No 7 Dial Sight

[Old Tom]

I have just become the owner of one of these, a Mk 2 by R&J Beck Ltd dated 1916 No 10009. (It is my birthday) The mechanical parts seem to function as does the optical path, albeit not clear. I believe I understand the use of these sights, but would like to pose a few questions, apologies if I do not use the correct names for the parts.

The main bearing scales, 0 to 360 degrees in brass surrounds a scale, white on black 360 to 0 degrees (i.e.a back bearing). Two screw adjustments marked 0, 20 40 and 40, 20, 0 minutes are also provided. I do not see why both scales are provided and wonder why the white on black scale can only be read from above, i.e. not visible to the layer while both screw scales are in front of the layer.

There are two, what I assume are locking devices. One, a screw clamp, seems to clamp the brass scale to the white on black scale, but this is firmly attached by 6 countersunk screws and a clamp seems redundant. The other, a sort of lever on the right screw adjuster, may be to lock the setting, but is worn.

I would appreciated any explanation or a steer towards any accessible detail.

Old Tom

[nigelfe]

The first point is that you do not have a WW1 No 7 DS, you have one that was modified in the 1930s for a different orienting and laying procedure.

I suggest studying http://nigelef.tripod.com/fc_laying

The basic reason for the two scales is that first the gun had to be correctly oriented in the 'zero line' (which could be any bearing) and record its aiming points. Then, when the gun had to be layed on a target it was given it a deflection from the zero line. Ie one scale (called the main scale) was oriented relative to North, the other (called the shooting scale) relative to the bearing of the zero line. Azimuth laying was to the nearest 5 minutes, hence the micrometer scales. Not forgetting that the dial sight only handled azimuth, you also had to lay in elevation, including taking account of the angle of sight (ie difference in height between gun and target). And in case anyone asks, this type of laying was pretty much the same in all armies, it was abandoned by UK c.1956 and most if not all European armies did the same thing. The notable retainer of the 'old ways' was the US Army.

[Old Tom]

Many thanks. From that I assume that before modification the brass (main) scale could be turned and then clamped. Hence the modification was to fit the 6 countersunk screws which lock the main scale to the shooting shooting scale. I must have a closer look at your laying web site.

Old Tom

[nigelfe]

Before the modification the scales were significantly different, the mod changed the scales.

[Old Tom]

Hope I am not flogging a dead horse. Am I correct in saying, in laymans terms (not a layer) That the sight started life with one scale and one micrometer, that it was modified to have two scales and two micrometers so that each could be set to different azimuths and then locked together, and that it was again modified so that the two scales were screwed to the rotating head so that one showed the back bearing of the other. These modifications were post WW1.

Old Tom

[nigelfe]

No, the original dial sights were based on the original German pattern although UK used the large diameter scale to make them a bit more 'user friendly'. The very first had a single scale and associated micrometer, but two scales were soon introduced. What did change was the shooting scale being 180 degs each way instead of 360 deg.

[Old Tom]

Thanks again!

Old Tom