IBM Model M Travel/Force Mods

[greyhounds]

I can't resist the buckling spring challenge - it's the engineer in me.

I'm looking for some trashed IBM Model M parts to do some spring/hammer/key modifications on. My goal is to alter the geometry and force profile in order to achieve some of the following:
  1) trigger the switch earlier in the travel
  2) reduce the force required to trigger the switch
  3) increase the force buildup after the switch trigger point
  4) increase the key travel after the switch trigger point

If anyone has any busted Model M's they could donate I'd appreciate it - I've only found one locally so far and it's perfect. I'll pay shipping of course. Maybe someone has the leftovers from tablesaw mini-mod?

Also if anyone knows of any mods or attempts like this that have been done already and could point me in that direction that'd be great. I've found that I'm rarely the first guy to try something on this planet.

Thanks!

[greyhounds]

I've already come up with a plan to extend the travel of the standard Model M beyond the activation point, but need to test it out. Depending on how tight things stack up in there it may take some additonal mods to realize significant additional travel. It'd be really nice though to be able to drive the M like you stole it without bottoming out.

On the spring side of things, I really plan to purchase every available spring of similar diameter and just start trying them to see if I can come up with an improvement. It may not be possible though with the existing geometry of the keycap and hammer.

There should be no reason I couldn't make new hammers with a different spring seat to change the force applied by the spring. You can get just about anything done via waterjet for pretty cheap. It's be sweet if all we had to do was put in a custom set of hammers with the original springs to get what we want.

I still need to see the various bits up close and slice and dice them some before I can really start to get my arm around this.

This is the kind of thing that mechanical engineers who don't golf do for fun and excitement. It's sad, isn't it.

[wcass]

i think a 3d printer would be the best way to prototype new hammer geometry.

[greyhounds]

The quickest/easiest first mod to shorten travel to the actuation point would be to add a spacer into the top end of the existing spring. I'm guessing something like a rivet with the center post pulled out might fit.

This would essentially add more precompression to the spring, so you wouldn't have to push the key down as far to get the spring to buckle as you're already partway there. If these travel 0.090" right now, it's be nice to cut that down to 0.045" or so. That'd probably give similar travel to actuation as a laptop switch, but then you'd have like 0.112" travel left to "pull up" and avoid bottoming out.

The spring force would be the same with this mod though - we'd just be shifting the travel curve. Still sounds fun to me.

[greyhounds]

After looking closer at the patent skectches for the Model M switch, it looks like we could easlity shorten the travel to the actuation point, but maintain the overall travel, without much work at all.

All we'd need to do is add 1 or 2 (maybe 3) washers UNDER the spring to precompress it a little. They'd have to be the same ID as the post on the hammer. The force/moment geometry is unchanged so it'll behave the same way on the downstroke, just trigger earlier.

BUT....

Due to the designed-in changing upper end connection on the spring (fixed -> pinned -> fixed) we'll be limited in how much shimming we can get away with before the spring won't "unbuckle". That upper end connection is key to why the "make" point is so significantly different than the "break" point.

Rip, do you still have that bolt modded Boscom function row handy? That'd be perfect for this experiment. My only M isn't bolt modded yet.