I was about to suggest that if his mandolin is always sharp, he’s not tuning it correctly.
Actually, DrFidelius hints at this in Post #3, and digs goes into more detail at Post #13.
In my long and storied life never have I heard of anyone confused by this subject before. The word is ‘mandolin’ in American, pronounced and spelled that way except for the makers of the devices who want to put a bit of snobbery into their product. Note that the Queen of All Snobs endorses the horribly incorrect spelling. Your ignorance indicates you likely have such misconceptions about other cooking devices named after musical instruments as well such as the xylophone and the slide whistle.
But you have since, as harmonicamoon - a man presumably well used to adapting musical instrument nomenclature to other purposes - has also entered the thread to confess his puzzlement. So the fact that you have never come across this problem before does not mean that it isn’t widespread.
For all we know, the aisles of musical instrument dealers up and down the land may be thronged with anxious cooks seeking vainly for vegetable-slicers. And the nation’s kitchenware emporia may ring with the sobs of frustrated musicians.
Won’t somebody *please *think of the children?
They’re sold at any serious kitchenware store like Sur La Table, as well as on Amazon.
I know “me toos” aren’t terribly appreciated, but this bluegrass nerd experienced the same dissonance. I clicked on the thread assuming it was about blades, but upon reading the first post thought it was apparently about tuning instruments.
We’ve got the slicer thing in a kitchen cabinet - my wife bought it a couple of years ago, but we never really found a reason to use it. Pretty much the same explanation for the instrument thing in the upstairs closet! 
Make sure whoever helps you is named “W”.
Ah, but my erstwhile ignorance was far more encompassing than you understand. Prior to this thread, in all my life I had only seen this device once or twice, and only at County Fairs, and I had never seen or heard any mention of what they were called. (Hence, my remark above that I now know how to ask about them at stores.) I never previously knew these devices by any spelling.
ETA: And I still don’t know what kind of dishes I might prepare using a xylophone, slide whistle, or any common woodwind. Stringed instruments, like a mandolin or a harp, are a little more obvious, as they can be used to slice hard-boiled eggs or other carbon-based biological units.
Good old Don Martin. Thanks, I remember that cartoon from the mists of my past. Obviously the xylophone is used to tenderize meat and the slide whistle is for basting. Woodwinds are less common in the kitchen save for the bass clarinet, more commonly known as a ladle.
That’s weird. I would expect that, over time, a mandolin would tend to go flat…
I suppose you could count me as additional evidence for your position, as I have never encountered confusion on this issue before.
I also had never encountered the word “mandoline” before, and had never before heard or seen the word “mandolin” used to refer to anything but a musical instrument.
That there is a word at all for those slicers that make julienne fries is news to me. Wikipedia says that word is “mandoline”.
I only came in here to learn what the OP meant by his mandolin staying sharp while his knives didn’t.
I’m surprised no one has mentioned, to avoid confusion this device is often called a “mandolin slicer” rather than just a mandolin.
Why would anyone want to slice up a mandolin?
Why we all still harping on this?
Calm down you guys, there’s no need for violins over a simple question.
Just as aside, I’ve noticed the same thing with my bow saws. They’re just your basic garden tool, but they’ve got some kind of wonder steel that will zip through log after log and stays sharp. Meanwhile, I’ve got pocket knives that need sharpening if I use them to open the mail.
My co-worker’s wife cut off a fingertip using a mandoline. Lots and lots of blood and they couldn’t re-attach the bit that was cut off. They did reconstructive surgery using some kind of cellulose material. The wound is tricky enough that she’s not allowed to replace the bandages by herself–she has to go to the hospital to have it done by nurses. Not fun.
The solution is obvious: Use your bow saw for cutting logs, vegetables, and opening the mail. Dump the pocket knives.
@blondebear: Yikes. Now I’m not so sure if I want one of them thar thangs.
Which is why I do the slicing instead of the wife and wear Kevlar gloves and use the food-gripper thingy whilst doing said slicing. Sucker is wicked-sharp.
Speaking of harps. They are a big-ass mandoline, eh?