Can stretched springs be restored to the correct length?

[tigpha]

Hi Deskthoritans,

I recently bought (yet another) IBM Model F Bigfoot. It is turning out to be a fine specimen, cleaning it has revealed almost pristine keycaps. I am very satisfied with it, except for one tiny detail:

One of the springs was kinked. I managed to straighten it, but by removing the spring from the paddle I seem to have stretched the spring by a millimetre. I have now discovered that the length of these springs in the Model F, and I suppose also the Model M, is critical for proper operation. The spring no longer buckles when the key is pressed.

Hardware lesson for today: Do not pull springs off the Model M/F paddles due to risk of stretching.

I have spares, thankfully. But for those who unfortunately do not, is there a remedy that restores springs to the correct length?

[tigpha]

I have a solution: bend one end of the spring to reduce the number of coils. It's ugly, but effective. The steel is too tough to snip with pliers, and cutting with a Dremel could potentially heat the steel, and change the elasticity, so bending might be the only option.

Fix stretched Model F spring.jpeg (585.27 KiB) Viewed 8795 times

[tigpha]

I tested the "solution" and it doesn't work reliably. It appeared to work outside the keyboard, using the keycap, barrel and paddle in isolation when I tested it before assembling the whole. But inside the assembled keyboard the spring won't buckle, and the paddle doesn't flip.

Conclusion: replacement spring and paddle assembly is required.