[Antennas] Andrews Heliax assembling

[G4GED Dave]

Hi
This is a query to do with the assembly of a connector onto Andrews Heliax 
such as LDF4-50A.

When I remove a length of the center polyethylene dielectric with my craft 
knife, a thin film is always left stuck to the conductor.

I'm afraid of scraping this away with the knife or using abrasives for fear 
of damaging the conductor's copper plating.

Does anyone have a sure fire method for cleaning up the conductor properly 
in preparation for assembling to a connector please?

Thanks in advance
Dave