So you took the platters out of the drive, physically opened up the drive and removed the platters?
If you open up a harddrive you have to be in a dust free environment. If you aren't you ensure that it cannot be read again as finest dust particles will settle on the surface nearly instantly and will only damage the surface further when you try to read from them.
A malfunctioning dust filter is one of the causes a harddrive would fail:
If the filter fails to capture a dust particle, the particle can land on the platter, causing a head crash if the head happens to sweep over it. After a hard-drive crash, each particle from the damaged platter and head media can cause a bad sector. These, in addition to platter damage, will quickly render a hard drive useless
There are companies that specialize in the recovery of data from failed harddrives, they all use cleanrooms, this is no living room job to do.