Which is why he is still working, even as, year after year, he mulls the idea of retirement.
"My biggest fear is that I'll be bored to death," he said at first, then amended, "My biggest fear is that my wife and I will argue all day."
For 50 years, Sommer has reported to work, and the world changed as he labored at his bench.
"In 1964, there were so many tool and die shops, I could have gone anywhere," Sommer said. At Tottser's, every bench was filled and there were two buildings. "We had a night shift and helpers," he said.
He outlasted the manufacturing shift to the South and to China - now some of that work is coming back to Pennsylvania.
Bernard Reichart, a German tool and die maker who started working for Tottser in 1958, bought the business in 1963, a year before he hired Sommer.
It's a male-dominated industry, but Sommer now works for a woman, Reichart's daughter, Linda Macht, the owner.
Technology has changed, as well. "You have to be computer literate," Sommer said. He's not, but his skills are nearly irreplaceable, even with the changes that come through computer assisted design, and a wire machine that helps with the precision cuts.
"You know what, we need him," Macht said. "As long as he wants to work, he has a job."
Not that Sommer wasn't fired - multiple times.
"He and my father had a love-hate relationship," Macht said, laughing. "My father would bring in the want-ads and circle [other positions].
"He'd say, 'You're fired.' And Don would say, 'I'm not leaving.' And Dad would say, 'I'm not paying you' and Don would say, 'I don't care.' "
"He got fired and he wouldn't leave," she said.
"He's stubborn. He wants to do it his way, and he wants to do it perfectly. But people won't pay to have it perfect. We had a work-around. We let him make things perfect.
"If we didn't make money on the job, it was, at least, perfect," she said.
What's perfect in the tool and die business?
A tool is attached to a press that slams a metal sheet into a die, shaping and cutting the metal into a part for an engine, or a stove, or a car door.
Sommer makes the indentations and protrusions that shape the metal. They must be precise, the tolerances exact. But that isn't enough for Sommer.
They must also be polished and perfectly square on the outside corners. They must be beautiful, even if they are only going to be attached to a stamping machine in some factory's back room.
"Some of our customers only want Donald to make their tools," Macht said.
Tottser Tool & Manufacturing earned its revenues from the auto parts industry, with Sommer and others fashioning the tools and dies that created metal parts for doors, roof panels and tailgates.
In 2003, Budd Co., which had Ford contracts, shut its Philadelphia plant. In the next five years, other auto plants closed.
Then the recession hit and employment at Tottser went from 60 to 25. To survive, Macht opened a second factory in Nashville, near Southern car manufacturers. When work gets too busy there, it gets sent up here.
Sometimes Macht outsources tool and die work to China, because it's cheaper. And sometimes, the work is mediocre and Sommer needs to fix it.
Sommer said he finds fulfillment in his craft.
He's proud of the white apron he wears. As dingy as it gets, it is the doctor's coat of manufacturing, denoting the skills and finesse he brings to the job.
"It's not boring and monotonous," although other jobs in manufacturing can be, he said. "You use your brain and you use your experience."
In February, to celebrate Sommer's 50 years on the job, Macht and other top executives picked up Sommer and his wife in a limousine and drove them from their home in Mayfair to an expensive and well-deserved steak dinner in Center City.
"This company educated me," he said. "They fed me. They paid for vacations at the Jersey Shore, presents under the Christmas tree. I feel blessed."
These days, there are no apprentices standing by Sommer's side at Tottser to learn his skills. Tottser's two other tool and die makers are both over 55.
What happens when they retire?
Macht jokes that Sommer and the others aren't allowed to quit, but she doesn't have a plan. "I can't make that investment in people and equipment again," she said. "Young kids don't want to go in manufacturing."
None of Sommer's four children, all college graduates, work in manufacturing. He's glad they don't.
"It's a dirty job," he said. "They all work in air-conditioned offices. It's dangerous, too. I didn't want my kids to do this."