Hello again Lads,
until I get to the glass installation of a dust cover, here is some quick information on that infamous hinge.
The hinge is three parts, hinge itself is just a rectangle of steel held to the plinth's backboard by a screw that threads to an insert in the backboard, and a steel spring washer. please note, the threaded insert is roll pinned to the wood to prevent it from moving along with the hinge, This pin also goes through the screw, to keep it from backing out during use.
To remove the screw, you will have to punch out the pin.
If you try to unscrew it without removing the pin, you will either snap off the screw, or so mangle the screw head to make it unusable
Of course you will have to repair the hole in your wood, and install a new pin. I did this, but used a solid pin so I could easily remove it in the future
Empire used roll pins in many places on the 598/698 I think it was to keep the user out of self repair.
It is my belief that, the failure point is the spring washer. It is a 3/4" diameter washer that is curved from the center on two opposing sides.
The pressure of the spring acting against the hinge and the steel insert in the board is what holds the dustcover in place. After 40 plus years, the spring washer just looses it's set, and can no long hold the weight of the cover.
I was lucky to find 4 of these sized washers in a neighborhood hardware store, and replaced the springs on two tables, a 598 and a 698 both have glass tops and fronts.
This worked quite well, and held the cover in place at a 90degree angle, plus a bit more in a forward position.
I found a few sources for them on the net, and I will order some in different thicknesses to find a match for the original
If you try this yourself, use care in removing the screw, as it looks like they used a thread locker along with the roll pin. if iit does not move under normal strength, stop and soak it with penetrating oil and wait a day or so.
Clean up the surfaces with a light abrasive and reassemble in the order it came apart.
DO NOT OVER TIGHTEN THE SCREW on assembly.
By the way, the screw in this photo came from a Empire tale with a broken hinge I got from an estate sale it is much shorter, due to the fact the the rest of the screw is still inside the inset.
The previous owner tried to remove it with out removing the pin, and snapped the head of the scre off at the pin pont.
Hope this helps.
Donald Bowman