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With the brake/clamping sleeve now working I added the tube rings and bare 8" tube for the 7" refractor. No counterweights were needed for this. Though I checked and found there was ample room on the Dec. shaft for at least three weights, possibly four.
The dirt cheap, cast iron, 5kg "Olympic" class 2" bore weights are 25" thick x 9" Ø. This was the maximum diameter I could swing in my lathe to tidy up the very roughly cast rims.
The slit would be open during observation so there would be more clearance provided care was taken. The dome certainly seems very much smaller with the telescope tube in place. Getting rid of the stepladders will help.
I need a larger knob on the PA brake to allow more torque without strain. I just happened to have a small hand-wheel on M8 studding so used it to test how well it worked. After endless searches using all sorts of terms I still haven't found a suitable knob/hand-wheel/stjernegreb/fingergreb/håndhjul/etc.etc.There is the risk that a large wheel will overtax an M8 thread, of course. The cheapo tap and die set I bought recently is proving as useful as chocolate teapot. So I have been using the better quality taps bought individually in the UK from flea markets. The new taps cannot even start a thread and are only useful for cleaning an existing thread and then only with great care.
I am tempted to add a rotary bayonet fitting for the 7" objective as I did with the folded refractor. That needed a bayonet fitting objective because of the weight of the lens and having to rebuild and dismantle it, high on the mounting, every time I used it.I even bought a wide set of sturdy aluminium steps for this specific job but never got around to fitting a suitable handrail to steady myself. Given the straight tube refractor will be permanently mounted I am just thinking of the initial ease of fitting the heavy lens to the long tube. A simultaneously awkward and delicate operation. Standing the tube on end makes it unstable and too tall to reach from the floor.
See the image alongside for a better sense of scale of a 7" f/12 refractor. The tube balance weights have since been moved to the cradle on the big mounting. Just to save having to lift them along with the OTA.
The alternative, in fitting the lens to the main tube first and then lifting the complete OTA into place is equally fraught! I use a spare tube ring to prevent the OTA sliding down through the clamping main rings, but still. It is a heavy and awkward lift.
I have tried pointing the cradle directly at the Pole. Or with the cradle horizontal or sloping. Nothing helps much with this weight, bulk and height. Such physical hurdles to mounting a delicate telescope quickly become psychological hurdles to do any observing. Which is what drove me to build an observatory and the folded refractor OTA before that.
The folded refractor was too prone to dewing of the mirror optics and I never completed a cloth shroud. It would have been too complicated to shield the folding mirrors with their own dewshields due to the odd reflecting angles. Too much shielding would have caused heavy vignetting. Too little would have made it all rather pointless.A folded refractor OTA needs to be fully enclosed or in the shelter of an observatory. It was certainly no lighter than the 'normal' straight tube build. Quite unexpectedly it was far more difficult to put on the mounting due to it being considerably shorter than the straight tube. So that it could not be lifted like a Scottish caber. Hence the keyhole bayonet front plate for the objective mounting. Just another hurdle to overcome for those whose instrumental ambitions exceed their physical strength and agility.
A hefty eye-bolt, or two, at the top of the dome for my block and pulley might be useful. If I could trust it for the vital lift. I am loathe to hang the chain hoist up there due to its own considerable weight. Lifting the hoist needs its own hoist!
Click on any image for an enlargement.
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