I just finished re-assembling and testing my model M space saver, after replacing all of the rivets with screws. The action and sound are much better then before I started. And the whole process took about 2hrs from start finish. I figured I'd share what I did. I'm sort of limited by the 5 picture limit, but I have a few more pictures I may include in the comments later on if they are needed. I'm pretty sure that keyboard is now completely indestructible, and will likely survive for a long time.
Tools you will need :
1) 7/32 deep socket.
2) Dremmel tool (or power drill), you don't want to use a pin vice for this.
3) #43 drill bit.
4) #4-40 Tap and handle (this is a common size, and you can probably get away without the handle if you're careful).
5) Flat head screwdriver.
6) #4-40 1/4" pan head machine screws.
I won't go into the whole process of disassembling the case, or removing the PCB as there are a fair number of guides out there already on this (and you likely won't know that you're missing rivets unless you've taken it apart already and looked =P ).
The first step is to locate the broken rivet heads and drill them out. You need to be very careful of two things when doing this. The first is the drill needs to be perpendicular to the metal plate. If its not, the head of the machine screw won't sit flush to the plate. Secondly you need to drill down the exact center of the rivet. The rivet sits on a ridge molded into the front plate if you slip off this ridge while drilling thee things will occur. One is that there won't be much plastic for the screw to thread in to, and the pressure the screw exerts will be on the face plate, rather then the supporting ridge. Secondly you will likely damage the rubber membrane while tapping, and thirdly the drill shavings will be trapped inside the housing between the rubber membrane and the key membrane.
Extra plastic inside isn't such a big deal if you're planning on replacing all the rivets, but can cause problems if you're just repairing a few.
Next you need to tap out the hole. Make sure the tap is perpendicular to the plate as well.
Finally simply tighten the screw in. If you use 1/4" pan head machine screws, the front of the screw will sit almost perfectly level with the front of the plastic housing. The screws also don't seem to interfere at all with any of the housing, and the board sits in the housing exactly as it did with the plastic rivets.
You can see the screw heads between the keys if you are looking carefully. If you are really worried about them, you can paint them black, to better blend in to the plate.
Repeat again for all the rivets.
Ignore the few hex head machine screws, I ran out of pan head screws. They work fine in the middle area of the board, but would hit the housing in the front part. Ideally they would all be the same type of screw.
If you're doing a fair number of rivets (especially in the same area) be very careful when you are drilling and tapping that you don't put too much pressure on the front plate. If the back and front plate separate too far the rocker and spring can come unseated and not switch properly. If this happens, you will need to completely take the keyboard apart (which involves removing and replacing any of the remaining rivets. I mention this because it happened to me, I had only planned to replace the broken rivets, but ended up having to cut and replace all of the rivets.
I hope this helps.
