Observatory: Lights and OTA hoist pulleys.

Tuesday: A cold day @ 40F with gales and showers. Which meant repeatedly closing the shutters to keep the rain out.

Rewired the overhead lights. One white bulb and one red on opposite ends of the top crossbar. I have used plugs and sockets to isolate each of them individually when not required. I thought of having a mains cable rising from above the mounting to avoid dome rotation conflicts. This might work with a hollow PA but mine is solid. Leading a wire over the outside the mounting would soon tangle with the telescope or the mounting itself.

This later image shows the 5mm rope size, 17mm Ø, original, micro-blocks below the 6mm rope, 22mm Ø blocks for scale. The difference in friction, when using 5mm rope with the larger pulley blocks, is literally night and day.

I stripped the rope from the 3x3 micro-pulley system and re-threaded carefully to maintain straight runs between pulleys. Still the friction was as bad as the dirt cheap pulley system with its thinner cord. The falls of rope [throws] were rubbing against each other. So I untwisted the system and maintained it that way. With my hand through the runs while lifting and lowering.  This was an improvement but not by much and was far too awkward for real lifts.


I was only using a 5kg weight for my trials. Which may have been far too low to stretch the system to a normal level of efficiency. The breaking strength is claimed to be well over 500kg for both the 5mm rope and the triple pulley blocks. Higher loads would probably tension the rope to take out twists and might even reduce the working diameter of the rope itself.

Boat owners surely wouldn't put up with the levels of friction I observed with these small commercial blocks. The pulleys are fine with very easy rotation. The problem lies with the multiple falls of rope being packed so closely together by the tiny, triple blocks.

I have now ordered a pair of 6mm triple pulley blocks for use with the same 5mm rope. Ever the optimist! I can go and pick them up from the parcel shop today and give them a try. As mentioned above, the difference in friction was truly startling. Just the weight of the free [pulling rope] was enough to make the lower [travelling pulley block] rise! Of course I am absolutely delighted with the ease of movement now. I'll try running thinner cord 4mm on the micro-blocks as a reserve system.

The rope diameters are nominal but there is no reason to use the maximum size. I have been doing a lot of online research regarding pulley systems. Some pulley block makers suggest 1:8 rope to sheave diameter. My mini-blocks were even less than 1:3. [5:12mm] 5:22mm is over 1:4. While 5x8= 40mm which is about the size of the dirt cheap system's sheaves.

I could have tried longer bolts and fitted spacers between the pulleys, on this cheapo set, but had no desire to be working on the lathe in such miserably cold conditions. I had already swapped to longer bolts and fitted Nyloc nuts because the original, plain nuts kept falling off!

This cheap and rather nasty block and tackle is widely sold around the globe. It works, but the friction of the rollers is much higher than the gorgeous, polished stainless steel, boating kit. The thin, original, stranded cord was unpleasant to handle and easily frayed. Making using it a bit of a pain without thick leather gloves. While the 5mm boating cord is an absolute delight to handle and any tangles soon drop out by themselves.

Click on any image for an enlargement.

*