Front derailleur (cable clamping)

[clarion]

I have a c.1980 Campag Record(?) front mech.

I've replaced the cables, but I can't seem to clamp it tight enough.

The clamp is surprisingly rudimentary for such expensive kit:  a groove for the cable next to a threaded hole.  The screw tightens into the hole, and can hold it.  Until you wish to change onto the big ring, that is

Any ideas?

[bikenerd]

Missing a washer?

[Zoidburg]

Wrap the cable around the screw so it points back on its self?

It may not be an inline design like the shimano arangement

[clarion]

It has an integrated washer on the screw, but I shall try wrapping it...

...just wait there a moment.

Edit:

I think I've found the problem.  The thread of the screw and the hole are not quite the same.  Someone's replaced it some time.  Means I think I may have a cross-threaded mech.