How warped can you get?

Ok, I should have looked closer at the LP before buying it. I was lifting a newly purchased copy of Renassiance Novella off of my cleaner and I noticed that the middle lifted quite a bit while the edge was still down. The surface looked really clean with no noticeable scratches so I decided to give it a test spin. I swear the cartridge is oscillating 1/4" in the verticle, but the playback is really good. I mean, it would be pretty hard to not to notice if Annie Haslam's voice was being distorted. I don't dare take the covers off of the woofers and have a peek.

So, I have to ask what is the most warped record you play successfully on your TT?
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I have an otherwise excellent copy of a John Klemmer Direct-to-Disk recording, that is warped like a potato chip about 3/8". Even with my record clamp, it is a nightmare. I can track it, but at the outermost groove, at the lead-in, it sometimes causes the stylus to leave the record slightly, but it doesn't skip. Once it gets in about 1/8" into the record, it plays well, even though the arm looks like a small boat riding the waves of the ocean in a storm. I keep this record, because it has some of the most excellent recording quality I've heard, and it is expensive to get another copy. I don't play it often, but sometimes I just get in the mood to hear it. This is the worst one I have encountered that I even tried to play.
Anybody ever successfully flattened a warp? I've read posts about putting a disc between two pieces of glass in a 130F oven for ten minutes or so. What do you think?
Ya I also have a couple favorite`s that are warped. I can track them, (VPI TNT JR / SME 309 / Benz Ruby H) with no change in sonics,with the clamp some still have a good dip. What concerns me is the cantilever on the Ruby it can`t be good for it. Thats why I use caution on those album`s I don`t know if will cause a shorter lifespan on the generator on the MC. David
Doug, I tried the heating the record between plates thing when I was in high school. Yes the record was flattened, and all the groove information was too. Totally non-playable after the heating. I then used it for a frisbee. It was a first pressing(when it was originally released) of Iron Butterfly "Heavy", their first album. At that time, new LPs were available for $2.99 each!

Maybe others have had better results, but that episode cured me from bringing any other records near the oven!
Tom, Thanks for the cautionary tale. I trust you were able to find another copy. A first pressing though... ouch!

I remember warnings to put the record in a cold oven and not to exceed 10 minutes @ 130F. Still, I wouldn't experiment on anything that isn't already scratched up.

I'm trying to remember what Frisbees cost in 1968. $2.99 seems a little high.
The only obvious trouble I have with warps is cueing. Once the stylus is safely in the groove I hear no warp-related problems.

Still, I don't like to see my woofers moving, and think of all the LF energy the electronics have to deal with! What does anyone think about a a low-pass filter? If it's a good idea, how early in the signal path should it go?
It should go in the phono stage, and many phono stages have them built in. However as any filter network, it has a "knee" with corresponding rolloffs. If the filter knee is set high enough to cover everything below 20Hz, it will have an effect up into the areas above 40Hz. This can compromise bass performance, since it is being partially filtered out. If the knee is set down below 10Hz, it may not be fully effective at some of the frequencies you want it to filter. It requires an educated design, based upon experience. There are compromises in everything.