June 17^th  2021 

I have had to take a break from Big Muskie in order to do quite an extensive carpentry job but now I’m back at my core business. The first thing to do was to complete the two minor booms ( one from scratch) with all their equipment auxiliary to the main structure which is tubular aluminium, similar to the main boom. Figure 95 is an overall view of the two 9 foot booms side by side. Figure 96 shows the top ends of the two units. Each is fitted with four 4 inch turned aluminium V pulleys which are part of the mechanism for pulling the 18 foot main boom up into position.These pulleys run on an 8mm rod which is journalled into a very strong box built from 2mm plate and which is fixed to the aluminium tubes of the structure. Also visible in figure 96 are the staff access stairs and working platforms.

 

Fig. 95: Overall view of two minor booms

Fig. 96: Closer view of the upper ends

Figure 97 is a close up view of the boxes alluded to above. It will be seen that there are two other devices which run on each of the 8mm axles. Each of these is a heavy gauge plate with 6 dice like fittings bolted to it. The latter are the anchoring devices for the static lines which will hold the main boom in position. Each is a 20mm length of 16mm square mild steel stock with holes drilled at right angles. One hole is 6mm and has an M6 bolt passing through it to anchor it to the heavy gauge plate while the 5mm hole will have an M5 static line passing through it. Figure 98 is a close up of the remainder of the 60 dice like fittings for the 30 static lines.

 

Fig. 97: Pulley clusters and static lines anchor blocks

Fig. 98: Some anchor blocks

The static line system consists of 12 which connect the top of the gantry to the tops of the minor booms, another 12 which continue these up to the top of the main boom, 4 more which connect minor boom tops to the centre of the main boom and finally 2 which will form a cross brace to prevent the minor boom collapsing sideways. The latter eventuality is remote as the anchor at bottom ends is via 2mm plates journalled onto M12 rods and 4.5 inches apart while the connection at the top end is by a length of 50mm thin walled aluminium tube which captures the look of the prototype well. (See figure 99.). I am waiting for some 70mm solid aluminium solid to machine two cups to anchor the ends of this piece of tube. All of this should give immense resistance to sideways moment.

 

Fig. 99: Length of 50mm diameter aluminium tube (cat for scale!)

Finally in figure 100 are shown the two winding drums each driven by two 12V motors which will provide the pull on the cables to pull the main boom up into place. Previously these winches were employed on the wooden wheeled crane used to handle the two heavy toroidal units which formed the basis of the swing facility.

Fig. 100: Two winding drums