Posted by Rick Denney on January 17, 2003 at 09:41:45:
In Reply to: Building your own flight case posted by Rob Edmiston on January 16, 2003 at 20:00:09:
Heck, I'm bored, so let's think about this from an engineering perspective.
User Needs:
- Portability (must at least be rollable)
- Acceptable to airlines (concerns both size and weight)
- Stowability (must at least fit in a minivan)
- Instrument protection against:
- Crushing (i.e. being a the bottom of a stack)
- Impact (caused by dropping)
- Puncture (from, say, the corner of another crate)
- Reasonable cost
Requirements:
- No heavier than 50 pounds, empty (to keep the horn and case under 75 pounds)
- Small enough to go through the back door opening of a reasonable-but-large rental car, such as a Mercury Marquis (you do have to pay something extra to travel with a tuba)
- Small enough to be acceptable by the airlines.
- Not too tough looking (airline gorillas are more careful with things that are obviously fragile, and an Anvil-syle case is the opposite of that)
- Rounded or chamfered corners to facilitate getting it through car door openings
- When dropped from four feet, will not break and will not subject tuba to more than 3 G's on the body, and 1.5 G's axially on the bell rim.
(Notice how the requirements connect to the user needs? That was your systems engineering lesson for the day.)
Anvil and other makers of flight cases want their cases to be as strong-looking as possible, because that's what makes you want to buy them. But I think it is a mistake, and a violation of proper requirements, to make it look stronger than it is, or to give the impression that it is indestructable.
My engineering sense (I'm doing no calculations) suggests that a fully rectangular box of 3/4" plywood will not meet these requirements at all. A rectangular box that would contain a largish 4/4 tuba with a 20" bell like my York Master would be about 36" tall, 26" wide, and 45" long. That is about 52 square feet of plywood, which would be something like 75-100 pounds for the plywood alone. Even if you could pick it up, you would never get it through any car door opening, and you'd even have problems with most vans unless you could leave the rear seat at the rental agency. The rectangular box provides a nice flat surface, which encourages gorillas to pile other hard, heavy luggage on top of it, and the flat surfaces of the box are not that strong against stress applied at right angles to the surface.
I have a wood flight case that I built for my Miraphone, but I don't use it because it is too bulky. Here's how I would do it now, though it would take better carpentry skills:
I would minimize the spacing around the bell a bit. Here's why: Bells are strong for forces applied at the rim at right angles to the axis of the bell, but they are weak for forces applied at the rim along the axis of the bell. Bells are also light, and have relatively little momentum of their own in an impact. I would therefore suspend the bell in free air by blocking foam around the body of the instrument. If you left two inches of empty air between the bell rim and the end of the case, and an inch of empty air around the rim of the bell, then the case could actually be a bit smaller than if you used foam there. Air exerts no force on the tuba, and you only need enough foam around the body to keep it from moving so far that the bell runs out of air. The inflated ball in the bell accomplishes a similar objective when the foam around the body isn't quite stiff enough, or when the space is tighter.
I'd stand the tuba on its bell on a big sheet of paper, and put a lamp above it aimed straight down so that the shadow is centered under the tuba, and trace the edge of the shadow with a pencil. Then I'd add an inche all the way around it, except for the off-side outer branch, where I'd add three inches. Then, I'd draw an 8-sided shape around that, like an elongated stop sign. Make sure the angled parts are at 45 degrees to keep it simple. I'd do the same thing for the bottom-bow end, though the shadow trick won't work there, and I'd leave three inches extra on all sides. I'd trace the shapes onto 1/4" marine-grade plywood, cut them out, and prop them up on a bench parallel to each other and aligned on the same edge as the off-side outer branch, at a distance equal to the height of the horn plus five inches (2 for the bell end, and three for the bottom bow). Measure from outside corner to to outside corner along the length to get the dimensions of the eight side panels.
After laying out the side panels on the plywood, cut them out. You now have all the panels you need. I would then screw and glue 1x2 hardwood (poplar is a good choice) around the edges of each side panel. If you want to be fancy, inset this frame a quarter of an inch on the ends so that the end panels will be flush. Cut 22.5-degree angles along the long edges where the side panels meet. The lid would be three of the panels and the other five panels would be the body of the case. Screw and glue them together at the edges. Use deck screws, not drywall screws (which are too brittle) or cheap wood screws (which are too weak), and put screws every six inches. Drill pilot holes, and also countersink holes so that the screw heads will be below the surface of the wood.
Clamp the end panels to the body, and make a cut between the points at the opening of the body. Attach the (now four) end panels to the body and lid, using screws and glue.
Then, take a two-inch-wide strip of 1/4" plywood, and attach it around the entire rim of the lid, so that it fits over the body with a one-inch overlap. Sand all the corners to a nice rounded shape, and paint both halves inside and out with a coat of primer and a coat of exterior house paint. Attach the lid to the body with a full-length piano hinge, and then mount clasps (use at least four, and preferably six). Gluing and screwing wood trim around the hardware will keep it from getting scraped off. Mount chest handles at appropriate places, but screwed into the frame, not just the plywood.
For the padding, I'd cut blocks of polyurethane foam that will support the body of the instrument along the outer branches and on the front and back of the tuba body every except for the valves. Leave the bell and the valves in free air. If you can push the tuba within the foam such that the bell can contact the wood, put an inflatable ball in it when you travel to keep it separated from the end of the case.
I suspect the resulting case would weigh about 40 pounds or less, depending on your choice of casters, and it would go in the door of most big cars if you move the seats around appropriately. It would have no flat surface on which to stack heavy items, so only soft luggage will get piled on top of it. It would be oddly shaped, so that it would look like a custom case and not like a pile of generic electronic equipment (which is what an Anvil case looks like). It would be stronger than it looks, instead of weaker than it looks.
If you have the skills and desire to build it, it would be a lot cheaper (but not as nice looking) as a commercially made case. If your time has value (i.e., doing woodwork is not a hobby that you enjoy), then you'll find a commercial case isn't so expensive after all.
Rick "who does not fly with tubas but who knows how to build things" Denney