doesn't make mirrors
In traditional machining (the old Decker high quality lathe or mill), the device is relying on passive mechanical stability. So the really precise machines became more and more massive and huge. Nevertheless when the room temperature changed or the machine heats up, because it's made of iron the machine expands or contracts, the precision changed. Old masters could compensate for this effect.
In precise new CNC machines, the philosophy is a bit different, they are surprisingly delicate-looking compared to old machines. Because there is an active feedback to measure the position of the tool very precisely and even actively correct for these mechanical or temperature effects while it is running, it doesn't need to rely only on passive stability anymore because there is this correction in the most expensive machines.
The eye of the optician is not making the mirror, his/her hands are. Laser interferometry is the eye, the computer is the brain. Nothing else has much changed, the machines are still made of iron (though of course much better ones).....
In a traditional lathe, the work piece is securely mounted and turns at high speed, for large glass pieces it becomes not that straightforward. In a modern CNC, the work piece is often stationary, the tool moves instead and can for example rotate at high speed to machine even glass. The computer can command the tool to turn in precise circles in a way which a human cannot. Precise manual lathes can't be purchased new so easily anymore except for special devices, partially because the CNC has become so dominant, it's even becoming not that easy or relevant to teach these old manual techniques anymore. I agree traditional lathes are great, they are more precise than a CNC if put into the hands of a master.
Edited by X3782, 20 August 2018 - 09:06 PM.