How best to eliminate LP warps

"No it is actually not, a wrapped record is stretched but all is depending on how bad the warp is"

optimize-

yes, that's what I envision what's physically happening. I'm thinking a  simple flattening during playback thru a VPI type outer weight makes more sense to preserve the LP, rather than any heating and prseeing/flattening of the disc?

Perhaps once an LP is warped, any attempts at straightening are technically(maybe not audible) compromising integrity of the groove? 

Because I'm a period press fan, I've got more than a few great albums, but they're real zingers-like a mogul ski run for the cartridge.

@lewm 

I think the premise behind flattening the LP by heat and pressure is the hope that the LP WILL return to its original flat shape, that the stretching represented by a warp, if it is indeed stretching, will be eliminated by a corresponding shrinkage.

Yes we might think and hope that shrinkage will happen.

Why should it shrink when we pressure it between two surfaces? It is not rubber.🤔

If you increase one, two or all three of the parameters temperature, pressure or time. It will only result in a bigger and thinner disc an it will never shrink back to its previous shape. Why should it? 🤔

That is exactly what is happening. The disc will be flatt (that is not a problem to achieve) but it's diameter has also increased by a very little bit when we apply as little force and heat we can get away with to just make I flat but the diameter will not magical decrease.

As I said it is small and something probably not something we can easily detect with small warps but the mechanics is the same. But if you have severe warped records you will also be able to flatten them out that part is not a problem to fix.

But you have now instead a severe wobbly grove that is not perfectly circular shaped. Yes you can only convert from one problem (warp) into another (egg shaped). When there is no shrinkage going on..🥰

I have first hand experience with a very warped record that I flatten out carefully over several iterations when I applied pressure and temperature during the whole night for each night and iteration when I did not get it as flat as I expected the first iteration. At the end I got it acceptable flat! (The iterations and time indicated that I didn't use to much heat so that it should destroy the record.) Yes, my happiness over that i had got the record flatter were shortlived when I saw the canteliver and cartridge work like crazy side to side! Never seen something like that in any of my 700 records and I concidered as still unplayable it looked as the needle should be thrown out of the grove, very disturbing. (Remember it were a badly warped record. So less warped will most likely give a less egg deformation). All the efforts was in vain. 🙁

Do you have any experience with record shrinkage? (Smaller warps will give smaller side to side movement but can be still OK and in tolerance, but it is impossible to know if it is little bit worse or not then it were before the warp event.)

@drbond , I have never measure the distance off center. I am not sure what for. Just watch your tonearm with a reference nearby. You can see the tonearm tonearm drift back and forth at 33 times per minute. That record? I'd guess it was somewhere around 0.6 mm off. The standard is within 0.2 mm. 0.6 is huge. That means the arm will drift back and forth 1.2 mm. 

optimize, You make a good point and it shows good thinking, but I question whether what you say is true for all warped LPs, because in many cases the warp you observe is compensated for by several smaller less visible warps in the opposite direction.  Let's call it "upward" vs "downward" warps.  This is one reason why trying to get around the problem with a central clamp won't work for both sides of that LP. Thus the LP itself has not lost its basic dimensions; they are just distorted in vertical space.  That should be reparable when you heat and flatten.  I don't doubt your story regarding the one example. 

Yes, you are right that there is "different" types of warps and severity of them.

The point is to get a better understanding of the material and how it works/act and flattening is not always the end goal and the assumption that we are done and all is going to be back to how it were only if we get it flat.. when there is other things happening and getting worse as a by-product. That we don't concider and take into account that is good that we know of and take it into account. (Oh, this record is to much warped or have a type of warp that makes that individual record "unrepairable" so it can be played again.)

Yeh the server warped disc experience I described before were a great educational thing for me that made me think about what really happened and how it works. When you have bigger warps then it is easier to see the actual effects of the flattening process. When the effects also will be greater.

I went into the project with the mindset that only I straighten it up to flat then all will be good and restored back to its original shape/state as a goal. And did not concidered any other factors that were a mistake from my side that I learned from.

And I probably think that many others also focus on to get it flat and think that it will be 100% restored back to its former shape. (But for smaller warps no one will notice any change or degradation even if they are there.)