Trapdoor/hatch revisited.

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The problem with climbing a ladder through the pyramidal pier is the lack of shoulder clearance. It is perfectly adequate until something projects into the space available. That projection would be the vital support for the free end of the hatch. I have racked my brains for ages trying to overcome this problem. Until today, when it suddenly dawned on me. 

I could have hinged toggles, one either side. These toggles would lift effortlessly out of the way if my shoulder struck one, or both, on the climb. The toggles would be smooth and well rounded to avoid impact or corner penetration injuries. They also needed to be lightweight to avoid inertial mass preventing free lifting on impact. This last requirement excluded heavy sections of aluminium.

The ideal material proved to be 3/4" Baltic birch ply. Offering adequate strength without unnecessary weight. The toggles would be made overlong so that the tail ends were stopped against the underside of the floor. A sturdy block would be placed directly under each toggle support area. So that the pivots were relieved of almost all of the downward loading. The trapdoor plus my own full weight must be safely supported without any risk of failure.

The pivots will be 8mm ss bolts with plain shanks passing through a 7.5mm hole through the 2x6 joists. The toggles must drop freely by gravity alone to provide absolutely fail-safe support. The toggle stop blocks are bolted through the supporting joists.

A micro-switch and battery driven, red LEDs will provide a clear indicator when the hatch is open.

Wednesday: Fixed the hinges of the hatch and trimmed the planking. After removing the tarpaulins I had a disaster in the afternoon when the slit frame fell sideways inside the dome. I had removed the bottom plank for routing. While using a block and tackle to pull the base back in the short rib extensions at the top of the dome cracked off. Allowing the frame to drop sideways.

I tried lifting it manually but it was well in excess of my strength. So I set up a 2x4 as a gin pole and was able to tip the frame back upright with judicial rotation of the dome. Thankfully it has remained in place overnight. It would be difficult to prop up the frame without losing the ability to rotate the dome. Which I need, to be able to bring each gore, in turn, to the 6m, 20' ladder for gluing.

Click on any image for an enlargement.

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