Getting the balance right (part 2)

Modifying a Synta AZ-3 mount to have perfect balance

By Antony McEwan

I determined that if there was too much weight at the back end of the telescope, I needed to counterbalance that with some form of weight at the front end. My idea of applying a single ankle-weight around the front end of the tube yielded only partial success - the weight was too close in to the tube assembly and, as the angle of elevation varied, so did the position of the centre of gravity! I had to have a moveable counterweight system, as used on the equatorial mounts. This was not too great a problem. I had read on the internet about several people who had made a similar modification with varying degrees of success, and the AZ-3 has some very handy non-threaded holes drilled through the head of the mount which are ideal for the budding mount-modder to stick things into.

I already had a spare 4lb counterweight from a previous telescope, but I needed a counterweight bar to mount it on and some way of attaching the bar to the mount itself. I realised that the bar would have to be mounted at an angle of about 60 degrees from the horizontal (or 30 degrees from the vertical) to allow for free movement of the weight when the tripod’s legs were splayed. This meant having an angled bracket manufactured to take the counterweight bar. To get these sourced, or made, I contacted Barrie Watts at Beacon Hill Telescopes. Beacon Hill used to manufacture telescopes before the huge invasion of mass-produced telescopes in the late nineties and early noughties, and so had all the materials and machinery necessary to make these bits for me. He supplied a 12” length of 20mm diameter aluminium rod with a thread at one end to allow a nut of suitable size to attach it to the aluminium bracket which he also provided. The bracket was angled perfectly to allow free movement of the mount head without the counterweight crashing into the tripod legs. These parts took a couple of weeks to appear, and he only charged me £20 including postage! Incidentally, Barrie Watts has a great deal of knowledge about many types of telescopes and accessories and is always very happy to share that knowledge. I needed a small spacer to go between the bracket and the underside of the mount head to give enough room for the threaded part of the bar to have its nut attached, and this was made simply from an offcut of wood found in the shed. Then I just needed some bits and pieces to hold it all together, which meant finding a couple of oversized washers, a couple of M6 bolts and a wing-nut.

Attaching the assembly to the mount was just a matter of bolting the spacer block and bracket to the underside of the mount with the M6 bolts, using the washers to spread the tension from the bolts over the surface of the bracket underside. I found that this seemed to hold it more securely. The wing nut was used to tighten the rearmost bolt, and the other one was placed through the front hole and held in place by the threaded tube ring on top of the mount. I then slipped the counterweight onto the bar, placed the bar through the hole in the front of the bracket and locked it in place with a suitably sized nut. The pictures to the left of these pages are clickable, and will open up larger pictures which show these details perhaps a little more clearly than my written explanation. Apart from a quick lick of crinkle-finish black Hammerite paint to match the mount hardware, that was it done. It did look a little weird without a telescope attached, but I suspected it would be pretty effective.

The result of this small amount of work is that on the occasions I’ve had the Televue 85 out on the AZ-3 since modifying the mount, I’ve been able to view objects at all angles, not just low down, and still have complete control over the altitude using the slow motion cable. Everything is smooth and there is no longer any ‘settling’ or dropping of the tube when viewing at high elevations. In fact, I can now view virtually at the zenith with no problems at all. As the altitude angle increases I simply loosen the counterweight and slide it further out along the bar and lock it in place (see picture) and that gives me complete control over how much counterweight force, or ‘moment’ is applied about the altitude pivot. Simple and effective - the way all things should be!

For carrying the mount and counterweight in the car, I can just unthread the bar and it then takes up very little space. This has converted my Televue 85 refractor from being an equatorial-only telescope into also being my grab’n’go scope, despite the fact that it weighs a good 10lb when equipped with a 2” diagonal and hefty 2” eyepiece. The total cost was about £23, allowing for the fact I already had a spare counterweight, and I feel that the work has made an already good mount into an excellent one.

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