Vinyl has amazing thermodynamic properties. When cool, it’s rigid. Heat it up, and it becomes bendable. Heat it further still, and it melts and eventually is destroyed.
When flattening records heat is important. Increasing the temperature of a record allows you to dramatically speed up the process of flattening. Without heat, records can take weeks, months, or even years to flatten under sufficient weight.
Every record has an Oh Shit Temperature (“OST”) at which it will start to distort under its own weight. Given the variability of record weight, vinyl composition, and warp shapes, the OST is different for each record, and it’s next to impossible to determine a record’s OST without damaging the record.
When flattening a vinyl, you never want to pass that OST to avoid damage to the record. Consider it the point of no return.
To visually demonstrate we created a simple video of us heating up a vintage 1975 135g vinyl in a kitchen oven from room temperature to 160°F. We discovered the OST of this record is probably in the range of 155-160°F.
Since you don’t know the OST of your warped record, how do you go about flattening it without risk of damage?
We recommend starting with the relatively safe temperature of 125°F, which is the flattening temperature we preconfigure every Record Pi to target. If that doesn’t work, then try to increase the amount of time you bake the record.
If the record warp still doesn’t seem to be improving, then it may make sense to increase the flattening temperature bit by bit… 3 or 5 degrees at a time. Remember, you never want to accidentally discover you’ve crossed the OST!
Heavier records do tend to have higher OST’s then lighter records, so it pays to do some research to determine the record weight or invest in a simple digital scale if you don’t already have one.
Happy flattening!
-The Record Pi Team