19.12.2021 Shutter support geometry.

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Sunday 19th 44F, mild but overcast. Forecast to be sunny all day after a clear night.

The next step, in the fitting of the new slides, requires the shutters be raised to their correct working height.  They must also be straight and the ribs vertical and parallel. 

Only then can I fix brackets to hold the new slides to the shutter ribs. One complication is the need for countersunk fixing screws to avoid contact with the skate wheels. 

Some considerable "fiddling" is guaranteed to be required. "Normal" cylindrical shutters would have been infinitely easier to arrange. My spherical shutters have cost me months of extra difficulties.

I am still thinking about the vertical rollers to replace the unexpectedly "fragile" drawer slides at the top. Even assuming that laterally and vertically displaced slides and rollers will work for a normal, sliding gate design. 

Do I need to tilt the steering channel inwards to accept the lateral loads? Are there any lateral loads if the shutters are stiff enough to act as a simple, sloping beam? 

There are certainly twisting forces applied when the shutters are pushed at the bottom. The top slides are well over 2m away measured horizontally. Which may explain the serious problems I had when opening and closing the shutters. There was considerable lag at the top. I would usually have to go outside and use a batten to shove the tops of the shutters. Not ideal when I am supposed to be inside the dome!

Regarding the share of the loads on the slides: It looks as if the lower half has much greater length of material than the upper. [When the shutters are divided equally and horizontally.] A horizontal beam would share the loads equally and each would carry half the total weight. 

In the case of a curved shutter it looks as if the lower slide takes a much greater proportion of the weight. Quite probably 2:1. Which could be an advantage. Since it reduces the flexure loads on the more horizontal upper half of the shutters. Where stiffness is most likely to be compromised. 

With a sliding gate, vertical roller guide, there is no support [at all] at the top of the shutters. All the weight is on the bottom. Should I build a pair of skate wheel slides for the top of the shutters to share the loads? Or carry on with the sliding gate [vertical roller] design? Build the vertical rollers just to see if it works? 

If not, I can use a similar design to the lower slides. Using my older set of smaller, skate wheels. An alternative design would be upright skate wheels in a channel for steering. The upper slide could then share some of the loads. Though at the cost of an extended channel guide rail at the top of the dome. The upper channel would be inverted. So it could not fill with wet leaves like the lower one. 

I found some sturdy brackets and tried to fit them to the slide channels. Unfortunately, the socket head, M8 screws jammed the wheels solid. The heads were simply too large for the space available. So I have ordered some M8, stainless steel, countersunk screws. Which will leave plenty of room for the wheels to turn. 

I have belatedly added an image of the completed pair of bottom, shutter slides. The M8, plain shank bolts were a better fit in the 8mm skate wheel bearings than the M8 threads. The sturdy brackets will be bolted to the shutter ribs. I used the large head, M8, countersunk screws to bolt them to the slides. After countersinking the inside of the slide channel.

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