The names of Flip Scipio’s clients — Paul McCartney, Bruce Springsteen, Bob Dylan, Jackson Browne, Ry Cooder, and Carly Simon among them — are testament to him as a guitar technician.

Other names you’ve never heard of are testament to him as a person. They are the names of soldiers in Afghanistan, whose music he also enabled. Not that he even mentions it until it comes up in conversation at his Aquinnah home.

He says he was outraged when he got an e-mail from a soldier over there, asking for guitar strings. Bad enough that private contractors to the U.S. Army were driving around in armored Hummers while regular troops drove unarmored ones, but the military could not even provide guitar strings for the guys.

“So I made a little package and sent it in the post,” he explains. “Then I hooked him up with a friend of mine who owns a string company, and they sent a big care package.

“Then there was another player who’d busted the neck on his guitar. Only in Afghanistan could you bust a Fender Telecaster neck, those are almost indestructible.

“So I had a neck that used to belong to Bruce Springsteen. I made it so it would fit on his guitar, and all he had to do was put it in the guitar and string it up.”

In return, he got to know a little about the men, like how they came to be in the Army and what music they played (Santana). After he got out of the Army, one invited Mr. Scipio to a party in Texas to celebrate. He could not attend, but he’s happy enough to have spent “some time making these guys realize people here do know you’re alive and we can give a little help.”

He recounts the story in the same understated, somewhat self-effacing way he talks about everything to do with himself, his customers and his work. Like none of it is at all remarkable.

Others might beg to differ. Mention his name to one of the Vineyard’s better guitarists, and this is the response: “Wow, he’s the guitar maker to the gods.”

Which is not quite correct. What he mostly is, is the guitar fixer to the gods, although he also makes very fine instruments. One of his guitars, the first one he ever made, the one he plays himself, is 28 years old now, its lacquer a bit battered and cracked. Over the years it’s been in the hands of the likes of Paul Simon, Jackson Browne, and the legendary Dutch guitar hero Jan Akkerman. It sounds gorgeous.

But Mr. Scipio demurs. The bracing is a bit heavy and the intonation’s not quite right. This is not his modesty speaking, it’s his perfectionism.

Flip Scipio admits a tendency to self-criticism. And obsessiveness and control-freakery. But then, those are the very attributes which make musicians seek him out. Ultimately, they are the reason someone has just made a documentary movie about him.

At the start of the documentary, Talking Guitars — which shows here at the Martha’s Vineyard Film Festival next week in Chilmark — Jackson Browne and David Lindley are chortling over Mr. Scipio’s perfectionism.

Mr Browne reads aloud Mr. Scipio’s written description, on a blueprint, of the imperfections of a particular instrument. Giggling, he calls it “the commentary and document of a disturbed individual.”

Then, more seriously, he goes on to talk of Mr. Scipio’s capacity to fix anything.

“In pursuing this kind of excellence, there’s really nothing that’s closer to the music than getting the instrument to work,” he says.

Few people, the testimonials in the documentary show, do that as well as he does.

The movie claims Mr. Scipio began fixing guitars when, as a teenager in Holland, he accidentally smashed his grandfather’s prized mandola.

In truth, that had not much to do with it at all.

“Really it was that growing up as a scared, anxious little kid, playing a guitar or holding a guitar or working with a guitar was kind of my little blue blanket. My little teddy bear. Something I felt comfortable with and didn’t feel threatened by,” he said.

But he was too shy to say that in the movie.

As a teenager he liked to play, but didn’t think he was much good (he’s actually very good), and so determined quite early to make his way by fixing instruments.

Those around him in Holland — although he does not directly say so, especially his father, a successful businessman — doubted he could make a living at it. And he found the instrument-making scene there not very helpful. So he left the country.

To cut a long, peripatetic story short, Mr. Scipio eventually found work with several of America’s better lutheries. First with Bozo Podunavac (best known as the guy who made Leo Kottke’s instruments) in San Diego, then with Guild Guitars in New York and then at Mandolin Brothers on Staten Island, where he was in charge of the repair shop. In 1995, he struck out on his own.

He moved his operation from New York to the Vineyard in May (he is married to Mitzi Pratt, a bookbinder and longtime Island resident).

Unusually, he gets as much satisfaction from fixing instruments as he does from building them.

“Most guitar repairers want to be guitar makers,” he says, “and they do repairs just to make bread and butter, which is completely the wrong attitude because it means they’re not putting their heart and soul into it.”

What’s more, these would-be guitar makers often try to overwork what they’re repairing, approaching them as if they were modern instruments, which, like “swiss pocketknives, do everything.

“But some guitars only do one thing very well. So it’s this kind of obsession, where you know there is something good in the instrument that is just not coming out, you just have to find out what it is.”

While his reputation means he gets to work on dream guitars, (the day of the interview there is an exquisite and rare d’Aquisto on the workbench), he gets joy too from fiddling with lesser instruments.

Thus his workshop also holds several garish, cheap, 1960s vintage electrics which might have originally cost “a hundred, bucks at Sears,” but are easy to work on.

“They look hilarious and they’re really good,” he says.

Function is more important to him than form, and not only with instruments.

“It’s like cars,” he says. “If you find a good mechanic, you stay with that. We drive an old Volkswagen because we really like the guy from Bug and Bus. What he fixes, we drive.”

It’s an attitude a lot of his clients share. He once had to do a rush job for Jackson Browne; in one night available, the only way he could make the instrument playable was to pull all the frets above the twelfth.

He gave it back to the artist, recommending more comprehensive work later, after his tour.

“And a year and a half later I’m in New York, and there he is playing the same guitar, and the frets are still out.”

Likewise, he was commissioned to make a one-off, electric instrument for Paul Simon. “So I screwed the thing together in two hours, then spent a day dickering with it, and took it to him as a work in progress. Paul liked it, and I wanted to take it away and paint it and make it look nice.

“And he was like ‘No, no, no. This is it. Go away. I’m going to record now.’

“So I wrote my name on it with a sharpie, and he plays it everywhere.”

Again, when Slash, from Guns N’ Roses, snapped the neck on his favorite Gibson Les Paul, it was a rush job. He reckons he got it because “I was the only idiot who picked up the phone at 2:30 a.m., when Slash was screaming.” The repair was effective, but there was no time to make it look pretty.

“Now, people tell me, Slash loves that scar.

“When I think of how crazy some people send themselves trying to make it look perfect, it makes me laugh,” he says.

Top flight musicians look upon their guitars as tools. What they care about is the sound, not the look.

If there is one job which made Mr. Scipio’s reputation, it was probably the 1993 commission to fix Paul McCartney’s bass — the one he used to play with the Beatles.

“After I did that,” he says a little ruefully, “people started calling me up for interviews. I sort of barricaded myself in the shop; I somehow got on all these Internet lists of Beatle fanatics. It drove me crazy.”

The story is that he got a phone call, asking if he knew anything about German Hofner basses.

“I said, unfortunately, too much. I have to fix those things all the time. They sound great, but they’re just awful to work on. I heard somebody laugh, and I think that’s why I got the job,” he recalls.

“It was an extraordinary, weird experience. They flew it over on the Concorde; it came with an armed guard, although I didn’t know he was armed until later when someone said, ‘Man he’s a real tough guy, he’s always got guns.’ ”

The guard was under instructions not to let the precious thing out of his sight, so for two and a half days Mr. Scipio worked with the man peering over his shoulder.

“Actually, I really had a nice time talking to him. He was a Cockney, smoked cigars, told great stories.”

About six months later, he got a call from Singapore. It was the security guy. Mr. Scipio affects a Cockney accent as he quotes the man: “Paul just played Paperback Writer and he played the note we were all scared of, and he gave me a thumbs up. We’ve done it mate, we’ve done it.”

“And I’m like ‘what is this ‘we’, white man?”

Mr. Scipio had never talked about it in any interview before this one, although word had leaked out almost immediately, despite Mr. McCartney’s insistence on secrecy, because “the guy I worked for was the biggest publicity hound in the world and he called everybody.”

The guitar man himself is quite the opposite. He notes that although he has a Web site, “I can’t put anything on it, because I don’t want to use peoples’ names to further myself.”

His reputation was entirely based on word of mouth, at least until now.

Which brings the story back to the documentary about him.

Its history goes back, indirectly, to German director Wim Wenders’ critically acclaimed 1984 road movie, Paris, Texas, for which Ry Cooder provided a haunting sound track. Thus began an artistic relationship.

Then, in 1996, Cooder gathered some of the greatest stars of Cuban music from the 1930s, 40s and 50s for his enormously successful album Buena Vista Social Club, which subsequently became a documentary, directed by Wenders.

“At that time,” said Mr. Scipio, “I was doing a lot of work for Ry Cooder. So Ry calls me and says ‘I need some help.’ We’re going to shoot it in Amsterdam, because I like playing in Amsterdam.”

Cooder needed someone to prepare all the instruments. It helped that Mr. Scipio spoke Dutch, English and some Spanish. And when he got there, in the hectic midst of it all, one of the camera people kept trying to talk to him. It turned out she was Dutch documentary maker, Claire Pijman.

He didn’t believe it when she said she wanted to make a film about him. He said no.

“I couldn’t imagine someone wanting to film this goofy thing that I do,” he says. He also was averse to the idea of trying to rope in his various famous clients.

“I didn’t want to ask anyone for anything,” he says.

But Ms. Pijman was determined and she approached a lot of big people to talk.

“Springsteen and Dylan didn’t even answer, but Paul Simon did and so did Carly Simon and Ben Taylor, and others.”

Then there was another obstacle. Ms. Pijman got pregnant, and produced three children in quick succession.

“But she fired it up again and between 2001 and now she made several bits, some here on the Vineyard, some with my folks in Holland, old customers in Holland, some in New York,” he says. Wim Wenders was kind enough to allow some of the Buena Vista material to be used.

Typically, Mr. Scipio was concerned about how the movie would sound. He’s very gratified that Ms. Pijman did it all on 16 millimeter film, not video. “Film has better sound,” he says.

The film is doing the rounds of film festivals and a distribution deal has been finalized for Europe, although not yet for the United States.

And the reticent Mr. Scipio is happy with the outcome, which is about his craft and about music.

It’s a funny thing, he says, but in a way he does not feel like he’s watching a film about himself.

“It describes this persona that I don’t know, because when I work I’m not conscious of what I am.”

Everyone else in it, though, seems to know exactly what he is: calm, modest, grounded and dedicated to making the music work.

And his favorite part of the movie?

“Well, the most hilarious thing is the hook for this film — that I busted my granddad’s mandola — and that fixing it’s what got me started.

“And it’s still in a box here.”

In pieces.