28mm Acessories
28MM ACCESSORIES
Besides the rewind attachment described below, I have built a new lamphouse as well, so I've added details of that further down. Click lamphouse to go straight there. And then there is this from eBay:-
Note the resistance and the rewind attachment!
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Having acquired some tatty KOK carcasses, I suddenly started to wonder if I could find a way to fit a rewind. The originals are nearly always non-functional, even if they are present the rewind gear with internal teeth is Mazac and distorts. Oddly, however, the similar arrangement on my 17.5 rewinder seems fine. I have heard that someone in France had a batch of these wheels made up years ago; even then, they were £50 or similar - it must be quite difficult to make internal teeth. So I decided to see what I could do, with the usual proviso that nothing I did should make holes or whatever in the projector and it should be possible to undo it all without harming the machine and restore the status quo ante.
This is what I came up with. Its quite complicated, and I have thought of several other ways of doing it as Ive gone along. For instance, if one could acquire a toothed belt of exactly the right length and tooth spacing, it might be possible to glue this to the inside of a part made up to look like the original rewind. Or maybe a toothed wheel in the rewind pivot hole and a toothed belt to another on the spool spindle, tho it would be difficult to get a very high gear ratio. No doubt there are other possibilities.
The heart of the new rewind is the cross with two arms, centre bottom of first pic in row 1 and seen again in pic 2. This is made up from a piece of steel about 8mm thick, partly cut away at each end to accept the cross pieces, which are screwed to the upright. This assembly is held to the back of the steel plate, top, with a couple of countersunk screws thru holes A in the plate into threaded holes AT. The plate has two large, over-lapping cut-outs B for the spool spindle bearing and the rewind pivot on the KOK. You may by now have noticed that the location of holes in the plate is not all that precise, partly because I was making it up as I went along and not always getting it quite right. A particular problem was to ensure that there was sufficient range of adjustment to allow the belt to be tensioned correctly (we come to the belt later). For the same reason, holes B are oversize. Note also the bent-up tabs E; these are to locate and fix the cover for the new mechanism.
The main job of holding all this together is done by the four bolts shown, which pass thru holes C in the plate and the cross arms and into threaded holes in the round bars. The plate goes at the back of the machine, the round bars at the front. These bars have cut-outs to fit over the edge ribs of the casting of the back upright of the KOK. Tightening these screws grips the upright between the plate and the bars, with the main rewind upright fitting between the raised ribs on the rear of the KOK casting. Its easier with pictures. I opted for round bars rather than square bars or plate for appearance and minimising the cutting needed to fit around the ribs on the KOK casting (the ribs are best seen in pic 2 in row 1 and pic 3 in row 2). I wanted a snug fit here to ensure the fitting would not foul the projector reels.
The rewind upright has a threaded hole. This takes a fixed shaft on which fits a large toothed wheel (pic 2 row 1). This is free to rotate on the shaft, held in the right location by a pin riding in a groove in the shaft (pic 2 row 2). The pin is spring-loaded, the spring being held in place by a grub-screw. The pulley wheel has a sort of one-way dog clutch, which engages the winding handle (a fugitive from a defunct 9.5 rewinder) only for rewinding. At other times, the handle is pushed back out of engagement by a spring (pic 6 row 1). A smaller toothed wheel fits on a replica spool spindle. Just to show the sort of thing that goes on in one's head, I realised a spring was needed to ensure the handle got pushed back out of engagement, then realised that I would no longer need the spring-loaded pin, as the job of keeping the pulley in place would be done by the same spring that pushed the handle back. You can see in pic 5 the washer and screw for the end of the shaft that would stop the handle coming off. Then I thought, why not make the handle loose/removable? In which case I needed the spring-loaded pin again. In the end, I did without both springs.
I can't see a way of removing the original gear on the spool spindle, so just made a new one, modified to suit my needs. I have shown in pic 4 row 1 a comparison between mine and an original, tho' I think this one has been tampered with - I don't think the screw thread on the end next to the gear is original. I did however borrow the original spool retaining spring and the collar/dog that engages the spool. I have to confess that I made a small tapped hole in this for a grub screw. A toothed belt then links the two gears.
The remaining pics show the rewind in various stages of fitting to the projector. This is a decided weakness of this design - the rewind has to be built up actually on the machine. Two of the main securing bolts are behind the large pulley, which therefore cannot be assembled in advance. Finally, a cover to (possibly) make it look a bit less makeshift. Note the riveted construction; I can remember as a teenager using one of these snap rivet tools which fix rivets from one side only, and the same tool is obviously still in demand 40 years on, as I only recently bought it and used it on this just to try it out.
Now I suppose it will all have to be removed and painted......... but first, measure and record, as much for my benefit as anyone else's as I am sure that 2 years from now I shall have forgotten what and how I did. because of the make-it-up-as-I-go-along approach, the measurements are a bit approximate, but should give enuff detail for you (or me) to replicate the thing, should anyone indeed ever wish to do so.
In pic 1 above, I have not measured the two holes used to fix the two-armed cross to the plate - they are there just to hold the cross in place during assembly really. In pic 2, the thru hole near the LH end is for a tommy bar to tighten the shaft firmly into the cross. There is another thru hole right at the opposite end, which was part of a rejected approach to fixing the winding handle in place; the shaft could probably be a bit shorter. Three and 4 now complete all that's needed for me to be able to make another when I've forgotten what I did. (One other thing; the big toothed pulley is 56.5 diameter, 60 teeth, the smaller one has 16 teeth. The belt is 9mm wide, 240 circumference, with 80 teeth @ 3mm spacing.).
A KOK Lamphouse
(NB you will find another KOK lamphouse I made on the KOK page.)
Given that, as usual it's a one-off prototype, it has consumed a lot of time as I made it up as I went along and went down various wrong paths and had to retreat and re-group. I also had a self-imposed restraint, in that I tried to work mostly with materials I already had to hand, which affected the design. It was obvious from the start that I could not hope to copy the real thing - it's too complex. So I just went for a straightforward (!?) design. I made it bigger because I wanted to use more lamp power and reasoned size would help and anyway it would be marginally less fiddly (hah!) and anyway I had some 75mm o/s diameter tube which was just right........
Above, in order, you see an "exploded" view of an original KOK lamphouse, two views of the new one and another couple of this exploded. Let me draw your attention to various aspects. Pic 2, note sprauncy knobs, all 3 re-cycled from odd parts lying around. (I suspect the two knobs I used to secure the back end are in fact ex-Specto back cover knobs.) The lump on the top - which is deliberately slightly off square to the axis - is my attempt at an air circulation system. Underneath the top are 4 ribs, each a quarter of a full circle whose inner diameter is the same as the outer diameter of the lamphouse, ie 75mm. Holes in the top of the lamphouse and in the sides of the ribs are for air circulation (I am considering some holes in the rear end plate as well), assisted by end "stops", best seen in pic 3, which run between the two innermost ribs but do not quite cover the gap. I am hoping the curve of the lamphouse will serve the same purpose as a further " baffle", with the gap at the top, a bit further in. I can always add this if needed. Can I draw your attention also to the neat, properly-curved-to-the curve-of-the-lamphouse lampholder entry (best seen in pic 2). The lampholder itself is just slightly larger than a standard 6.35mm lamp base, so the bulb can be changed by sliding the holder right out. This also provides up and down and rotational adjustment; I just hope I got the fore and aft right 'cos that's fixed. The knob that fixes the holder in place is home-made. The exploded views show you how the thing is put together. Start with pic 4: here is another example of a self-imposed constraint. I had a piece of thick-walled aluminium tube which I decided to use for the nozzle that connects to the back gate and condenser lens assembly. Ideally, this would have been a bit bigger in diameter, so as to provide a wider flange that I could screw into from outside. As it is, I had to resort to the curved brass bits to make an artificially-enlarged flange before I could screw the nozzle into place. I didn't find this very satisfactory. The two lamphouse ends are 3mm sheet aluminium, turned to size and with a shallow flange for location; both are secured by a variant of the method used on the nozzle. I happened to have the mirror assembly, scavenged from some old machine (probably a slide projector), which is an almost perfect fit inside the bore; I shall have to think of something else if I ever do another. Also in these last two pix are views of the replacement top arm I made, basically a simplified copy of the original.
A final point; you may spot that I have yet to cut the slots which are used to secure the nozzle to the back of the gate. And yes, the gate will still open.
Some months later...... That last statement is true, but only if the arm that holds the top roller is NOT in place. I had to shave just a bit off the arm's front corner to get it to miss the lamphouse. I also changed the mirror for a much lighter one, held in situ by long bolts from two of the holes used to secure the heavyweight one. The third hole serves for the wire from the 40mm 12v DC fan I have now fitted on the inside of the back of the lamphouse, with a circle of holes to let it suck a bit of air in. And I have now cut the slots to secure the nozzle to the back of the gate, and given both lens and condenser a good clean. Here are some more detailed pix that show more detail and the new mirror and the fan.
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I've been fiddling with a lamp conversion for a KOK, using a ceramic lampholder which will take 12v 35 -100w lamps and maybe higher wattage.
Pic 1 shows the KOK lamphouse "cap" which slides onto the front part of the lamphouse, which is fixed to the projector. (This is a "mains" model; no dynamo, smaller crank handle and smaller pulley wheel at the rear). The lampholder is incorporated into the cap. The bit on the right screws into the tube in the cap and incorporates a spring-loaded lower contact. This part is not used in this conversion.
There is very little room to do anything; getting the lamp at the right height is hard enough. As usual, I was constrained by my desire to avoid any changes to the original. I made the holder unit to fit into the existing tube from the top, just as a lamp would be inserted; this enforced considerable miniaturisation. The unit is a force fit, basically wedged in rather then fixed with screws or whatever. In pic 3, you can see a short piece of brass rod, about 8mm in diameter. This has two thru holes which take the wires from the ceramic holder. One of these wires is cut off short, with the end stripped and folded over so that it wedges into its hole. This provides a contact thru to the terminal on the side of the lamphouse cap. Because the rod is smaller than the ceramic holder, the wires don't fit neatly and the ceramic holder flops about. This is therefore fixed in place with Araldite, so that the holder and brass rod are permanently joined and not floppy.
A third hole is drilled and tapped into the lower end of the brass rod. A screw (with its head much reduced in diameter) passed thru the teflon rod (see pic 4) and fixes it it to the brass rod. Another hole allows the second wire from the the ceramic holder to pass thru. As for the brass rod, a third hole is drilled and tapped into the lower end of the teflon rod. The wire connecting to the power supply, and the end of the second wire from the ceramic holder, are soldered into rough loops. A nylon screw then passes thru the two lops, thru a small spacer and into the threaded hole in the teflon rod. This keeps everything insulated. In practise, it's easier to fit the unit into the cap if the nylon screw is first removed, but that's not a major problem. The aluminium sleeve has a grub screw which grips onto the brass rod; this allows a bit of up/down adjustment. Unfortunately, the unit has to be removed to get at the grub screw.
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From among my KOK bits, I have ended up with a spare mechanism, which has obviously been painted over at some time in its history. I had no qualms, therefore, about taking it apart to see what makes it tick. The mech is actually pretty simple, as there is only one cam, in and out movement coming from the sprung claw instead. Here are some innards pix for you.
The most complicated part is the shuttle, ie the up and down slide operated by the cam. The final pic above shows you some close-ups of how the claw works - the intrusion in 3 is a screwdriver to push the claw into (in fact well past) the point it would get to as it is forced back by the film as it (the claw) travels back up for the next stroke. The shuttle has to have the extra fitment to which the claw spring is fixed and which serves also as the stop for the claw as the spring pulls it into engagement with the film. It then extends further to provide pivot points for the claw frame.
What I was particularly looking at, however, was the shutter. It's a simple, one obscuration per frame jobbie, which will of course lead to flicker if the pic is at all bright. I think if I undid the screws you can see in the second pic above, and removed that pin, the shutter would simply slide off. I could then fabricate a new one. I was wondering about adding two additional blades, each of the exact width of the picture aperture. I theorised that all that was needed was an obscuration, but it didn't need to be as long as the obscuration of the main blade, which has to cover the movement of the film as well. Hopefully, a higher-power lamp would more than compensate for the additional loss of light to the shutter. Can anyone comment knowledgeably on this? At least, I now have a way of experimenting, since the mech is only secured to the projector body by 4 bolts and I can easily swap it to a working machine. I also want to look at the lens question - the hole left after removing the lens mount is 30mm; hopefully it will be possible to find a decent replacement. Note that, as usual, the aim is to avoid any irreversible changes.