Damaged Lomo Kf-4 Phase contrast condenser

[Amoeba]

I recently purchased a lot that included a Lomo Kf-4 Phase contrast condenser. Unfortunately the condenser is damaged. The small lever that operates the diaphragm is broken off and missing. Is there any way to repair the broken part? Can the part be replaced? It seems to be made from some sort of diecast metal alloy.

[imkap]

You can drill a new hole and use tap and die set to make threads inside. Then take a screw (stainless), sand out and polish the threads not in use and have a new shiny handle. Or paint it black. Depending on the size use m1-2-3. Or you could just drill a new hole without threads and glue the new rod inside... Just do everything slowly You could make a flat hole too if you want and glue in the new flat rod, that seems harder, maybe find someone with the right tools to do it. Maybe a jeweler will have the means to do it, or a metal turner.
Also you could have a metal turner make the whole new piece for you...

[patta]

Can also braze / solder a new handle to it, with the soldering iron and tin as for electronics

[Amoeba]

Thank you for the suggestions. I guess it would probably require an expert in metals. The thickness of that part is probably no more than about 3mm so it would require a jewellers precision to tap any holes for tiny screws. I could try brazing, although I have reservations as to whether anything will stick to this mu-metal type alloy but one never knows until one tries. I did also wonder whether a part could be 3D printed, although I don't actually have a 3D printer yet.

As a stopgap I could always buy a basic ABBE condenser which would at least make the stand usable as a microscope. of course that means more investment....

[Hobbyst46]

I would suspect that any brazing/welding/silver soldering will deform the ring and hamper with the smooth operation of the diaphragm.

[imkap]

As a stopgap I could always buy a basic ABBE condenser which would at least make the stand usable as a microscope. of course that means more investment....

I once had a jeweler repair something on my condenser and he was quite enthusiastic about helping with the old microscope... He was quite interesting and knowledgeable, so overall a nice experience...

[Amoeba]

BTW, does anyone know what type of lubricant should be used on the condenser aperture and rings? The 'stuff' on them is quite a thick gunge, making the rotation of the ring difficult. One wonders whether this maybe led to metal fatigue and eventual failure of the lever, although most likely it got banged and broke. I intend to clean off the gunge but would like to know what to replace it with? I have read about Nye oils and grease? Would Nye light oil be appropriate?

The standard condenser on my other stand seems to have quite a bit of resistance as well. Although it isn't too bad and seems operate reasonable smoothly at present, I certainly would not expect quite as much resistance from an aperture control. I am basing my experience on an aperture control on an old camera, but that's a little different I guess. In any case, I would be nice to have it operating with a little less resistance.

[MicroBob]

Lubrication: The blades are not lubricated or get a fine coating with graphite powder. Due to the big contact surface oild or grease would make them hard to move.
It may be that the ring doesn' t move too well in the barrel so a very small amount of light grease could help, but so that it can't creep between the blades.

Lever: I would suggest a HSS drill bit as a new lever. They are really hard only at the fluted tip, the back is half hard, just right. You could use it to drill to hole and then glue the back end in and cut the fluted part of with an angle grinder or Dremel. To get the hole in the right place you would need to file a little flat and make an indentation with a center punch where you want the hole. A drill press or drill stand and a vise will be necessary. I thin I have done a repair this way but I'm not sure as I repair things all the time.

[imkap]

I would suggest a HSS drill bit as a new lever.

This is a great idea, if I brake mine, I now know what I'll do...

a fine coating with graphite powder.

like this one?
https://www.bauhaus.info/schmierstoffe- ... h=22560100

[MicroBob]

That is the right graphite. Dig a finger it an rub a little on the blades so it barely becomes visible, blow away any loose powder.

[Amoeba]

Thank you. Graphite makes sense as it doesn't gunge up over time. There is oil residue present on the diaphragm which will need to be rinsed off with white spirit or IPA perhaps.

Interesting idea regarding the drill bit. I will have to find something with a small enough diameter.

[imkap]

Thank you. Graphite makes sense as it doesn't gunge up over time. There is oil residue present on the diaphragm which will need to be rinsed off with white spirit or IPA perhaps.

Interesting idea regarding the drill bit. I will have to find something with a small enough diameter.

100% (or a bit less) Ethanol cleanes grease/oil better in my experience, be sure you remove the old gunk thoroughly as it tends to become sticky again. Wd-40 contact cleaner (not the usual wd) is also good... Never tried with other brands, but should work too.
Gasoline cleans good too, but it evaporates toxic fumes, not good for home indoor use.
I'm cleaning a Zeiss phase condenser just now.

[Amoeba]

Well that seems to have cleaned up OK. Phew! Each blade of the diaphragm had to be cleaned individually and re-assembled. It was the only way to guarantee that all of the gunge was removed. It moves a lot easier now, but I think the connecting ring will need some lubrication to make it operate smoothly. I presume the graphite would work here as well? I am not going to do anything regarding that until the handle is fixed anyway.

[Amoeba]

I think I have managed to repair it!

I had to wait a little while for the fine drill bits to arrive. I then had to order a chuck adaptor to hold them!

I started by filing down the rough edge where the original handle had broken off. I then set about drilling the hole. I seemed too risky to drill in the exact same position as the original handle as the metal was at its thinnest at that point so I chose a point some 2-3mm to one side of the original break where the metal was at full thickness. This does compromise the aperture range very slightly as it means it does not go to 100% open, but the difference is so slight that it is barely noticeable and not likely to make a difference. The hole took a little while to drill but I wanted to proceed steadily and carefully so I took my time starting from the smallest (0.5mm) diameter and working upwards, eventually ending up with a hole a little over 1mm in diameter.

I then used MicroBob's idea except that I used a drill bit from hobby drill set. I found one that had a particularly small diameter which looked just about the right size to be useful. Once drilled, I actually used the bit itself to widen the hole for a snug fit. The bit was then cut it to the required length and carefully bent so as to avoid colliding with the position adjuster. It was then glued it into place using two-part epoxy resin. The blob of solder was added to strengthen the bend a little. I am not sure how effective it will be but plenty of flux was used to ensure that the solder sticks.

Everything was then re-assembled. The lever operates quite freely but does stick slightly. The fit is very tight so it may be catching somewhere or it may just be the friction of the blades. I am not sure which.

I now intend to order the graphite. The item that was linked is from Germany and shipping costs 3,90€, a total of 6.80€ or approximately 5.70GBP. I had a look around to see whether I can get it in the UK. I couln't find the exact brand, but I did find this on Amazon:

https://www.amazon.co.uk/gp/product/B00BTOBHH6

It is also available on eBay for a similar price with free postage. Before ordering, can I check whether this is the same stuff?