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# How to define an offset between a cylindrical surface and a flat surface

Member Posts: 3
I'd like to assemble a cylindrical part so that it is centered between two flat surfaces, not sure which mating tool I should use.

• Member, Moderator, Onshape Employees, Developers Posts: 1,381
Can you take a screenshot or share a doc or upload a hand drawing?
Not really sure  - does the cylinder touch both plates? Are the plates parallel? Is the distance between the plates equal to or greater than the cylinder diameter? Does the diameter determine the distance between the plates? If parallel and further apart than the diameter, is the cylinder centered or resting on on of the plates?
Philip Thomas - Onshape
• Member Posts: 3
See attached screenshot. I'd like to place the highlighted cylinders right at the middle of the space between the two blocks. The blocks are in parallel. I know how to define the distance between two parallel plane, but don't know how to define it between a cylindrical surface and a flat surface.

• Member, Moderator, Onshape Employees, Developers Posts: 1,381
Mr XXX - thank you, that helps.

Yes, you have a perfect storm here - no easy way.

A number of solutions are probably workable.
1) Import a sketch into the assembly - mate the blocks to each side of an entity in the sketch and the cylinder to a mate connector at the mid-point of an entity.
2) If the distance between the blocks is known, then in the part studio defining the block, create a mate connector that is offset by half the distance between the blocks. Then in the assembly, just mate the two mate connectors together to position the blocks and then use the same mate connectors to the position the cylinders.
3) position the blocks offset from mate connectors generated on the cylinders.

3 Is my favorite (but they would all work) - here is an example.