Sunday build diary. Balancing tricks.

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Another horribly wet day but no sign of any leaks yet.

Yesterday's additions made the OTA too heavy for 15kg of counterweights. So I added another 5kg weight and it was too much. I am right on the limit with Dec shaft length now. Then I added a c/weight on a bar at right angles to the cradle to help balance the 6" on the other side and to add some weight to help the balance.

Still not enough to balance the RA. I shall have to add another weight to the projecting bar on the cradle. The 6" refractor is far heavier than all sliding weights put together. I still have a lump of brass bar left for a similar weight to all the rest. So I had better get back to the lathe.

Or not yet. I stacked some small barbell weights on the right angle rod to check the total weight required. Overall [RA] and the OTA balance was achieved with 4.25Kg plus the little weight.

A total lash-up but the real weights will be moved to the top of the shaft with a spacer tube below to maximize their effect on the 6". Once fitted they should not affect the RA balance. Only the symmetry of the torque around the Declination axis by counterbalancing the offset of the 6".

At the moment there is still some asymmetry in the Dec/OTA balance. Probably the extra weight of the 6". The OTA still has a preferred poise. Fine when level. Not fine when nose down or tail down. It wants to dive at the low end. I was tying off the ends of the 7" OTA with cords to the dome wheel brackets to keep things safely under control. Having a telescope of this size and weight swinging freely is very risky. The ends move very rapidly quite close to the dome and the pier! It could do quite an injury or damage itself. Better not to take the risk of being hit right out of the observation slit! If it were open.

Talk about sensitivity! With the worms withdrawn for perfect freedom, simply adjusting the focus slightly altered the OTA's balance. Just the price of a long OTA where the distance from the pivot rules the roost. With the worms engaged the friction in the clutches easily absorbs such minor problems. Thankfully, test drive slews were fine.

Another wet and windy day made opening the shutters much too risky just for photography. There were dark spots on the floor every time the shutter  doors were opened. Now I'm worried about spin-drift if it snows! I may need a snow shovel in the dome!

My wife has suggested making or finding a transparent, or glass fronted, protective case for the digital clock. She may be right. I'm not sure how low a temperature such items can stand. A case might slow temperature swings and keep the damp out. A tour of the charity shops might turn up something useful. Or at least provide some inspiration for DIY. No idea what, until I see it.

Click on any image for an enlargement. 

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