It really doesn't matter how you scuff the brass tubes. It's a matter of convenience. What matters is that you get a surface that is free from dirt and oils.
Most of our tubes are fairly highly polished, minimizing the adhesion surface. Additionally, most are coated with a lubricant during manufacture such that they go through the machinery more easily. They don't oxidize with the lubricant coating and that's why they look shiny and new when they come out of the bag. We scuff the surface of our brass tubes to both add more surface holding strength and to remove the light layer of lubricant. This allows the glue of choice to work more efficiently.
<b>More info than you probably want to know</b>
Glue only works in two ways: direct bonding and contact bonding. In direct bonding you apply the adhesive directly between two surfaces. In contact bonding, you apply a layer of adhesive to each surface, and then the two layers of adhesive are put in contact to stick to each other. Contact bonding is not often used in craft work as the bond is near permanent the moment the two adhesive surfaces touch.
The glues most commonly used in woodworking fall into three categories: water based, solvent based and chemical curing.
Most wood glues are water based and cure through evaporation. They stick best to highly porous surfaces (such as wood) and thus are not a good choice for plastics and metals. Poly and CA glues are solvent based and also work by evaporation. They work best with less porous surfaces such as metals and plastics. Epoxy is a chemical curing glue that involves a physical change when a hardener is introduced to a resin. This is a fast bond, but can be slowed by the introduction of a third chemical to increase the amount of time the chemical reaction takes. Epoxy works well on a wide variety of surfaces.
With all of this in mind you can more easily select the appropriate glue for your need, BUT, regardless of the glue the surface needs to be clean and free from lubricants (other than water).
