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

@slaw Don’t have a picture yet. I’m still finishing the DIY air bearing tonearm - just installed the Koetsu, and it sounds even better than before. My platter has a 0.008" recess for the label, so to implement the reflex clamp I needed a washer to correct that as well. My first attempt is a 3" diameter black Delrin disk, whose outermost 0.25" is 0.008" thick to correct for the recess. The disk then rises to 0.055" thick at the spindle. Flat side is down, obviously. Design is after "Niffy" at DIY Audio.

@mijostyn Your intuition is flawed. It works as indicated.

@mijostyn A spindle within a Bearing Housing and rotating being guided by Bush Parts with excessive wear on the inner walls will allow for the Spindle to take on a eccentric 'off axis ' rotation.

As said it would be good to know if the device was able to detect this being present.    

Two mechanical comments on warp removal.

1. Sometimes you just want the record flat for recording purposes. I have used small pieces of transparent tape with mostly good results. I tape over about half the lead-in-groove width and adhere the remaining tape to the vertical edge of my platter. This usually moves the warp a few inches away so that more tape is required. If more than three pieces of tape are required it’s usually not worth the effort as the warps will just continue to appear. Extreme care must be used in placing in the stylus into the first track to avoid catching the tape. I use the arm lifting mechanism to lower the cartridge.


2. Rather than using a soft foam washer under the record to reduce warps I use four small pads near the spindle under my rubber record mat. Their height is roughly 1/8 of an inch tall. I use a custom made screw on clamp that looks like a VPI but has a longer and lowered thread height. This is to accommodate an acrylic disc under my rubber mat. ( but, that is a different topic) Being careful to watch the amount of warp as it is tightened. Warps are usually reduced or can actually increase with excessive clamping pressure. Each record has its own requirement. The hold down pressure will vary a little with each album. I used to use a rigid spacer under the record over the spindle, but think pads under the mat are better.


I’ve experimented with record clamping for over two years to come to the conclusion in item number two. Item one is still a valid option but, item two is repeatable and less risky, (though maybe not as visually correct). Sometimes a mounted and clamped record will not be as flat as you think, but have a slight curve which can affect azimuth and antiskate. In my experience these undesirable variables are manageable and better than excessive warps. FYI, I have not tried a ring clamp for comparison. 

Pindac, You seem to have more than average problems with wobbly spindles caused by excessive wear in the bearing shaft, or your friends do.  I can't recall ever having observed it.

@terry9 , you have to be kidding me! Both Kuzma and SME use reflex clamps. Check out their manuals.

@pindac ,what are these jet engines? The bearing wears at the thrust plate and ball. There is virtually no stress on the bushing. They never wear unless you put sand in them.