The Fullerscopes MkIII

*
The MkIII is/was a simple, solid, German, equatorial mounting employing 1" (25.4mm) solid steel shafts and Oilite bronze sleeve bearings. It offers silky movement and stable support for up to an 8" reflector or classic 4" F/15 refractor. It cheerfully supported my 6" F/8 refractor until I obtained the MkIV. When supporting the lighter load of my 90mm F/11 Vixen refractor it leaves nothing to be desired except (perhaps) GOTO. Any mounting which allows a digital camera to be held up to the eyepiece without camera shake is well worth having. I took lots of images this way with the MkIII on the massive welded, stainless steel tripod shown below.


The MkIII Fullerscopes mounting carrying a 90mm F:11 Vixen refractor. An easy load for such a robust mounting.

Originally the MkIII was provided with a great many different options. The cast base was available as a hollow pot with radial fixing screws to fit on a pipe or pier. Alternatively a flat base was offered to screw down to a post or home made tripod. The third base option had cast tabs to accept simple wooden legs for a tripod. The base shown above is the pot option with three thumbscrews for fixing firmly to any pipe of suitable diameter. The welded tripod shown above is almost too heavy to lift comfortably. I use a sack truck and a plank beneath two of the feet to move it around the garden. The base of the MkIII can be swivelled around a central screw and polar altitude adjustment is easy after loosening the pivot screw with a spanner.


This particular MkIII has the optional cast setting circles, synchronous drive in RA and manual slow motions. The large black plastic knobs are for secure locking of the axes by hand to allow mounting of the telescope tube or adjusting the counterweights. The motor body has suffered an injury over the years but still works well. Note the solid bronze, slow motion wormwheels.

Note: There is a high risk of shock given the usually damp conditions when observing out of doors at night in heavy dew.

With a 240Volt mains motor the mounting must be properly earthed and an RCD safety device placed at the source of the mains supply cable safely indoors.

en.wikipedia.org/wiki/Residual-current_device


Click on any image for a larger version. Back click to return to the text.

I have now replaced my original shafts with polished, stainless steel 1" bar. Due to the serious risks involved in swapping shafts I have omitted the exact details here. You either have the necessary manual and technical skills to swap shafts or you do not. Carrying out the work badly might easily lead to your death or very serious injury if a shaft should come loose unexpectedly. Particularly when observing alone after dark. The risk is just not worth it and you could permanently ruin your mounting or smash a valuable telescope!

If you absolutely must fit stainless steel shafts to your mounting then I strongly suggest you approach a professional engineering workshop to have the work done properly. The shafts are held by cross-pins or screws hidden beneath the paint. On my particular MkIII there was one hammered in pin on one shaft. With a sawn off screw in the other. Getting these out takes luck, some manual skill and reasonable tools. All the screws on these mountings are old imperial sizes which are hard to match in these times of universal metric threads. The alloy used for these castings is very soft and re-cutting metric threads to fit modern stainless steel screws is very risky. So if you do manage to swap your rusty shafts for stainless steel you may not get a strong fixing. Imagine you are up a ladder, in the dark, in a hard frost, looking through your priceless APO refractor and one of the mounting shafts just drops out onto the ground! On a cold night you could get hypothermia if you lie there unconscious for very long. If you live alone you could lie there forever in a secluded rural garden!

Even obtaining 1" Imperial round bar stock in stainless steel is not very easy these days.

Metric 25mm bar is completely useless for this task! It certainly won't fit the original castings and your slow motion wormwheels, setting circles, counterweights and fixing collars will all become too loose and dangerous! So don't even think about using metric bar. You must use 1" Imperial bar.

Warning: Getting the original shafts out of the castings could have been a serious problem thanks to the incredibly poor workmanship by the Fullerscopes workshops. The declination shaft was so loose in the badly drilled (or bored) saddle casting that they had butchered the shaft end into a tighter fit by hammering it into a mushroom! This is totally unacceptable workmanship by any standards. Had I not recognised the problem I could have cracked the saddle casting by removing the shaft by the "shortest route". Instead I had to drive the saddle carefully down the full length of the shaft using a block of wood to protect the soft casting. Believe it or not; the other shaft had been roughly knurled to get a fit in the T-shaped declination casting! It seems Fullerscopes did not even own a usable 1" drill! So you have been warned! Don't do a shaft swap unless you have the necessary skills.

The lack of skill in the machining doesn't usually show and doesn't affect the MkIII's performance, solidity or safety. Given the usually low cost of obtaining one of these Fullerscopes mountings secondhand I really wouldn't worry about it. Just don't pay a lot for one. Particularly one in poor condition or without basic slow motions. Nor in the mistaken belief that Fullerscopes is a classic antique from the great age of hand-finished brass and glass. The MkIII is a cheap, simple, solid, slightly agricultural, telescope mounting and nothing more. Charles Frank and AE mountings were far better built and finished in comparison with the simpler and probably cheaper Fullerscopes mountings. But these other makes probably fetch more and are usually much more difficult to find in the online astro ads or the backs of the astronomy magazines.

The dreadful Fullerscopes workmanship carries over to the MkIV which I will discuss next.

You may find the following link interesting as an insight into Fullerscopes at the "height" of their manufacturing activities:

http://www.brayebrookobservatory.org/BrayObsWebSite/HOMEPAGE/forum/So%20Called%20Telescope%20Makers.html
*