Slide tubes are pulled through a specifically sized die using a specifically sized hardened steel mandrel
On the surface, drawing slide tubes is a simple process: tubing is pulled through a specifically sized die using a specifically sized hardened steel mandrel. The die and mandrel are designed to achieve the inside and outside diameter dimensions desired for the finished slide tubes.
The mandrel and tube blank are pulled, using great force, through the ceramic die. As a result, the tubing is pressed to match the size of the gap between the mandrel and the die. This process also stretches the tubing and creates the desired dimensions.
Various factors, including tube quality, material, and drawing speed, affect the outcome. At Getzen, we use special mandrels, dies, and even a special draw bench solely for drawing trombone handslide tubes. All work together to ensure the straightest possible tubes. A straight tube means faster and smoother action on the finished handslides.
As the clip begins, the tubing has already been drawn once. This is to achieve the stocking or bushing end of the tubing seen on most trombone inside slide tubes. The next draw is to take the diameter of the tube down further, leaving approximately three inches of the larger diameter stocking at the end.
Next, Vince slides the tube blank over the mandrel. The mandrel end is then slipped through the die and attached to the draw bench piston. Slowly, the piston is drawn back and the tubing is pulled through the die until the three inch stocking remains at the end.
The mandrel and die are then flipped and the draw piston is used to remove the die. The fit of the die to the mandrel is so tight that the force of the piston is needed to break the die free.
Once the drawing die is released, a backing die is used to remove the tubing from the mandrel. The backing die is a few thousandths of an inch larger than the mandrel and is actually used to push the tubing from the mandrel. The only other way to remove the tubing would be to peel it away like a banana.
From here, the tubes are sent in batches to the slide room and inspected for straightness. If they pass, the tubes are buffed, barrel shaped, chrome plated, hand straightened, and finally mounted into a handslide assembly.
For more information on the construction of trombone handslides, read The Birth of a Handslide in the September 2005 Getzen Gazette.