Thanks for the tip Cubitt!
@Denny:
Michael’s last visit to C&F was sometime early last year and optake’s last visit isn’t even recorded any more lol… It’d be darn hard to get in touch with either of them, so that doesn’t really help me much…
I know a couple of whistlers who are acquaintances here, but they don’t know much about flutes 
It was a perhaps too-clumsy expansion of my point that we hear subjectively, and sometimes faultily, with or without the benefit of slides.
I’ve had a few Casey Burns slideless flutes and found them quite tunable. I would play it at a centimeter out, no problem. But yes, fluters (myself included) tend to be sharp, and the conical flute itself is by its nature/design out of tune. The player has to tame the intonation of any flute to minimize its impact.
And that’s the final analysis, really. Flutes don’t regulate themselves.
Flutes don’t play sharp,. players play sharp.
And some flutes, although they may look attractive in the sales ad, don’t play at all. After some experimentation today, I’ve decided that I own two of those flutes. I think that I will plant them in the garden for the squirrels to chew on.
One of the things I’ve been doing lately is occasionally making flutes with much longer socket and tenon joints, so that players have a wider range for tuning without having to go for a tuning slide.
Mine are pretty long to begin with, compared with the originals. I recall that many of the Prattens and Rudalls had tenons in the 27-29mm range. My regular tenons tend to be around 33mm. But occasionally I’ve gone up to 40mm or more with no detriment to the instrument and certainly more tuning range. In blackwood there is no danger of tenon compression as the wood is tough, and I tend to leave my tenons a little on the thick side anyway.
Remember that if one plays sharp, one can also flatten the flute by rolling the embouchure towards you. Some players play with the embouchure edge lined up a little farther than the fingerhole centerline. I find that lined up right at the centerline that my flutes play sometimes a bit better to some (myself included).
Occasionally one has to make adjustments to the flute itself - as some players habitually play sharp or flat, compared my own pitch center. Grey Larsen is one for example - so its certainly not a sign of playing poorly! Its just the way it is. So if someone gets a flute and it plays too flat to them, I simply deepen the socket and add length to the tenon (2mm each makes the flute 4mm shorter which is a bunch, and can sharpen the flute by 10-20 cents). If the flute plays sharp, I either swap the middle joint for a longer one, adding length, or fit a slightly flatter head joint. But most times my flutes play spot on for the ones who get them.
Casey
Tell that to the unlucky owners of flutes that are outside adjustment range for concert pitch regardless how they’re played..
The thought of playing out of tune in sessions and not knowing it bothers me. I may well do it. But I don’t see how telling me that I need to adjust my tuning slide would help. I would make it sound just the same as before by rolling in or out a bit. Echoing mutepointe’s point, it is me and my ears, not the flute. Actually I don’t think it is a big problem for me - though early on an experienced player did start a conversation about cork position that I later realised was a hint that my second octave was sharp (me, not the cork).
Playing one of Casey’s flutes along with ‘fixed pitch’ instrument I have only had to ease the tenon open on a very hot day because I was rolled in too far. If a room is colder than is comfortable to sit in I sometiems find I have to roll out more than I like. It is the tone that suffers because I am working near the extremes of how much the hole is covered, not the pitch. It feels like hard work.
How do recorder players manage ?
(edit was for a typo)
Recorders, like whistles, don’t have embouchures; some tenon adjustment is possible, but the pitch doesn’t go up and down with rolling in or out - a good recorder should be more or less in tune with other instruments of fixed pitch.
There’s two issues with tuning, I think; being in tune with yourself - several posters have mentioned upper register sharpness, or lower register flatness, etc. - which implies that, even when playing solo, the flute (you, really) are not playing in tune. Sometimes it’s the flute (old German flutes, say..), and you have to learn to lift the flute on specific notes, and roll in on others, and vent keys, etc. Or say screw it, and sound like one of the old records where no one plays in tune, but it sounds cool anyway.
So, the first issue is really making sure that you/your flute is in tune when you play solo. Playing with someone else, then, becomes a bit easier, and I think that’s where the slide becomes important, since you adjust the slide up or down slightly without modifying your already in-tune-with- yourself embouchure. There’s no real reason why slideless flutes that have allowed for longer tenon movement won’t do the trick, too, but IMO slides make it easier and do less harm to the internal tuning as you slide out.
So the second issue is being in tune with others, and at varying volumes. Sessions get dicey, because everyone thinks they are in tune - especially fiddlers(!) - who are often not. Most of the time, if things are really loud and if you hear yourself too clearly, you’re playing sharp. Several people have given great suggestion (sit next to a player that’s as close to in-tune as possible, sit so that you can hear your instrument as it bounces back to you, and several others I’ve forgotten).
But I go back to my original comment - if you’re in tune with yourself, and - as far as your ears can tell - in tune with your neighbor, don’t get louder to match the room volume. Chances are you are loud enough - have someone record a session, and see if you can be heard. It all becomes an acoustical quagmire; you try to play louder than you ordinarily do, and that changes your well-practiced relationship with your flute, and that changes your tuning.
So if a recorder can use tenon adjustment to cope with changes of temperature then using the tenon on a flute, which also has embouchure control, should be workable shouldn’t it ? Slide or tenon the internal tuning of the flute will change, so it won’t be quite the same embouchure. I have very similar flutes one with and one without a tuning slide. I do use the slide but I am surprised at the importance placed on it in this thread, since with or without it the main considerations of Gordon’s post above still apply. And I find Nano’s post about out-of-tune fluters worrying and depressing. It’s not the first time someone who knows what they are talking about has said that.
There are two reasons I prefer a tuning slide: It provides a more precise seal against air leaks when pulled out and it usually implies a metal-lined head which I believe gives a much better (and louder) sound.
Of course roll has an affect on pitch, but as it is mutable, roll doesn’t negate the instrument’s overall pitch established from one slide position to another. So if I’m overall flat, I push the slide in until pitch is as dead-on as I can get with tones I want and that I am most likely to play in my own roll-range’s average position, taking octave adjustment into account. Likewise vice-versa if I’m sharp (personally, usually I tune initially to G, less frequently A). But after that, yes, then we must mind the roll of the headjoint, but in my world overall pitch comes first. There’s no point to making minute pitch corrections if you’re out of tune in the first place. There are a number of combined things at play: in overall tuning, there are the slide’s and the headjoint’s fixed positions, and that of the stopper; and in tuning on the fly, there are such things as roll, embouchure, lower jaw, air stream pressure, and some crossfingering options. None of these is sufficient unto themselves as none of them operates in a vacuum. They all come together, interdependently.
Look, the last thing I want to do is make people depressed over imagined problems. What I am trying to do is point out that we have a broad range of factors affecting flute tuning and intonation and thus, in having many options to help get the job done in the big picture - that is to say, how it all sounds when you’re actually in the trenches and playing - arguably, having that wealth is good news. IMHO a fluteplayer is best served by a holistic approach to tuning and intonation, and that in having options, it’s good to use them as they serve and be flexible, not stiffnecked.
Is there any reason not to have a tuning slide? Other than not having it on a particular flute or some additional cost, it seems like it doesn’t really have any draw backs.
IMO the only drawback to a well-made slide that is in good order is when one’s budget counterindicates it.
Oh yes, I wasn’t arguing with that.
To clarify my concerns. I can adjust to the equivalent of a few millimetres worth of slide adjustment just by how much I cover the flute (lips, jaw, ‘roll’ combination) and so far as I can tell I do it automatically to play in tune. Something has to be changed on the flute when it gets hard work (as when playing with a 15 cents flat recording carelessly taken off vinyl). But that adjustment is enough to sound well out of tune if I did/didn’t do it when I shouldn’t/should have. So if my ears were not telling me I am consistently sharp and someone else had to tell me then the chances are I was ‘hearing it wrong’ and would extend the slide but then adjust myself to hear the same way as before. So my quibble is with the ‘solution to consistently off flute player is tell them to adjust their slide so woe is you if you don’t have one’.
Understood. Get one anyway. 
But no, seriously, if you’re able to play in good tune by corrections and with no slide, good for you! Not having a tuning slide gives me the heebie-jeebies, personally. 
Another thought is this… the few flutes I’ve tried without slides were fairly on-pitch when the tenons were fully closed; this also helps negate internal issues brought on by the gap of a pulled-out tenon. Therefore, the only adjustment possible will be to flatten the pitch by pulling out, never to sharpen it. Slides, OTOH, are generally set out a bit and if necessary (although rarely needed), can be sharpened by bring it in or closing it. The thin metal of a slide makes a minimal disruption, which is what Terry’s minimal disruption tenon idea is all about. I’ve never tried it, so I can’t comment on it, but the idea is sound. A normal tenon, pulled out too far, will affect the overall tone and tuning of a flute much more-so than a slide.
I deliberately left out the effect of rolling in or out, as that, IMO, gets into other issues besides pitch adjustments, such as tonal choice. Minor adjustments are often necessary - we do this without even thinking once a flute is very familiar - but if you roll a flute way out to raise the pitch, or way in to lower it, you are losing control over tone control for pitch sake. A slide helps avoid this - if you tend toward sharp playing, or your flute does, the slide compensates without you changing completely whatever angle sounds the best.
As for worrying about playing out of tune when we think we’re in… it happens. It happens to good singers, too - that’s what good monitors are used for when there’s lots of volume. Without it, people sing off a bit. More experienced singers, and fluters, learn how to find the pitch even when they can’t quite hear themselves. The Beatles were remarkably on-pitch and in harmony at Shea Stadium; they were very well rehearsed!
The tuning slide is not necessary. Flute were played for decades before these were even developed. Alternative pitches were possible through using alternative upper middle joints of varying length. The tuning slide eliminated this necessity partly. Its primary function was to allow the flute to play at several different pitch centers, necessary due to the wide range of standard pitches at work in the 19th century between one orchestral setting and the next. Rudall even added another feature where the cork position was adjusted towards the embouchure as the slide was pulled out farther and flatter, to preserve the internal tuning of the flute.
But then came Standard Pitch which most everyone uses now. Thus the range of tuning required is really a lot less. Any gap in the tenon area will have little or no effect on tuning in the first few octaves which is the normal working range for traditional flutes and Irish music - so this is another worry you can dispense with!
As to whether or not a lined head improves the tone - this depends upon the flute and who makes it. Some of my best flutes have been without any tuning slide.
Casey
I dunno, Casey…while I get your point, I must say I’ve had to adjust at different times for differently-pitched boxes, uilleann pipes, or stringed instruments where it would be easier and more considerate for me to tune to them, than vice-versa. And they’re all supposedly hovering around A440, but in fact they can be off - some substantially so - in their own little pitch centers. I think there’s no question of this, or I wouldn’t have to be adjusting so, at times all at the same venue. Maybe I’m just that poor of a player that I think I need the slide, but I can assure you in no uncertain terms that it’s saved my bacon plenty of times. I for one am quite glad to have it.