1.10.2021

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Friday 1st October. Overcast with wind and rain.

Trying a full mock-up of the triple layer base ring showed inconsistency in level. The skirt was level but the top of the reinforcing rib, around the base of the dome, was not. So I set about trying to even out the difference. Mostly by adjusting the packing under the dome. This eventually tilted the entire dome slightly towards the shutters. 

The 360° laser level then showed much better agreement. The image alongside shows the perfect height. With the laser just grazing the top of the rib.

My laminated base ring is intended to rest on the dome rib. This was the easiest way to hold the ring in place with added brackets. There being no obvious way to do so from below. Particularly when the rollers need a clear track. Glass fiber could have been laid over the ring but this would still need the ring to be level. Without any obvious way of ensuring this was the case.

The image here shows the rib as being 20mm too low. The green laser line indicates that the skirt needs to be raised. The dome is stiff so does not readily adjust itself locally to a higher stack of packing under the skirt. This much is obvious when I lever under the dome skirt. The dome lifts off from several packing stacks simultaneously.

I hoped to avoid needing any packing between the ring itself and the dome rib. The rib is simply a reinforcement and stiffener for the skirt. On which the dome normally rests on the ground. 

Variations are to be expected with a non-precision moulding.  Only the outside of the dome is against the mould. The inside is laid up with variations of thickness. Depending on the strength and stiffness required. A raised rib provides stiffness out of all proportion to the thickness of the glass fiber laid over it. The foam provides no extra stiffness. Merely acting as a former. Which usually needs to be lightweight and impervious to resin or water. While being stiff enough to cope with the modest loads applied during manual or sprayed lay-up.

The reinforcing ribs start with these lightweight foam strips. Probably just tacked onto the inside of the sticky, partially finished moulding. Before further reinforcement is applied over the foam. Being a weak material the foam must be difficult to place accurately over any length. 

Why bother to achieve perfection anyway? When the structure is simply an animal housing unit. Calves are not usually given to criticism of the construction, or precision, of their quarters. Even the farmer is unlikely to notice a variation of 20mm in the height of the rib above the ground.

Unless I decide to enter the next Olympics, in the manual dome rotation event, nobody will ever notice the slight variation in height at the skirt. The one, major difficulty is translating the position of the bracket fixing bolts from the interior to the exterior. I now have the spacing measured off from the center  of the roof segment. 

The height at which to drill pilot holes is quite another matter. It is no use measuring up from the skirt. Because the dome rib and base ring both get in the way on the inside. I ought to take a bright headlamp to the job. Because I can't even see the all magic marker lines I made over the laser lines in the deep darkness of the dome. An overcast day helps to see the projected laser lines. But! It makes the dome seem more like a cave.

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