Following the Nipkow disk patent, many attempts were made to improve on the efficiency of mechanical disk scanners. Lens disks provided larger brighter images, as did mirror drums even more so. However, these methods added greatly to the cost. It was not until 1928, with the patent by Gardner of the mirror screw, that it appeared that a better solution had been found. The mirror screw was the first to provide images without the scanning line structure plainly visible. Compared to any of the other scanners, it would provide brighter than expected images and produce them as large as itself without any secondary magnification.

Cost-wise, if mass-produced, the cost of a mirror screw scanner would be amongst the lowest. The mirror screw consists basically of an assembly of an axle and a set of permanently adjusted mirrors. This assembly is then mounted on a motor shaft and that completes the scanner. By far, this is the most simple of all mechanical scanners. However, the mirror screws must be very precise in their construction. The mirrors themselves are all part of a matched set. More like lenses than say a shaving mirror. Made from stainless steel, there is nothing to wear out and it will last indefinitely.

Getting involved in mirror screw technology has been somewhat difficult in past years, partly because of the lack of good historic information but mostly because of the total lack of hardware. If there were more hardware around, most people upon seeing it, would be inclined to find out more about these mirror screws. The site you are looking at right now is as good a source for this information as is available anywhere.

Any reluctance might be partly due to the thought that it appears it will cost a lot because of the need to obtain a mirror screw, which because of its rareity, might likely cost as much as a few thousands of dollars. Wow! And that is a lot of money! It's not likely that someone slightly interested could or would justify that sort of expense, without thinking of it for a time.

Let's look at some facts about mirror screws and the cost factors. 1st: Mirror screws are very rare! It is likely that at most, fewer than a dozen original mirror screws exist. 2nd: As for complete original mirror screw receivers, the number must be very low and is likely to be zero. As yet, not even one has been found to exist. In fact, there is no known detailed information available that tells one how to actually build one.

Somewhere along the way, years ago I managed to locate two original mirror screws. One was made of stainless steel and in perfect shape. It weighed 15 pounds and was just under 7 inches on diameter.
The other was made of aluminum, about the same size and half the weight. I built two similar receivers, based on a photo of an original German set. The stainless steel screw produced an excellent 120-line picture. The aluminum screw had some corrosion that degraded the picture quality. I later replaced that screw with a 60-line stainless one that I built and it too produced a good picture.

After the successful construction of those two sets, I decided I wanted some smaller mirror screws, Within a few months I was able to develop the necessary procedures and special tools, to build a medium size 32-line screw. I then expanded the tooling to include a 60-line model. The selling price I decided on was $850 and $1250 plus shipping, for the 32-line and 60-line screws. I later decided to build an even smaller set, ¾ size, one that would allow smaller motors to be used. These provide an image size of approximately 3" by 4" inches or 6cm by 8cm. They can usually be mounted directly on a 5/16" diameter motor shaft, as shown below, greatly simplifiying construction. These mirror screws are being offered at the same prices.

I have added to the world supply of mirror screws about 31 or 32 pieces. I have absolutely no plans for building more. So the number of screws available is fixed. As others see them, their interest will increase their value. Because of their rarity, their value will never go down. Collectors will want to purchase them, because they fit into a part of television history that has not been known or even recognized until now.

As for value, two 32-line stainless steel mirror screws have recently been sold to separate customers for $850 each. They are absolutely worth that and most likely, much more. So their value will certainly increase with time. Should you happen to purchase one of these screws and actually put it into use, it will become more valuable instantly, because it actually has worked and produced pictures. If you build nice sets around these as I have, in ten years, such sets could easily reach a values of $10,000. Maybe more. This is what is known as a good investment. Join me. Its Fun Too!

If you are really getting interested, here is an example of a way to set up a mirror screw to provide either horizontal orvertically scanned images. This uses a DC motor to drive the the mirror screw through a rubber belt. The belt also rotates a disk with 32 evenly spaced holes, the same number as the mirrors on the screw. The holes are detected as the disk rotates by a LED/Photo diode to provide feedback to the motor drive circuits, in order to keep the mirror screw speed correct and constant. The mirror screw as shown here is supported on a shaft running in ball bearings. PY

Peter Yanczer

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