23.02.2021 Mitre angle for the cross braces.

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Tuesday 23rd 50F at 12.15. Heavy, grey overcast but only a light breeze. I dragged both saws out of the shed and spent half an hour cleaning them up with a dustpan brush.

There followed trial mitres of [47x95mm] 2x4s for confirming the cross bracing angles. After adding the steelwork to three foundation blocks I could see that 12° is the ideal mitre angle. The cross braces will make useful, but narrow shelves once the walls are completed. For storing jars of screws and nails. The DeWalt mitre saw measures angles from 0° [in brackets] rather than subtracting from 90°.

The length of the cross braces is simply obtained by subtracting twice the 2x4 thickness [for twin upright posts] from 85cm [The spacing between the centres of the steelwork studs.]

The simple, screw jack metalwork is shown fitted onto a foundation block. Two heavy brackets clamp the 2x4, timber, upright posts between them. The nuts allow the screw to be locked at top and bottom once the correct height has been set. The square washer spreads the load onto the concrete. These blocks and metalwork are intended to support the joists of raised, timber terraces and for anchoring carport, upright posts.

Carports are very prone to wind lift acting on their open, gently sloping roofs. Hence the concrete block's slightly tapered, pyramidal form. To lock the block firmly into the ground once the excavation is backfilled with self-compacting sand & gravel. Their individual weight of 70lbs is cumulative. I have added 12 blocks for 840lbs. That should help to overcome any lift in the wind. Or any unlikely lean due to drag. The curvature of the building and dome resists wind loading in comparison with square sides and normal roofs.

There is a metal thread cast into the concrete foundation block. Which provides vertical adjustment as the stud is turned. The nuts turn freely on the thread. So cannot apply torque to the height adjustment stud until two of them are locked together. The stud has a very large head. To support the timber when the height is being adjusted. 

An extra nut would aid speedy, height adjustment. By allowing a spanner to be used once a heavy load is already applied. Without the extra nut the top nut has to be wound right down to be locked against the other nut at some midway point. The disadvantage of an extra nut would be the limitation it places on the lowest possible, adjustment height. 

I chopped up every bit of scrap 2x4 which was long enough to turn into cross braces. Then laid them around the building on the prepared steelwork. Short offcuts of 2x4 were used to bridge the gaps. This suggested that the braces could be made shorter. The gaps between the mitred ends were less than the desired 94mm. [2x47mm] Better too long than too short! Cutting perfect mitres of any thickness is effortless on the 12" mitre saw.

You'll have to imagine that these braces are fixed across the bottoms of all the wall panels/frames. The braces nearest the shed are supposed to fit onto the existing posts. Since I can't expose them for now I just left the braces touching the octagon walls. The 4.2m, upright posts, will be clamped in pairs, of two frames, placed side by side, into the steelwork brackets.

Now I have a lot of braces cut, I can build a panel, or two. To get a feel for the weight, dimensions and manageability. If they prove easy to handle I could add the lower area of cladding. Just to see how that goes. I have yet to bevel any of the the outer surfaces of the 4.2m posts to 12° on the table saw. I shall do that tomorrow.

There are only a few sections which are completely clear of the veranda when the wall frames are raised upright. So I shall try fitting frames there before partially dismantling the veranda to add more. The veranda is a handy and secure scaffolding for erection of the new building. I shan't be in any hurry to dismantle it until I really need to. A few veranda floorboards may be all I need to remove to get some of the frames/panels into place. 

I am juggling the terms panels with frames, sections and walls. A frame becomes a panel once it is clad in plywood. When it is completely clad, from top to bottom, it becomes a wall. A section is a space between the steelwork. I hope that makes sense.

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