28.08.2021 More wet weather and a better base ring.

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Saturday 28th, heavy overcast, wet and windy. The picture shows the reality of working outside in the rain. With the ongoing bad weather all thoughts of imaging are gone. So how do I maximise my efforts on the dome when it cannot be uncovered?

I usually picture the details in my mind and scribble endless text. Which helps me to make design decisions. Whether it saves time when the actual work begins is another matter. 

I am afraid of making irrevocable mistakes. You only get one chance to do it right. Hence my relatively slow progress. Making it up as you go along is not how most things are made.

Photography is a vital part of my work ethic. If I lied on my blog the hideous truth would still be obvious in my images. So I use photography as my main critic and stern supervisor. I have to set high standards for myself to avoid crippling expense. There are no spares. No new sub-contractors. No back-up plan if it falls to pieces. 

I had a full dress rehearsal with the plywood dome and octagonal, observatory building. It taught me a lot. More importantly, what mistakes to avoid. I discussed using a calf rearing shelter as a donor dome back then. Luckily I avoided going ahead at the time. I wasn't ready for the challenges involved.

A new idea: Triple layer base ring  on top of the dome rib and bolted brackets. The 180mm/7" rotation roller is placed roughly where it will track and support the dome. The roller's axle is just above the dome skirt. Meaning that quite a low, add-on, weather skirt is required to protect the building below.

The roller track is well out towards the dome wall. So there are no serious cantilever forces trying to lift the ring's inner edge. The upward "leverage" on the base ring, from the roller, is safely minimized by simple geometry. The track can be even less than 80mm from the dome wall. So 90mm reinforced, angle brackets are ideal and readily available. This assumes the dome is perfectly round and runs concentrically. 16 steering rollers will help but it might be a bit risky to aim for minimum clearance!

Triple ply, ring laminations will be very stiff compared to thinner options. Reducing potential undulations during gluing up from multiple arcs with staggered joints. It looks solid enough to be serious.

Longer fixing screws for the brackets can be used from above. Without any risk of them piercing the roller track. The middle bracket, of the three shown, is probably best for this purpose. It has low height where it meets the dome. Helping to reduce any, upward, twisting forces. I'd prefer thicker, reinforced brackets to avoid flexure.

The plywood dome build was [unintentionally] my full mock-up for "the real thing". Lots of things worked well. Some things less so. Most of the problems were due to the materials I used. Plywood domes should be fibre-glassed for weather proofing and strength if roofing felt is to be avoided. Roofing felt is heavy and hot. 

Plywood is difficult to seal adequately. Even using the most expensive "marine" seam sealers. Covering a dome with rubber pond liner is another option. Though usually of limited colour options and very heavy. It will not conform readily to a spherical dome.

You should always go shopping for wet weather clothing during a period of cloudbursts. It concentrates the mind wonderfully. The same goes for building observatory domes. False optimism has no place to hide when the rain is constantly "tipping down." 

You won't get much done without a much larger shelter for a workshop. Working outside you probably won't do anything really daft. Not when you desperately need the shelter of your own construction. To have somewhere to sit and think furiously about what you are actually doing. How many people build their own observatory domes? There can't be that many. Not even globally.

Most dome builds are probably smaller than this. So the scale and costs are minimized. These days most observatory builders prefer a roll-off roof. Which means being outside for observing. Or having a "warm room" and remote control for imaging. I much prefer the shelter of sitting comfortably in a dome. More protection from the wind. Shade from the sun and shade for the computer screen. I cannot imagine being such a keen solar imager. Not if I was sitting within four walls completely open to the sky.

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