How best to eliminate LP warps


I own about 2500 LPs, and I like to think they're flat.  Furthermore, I espoused the view that warped LPs ought to be discarded.  But lately I have found 2 or 3 of my LPs that do have warps but sound too good and are too precious for the music recorded on them to throw away.  So I am in the market for ideas on how to remove warps.  I am aware that there was a device on the market that looked like a large waffle maker, to be used for warp removal.  I think Furutech made it, but I never see it advertised these days.  I am also aware of the DIY method of placing an LP between two glass plates and heating the ensemble.  The question there would be how hot and for how long?  Any suggestions are welcome, especially opinions on the efficacy of the Furutech.  Thanks.  Please no comments on vacuum hold down; I think it's a great idea but none of my five turntables has that feature.

lewm

@mijostyn

"You simply adjust azimuth until the hourglass stands up perfectly straight. It hardly takes any practice once you get the set up down."

It seems to me that the adjusting eye or lens needs to be perfectly normal to the cantilever, which means simultaneously adjusting two right angles. I doubt if anyone can do that without an adjustable, stable platform, repeated accurate measurements, and statistical analysis.

Whereas anyone can listen to a dozen challenging, flat, LP’s and set for the ’best’ sound and take measurements. Then throw away the two top and bottom measurements, and set to the mean or the median as indicated. At least, anyone with accurately calibrated azimuth-on-the-fly and a statistical background.

YMMV

Actually, this whole discussion leads me to the conclusion that we are chasing a ghost. As @optimize notes, there are irregularities in LP manufacturing, whereas we are treating the LP as identical precision instruments that just need to be set up via the cartridge.

Instead, we should be looking for a tonearm that can be easily and finely adjusted on the fly to suit each LP as it is played. Preferably, the tonearm should have a precise measuring system built into it’s adjustment mechanism, so that these numbers can be noted on the record sleeve, and the adjustment made in two or three seconds prior to each play.

And, of course, we should remove warps and dishes from the equation, coming back to Lewm's point.

All of this discussion about azimuth involving USB microscopes, test disks, oscilloscopes, Fozgometers, hour glasses, adjustment for each disk and such leaves me LOL. Better to put more faith in one’s hearing.

Assuming you have easy adjustment for azimuth, and if your stylus is symmetrically placed, adjust roughly for level by matching your cartridge parallel to its reflection on a disk. It doesn’t take much of an eye too get very close. Use a flashlight and/or thin mirror if that helps. If the stylus is a bit crooked, use a mirror and do the best you can to have the stylus as vertical as possible.

Then put on your disk with the best, widest, soundstage in your collection. Listen carefully as you adjust azimuth just a bit, first one way than the other. If the soundstage widens, continue slowly in that direction. If it doesn’t widen you’re done. If it does widen continue in that direction to the max soundstage.

it's scary to see your expensive cartridge and stylus on a badly warped record.

@terry9 , we already established that the two channels can have very different cross talks. (Peter Ledermann) So, by taking measurements you can assure that your stylus is digging into your records. If you want to do it this way then confirm it with a visual inspection, OK. I think it is a waste of time and money. Money that would be better spent on a USB microscope.