recessed center in old turntables platters ... why

Wow i never knew that.

As far as I know, all VPI tables have recessed platters. Which ones don't? There was a thread about a raised Classic platter a few months ago, but it turned out to be a machining error.

SME tables have the recessed centre of the platter too.

As mentioned, the recessed area of the platter is intended to accomodate the thickness of the label, that way the record has better contact with the platter. However, most records (at least in the USA) have a raised lip, which was to keep the record surfaces of stacked records (using the record changer on vintage turntables) from rubbing on each other when the record dropped. But that negates the idea of having the surface of the record in contact with the platter. So platters should have both a recessed area for the label and a recessed area for the raised lip.

I wonder why most modern LPs are still produced with a raised lip since modern turntables don't include record changers and I doubt many people use the changer on vintage turntables. Records should be flat all the way out to the edge.

As for recessed areas on modern platters, two of my turntables (both with acrylic platters) do not have recessed areas and the other turntable (acrylic/vinyl sandwich platter) does. My hunch is that the platters made without recesses were done that way because it's less expensive to manufacture. That and perhaps the company doesn't think it makes any difference in playback quality.

For me, the label and raised lip of LPs aren't even a consideration since I use Herbie's Donut platter mats on all three turntables, which provide full contact of the record surface and the platter no matter what the platter/LP combination. If you're interested, the Donut is available here:
Herbie's Donut mat (Towards the bottom of the web page.)

Regards,
Tom

My Nottingham Mentor has both recessed areas machined into a 1 inch cylinder of graphite. Aftermarket mats invariably diminish performance.