My Observatory. 8a. The saga of the hurricane ties.

I was somewhat concerned that the rafters are each attached to the runners by only a single screw on each side. Would that be strong enough in a gale? I've received a lot of help and encouragement from members of the LX200 Yahoo group, and two or three of them expressed the same thought and suggested that I add what Americans call hurricane ties to add strength to the joint. I searched but could find nothing equivalent in the UK except for "twisted ties" which are at least 1200 mm long—a little too long. So a friend on the LX200 group suggested I made them by bending a flat plate along a line at 45°. This resulted in the two parts not pointing in the same direction. To achieve this alignment I had to complete the bend right over and add two more right-angled bends as shown here. This was quite difficult to bend and it took me almost 15 minutes to make this one.

My next idea was to bend an L-plate. This was easier but I needed to take care, or the bar bent at its weakest point, the hole.

Finally I thought "Why not just twist a straight tie?". Obvious really, but I was slightly concerned that the bar would tear. I put one in the vice with the screw hole in the vice, gripped it at the next hole up with a large pair of pliers and twisted it. Easy! Note however that the resulting bar is handed—there is a left-hand version and a right-hand version, each of which is the mirror image of the other*. The right-hand version can only be fitted on the right-hand side of the rafter, and I have three places where I have to fit it on the left. So I need three left-hand ties, two right-hand ties, and five that can be either way.
When I bent all ten ties one did in fact tear slightly. I decided it would not weaken it too much and used it just the same. When I came to fit them, I found I could not fit one because the block to which the securing bolts fit got in the way, so I simply bent one by 57° and screwed it below the rafter with 1¾-inch screws. In theory this won't be as strong as the twisted tie but I don't really think the roof is going to come off.

*Chemists refer to this as chiral and I don't know of a better term. The most obvious is handed as in left-handed or right-handed threads—a normal screw is right-handed. (The human hands are chiral.)

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I was somewhat concerned that the rafters are each attached to the runners by only a single screw on each side. Would that be strong enough in a gale? I've received a lot of help and encouragement from members of the LX200 Yahoo group, and two or three of them expressed the same thought and suggested that I add what Americans call hurricane ties to add strength to the joint. I searched but could find nothing equivalent in the UK except for "twisted ties" which are at least 1200 mm long—a little too long. So a friend on the LX200 group suggested I made them by bending a flat plate along a line at 45°. This resulted in the two parts not pointing in the same direction. To achieve this alignment I had to complete the bend right over and add two more right-angled bends as shown here. This was quite difficult to bend and it took me almost 15 minutes to make this one.
My next idea was to bend an L-plate. This was easier but I needed to take care, or the bar bent at its weakest point, the hole.
Finally I thought "Why not just twist a straight tie?". Obvious really, but I was slightly concerned that the bar would tear. I put one in the vice with the screw hole in the vice, gripped it at the next hole up with a large pair of pliers and twisted it. Easy! Note however that the resulting bar is handed—there is a left-hand version and a right-hand version, each of which is the mirror image of the other. The right-hand version can only be fitted on the right-hand side of the rafter, and I have three places where I have to fit it on the left. So I need three left-hand ties, two right-hand ties, and five that can be either way. When I bent all ten ties one did in fact tear slightly. I decided it would not weaken it too much and used it just the same. When I came to fit them, I found I could not fit one because the block to which the securing bolts fit got in the way, so I simply bent one by 57° and screwed it below the rafter with 1¾-inch screws. In theory this won't be as strong as the twisted tie but I don't really think the roof is going to come off. Chemists refer to this as chiral and I don't know of a better term. The most obvious is handed as in left-handed or right-handed threads—a normal screw is right-handed. (The human hands are chiral.)