13.10.2021 Lower shutter drawer slide fixings.

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Wednesday 13th, 33F, first frost of winter. Clear start followed by cloud is promised. 

I have been thinking about the drawer slide fixings at the bottom of the shutters. The mounting surfaces must be parallel, in all planes, to those at the top. Simply to avoid adding stresses and friction. The shutters, despite their great length, must be treated like a pair of [opposing] drawers. The difference is that these "drawers" are already loaded with their full weight capacity. 

This means I need wedge shaped cross-pieces [more boards] on the bottoms of the shutters. On which to mount the slides. They will need an asymmetric curve on their fronts to fit inside the spherical GRP covers. I can't easily produce these cross-pieces unless I shorten the remaining shutter ribs. So that I can hold a pattern underneath the shutter to trace out the complex curves. The spherical shutters have highly asymmetric ribs. So they are impossible to join in a straight line.

Where to draw the cut-off line on the ribs? Ideally the shutters should overlap the dome skirt. Just to avoid the need for additional weather proofing measures. Since I already have the outer ribs chopped off there really isn't much choice in the matter. I'll just need taller props for the shutters while I make the drawer slide supports. 

I shall close the shutters and use a double length board for marking out the cross-piece patterns. This will ensure the inner face is parallel to the shutters and each is properly aligned in plan view.

Once the height of the cross-pieces is established I can fix a sturdy crosspiece between the slit ribs. This will support the opposite faces of the drawer slides. The slides ought to be placed low enough not to block the view of the horizon. Though they can't be physically lower than the base ring. Which passes directly though this area. The cross-pieces must clear the base ring. 

If I use a 2" x piece of timber for the slit rib, lower crossbar than that sets a minimum height for the drawer slides. The timber brace will provide support for the base ring across the open gap between the ribs. I shall use sturdy angle brackets to ensure a sound fixing. A few screws into the end grain are hardly sufficient for this vital component.

I cut off the long, shutter ribs to match the others. Then pulled the shutters outwards to prop them up. This was to allow unhindered access to the inside of the shutters. Without the slit ribs getting in the way. Next I have to make patterns. Probably out of cardboard packaging.

Too much cloud for imaging.

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