CHAPTER 20 ■ COUPLERInsert a heavy-duty or fiberglass-reinforced cut-off wheel attachment into the rotary tool. Bring the
rotary tool to the lower range of its speed and lightly maneuver the blade through the tubing at the marked
location.
The picture in Figure 20-11 was taken for illustrative purposes. You actually want to start cutting at the
first mark on the tube, with the remainder of the tube firmly in the vise. If the tube is hanging way out of the
vise, it’s going to vibrate a lot, marring the cut. If a middle mark is cut before the first mark, half of the tubing
is going to fall on the floor.
The bulbous front of most rotary tools sometimes gets in the way of cutting straight across the tubing.
To make things worse, the cut-off wheel shaves down over time, becoming smaller with use. A fresh cut-off
wheel helps, as does a flexible shaft extension. However, don’t be overly concerned with the angle of the cut,
as it can be corrected with sanding and, in any case, it doesn’t cause the coupler to wobble.
Finishing the Cut by Sanding
Depending on the method chosen for cutting, freshly cut tubing commonly contains hanging metal particles
called burrs. Rubbing the cut face in a circular motion against sandpaper cleans the rough ends of the tubing
(see Figure 20-12). You can use a fine single-cut or Swiss-pattern file, but sandpaper seems gentler.
Sandpaper is usually available in assorted packs of different grades of coarseness. Choose a variety pack
labeled for use on metal, like aluminum-oxide sandpaper. It should contain sheets from medium (100 grit)
through extra fine (225 grit). For a beautiful finish, also pick up some sheets of super fine (400 grit)
silicon-carbide sandpaper and even finer grades of sandpaper.
■ Caution Always wear a dust mask and safety glasses when sanding.
Lower grit numbers remove more material more quickly, but scratch the workpiece. Start with coarser
sandpaper (100 grit) to straighten out the cut or remove large chunks. Then, work the piece through finer
and finer sandpaper (225 grit) until you achieve the desired smoothness. Other than aesthetics, there’s no
reason to put a mirror finish (1500 grit and buffing compound) on the tubing. But, at the very least, remove
all burrs and sharp edges.
Figure 20-12. Freshly cut tubing showing scratches and burrs (left). Finished tubing sanded flat and
clean (right)