German Equatorial Mount (GEM)


Assembly of the Axes and the Telescope Mount

The next step was the making of a piece to join the shaft assemblies at exactly 90 degrees to each other and the making of a telescope mount platform featuring dovetail slides and quick release toggle clamps.

Axes_A.jpg

One side of the joining piece was to fit the end of the R.A. shaft and the other was to hold the 76mm square extrusion of the DEC axis. I roughed out a piece of 130 diameter by 50 thick 2011 T6 in the lathe, leaving 1mm all over. I then made up a jig for mounting it in the mill by the shaft bore. this would ensure all milling would be square to the shaft.
Axes_C.jpg

The Linden Observatory has a fantastic machine shop that produced optics for the military up to the 1970s. One of the nicest machines is a small Schaublin Mill so this was put to good use to machine the housing for the 76mm square extrusion. Using a 12mm ball nose cutter, the R16 corner radius was machined in 9 steps leaving small ridges which were removed by dowel and emery paper.
Axes_D.jpg

Back to the lathe to finish machine all over.

The joining piece is a very snug fit on the RA shaft and 4x M6 stainless steel cap screws secure the deal. A M12 hole was left in the centre for future extraction off the shaft. The joining piece is then bolted to the DEC housing by 12x M5 stainless steel cap screws


Axes_E.jpg

This photo shows the DEC housing bolted to the RA shaft.
Axes_F.jpg

The tilting table of the Schaublin Mill was very useful for machining of the dovetail slides.
Axes_G.jpg

Like the joining piece, telescope mount platform is bolted to the DEC shaft by 4x M6 stainless steel cap screws.

Here are all the components that make up the assembly. The right side (west) is fixed while the left side (east) is movable over a range of 1.2mm. This is sufficient to allow east sliding of the telescope into the dovetail and secure clamping by the two toggles. The dovetail is held open by 2 small rubber plugs.


Axes_H.jpg

The assembled telescope mount platform shown with the toggles open and a mount plate. A 45 degree pivot of the toggles moves the slide in to clamp the telescope.

I made up 2 mount plates, one for a wide field camera setup and one for the future 10inch newt.


Last updated - 9th January 2002 Return to Dave's HomePage email Dave (d a v e g @ t p g . c o m . a u)