Like this?
Here with Rail Revolve seems works, no ?
Call the Edit / "View Points" on the arc and move the control points for have a pendicular on each vertex so tangency!

Here on view top Profil is at the middle of the edge, you can also put it at the perpendicular from center to the edge.

Hi Doug,

> The surface in the image was achieved using revolve rail
> to revolve a spline around the profile which works well on
> simpler profiles but on these buttons it doesn't meet the
> edge properly so is difficult to join properly.

Can you please post the 3DM model file that has the pieces that don't join properly so I can take a look at what's going on there?

- Michael

Hi Michael,
Scrub my comment about not joining, I had another go at using rail revolve and used Boolean union instead of join and top and bottom became a solid OK.

Anyway this is what I ended up with, which is pretty close.

Time to come up with a design of my own maybe.

Thanks,
Doug

Hi Doug - so probably what happened is your rail revolve result was a solid that had an end cap on the bottom.

Join only tries to join together open unattached edges between things, so your revolve would need to have its end cap deleted (or uncheck the "Cap ends" option so it's not created in the first place) in order for it to be set up for join.

Basically Join does not try to intersect objects or remove material, unlike the boolean commands.

- Michael