06-11-2017, 04:12 PM
ok I see what your saying.
you have a casting of a piston that has no reference points to it, its fat in every dimension but there is a piston hiding within it, its cast that way so as you know there is room to remove material from every facet to machine out a finished piston head, which poses a problem... you have to start somewhere right.. so in studying what you have you have to decide what are the critical references within the shape to make a start from, references B & C is a great place to start because you hit center and you hit square for the pin. Everything will be dimensionalized from it.
i see in the picture the boss housing relative to its bore appears to have a wall thickness difference, it doesn't make it wrong if the bore was put in true to the center of the piston head, it could have been cast slightly wrong ... casting are not exact within reason... or they bored the gudgeon pin hole not 90 degrees to center i dont know.
going back to a starting point, once the flat surface has been machined and once the piston head is on the mill table the bosses can be eyeballed to get the best line of attack to square the edges. You do however need to know the head thickness that should correlate to a distance from the head surface to the center line of the gudgeon pin bore as this related to how much you take off the top of the piston relative to the pin bore.
do you have a detail drawing of the piston head, if so send me a copy and i will give you the machining steps to machine it.... its very hard to cover the variables without knowing the facts to deal with..
all the best Anthony..
you have a casting of a piston that has no reference points to it, its fat in every dimension but there is a piston hiding within it, its cast that way so as you know there is room to remove material from every facet to machine out a finished piston head, which poses a problem... you have to start somewhere right.. so in studying what you have you have to decide what are the critical references within the shape to make a start from, references B & C is a great place to start because you hit center and you hit square for the pin. Everything will be dimensionalized from it.
i see in the picture the boss housing relative to its bore appears to have a wall thickness difference, it doesn't make it wrong if the bore was put in true to the center of the piston head, it could have been cast slightly wrong ... casting are not exact within reason... or they bored the gudgeon pin hole not 90 degrees to center i dont know.
going back to a starting point, once the flat surface has been machined and once the piston head is on the mill table the bosses can be eyeballed to get the best line of attack to square the edges. You do however need to know the head thickness that should correlate to a distance from the head surface to the center line of the gudgeon pin bore as this related to how much you take off the top of the piston relative to the pin bore.
do you have a detail drawing of the piston head, if so send me a copy and i will give you the machining steps to machine it.... its very hard to cover the variables without knowing the facts to deal with..
all the best Anthony..
ieezitin, proud to be a member of MetalworkingFun Forum since Jan 2013.