[Public-List] Bronze Casting Shrinkage Issues ......Making of pattern for the pintle/gudgeon

[crufone at comcast.net]

Hello all, 

In the past I have done metal casting from both the engineering and the fine art point of view. Because in the case of both of these parts they will be mounted to a substrate, i.e., fibreglass, which can very easily be adjusted the shrinkage issue I believe is a non-issue. If we were making parts which must mate up to a non-alterable surface then that would be another story. 



If the group can not come up with a decent original pintle/gudgeon set then I might be persuaded to make the pattern. I have done some thinking about this and would like to consider making the pattern one that could be used on the entire production line of boats. Again because these parts are to be mou nted to fibreglass, both the rudder and keel, I feel that this is a possible task. I would also like to improve a bit the design, i.e., make the pintle 5/8" diameter and increase the height and thickness of the " U" shaped areas.  Most of the failures I have seen , beyond the bushing wearing out, are fractures thru the fastener holes of the "U" straps. Because the pieces are to be faired to the outside surface the increased thickness would have to be toward the inside of the "U". I believe that this is possible because on my boat anyway the inside dimension of the "U" is something like 1-1/2" to 1/3/4", plenty of room there to loose a little beef. The height would not be an issue. The original installation on my boat was so sloppy that the cut away part in the keel is about a 1/4" wider on both the  top and bottom of the strap. The space was just filled in with 'Ackupucky' and has since mostly fallen out. 



It looks like we can count on  Peter McEvoy to accomplish the foundry work. thank you Peter. If I end up making the pattern I will work closely with him to get it right the first time. I do hope that someone comes up with an original to use as a pattern as I do not really have the time to take this on. 



I wonder if some person in the know from both the CBAA and GLAA w ould come forward to respond to this as a joint project for the 50th anniversary celebration. I have suggested this prior but no one has taken the bait, ;-). I firmly believe that when we finally have decent molds made for these pieces that they are archived and taken care of properly so that anytime in the future parts can made for our boats. 

Michael #133