Sparks fly in room 251 of the science building at SF State as Michele Bishop holds a foot-long piece of steel tubing against the whirling disk of an electric grinder.
The powerful hum of an electric motor adds to the cacophony of creation that fills the air around her.
A sharp, metallic clang of a hammer striking steel resounds loudly.
There is a pop and a hiss as the orange-blue flame of an acetylene torch comes to life.
A sigh comes from glowing, orange-hot metal as water cools its surface.
From a red-framed wheelchair he designed and built himself, Ralf Hotchkiss observes Bishop and 11 other students as they work in his Engineering 620 class -- Wheelchair Construction.
Like a symphony conductor with a perfect ear, Hotchkiss calls to Cathy Shin, a rehabilitation engineering technology student, as she pulls the handle of a drill press that drives a spinning bit into a piece of metal. Through the competing noises in the small shop, Hotchkiss tells her she is operating the machine at too many revolutions per minute.
"You can tell that it's running too fast just by listening?" Shin shouts back incredulously.
Hotchkiss, 47, adjusts his glasses as he nods to Shin, his bushy, light-brown mustache riding his smile.
The curly-haired father of one is technical director of the Wheeled Mobility Center that has been at SF State for six years.
Hotchkiss started the program 15 years ago after visiting Nicaragua and seeing several riders sharing one wheelchair. Hotchkiss says the cost of owning a wheelchair for paraplegics in developing countries is too great for most to bear.
So, with the help of people active in the disabled rights movement in Berkeley and USAID, a U.S. government agency, Hotchkiss started work on the project that would eventually spread practical, affordable wheelchair designs to more than 20 developing countries.
Students in the wheelchair building class at SF State construct chairs using methods developed by earlier classes and from other shops worldwide which Hotchkiss helped to establish.
One example of the low-tech technology transfer that has taken place comes from Africa. In many developing countries, ball bearings are a prohibitively expensive but essential element in affordable wheelchair construction. Students in Hotchkiss' class use an African inventor's less expensive yet equally effective idea.
Using nails that have had both ends nipped off, students line the inside of each wheel hub with them. Practically as smooth a ride as bearings, says Hotchkiss.
Sharing information is the main goal of the Wheeled Mobility Center's program. Students from Gaza and China have gone through the program, each bringing, and leaving with, new ideas.
But Hotchkiss says that for 30 years there was very little innovation in the design of wheelchairs. It wasn't because designs were the best they could be, but because one company, Ernest and Jennings, had a virtual monopoly on wheelchair construction.
"The standard Ernest and Jennings was the best chair we could get from the '40s through the '80s," Hotchkiss explains. "And the design actually slipped backward during that time."
After an anti-trust lawsuit against the company in the late 1970s, Hotchkiss says, the marketplace boomed. Within two years, over 20 new companies opened with radical new wheelchair designs.
Yet wheelchairs made in this country are still financially out of reach for the 20 million people who need them worldwide, Hotchkiss said.
Through the Wheeled Mobility Center, however, design modifications have traveled around the globe. Another example Hotchkiss gives is in countries where dining tables are low to the floor. This puts a wheelchair rider out of the loop at meal times. A design from China allows a rider to move from the regular seat of the wheelchair to a step-like seat lower to the table, enabling a person to reach what they want. This design is now built by students at SF State.
Those students exude a satisfied air as they describe their experience in the class.
"It's pretty fun," said Bishop, who is also working toward her rehabilitation engineering technology certificate. "After a long seminar when you're tired, it can be hard to get here. But it's really neat what Ralf does. It's a class you don't want to miss."
Shin, who has an interest in prosthesis design, says she didn't know anything about wheelchairs until a year ago.
"Go to any post-war country, where there are a lot of mines, and they don't even think about wheelchairs," Shin says, punctuating her words by waving a hammer in the air. "Ralf is 90 percent of why I'm in the class. He's been there and done it for the wheelchair thing. He is probably one of the few people who is doing both the technical and the practical. He's doing things with wheelchairs I want to do with prosthesis."
For Hotchkiss, satisfaction comes from sharing ideas and experiences with people from all over the world.
"The extent technology has flowed in both directions, from wealthy nations to developing -- but more so from developing -- is a gratifying thing," Hotchkiss says.
That innovation has touched him on a personal level as well.
"I've gotten to know and fallen in love with people from different backgrounds," he says. "I've seen people with significant disabilities raising children, staying healthy, doing amazingly well. They do so well with so little. It gave me no doubt I could do it myself."