Guy Clark likes what he calls "mailbox money". It's a term the Texan singer-songwriter, widely regarded as the doyen of a very large school, coined for songwriting royalties.

Although he has a loyal following which reveres his craggy delivery of the songs that emanate from his work room, a substantial part of Clark's living over the past 30 years has come from having his songs turned into hits, some major, some minor, by more-music-industry-friendly artists.

Johnny Cash took Clark's Texas 1947 and The Last Gunfighter Ballad into the American charts in the 1970s and later introduced Let Him Roll to a wider audience. Vince Gill had major success with Oklahoma Borderline, and recent Glasgow visitor Ricky Skaggs had a number one country hit with Clark's Heartbroke.

When not turning out songs, Clark makes guitars. He actually worked in the Dobro guitar factory, where that most rootsy of country slide guitar sounds is produced, in the late 1960s. But making guitars - or rather disassembling them - is where music began for Clark.

"In south Texas, where I grew up, the first guitar you get is a Mexican guitar from Parracho, a town where virtually the entire population is involved in guitar-making," he says. "And the first guitar I got, the first thing I did was take it apart and put it back together again. I built a few guitars in the 1960s, back when I was still living in Texas, and it's something that's always come very naturally to me. I just enjoy doing it.

I'm not looking to sell the ones I make, just to get better at making them. It's a form of therapy for me."

It was when Clark, a small-town boy from Monahans, moved to Houston via the Texas gulf coast in the 1960s that playing music and writing songs really became a passion. In those days, Houston was home to blues legends Mance Lipscomb and Lightnin' Hopkins and, inspired by them, Clark joined two more Texan legends-in-the-making, Townes Van Zandt and Jerry Jeff Walker, on the Austin-Houston folk circuit.

"Apart from the blues, it was all a bit Bob Dylan wannabe at the time," he says. "No-one was really writing to begin with, although Townes had written a couple of songs when I met him and as well as becoming a great friend for the next 35 years and the funniest guy I ever met. He taught me a lot. His use of language - I'd call it respect for the English language - I always thought was really good."

Right from the beginning, Clark's songwriting maxim was and remains: write about what you know. Emmylou Harris, who's sung Clark's songs, as well as his praises, since they met in the 1970s and who volunteered her harmony singing services on Clark's early albums, says that Clark has done more with the notion of "three chords and the truth" than any other writer of her generation.

This didn't win Clark instant success. He worked in television and as a photographer, as well as the Dobro factory and a guitar shop, during a spell in California while trying to make it as a songwriter. Then an old friend, Jerry Jeff Walker, had a US top 100 hit with Clark's LA Freeway, inspired by an aspect of California life that Clark had grown to loathe.

Walker also recorded Desperados Waiting for a Train, a song Clark had written about a character he'd seen hanging around his grandmother's hotel. Long regarded as one of the real gems in Clark's canon, this song introduced Clark to many British listeners through a perhaps unlikely medium - the former members of Captain Beefheart's Magic Band who were then trading under the name Mallard.

By this time Clark had settled in Nashville and, with illustrious help - as well as Emmylou Harris, Waylon Jennings, Hoyt Axton, several members of Elvis's band and Rodney Crowell were among those on the sessions - he had recorded two classic albums, Old No 1 and Texas Cookin'. With Crowell, Clark wrote She's Crazy For Leaving, which gave Crowell a big solo hit when he departed Harris's Hot Band, and, as a slow drip of carefully crafted albums followed, including Old Friends for U2's Mother Records label, Clark developed a taste for co-writing.

Aside from Townes Van Zandt's No Lonesome Tune and the traditional Diamond Joe, all the tracks on his most recent album, Workbench Songs, were written with a team of accomplices.

"I learn a lot that way," he says. "I mean, how could you not learn from Darrell Scott co-writer of the amusing, incident-packed Out in the Parkin' Lot? He's marvellous, a stunning musician, so creative and supportive of what you want to do. One of the things I really like about co-writing, though, is, when you write something alone, you just sit mumbling it to yourself, thinking: that sounds pretty good.

But when you write with someone else, you have to say it out loud. So it becomes oral, and then everything falls into place much quicker."

In addition to uniting him with Darrell Scott, Out in the Parkin' Lot, covered by country star Brad Paisley on his recent three-million selling Time Well Wasted album, has just earned a hefty amount of "mailbox money".

So is there any part of being a singer-songwriter that Clark enjoys more than another? "It's all part of the one thing, really. I love it all, the playing, the singing and the writing. The travelling gets a bit rougher as you grow older but I have no reason to sit home and write songs all day without going out and playing for the folks. And I have no reason to go and play for the folks unless I'm writing new songs. So these activities can sort of feed off one another, and there's no big spiritual plan, I just try to do the best I can."

Guy Clark plays the Queen's Hall, Edinburgh, on Tuesday, September 18.