I currently have 5 101 key Model Ms from 1988 to 1994 and my latest 2 got me wondering.
The latest 2 keyboards are from 1993-1994 with the drainage channels and the frames have cracked along the flex lines. One above ASDF the other on the numpad. I didn't see this on my 1988 keyboard and other non-drainage frame and it get me to thinking.
I'm aware that certain plastics will break down over time due to chemical decomposition of the various additives. What I'm wondering is if in 1988 the keyboard manufacturers were using more virgin plastic and less regrind? Many companies now, if not all, will grind up parts that don't meet specification and re-introduce them into the process as a percentage of the mix (20% regrind, 80% virgin). That % is critical as too much regrind will reduce the overall quality of the part and too little will drive up the cost.
I wonder if that is what is going here. The 1988 keyboard was more virgin plastic and the 1994 was more regrind.
It's also conceivable that when they created the new molds with the drainage channels that they also made the frame thinner to save on material. Or that the formula changed and the additives are different.
