The current set up has a roller rolling on a conical plate to allow the boom to rotate. This was too complex and had too many parts thus it was re-designed to work with the new cross member.
This old design was the trunnion rest model.
A new mechanism was done up to move the rotating part to the mast thus allowing the cross-member to be fixed. The rotating components are now affixed to the mast and rotate around it entirely. It was clear from the early simulations of the numerous upper parts that attached the boom to the cross-member that these many parts meant that the chance of re-design was higher if any other part needed modification, thus the need to simplify and reduce the number of parts, an obvious conclusion well in keeping with industry practice.
The first part of the new rotating mechanism are the 4 bolt hoes that the cross member attached to. The bolts can in this case be drilled through and bolted on the back end.
Again this allows for the the ability to be dis-assembled.
Along the lower edge of this part sits a groove where a bearing is to be mounted. There is a component lower part that will seat the bearing. This part however will be fixed to the mast. Thus the bearing will promote the rotation of the upper part while staying fixed and firmly mounted in the lower part.
Together they will sandwich the bearing but with the lower part fixed only the upper part rotating thus allowing the cross member and boom to move as well.
The arrangement shows how the parts are arranged and how they will interact with each other. The gap between the two parts are exaggerated, the bearing will sit within the recesses of each part and the 2 parts will sit closer and still be able to rotate. The lower part will be stationary bolted to the mast in 2 places. As such it was necessary to see whether the part’s bolt holes could withstand the stresses. As the part would be resting on theses bolt holes then they were modelled as fixtures.
As can be seen with a load of 37.812kN the maximum stresses don’t exceed 11.174MPa. This is quite suitable for the design purposes.