*
Sunday 26th 55F, heavy overcast.
I have several serious hurdles to overcome with constructing and fitting the base ring. As usual, I shall discuss the problems in text. I find this helps me to see possible options for progress.
Fitting the arcs together into the base ring requires a second layer. Then a third. The arcs are butt-jointed and rely on lamination over the many [staggered] joints for strength. The base ring soon becomes impossible to move let alone fit into the dome. Despite the considerable weight the ring will be flexible and fragile until the glue is fully set.
I can slide the part rings under the dome skirt and into the dome. Rather than carrying long sections around the dome and in through the narrow access triangles. Having the shutters open would help. As well as providing much better working light. Though the open observation slit is still on the "wrong side" of the dome from the working area ground outside with any pretensions of flatness. Not to mention enough room for a full, 4.3m Ø circle.
The ground under the dome is sloping from a minimum of about an inch clearance to well over eight inches. So packing up to the base ring level from the bare ground is a serious problem. The battens and nails I used to support the ring are merely guides and could not support the full weight of the triple laminated ring.
I could bring in a load of self-compacting gravel. To bring the floor up to level. Lots of hard work just to support the base ring for assembly! Poor access for wheelbarrows too unless I remove the heavy shutters. No room to bring the car trailer near enough to shovel straight in though "the doorway."
Clamping the arcs into a ring, while the glue sets, would require a huge number of clamps. The full circumference is over 12metres or 36'. Clamps need space above and below for the jaws. Not ideal when working on uneven ground.
Spring clamps may be more affordable but probably don't have the required pressure to assure the glue joints are close enough. The butt-joints need to be brought closely together for maximum strength and stiffness and kept that way. Or final accuracy of diameter goes awry.
The base ring's shelf brackets or [simpler] angle brackets need to be bolted through the GRP dome. This requires accuracy of level to avoid wandering lines. They must all be evenly spaced not to look horribly amateurish. I can only mark the level with the 360° laser from inside the dome.
Until all three layers of ring are complete the brackets can't be used for support. Or can they? Longer bolts to support the rings while the glue dries? The bolts can't project downwards or they will strike the dome rotation rollers. Countersunk bolts, fitted from below the ring, make most sense. These would leave the roller track free of obstructions.
Do I glue sections of arc together on the ground outside? hen carry them into the dome? The joints between sections are unlikely to remain tight enough. Lots of wood screws can be used to hold the layers together while the glue dries. Though this can only happen from above. There isn't room to drive screws from below. Screws could be lost inside the ring for holding the first two layers together. Hidden by the third layer when glued on top.
Wood screws have to be shorter than two laminations. Or vicious points protrude! Which means shorter screws with limited holding power. The screws need pilot holes to avoid locking up without adding any clamping pressure. I normally drive the screws home. Back them out again. Then finally drive them home. This helps to ensure some clamping between layers. I use a rechargeable drill as a Torx driver of course.
Now add the lack of a solid dome at the entrance and the ongoing requirement for easy access. Once the ring reaches the slit area there is a huge potential hurdle. A full ring is much easier to measure and ensure roundness. Once the ring is compete there is an exposed length well above the ground. Which needs to be strong enough to support the considerable weight of the shutters. The shutters also have to be accurately shortened to sit on top of the base ring. Catch22 at every stage. I had better come up with a workable plan!
*
No comments:
Post a Comment