I find there is an old on eof these in the bowels of the office where I work. I will drag it out and give it a test soon and report.
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From my experiments in the oven I might postulate that you may have set the heat 20 degrees to hot and the weight of the platten may have been too much as well. I have had best luck at 140 or so, and letting the weight of the glass(although I used 1/2" glass)do the gravity thing. The heating up could take several hours. I cooked a few trying to speed it up.
Interesting -- I suggest you do not use the acrylic, but rather two glass pieces (and 3/8" thick should be adequate since the glass is fully supported and you are only applying the weight of the platen. Lower heat would be good too as someone else suggested.
My reason for nixing the acrylic is that it has a large coefficient of expansion, and so as it heats and exoands, it may be carrying the record with it and giving you the radial runout. Then, as it (the acrylic) cools and contracts, it's trying to "scrunch" the record up, giving you all those nasty lumps and bumps. Just a thought.
Photon46, your efforts are promising.
If the Seal press works for you, I may copy your efforts so I can flatten out those few warped LP's in my collection that are otherwise perfect.
It's likely that you must hit the exact heat and cool ratio to achieve success (as suggested by other posts here).
You might even test your Seal with an oven thermometer to determine the exact temperature. That would verify the control on the Seal has not gone off the mark over time.
Interesting concept. I know a fair bit about dry mounting but don't know if any of the same information may apply to flattening LPs. With boards and paper it is always good to use a heavy, flat steel plate immediately upon removing the hot board from the press. This allows the heat to dissapate more evenly and quickly while continuing to be under the pressure of a heavy plate. Without the plate If the hot board cools too quickly and or unevenly it will tend to curve. Also, I'm not sure if they are still available, but Seal used to produce "temperature indicator strips" to quickly and conveniently gauge the temp of the press. These were made at with two colored 'buttons' of some plastic-like material. Each color melted at a specific temperature. They were made for to accomodate the more specialized low-temperature mediums for dry-mounting which would make a mess at higher temperatures. I can't recall the temps they'd indicate. My best recollection is 120 and 160 degrees. It was in the lower range for sure. There is also "release paper" which is a heat-resistant paper with a thick glossy coating of some sort that does not stick to dry-mount medium. It is is non-reactive at high temperatures. It is made to be put between the metal platen and the materials being mounted. You can also do this with a piece of white mounting board since you are not using the messy mounting material. But do check each time you use it that no loose dirt or debris gets embedded in that cardboard or you may be pressing it into the grooves of your LP. The Release paper is very resistant to holding any dirt since it has a somewhat glossy coating to it. I'd imagine that a softer buffer, like the cardboard, and or release paper, between the warped LP and the hard steel platen might be safer for the grooves. Keep it clean though!
Neat idea...good luck!
As an addendum to my post, here is one source for some of the dry mounting supplies I mentioned. They don't seem to have the temp indicator strips, but I like Albert's idea better anyway.
The presses themselves can be had on eBay at any given time for much less than new. I own two of them and the smaller, older one is ideally sized for an LP. If this thing turns out to work well for LPs I'll sell it to whoever may be interested for a good price. I no longer have a record collection so it won't serve me in this respect. Keep in mind, in seeking one out, they are a bit heavy to ship, so a local purchase is best. I think the smaller one I have must weigh about 40 lbs.
Ok, round two in the saga, much better results this time. Thanks to all for the input and suggestions. Nsgarch, I thought your ideas about the possible problems with acrylic warranted removing it for this experiment. I also thought that if the lp is sandwiched between two pieces of glass, there is going to be a small void between the raised label and the raised rim that might allow the small ripples to form in the groove area on cooling. So I used this material sandwich from the bottom layer up: 3/8" glass, 1/4" paper surfaced "foam-core" mounting board, 2 thick sheets of artists' drawing mylar (smooth sides facing the lp which is between these mylar sheets,) and last, a 4 ply cotton rag mounting/mat board (ordinary mat board would work too.) My thoughts were that the slight deformation of the softer foam core and mat board would cushion and support the thinner groove areas of the lp on cooling. I used my digital darkroom thermometer to make sure that the thermostat was accurate and heated the press to 140 degrees f. I preheated the boards to drive out moisture (less expansion/contraction,) made sure the mylar surfaces that would contact the lp were clean, and then put everything in the press for 15 minutes. No clamping, just the weight of the platten pressed things. After 15 minutes, I turned the press off and didn't open it for 4 hours as it cooled off. I don't think you would want to try and remove the lp to cool under a weight because the vinyl cools, contracts, and warps very quickly when it's soft. By the way, this was a THIN lp, not a thick 180 gr. lp. If you were working on thicker, heavier lp, I'd think you would want to heat things a few minutes longer. This time, everything worked like a charm. The vinyl is perfectly flat, no radial runout, no groove damage. It plays fine with no increase in surface noise or other audible defects. I will repeat this on a few more warped lp's to make sure things are repeatable and predictable and report back. Thanks again for the ideas, Will.
Will, success! However, just to make sure you are not getting unnecessarily complex (with your sandwich) you might just want to try the two-sheets-of-glass thing. I mention this because if it works as well, it makes things a lot simpler, and because two-sheets-of-glass-in-the-sun is the old standard way of doing this -- and it does work, it just takes a lot longer, and of course you need a good sunny day.
On the other hand, it's 108 in Tucson today, so it shouldn't take more than 5 minutes in the sun and 30 minutes out!
Nsgarch, yeah I know the sandwich thing uses materials that may be difficult to obtain for some. My job developing and photographing Fine Art sculpture editions gives me easy access to many materials. Plus it encourages my propensity for overly elaborate solutions! There hasn't been much sun here in Florida for the last month to try the glass sandwich, it's just rain, rain, rain.
pdennis -- If you want to try the glass/oven method, use 3/8" thick glass. 1/4" may not provide enough even weight, and 1/2" may not heat and cool evenly. You should also observe the following:
1.) Make sure your oven really goes down to 140 degrees. Many don't. Test it with an accurate thermometer first.
2.) Believe it or not, gas ovens are better (more even heat inside the oven chamber.) If you only have an electric oven, place a large broiler or baking pan on the lowest rack position right over the heating element to avoid direct heating of the lower piece of glass.
3.) Wait until the oven has remained at the desired temperature for a half hour or so to insure even heating. And then place the record/glass sandwich on the middle rack.
4.) For cool-down, don't move anything. Just turn off the oven and crack the door open until everything reaches room temp.