When?
Before it was a musical instrument, the chainsaw was a medical instrument; the chainsaw, operated by hand to remove diseased limbs from living patients, was invented in 1785 by Scottish doctors, proving that the stereotype of Scotsmen being such drunkards that they thought a hand-cranked saw used to sever legs off of their living owners was a good idea is not a modern construct.
Who?
The gasoline chainsaw we use in music today was first developed in 1927 by Emil Lerp. That’s his real name. That’s the joke.
What and How?
Unless you’re crafting a sexual metaphor explaining what Metallica’s eponymous album did to the world of thrash metal music, the painful, genital-destroying, and disappointing saw blade of the chainsaw isn’t really the focus for musicians; the focus is actually on the two-stroke engine.
This is going to sound like some hippie rambling, but it’s the only way to articulate it without a physics lesson; everything has a frequency, and everything resonates. Everything. That’s why the glass breaks when the opera singer sings juuuuuuuuust right at it. It’s why the humming of the great “Om” makes the bones in your head vibrate in a way as to relax and reset your brain. It’s why I used to sit at acoustic pianos as a kid and strike sevenths and ninths with the sustain pedal down and try to count with my ears the number of other strings that were vibrating. This concept of the presence of music physically existing in everything is a major part of why I love music the way I do.
The vibrations of the world around us inspire musicians from time to time. I own “Just Stompin'” a recording of LaMonte Young and The Forever Bad Blues Band performing a song that is 122 minutes long. It takes up two cds, and it’s one track long. It’s not even something you’d want to listen to. But it’s worth mentioning here that all the instruments are tuned to the frequency of a fish-tank aerator that Young found pleasing(Fun Fact!: he finds nothing else pleasing).
Not everyone stops short of inspiration from mechanical objects, though. Some people go that extra length and learn to play and to eek out those coveted frequencies from things not purposed to be musical instruments, like in the case of Frank Zappa, a bicycle, or like in the case of James Hetfield, James Hetfield’s voice. Including the chainsaw.
Why?
There seems to be at least two reasons why. The first reason? JAPAN.
“JAPAN” is a good answer to a bunch of “why” questions: “Why are we eating at a medical-disaster themed restaurant?” “Why did a muscular and ultra-gay go-go dancer help me change my flat tire on the freeway?” “I tried to buy a Coke Zero in the vending machine. I got a used pair of Rainbow Brite panties instead. Why?”
Hearing it in this Shakuhachi Surprise song, out of context and explicitly listening for the chainsaw part, may make perfect sense. I particularly love this album, Space Streakings Sighted Over Mount Shasta, but it is such a noise-bomb of an album that a chainsaw part actually sounds subtle, and even easily missed. Glory!
Reason two of “why a chainsaw?” is a bit less subtle: You’re the band, Jackyl, and that’s all you’ve got.
There was a time when bands like Jackyl were the next big thing: basically hair metal without the glam. Trixter, Slaughter, Dangerous Toys, Kix, Bullet Boys, Saigon Kick… oof, it was tough time to watch Headbanger’s Ball. If you played any song from any of these bands other than “The Lumberjack”, I really couldn’t tell you which band performed it. Not even their hits. If this video was on mute? Before the chainsaw makes it into the frame, it could have been any one of those bands. But this chainsaw song, like it or not, made them stand out from the crowd.
“The Lumberjack” got Jackyl their opening act spot for noted dick-substituter and sex-metaphor enthusiast Ted Nugent. I can only imagine what those encores were like; did they carve labia out a block of wood, then shoot crossbow bolts into them? Maybe Jesse James Dupree(I know, probably not his real name…) used the chainsaw to fashion a huge Norseman’s Prick that The Nooge strapped on to a scaled-down Statue of Liberty. Did they bring up a puny nerd from the audience to try and pull start the chainsaw and fail, only to have Ted escort Tits McGee on stage to show the boys how to really pull? I’ll never know, because fuck Ted Nugent.
Thanks for rocking, chainsaw! Celebrate this week by turning a home appliance or small-cycle engine of your choice into an instrument of rock pleasure(sex metaphor is optional, unless you use a vibrator to play along to Steely Dan, which in truth is less metaphorically whimsical than historically accurate).
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Suggested Viewing:
pirategeorge.com 
I normally wouldn’t leave a comment like this, but I believe this mind-boggling BBRA entry deserves a “Da fuq?!”
It’s the mystery of rock!
Of particular note when considering chainsaws in Rock, Wendy O Williams of the Plasmatics had the habit of taking a chainsaw to a plugged-in guitar during “Butcher Baby”. To be honest the noise it made was probably the most tuneful sound the Plasmatics ever produced: