Why do some CDs crack at the inner edge?


#1

Something, that never happens to DVDs, but only to CDs:

This is a rare phenominum, which did occur on frequently used CDs. The crack itself gladly prevents the drive from speeding up, because it makes high speed reading impossible. However, what exactly causes these mysterious cracks? Is it because of slim drives,where you sometimes have to push the discs in with pressure, if the drive is badly designed?


Safe rotation speeds for partially cracked CDs?
#2

My theory is that focused, long-term mechanical pressure from within, is the culprit.

I suspect that, barring any violent abuse while inserting a disc into a slim drive, the pressure is not narrow / strong / long enough to cause this type of stress on the hub.

I have, however, noticed this damage on CD’s (and DVD’s) in storage when using a specific type of jewel or library case. I have chalked it up to poor design of the hub retaining mechanism (e.g. 3-point contact instead of multiple places as in the original design jewel case). All of those cases are now in the garbage, the discs recopied and placed into less stressful storage cases.


#3

Also slim drives and many cases have this design.


#4

I sacrificed one CD-R CQ (actual writing quality was pretty good. Only €8 for 100 pieces.).

I put it into a BU20 and took it out again repeatedly, around 100 times. No cracks.
One has to grip the disc where two of the theee holding pins are at the inner edge, but in the middle at the outer edge.