All right, I always apply cork grease to the tenons (and to the top/end grain of the second section) because I’ve been told to. Why am I doing that? Is it to lubricate the joint or is it to seal the joint or some other reason? (Or is it like Shimmer; a floor wax and a desert topping?)
Thanks and best wishes.
Steve
It’s to keep friction from tearing your cork and/or cracking your socket if the fit is tight.
Steve, I can elaborate further, if necessary, on how the socket/tenon joint fit can become too tight (not unique to corked tenons), and why friction can cause the socket to crack when under pressure, but I figure all that stuff has probably been talked about in the past.
Yup. Pretty simple. 1, lubrication. 2, a degree of water-resistance.
As well as the earlier mentioned, as a secondary benefit one would assume the grease helps to achieve a marginally better air - tight seal, filling in any small indentations/irregularities between tenons outer cork surface and the wooden inner surface of the socket. It’s effectiveness in this capacity would depend on the quality and condition of the cork.
All of the above, plus I think it helps the cork stay elastic (don’t know about this, just speculation), and I can elaborate a little on 2toots’s post. Virtually all of my work is in vacuum systems – these are generally at a few trillionths of an atmosphere (10^-9 millibar). So it’s much more difficult to keep a vacuum than to keep something pressurized. People who work in what I would call low vacuum, a billionth of an atmosphere, generally seal their vacuum systems with O-rings. With a high-quality low-outgassing O-ring, the amount it needs to be compressed without (specialized vacuum) grease is about 1/5-1/10 what’s necessary on a dry O-ring. So with cork I’d expect that it’s a lot more forgiving when greased than dry.
Plus, as Loren said and everyone has corroborated, it’s just way safer. I lost a cork joint once when I absentmindedly assembled it without greasing it.
So do most people grease their joints at each assembly or just when the joint seems tight and not slipping together easily?
Just wondering.
Mando
Keep your corks greased, don’t wait until a joint feels tight or loose. Depending on the cork itself and the current fit, this might mean greasing evey time you assemble the flute, or only every 2-3 times. When in doubt, grease before assembly - it only takes a moment and it’s a lot cheaper than replacing a cork or repairing a cracked socket.
Also, use good quality cork grease, the Vandoren brand is reliably good, and happens to smell nice as well. I’d recommend NOT using “Doctor Slick Cork Treatment” as it provides insufficient lubrication for wood socketed instruments, in my experience. I’ve seen people recommend it in the forums, but it’s really not one of the better options for our instruments.
Loren - Do you happen to know who makes the cork grease that the Von Heune Workshop sells? Is it, perhaps, the Vandoren brand remarked as Von Heune?
And thanks to all who have added to this thread. I’m more enlightened. 
Best wishes.
Steve
Steve, I don’t know the answer to your question. The funny thing is, in the workshop we just used petroleum jelly on all the instruments - didn’t matter if it was corking new production instruments, re-corking instruments with torn or lost corks, or just cleaning up old instruments with dried out corks. This is largely because we (and by that I mean I, lol) cork lapped 50 or more tenons a week. Those little cork grease sticks wouldn’t have been cost effective, and when you’re doing production work, and open container of petroleum jelly on the bench is just quicker, easier, and won’t roll away.
The workshop is in one building, along with “administration”, and the retail shop is next door. I spent very little time in the retail shop, too busy making and repairing instruments lol, and never noticed what they had in the way of cork grease. I imagine there are only 1 few manufacturers in the who supply and brand for almost everyone in the U.S. But I could be wrong. The Vandoren grease is a little more expensive and may be made in Europe, but again, I’m not certain.
So there ya go, I’m of no help at all on your question. 
Like Loren, I use petroleum jelly on all cork lapped tenons both for repairs and on our own instruments, and have done so for many years now without any evidence whatsoever of any detrimental effect to the cork wrapping itself, as has been mentioned in previous discussions here on this forum. I find Vaseline the most reliable ( other cheaper varieties are often too thin/not viscose enough ). When you consider the laughable prices many music shops and suppliers charge for those miniature pots and tiny jars that do not last any time at all ?? I’m sure others will disagree, but until I see evidence to the contrary ( 5 years and waiting ) I am more than happy to employ this readily available, effective, inexpensive method.
Loren: But thanks for a peek behind the curtain…
All who are still with this thread: Do the same effects apply to threaded joints?
Best wishes.
Steve
And some of us Highland pipers use toilet bowl wax to grease tenons and hemp. A single ring of the stuff lasts halfway to forever.
With best regards,
Pfreddee(Stephen)
I use the tubes that look like little chapstick containers (and it’s actually not terrible when you get the two mixed up). I think they’re for clarinets originally? They’re not terribly expensive and last me a while. I don’t grease on every assembly, but maybe every week or so.
I saw a clip on the internet once on how to mke your own grease, so I followed it and filled a tin which used to contain Violin Rosin, with the mixture. It contained Patroleum Jelly and the wax from cheap tea lights, heated up in saucepan and mixed. I had to reheat it and add more Petrolleum Jelly as it set too thick the first time. I have been using it for a couple of years and its fine.
Although I have flutes with corks, I prefer tennons with embroidery cotton.
Personally I wouldn’t use that, Stu, although it is a traditional concoction. Paul Davies used to make his own with a mixture of rosin, beeswax (rather than paraffin wax) and petroleum jelly and gave me some once. The late Conor Moloney also used it. I dislike it because (due to the rosin) it builds up rather quickly on the tenon lapping and is also very inclined to being sticky rather than lubricative, especially in cool weather. I found that a few months of even sparing and not especially frequent use and I had to scrape off a thick layer of nasty, hydrogenated muck which was making the tenon too tight in the socket and sticky/hard to twist in and out. That’s a risk factor for socket cracks, and scraping the stuff off isn’t good for the lapping. I stick with woodwind supplies “cork grease”.
Like accordionstu, I prefer thread wrapped tenons (cotton). Use toilet ring wax on all of my flutes, cork or thread wrapped. Seals well, keeps moisture out of the end grain of the wood tenon, and lasts quite a while, I use it about every third of fourth time playing (very small amounts); during the summer when it is hot I use it more frequently. No ill effects noted after about 4 years of use. Also use it on the hemp wrapped tenons of my bagpipes. Prior to using the toilet wax ring seal, I would use a commercial beeswax mixture. Had a tenon swell once and stick to the point that I was unable to separate it (on a D boxwood flute). Had to let it dry out for a couple of days before I could get it apart. Switched to the toilet ring seal and have never had a sticking/ swelling problem since.