poorly working focus

[cmug]

What is this construction called? See Photo.
I have an antique camera with poorly working focus. I.e. it runs anything but smoothly.
It is not a Helicoid. But some kind of variant on it.
The lens system is housed in a brass bush with 2 protruding bolts. This is seen on photo at the right side.
That system goes in 2 buses. In 1 is a groove diagonally. In a one groove vertically. (see the photo again)
Completely dry without bolts, the bushes fit very nicely and everything can turn freely. All parts are made of brass.
As soon as I put in the two bolts in I don't get smooth operation.
The choice of grease (the viscosity) influences the successful turning. But very thin or very thick, the effect remains inadequate.
How do I get it really running smoothly? Someone suggestions. Tips are welcome. + grease tips welcome.

 

[cmug]

Already succeeded the repair. Polished all grooves with water + 2000 grit waterproof sanding paper. Carefully cleaned. Then special grease used (little and little pasty)

 

[Livesteamer]

I'm glad you worked it out. I was going to suggest machinists non drying blue. You clean the parts carefully, apply a thin layer of the non drying blue, re assemble carefully and cycle once. Carefully take it apart and see where the non drying blue has been rubbed off to find the point of interference. Keep up the good work! Joe