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So I started gluing some arcs into my first dome rib. This will be one of two ribs. Each reinforcing one edge of the observation slit. I had allowed the arcs to stand in the sunshine all morning to ensure they were fully dry. They were rotated at intervals. Just prior to gluing I had used an orbital sander to smooth off any lumps and bumps from earlier screws.
The Titebond III "Ultimate" glue is pleasant to work with. It is about as runny as any other wood glue and spreads easily and evenly with a paint scraper provided one is generous with the glue. I didn't notice any odour.
Having read that clamping can be easily overdone I just used spring clamps all around the edges. I soon had to flip the rib over. To check the joints of the short central section of the lower layer. Which is why all the supporting, timber scraps on the ground are now in the wrong place.
I shall pause at only two layers to check the rib's lateral stiffness before adding a third layer. I used 2x16mm on the plywood dome and this left joints on each face. Which are potential hinge points of weakness. Three layers allows staggered joints. Skewing the joints increases joint strength.
I had previously chosen the flattest section of the parking space using a 2m straight edge. The spring clamps were bought in small quantities back when I was building the plywood dome. One can never have enough of them when lots of ribs have to be laminated. Fortunately I shan't need lots of those with the glass-fibre dome. It is meant to be self-supporting and has its own reinforcing GRP ribs moulded in.
I just need to stiffen the dome where I have cut out a large rectangle for the observation slit. No doubt the dome could survive without these ribs. Though not if the dome has to be lifted in one piece. Certainly not lifted from the supplied rings at the top. Which were designed to support the weight of a much more solid hemisphere. Not one with a meter wide hole cut out of it from the skirt to just past the zenith!
With the shutters removed I had easy access to the dome to store the rib, upright overnight. No point in leaving it lying out on the grass to get damp. It is still clamped up. Glued joints should not to be stressed for 24 hours. So I used G-cramps to clamp some boards across the joints to support the rib securely.
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Next morning I discovered I had not been generous enough with the glue. Or the clamping? One joint section had an air gap. So I poured glue into the gap and clamped it up well with G-cramps. Since I now have so much glue I'm going to apply it to both surfaces, spread it evenly and clamp it more firmly. The spring clamps probably don't apply enough pressure over such a large area.
A quarter arc, 24mm thick, two layer rib, 200mm deep is really quite heavy. It will need temporary, internal support to avoid the dome sagging under the weight. I had slotted the end of the rib to slide over the dome material at the zenith.
The zenith board needs to be marked and cut out first. To ensure the dome hasn't sagged from the weight of the ribs. Despite being sturdy down near the skirt the dome is much thinner away from its panel edges. In fact, light can be seen through it in places. Not a problem provided I respect its limitations in stiffness around the entire slit area. Hence the ribs, of course.
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