Hilger & Watts Angle dekkor TA130-1

Hi,

Has anyone got a user manual for the Hilger and Watts TA130-1 Angle dekkor? I've dug out all the associated kit (transformer etc) but am having some difficulty getting the dekkor to reflect the double graticule scale. I realise its an old bit of kit and the chances of a manual being found is low...but worth asking all the same. Thanks.

cookey100 --

I don't have a manual, and it's been a couple of decades since I used a Angle Dekkor that I don't remember the model number of . . . but in the dusty way-back of memory, I'm recalling that the Angle Dekkor had a fixed reticle that was viewed in the eyepiece directly (in other words, not projected to and reflected from the surface being checked). A "negative reticle" cross of collimated light WAS projected onto and reflected from the surface being checked, and the surface angle error was read at 1) the crossing of the vertical reflected-image line with the horizontal scale, and 2) the crossing of the horizontal reflected-image line with the vertical scale.

In setting up the instrument, a Standard / Master was placed on the Angle Dekkor's stage, and the brackets adjusted until the projected-and-reflected cross image was centered on the eyepiece reticle.

So my first suggestion is to put a piece of white paper on the stage, illuminate it, and see if you can focus the eyepiece on the reticle. My second suggestion is to turn on the "negative reticle" illumination, and hold a flat -- ideally a good first-surface mirror -- directly against the ring around the objective lens, and see if the projected-and-reflected image of the negative reticle is being formed inside the telescope barrel in the same plane as the graduated reticle.

Provided you can both see the graduated reticle in the eyepiece, and see the reflected image of the negative reticle, your instrument should work . . . provided you've set the pointing (with the stand adjustments) to a Master, and have a to-be-tested piece that's close enough to right that the reflection of the negative reticle image finds its way back into the telescope.

John

John,

Many thanks for your detailed reply. I have gone through the steps suggested but there is no full negative of the graticule appearing (even with holding a mirrored piece up against the end of the scope) - there is however a small portion of the negative visible which suggests to me some misalignment within the scope itself. I guess I'm looking at repair and calibration. I have located a company (Spectrum metrology, part of Taylor and Hobbs here in UK) that can undertake this work - I'll see what they have to say. Thanks again.

Mike

cookey100 --

There is some possibility that the objective ring of your Angle Dekkor is simply not square to the instrument's optical axis (which should itself be very nearly concentric and parallel to the axis of the cylindrically-ground barrel). Before you pack it up and send it to Spectrum, I think you'd be wise to fixture the AD's barrel in a clamped-in-place V-block in a location where you can use another telescope, focused at "optical infinity", to look for the projected images of both the negative and real reticles . To project the real reticle, you will need to provide some illumination through the eyepiece of the AD, which I usually do by mounting a white index card behind the eyepiece in such a way that ambient light is reflected into the instrument.

If my recollection of the Angle Dekkor is right, the projections of both reticles should be closely superimposed, and if your viewing telescope has its own reticle, you can check their alignment relative to the instrument barrel axis by first pointing to the image of the projected reticles you see in your viewing telescope, and, without changing the pointing of the viewing telescope, roll the AD a half turn in the V-block. If the AD reticles are well-adjusted, their images after inverting the AD should still be coincident with the viewing telescope's reticle.

I suspect that both the real and negative reticles of the AD are independently adjustable, but you might well have to remove cover rings or screws to get to them, and making the adjustments is -- to use what many of we 'Merkins consider a stereotypically British term -- "fiddly". In the absence of an AD adjustment manual, I'll suggest you refer to a couple of the alignment telescope and jig transit manuals that Brunson Instrument Company makes available for download on their website Default Parallels Plesk Panel Page

John

Hi Cookey, and welcome aboard.

A significant question is whether the instrument will be used to certify some measurement, or if it's simply an in-house tool used for setups and non-certified measurements. At least that's significant here in the States. I presume the standards are the same on your side of the pond.

If the intent is to certify the results, then it needs to go back to the factory for them to adjust and certify its accuracy.

For your own use it does not matter.

- Leigh

So what is the difference between an Angle Dekkor ,an Alignment Telescope and a Auto Collimator.

sable --

H&W's Angle Dekkor is an autocollimator having graduated reticles. After some internet research, I now think that my earlier recollection -- that the AD uses a "crosshair" real reticle that is read where the reflected image of a cross-shaped "negative" reticle's arms intersect the real-reticle arms -- was wrong, and that the AD projects a graduated linear reticle, and the reflected image of that reticle crosses a real graduated real reticle that is perpendicular to the reflected image. The projected-and-reflected image crosses the real reticle, and the readings are made at the point where they cross.

A reticle-reading autocollimator such as the AD generally can't be read with anywhere near the precision of a micrometer-reading autocollimator such as is commonly used to measure the rise-and-fall error of a surface table or machine's movement, but the reticle-reading autocollimator is adequate for some jobs and a heck of a lot less expensive than a micrometer-reading autocollimator.

Both types of autocollimator sense the tilt of a mirror relative to the autocollimator's optical axis, but can't sense translation of the mirror across the optical axis. In contrast, an alignment telescope needs to be focused on a target, is sensitive to target movement across its line-of-sight, and is totally insensitive to small rotations of the target around an axis perpendicular to the line-of-sight.

John