Making cabinets and furniture for sophisticated corporate jets has its unique challenges. Weight is always an issue, space is limited and all materials must pass a burn test. And perhaps the biggest challenge is time. The aircraft owner doesn't want his airplane on the ground one minute longer than necessary.

One of the leaders in corporate aircraft maintenance and refurbishment is Duncan Aviation. Its Battle Creek, Mich., repair station performs completions of new aircraft, maintenance and interior work.

Tim Briscoe, manager of interior work, says that business has been strong over the past five years, both at Battle Creek and Duncan's headquarters location in Lincoln, Neb. Both locations perform major maintenance, completions of new aircraft and refurbishments.

Generally, a refurb includes three steps: exterior paint, avionics (communications and navigation electronics, including radios, radar, etc.) and interior completions. Aircraft owners try to schedule refurbs so that major maintenance and scheduled inspections can be performed at the same time.

Duncan divides its interior work into three sections: cabinetry, upholstery and finishing. All of the groups have to work closely together, particularly the cabinetry and finishing departments.

Brian Koski, team leader of cabinet work, says that space, weight and fire resistance all affect cabinet design. "Our customers are interested in saving weight for fuel," he explains. "Some aircraft are more weight-sensitive than others."

There are also burn certification issues with the FAA. Koski says that all veneers and virtually every material that goes into the aircraft is burn tested.

"In every place you find a combination of materials layered in a buildup, we have to duplicate that buildup and make three test samples," he says. In one such test, 1200 F flame is applied for 30 seconds, and three samples have to self-extinguish within 45 seconds.

Also, every material from Duncan's vendors gets a lot number assigned to it. If another shipment of the same veneer is received, it gets a different lot number. Anytime that lot number appears in a buildup, at some point in the refurb process, it must be tested.

"We also have to make sure the avionics are easily serviceable," Koski says. "If there's a failure with one of the components, they don't want to take half the airplane apart to get to it. We consider a quality job one that's not only beautiful, but serviceable. It has to be user friendly."

The design process involves several departments. "First, sales finds out what the customer wants, and our design department will develop a conceptual drawing," Koski says. "Once that's approved, it's turned over to the engineers, who will generate the shop drawings. Then the builder on the floor decides how to generate the cutlist and goes from there. If it has the time, the engineering department can give us a breakdown."

The cabinet building process starts with large 4 x 8 foot sheets of Nomex composite panel, usually 1/4- or 1/2-inch thick. Lightweight Nomex panel consists of two thin composite surfaces with a honeycomb in between. If the engineers want additional strength, they will sometimes use an aluminum honeycomb material.

"Typically the cabinet is fully constructed before we start applying veneer," Koski says. "Usually, we construct the majority of certain internal panels if it's getting laminate on the inside. We'll prelaminate some of the substrate before it is cut up and assembled."

Veneer can be applied directly to a Nomex panel after a light sanding with a dual-action sander with 80-grit sandpaper. Koski says that the pieces of Nomex are assembled with a panel pin, which is a hollow, serrated pin with small holes down the side. First, panels are butt-jointed and then preassembled with some CA glue. Next, they are drilled for the panel pins.

Once the holes for the pins are drilled, pins are inserted using a small metal bracket so the honeycomb isn't damaged. A structural epoxy is injected in the pins, which flows out into the honeycomb of the panel and creates a strong cabinet.

"Because of the nature of the material, fasteners have to be potted in. If we can plan ahead for that and put those inserts in prior to assembly of a cabinet, it's a lot easier than doing it afterwards when we have narrow compartments to reach into. We try to do as much of the preassembly as we can before we commit to pinning the final product together."

Some structural testing is performed in house. Duncan has guidelines on minimum pin spacing (3 inches) for constructing the cabinets. After assembly, veneer is glued on and hardwood trim is added.

Briscoe says that Kydex, an ABS plastic, is another material used to make interior structures where space is very limited, such as the front of tables. Fabric can be wrapped around the Kydex, which vacuum forms easily. Nomex panel is often used on aircraft sidewalls where there is room.

Duncan's new finishing shop in Battle Creek opened in January. Six full-time finishers work here, using two new booths. A prep station is partially enclosed and a spray booth, built by CMC, has walls and was originally intended for automotive finishing. Both are 100 percent downdraft.

"We try to do anything we can in the prep station without tying up that spray booth," says Brad Hewitt, team leader of finishing.

The finishing crew does light spraying on the bench, and a spray stain is applied in the prep station. Most sealer work, primer work and paint work is also done in the prep station. They try to ensure that a dust-free area is maintained in the spray booth so it can be used for clear coat application.

Hewitt says that the process typically starts out with a vinyl sealer, after sanding and stain work.

The sealer application ranges from eight to 14 coats, depending on the porosity of the wood. Sometimes a grain filler or case filler is used. For the topcoat, an additional 12 to 20 coats are applied. Polyurethane finish is used on all surfaces. Burn testing is also a consideration for the finishes.

"If they're building a cabinet with a half-inch substrate with veneer on one side and laminate on the other side, then that's exactly the way the burn coupons are built up," Hewitt says.

Woodworking experience is usually required for the cabinet shop. "We're looking for a strong background in laminating," Koski says. "We do solid wood trim, so solid woodworking skills are good, but our bread and butter is someone with a strong laminating background."

He says a good cabinetmaker should, within a year or two, be up to speed. "The thing that takes the longest is learning what you can and can't do in an aircraft, and we have a lot of experienced people in our inspection and engineering department that help us with that."

Duncan's shop has basic cabinetmaking tools, but no high-production equipment since all product in Battle Creek is custom. "Our counterparts in Lincoln are getting ready to put in a CNC router, but they're doing more on the production end," Koski says.

In Battle Creek, equipment includes a Powermatic jointer, SCMI S50 planer, Jet band saw, Delta table saws, Delta pin routers, Jet disc sanders, Delta edge sanders and Sunhill Machinery widebelt sander.

"A lot of the guys have little detail saws," Koski says. "One thing that the aircraft cabinetmakers use that you won't find a lot of in other shops are pneumatic tools. We use a lot of angle die grinders."

He explains that if you need to take some material off somewhere, you can slap a 2- or 3-inch disc on an angle die grinder and whiz away at it at 20,000 rpm. You can follow a close line and yet do some delicate work, especially when a cabinet hasn't been fit into an aircraft yet. "You can take a little bit of material off so it does fit," says Koski.