I need some help with constructing a cylinder

[Jim Poehler]

Good day all,
I have a problem that I can't quite figure out how to solve. I have a datum that is composed of 2 features, both in line with each other, ie both have y and z at 0.0 with the variant being along the x axis. Both have a diameter of 0.8748 with one being a circle and the other being a sphere. I need to construct a cylinder which is to be datum A. This is the primary datum for the entire program. Help please.

[AndersI]

Create a 3D line from circle to sphere?

[Jim Poehler]

Thanks, but how can a 3d line be my primary datum?

[Matthew D. Hoedeman]

Because it will lock 2 rotational degrees of freedom, and it will (can) lock 2 degrees of translational freedom (4 DOF). That is better than a plane can do (a plane does 3 DOF).

[JEFMAN]

I would measure (or construct from measured features) a min circ circle and sphere, construct the line between centers, then dimesion the max distance between hits and line, and construct a generic cylinder with the line as axis and the max distance as radius (a cylinder as datum should be a max inscr / min circ cylinder...)

[Jim Poehler]

Thanks all,
Suggestions are all good. After having constructed a 3d line between the features as Anders suggested, I looked over the coordinates and saw that it had an x value of 0.53 which gave me the idea to take the original circle and copy/paste it and change its x coordinate to that of the sphere which happens to be 0.10 in x. It now measures directly at the hemisphere of the sphere and allows me to use 2 circles to construct my cylinder in the correct position and value. Of course all will depend on some very accurate machining but I will find that out soon when the 1st piece is ready for a real run of the program. If it works, great and if not then I have some good ideas and advice from you guys to change my approach. Thanks much for all your help, appreciated.