Winfried
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 13, 2004 - 10:54 am: |
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Just a correction, the IPO shutters do have a booster spring for 1/350 but it is less obvious than that of the Compur shutters. |
rick again
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 13, 2004 - 12:25 pm: |
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Castings do shrink; aluminum shrinks quite a lot from the mold dimensions, and a casting that doesn't cool properly (or maybe one with a poor alloy) can warp over time afterwards. I haven't seen this happen very often, though, and I don't recall ever seeing anything grow.
= |
Peter Wallage
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 13, 2004 - 03:53 pm: |
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I'm told that most diecast camera bodies are cast from Mazak (sometimes called Zamak), an alloy of aluminium, zinc, magnesium and potassium. This is also used for toy cars, auto parts, domestic appliances and a host of other things, the quality of the mix - and the cost - depending on the application. Some of the cheaper, less closely controlled, Mazak alloys age badly. They walk all over the place, some develop surface 'crazy paving' cracks, and some just crumble to pieces. I was also told that Braun had quite a lot of problems in the 1950s with the diecast bodies on a batch of its Paxettes which began to distort after a few years. I believe the company extended its warranty and replaced the cameras, but some may have escaped. Possibly other makers suffered as well?
Peter |
Henry
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 13, 2004 - 04:43 pm: |
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The dimensional changes of die-cast parts is most probably internal stress relieving. The parts may not have grown as much as they warped.
But it is not impossible for castings to "grow" either. If the bonding of the molecules is not complete--as in not perfect component proportions--bonding may continue by absorbing similar valence components from lubricants and even from the mating parts.
Henry |
Winfried
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, March 14, 2004 - 09:31 am: |
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We have some specialits in material technology in our companies - not exactly metallurgists, but maybe one of them knows the answer. I will see them tomorrow. |
Winfried
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, March 15, 2004 - 04:13 am: |
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Today I asked our master mechanic who also has at least two decades of experience in advanced mechanical design. He believes that the dimensional changes I claim to have noticed may be due to a layer of corrosion on the die-cast part. The surface of the shutter bottom looks dark grey, it seems to be minor corrosion only but he thinks it's sufficient to make the parts which are supposed to have a snug fit to have a very tight fit. |
David Nebenzahl
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, March 15, 2004 - 08:17 pm: |
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So in other words, castings don't magically change shape of their own volition over time. Corrosion makes sense as the culprit. |
Winfried
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, March 16, 2004 - 05:34 am: |
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OK, in the meantime I have re-shaped the thread of the shutter nut (which was awfully tight) and the shutter retainer ring, and reassembled everything. After a few (actually more than a few) adjustments I checked shutter speeds which are as follows (first column nominal speeds, second and third measured speeds)
1/10 = 120 msec = 1/8
1/25 = 40 msec = 1/25
1/50 = 25 msec = 1/40
1/150 = 11 msec = 1/90
1/350 = 5 to 6 msec = 1/150 to 1/200
Speeds longer than 1/10 (up to 1 sec) were not tested, 1 sec seems a bit too fast.
1/350 could be speeded up a bit by rebending the booster spring (originally was the same speed as the 1/150 setting). Otherwise, this does not seem to bad for a shutter which originally was completely stuck. At least the range from 1/10 to 1/150 will be sufficiently accurate for b/w work. |
