*
A morning of light showers didn't put me off working on the dome. I had to replace all the 57cm C2s before I could add all the short gores to the three, full length ones. There was a minor panic when I realised I couldn't pull the resulting skeleton into a circle of the correct diameter.
It seems the architect had decided to make only 15 gores to save on materials but forgot to tell the foreman or the labourer. Problem solved by adding a couple of extra struts for decoration where the observation slit will go.
By the time I had finished lunch the dome was enjoying heavy drizzle. I rapidly unclamped it all and put it in the octagon with a tarpaulin over the top. I have ordered more Rawlink clamps online. I know I keep saying it but they offer remarkable clamping pressure for small change. Yes, the jaws fall out all the time and the widely splayed, slippery plastic handles are very hard to grip.
Nevertheless, for my purposes in holding gores together, they are ideal. The Bessey clamps, for comparison in the same size, are very weak and need at least two or three, to hold as well as a single Rawlink. I never had any of these spring clamps before starting the observatory. They made dome construction so quick and easy I should call it Insta-dome. Or perhaps not. The entire dome can be erected and dismantled again in under five minutes.
What's next? I need to mark the observation slit on the gores. Then add side reinforcing ribs to replace the missing strength from, quite literally, cutting the dome wide open on one side. I was advised to stiffen the dome with cladding panels before attacking the ribs.
The opening must be left without any obstructions even up over the zenith. That means a considerable loss of strength without really stiff, additional materials built right around the opening. The dome is very likely to sag around the slit unless it is well support with vertical edge ribs. Conversely, I can't add these parallel reinforcements without the dome being supported evenly.
It also means cutting 4mm birch plywood panels on the table saw. Which means working outside to have room to swing a 1.5x1.5m [5'x5'] sheet freely. The largest [lowest] panels are 60x50cm but they'd have to be cut from 50cm wide strips. Three strips from each sheet. I'll lose a little bit of that width to the two saw kerfs as I divide up the sheet into three. Working outside needs dry weather. Or a temporary roof to work under.
Perhaps I'd better get some white, lightweight tarpaulins to hang a sloping canopy off the octagon and shed. Otherwise I shan't get much done in steadily deteriorating weather. It would be easy to run a 2x4 or 2x6 off the veranda to support the side furthest from the shed. A sturdy post will hold up the corner using truss plates. The shed will be providing support on the other side.
It needs to be windproof as well as waterproof and absolutely must shed rainwater easily. Rather than collecting it in heavy puddles ready to destroy the entire structure. One of my earliest memories was of a neighbour trying to push an enormous puddle off the roof of his tarpaulin or canvas "garage." Which was hung between two buildings. Unfortunately the length of timber he was using to prod the puddle pierced the canvas and he and his motorcycle were drenched! I remember being fascinated by the bright, lens-like puddle in the roof. History does not record whether I was also soaked.
The latest iteration of the dome has the upper C4 [35cm] struts fitted near the tops of the [still] shorter gores. Some to the ribs have taken on a slight set from being damp and twisted by earlier struts of the wrong length. They will soon respond to being straight again. Next step is to extend more of the ribs towards the pole.
By the strangest coincidence I saw a telescopic, big bale loader on my morning walk today. I was just discussing these machines as a means to lifting my completed dome into place. Though I still think I will lift each gore/segment effortlessly up the ladder using my hand-cranked, boat winch. Perhaps pairs of gores will be quicker to build with and more stable on the ladder. The important thing is to have rehearsed the entire build down on the ground before lifting anything.
I can build a derrick off the pier with a pulley on top. Then the gores will remain upright throughout the lift and just slot neatly into place on the base ring while still safely restrained. Their forward balance point will ensure they don't tip backwards. Access, via a stepladder, through the open observation slit should be fine for working on the top of the dome.
I have received the white, 4x6m lightweight tarpaulin I ordered to form a work shelter. The 18 extra Rawlink spring clamps should be here tomorrow. I am using storage tubs for carrying the clamps about now. Bags were hopelessly awkward and bringing them in an out by hand meant lots of trips, due to the bulk. I can't believe how many clamps it takes to hold the dome together when I had none at all before starting. I need lots more to be sure the dome is safe as I build it up on top of the building. The gores should be mostly clad by then so I don't want 'bits' blowing away across the fields!
By the time I had finished lunch the dome was enjoying heavy drizzle. I rapidly unclamped it all and put it in the octagon with a tarpaulin over the top. I have ordered more Rawlink clamps online. I know I keep saying it but they offer remarkable clamping pressure for small change. Yes, the jaws fall out all the time and the widely splayed, slippery plastic handles are very hard to grip.
Nevertheless, for my purposes in holding gores together, they are ideal. The Bessey clamps, for comparison in the same size, are very weak and need at least two or three, to hold as well as a single Rawlink. I never had any of these spring clamps before starting the observatory. They made dome construction so quick and easy I should call it Insta-dome. Or perhaps not. The entire dome can be erected and dismantled again in under five minutes.
What's next? I need to mark the observation slit on the gores. Then add side reinforcing ribs to replace the missing strength from, quite literally, cutting the dome wide open on one side. I was advised to stiffen the dome with cladding panels before attacking the ribs.The opening must be left without any obstructions even up over the zenith. That means a considerable loss of strength without really stiff, additional materials built right around the opening. The dome is very likely to sag around the slit unless it is well support with vertical edge ribs. Conversely, I can't add these parallel reinforcements without the dome being supported evenly.
The gore on the left shows the latest dimensions and angles.
It also means cutting 4mm birch plywood panels on the table saw. Which means working outside to have room to swing a 1.5x1.5m [5'x5'] sheet freely. The largest [lowest] panels are 60x50cm but they'd have to be cut from 50cm wide strips. Three strips from each sheet. I'll lose a little bit of that width to the two saw kerfs as I divide up the sheet into three. Working outside needs dry weather. Or a temporary roof to work under.
Perhaps I'd better get some white, lightweight tarpaulins to hang a sloping canopy off the octagon and shed. Otherwise I shan't get much done in steadily deteriorating weather. It would be easy to run a 2x4 or 2x6 off the veranda to support the side furthest from the shed. A sturdy post will hold up the corner using truss plates. The shed will be providing support on the other side.
It needs to be windproof as well as waterproof and absolutely must shed rainwater easily. Rather than collecting it in heavy puddles ready to destroy the entire structure. One of my earliest memories was of a neighbour trying to push an enormous puddle off the roof of his tarpaulin or canvas "garage." Which was hung between two buildings. Unfortunately the length of timber he was using to prod the puddle pierced the canvas and he and his motorcycle were drenched! I remember being fascinated by the bright, lens-like puddle in the roof. History does not record whether I was also soaked.
The latest iteration of the dome has the upper C4 [35cm] struts fitted near the tops of the [still] shorter gores. Some to the ribs have taken on a slight set from being damp and twisted by earlier struts of the wrong length. They will soon respond to being straight again. Next step is to extend more of the ribs towards the pole.By the strangest coincidence I saw a telescopic, big bale loader on my morning walk today. I was just discussing these machines as a means to lifting my completed dome into place. Though I still think I will lift each gore/segment effortlessly up the ladder using my hand-cranked, boat winch. Perhaps pairs of gores will be quicker to build with and more stable on the ladder. The important thing is to have rehearsed the entire build down on the ground before lifting anything.
I can build a derrick off the pier with a pulley on top. Then the gores will remain upright throughout the lift and just slot neatly into place on the base ring while still safely restrained. Their forward balance point will ensure they don't tip backwards. Access, via a stepladder, through the open observation slit should be fine for working on the top of the dome.
I have received the white, 4x6m lightweight tarpaulin I ordered to form a work shelter. The 18 extra Rawlink spring clamps should be here tomorrow. I am using storage tubs for carrying the clamps about now. Bags were hopelessly awkward and bringing them in an out by hand meant lots of trips, due to the bulk. I can't believe how many clamps it takes to hold the dome together when I had none at all before starting. I need lots more to be sure the dome is safe as I build it up on top of the building. The gores should be mostly clad by then so I don't want 'bits' blowing away across the fields!
Click on any image for an enlargement.
*
No comments:
Post a Comment