November 2015

I said earlier I would come back to the early Bolex Model C. I think the one I showed you at the top of Page 1 (borrowed from the PPT) is the earliest I have seen, because it has no reversing and, presumably, no power rewind. Here it is again.

I am sure I do not need to tell you that the motor worked fine; I should have carried out this test before I started. I now face the problem of tracking the fault thru the even older and more decrepit wiring of the old machine, or adopting a radical solution with a heart and lung transplant of the speed control resistance mat, the direction-changing switch, lampswitch and the associated wiring. I should mention here that one of the screws holding the resistance mat in the base of the old machine would not shift. In the end I had to drill it out and re-tap the hole, as the thread inevitably got damaged - I needed to do this anyway to check what lay beneath. 

This all seemed like a lot of work for a machine that would still look pretty rubbish at the end of it all, as age, rust and heat (in the case of the lamphouse) has made a real mess of the paint finish even - and here is the main point - even if the finish was actually meant to look like scales on snake or lizard skin. The size of the "scales" varies so much I begin to wonder if in fact this was not some obscure fault of the paint shrinking, especially as I can see no real sign of any coating remaining between the scales. If the finish is original, is it worth the bother of making the machine work; if not, is it worth the bother of re-painting? The machine seems very early, with a few unique and interesting features. The lamphouse is many-sided rather than round, and there is a nickel-plated cover beneath the direction-change switch. But the original motor is kaput and the snake-finish cover of the original motor will not fit over the donor motor and anyway, much of the uniqueness lies in the paint finish. And it's a Model C - two gauges but no notching, just a still picture device and a centrifugal heat filter.

[The lamphouse, pic 1, shows clear signs of the use of too powerful a lamp. The "skirt" was missing from the earlier PPT machine; this is not surprising as the lamphouse pivots on a removeable rod (as per 200B Plus gate - you can just see the tail of it) thru lugs on the side of the lamphouse and the machine back plate (pic 2). Thiers is also a spring clip on the back plate to hold the lamphouse in place. The problem is that when the spring clip is released, the lamphouse is free to pivot and the skirt promply bangs into the flimsy skirt and damages it. Pic 3 shows the basic casting of my earlier and later machines is the same and, interestingly, there is a brass gear where the later one had paxolin; pic 4 illustrates the centrifugal mech over which fits the heat shutter, here seen sat (upside down) on the normal shutter. Pic 5 reveals why there is a metal plate where the direction change swirch is fitted. As you can see, there is a second, surplus hole intersecting the one for the direction control; I assume this is a relic of the very early PPT version which had just a switch and no direction control. Pic 6 contasts two very different fans, a basic early one and a more turbine-like later model. And finally, the basic simplicity of the direction change mech is shown in pic 7. The earlier one has moulded-in spacers for the three fixing screws, the later one uses separate little spacers.

      

Some time ago I had some replacement gears cut (in brass) for pre-1937 Bolex DAs (ist pic) and am now contemplating the same for 1937 onwards machines (pic 2). The issue is of course fibre gears - these two are thin and prone to stripping some teeth. I can never accurately count the number of teeth, so hit on this method using an Adobe-type drawing programme.

On a matter that will turn out to be related, I spent an enjoyable few hours one morning wandering about Leighton Buzzard and visiting various engineering establishments. I was well surprised at how many there were and the expensive automated machinery I saw - the town seems to have far more than its share of engineering capability. What it doesn't have, however, is gear-cutting capability, which is what I was looking for. It appears that a) gear-cutting is a highly complex and specialised task, which requires special equipment if you're going to do much of it and b) in consequence of a), gear-cutting has become the province of a few specialist companies who can do it easier and cheaper and are thus used by most companies as a better option than maintaining their own capability in this area. What I was looking to do was to have some gears made to replace the paxolin gear in the post-1937 Bolex DA (I already had some done a few years ago for the pre-1937 model), that tends to strip its teeth after the first 75 years or so. We shall see if I can find another way.

 I tried one of these specialist firms for a quote, but it was, as ever, far too costly to be worthwhile - around £100 for a single gear/shaft. After much head-scratching and discussion with very helpful staff at the gear company, an alternative idea emerged. Although they did not manufacture an exactly identical gear, they did have one almost identical. It had no boss, was thicker than needed and of course there was no integral shaft. It was also slightly oversize. Nonetheless, I reckoned it was worth a try to see if my limited engineering skills could do the job. The cheapest material would be steel, but one thing I had picked up in my various discussions up to this point was that there were basically two reasons for the use of Paxolin/fibre (which is what the original was) in a gear train. One was noise, but the other, possibly more significant reason was as a "sacrificial" gear, that would break first before anything more important was damaged. For this latter reason, I opted for the next cheapest option of nylon (Deldrin) and purchased a couple of gears. What I then had to do was to reduce the thickness of the gear whilst leaving a central boss to match the original, make a new shaft and trim just a smidgin from the diameter. Having done this in my rough and ready way, I found, somewhat to my surprise, that it actually worked quite well. Having been successful thus far, I felt emboldened to smash up a broken original gear to extract the shaft, re-use of which would reduce the work involved. I reckon this reduces the cost to around £35/£40, which is considerably more palatable.

 February 2018

I have been experimenting with converting a Bolex DA to one of those High Intensity Discharge (HID) lamps like wot Tony Saffrey added to his Specto. The idea was to bring the projection of notched films up to a decent standard as, even converted to Tungsten Halogen (TH), the DA's light is not good enough for a decent size of screen/audience. As I have already converted several DA's to TH, and as there is an HID lamp that will fit the same lampholder, the first part was a no-brainer. Just for info, here are pix of a conversion.

Pic one shows the components. Basically, all traces of the old lampholder are removed. The base-plate, which forms the bottom of the lamphouse and is shaped accordingly, is secured by two oddly-located screws. With these removed, a couple of additional holes are made, counter-sunk from the underside of the plate. This permits the addition of the two nuts and bolts seen here (I used half-nuts as they are thinner). Once the base-plate is screwed back into place, the bolts plus a flat strip secure the main fitment in place.
The main fitment is just a strip of aluminium bent at the appropriate place. The hole at the top needs to be fairly accurately placed to secure vertical alignment, tho' precise placement of the holes for the grippers leaves a bit of scope for adjustment, or one could put a plate under the foot of the main fitment. The foot has large square holes to give a good range of lateral and to and fro adjustment both at the same time. Pic 2 shows the whole assembly. There are a few left-overs from earlier uses (waste not, want not) and I get the vertical section away on each side to help air flow.
Precise adjustment is going to be just trial and error, as the old trick of applying a low voltage to a TH lamp and adjusting by hand and eye with the lamp on is not safe for HID, because of voltages and the considerable UV emissions.

There was always going to be a snag, of course. Although on test the light output seemed good, as expected, there was a tendency to burn the film; not immediately, but soon enough to risk long-term damage to the film unless additional measures were taken. This is where it got complicated. 

 
The basic problem is that a) there is very little spare room inside the DA mech and b) the heat filter must synchronise with the stopping of the mech for the notch. An alternative approach might be to put a permanent piece of heat-stopping glass inside the lamphouse, but this would reduce light output at all times, not just for titles. I decided therefore to try adding an additional layer of mesh to the existing heat filter. This involves something I have not done before, ie removing the re-set knob for the notching mech as this is directly coupled to the heat filter. 

In pic 1, you can see the original filter is held, round only part of its circumference, by 3 small screws which pass thru a retaining strip, then the mesh, then into threaded holes. I was a tad reluctant to take all these screws out, as I feared the whole lot would just disintegrate in my hands. So I cheated by making two new holes, as seen in pix 2 and 3. Part of the aim of doing this was to keep a small air gap between the different layers in the hope this would slow any build-up of transmitted heat. Pic 4 shows the whole thing in situ.
My original thought was that I could get away without a dowser, simply by opening the little door behing the lens and re-directing the light from the lamp to the rear of the machine. After a little more thought, I decided against this as it is quite easy to knock the little door shut while re-threading, and also because of the UV warnings on the lamps.
So I decided to fit a dowser, although this involved rather more mods to the machine than I was 100% happy with.

Here is what I came up with. Two guide strips are screwed to the mech side plate from the inside (with counter-sunk holes as the shutter is very close), to take a vertical lock-gate-paddle sort of affair. I had to reduce the lip on the straight edge of the lamphouse top to make room for the handle. Another nut and blot near the top of the projector serves as a travel-limiter for the sliding plate. Down is off for obvious emergency/safety reasons.
Testing must now follow - re-assembly has been awaiting taking these pix for you, but I will report the results later.

(Later)

You will recall I told you about my attempts to fit an HID lamp to a Bolex DA. I was using the lamp with the integral mirror, which needs to have 32mm from the plane of the film to the front edge of the mirror. There is unfortunately no way this can be achieved with the DA and the results were no better than from a normal tungsten halogen lamp.