Of all of this mechanical stuff, this is the part where I am the weakest. Springs and buckling points in regards to outside lateral forces are just hard.Wingklip wrote: ↑http://www.rccoilspring.com/rectangular-springs.html
Found this that could work for low profile bucklesprings
I have a feeling IBM made MANY attempts/prototypes to be honest to get the feel they really desired. For the quantities they knew they would be producing, it would have made proper business sense to have a spring CNC on hand and run T&E to prototype, and then capitalize the machine somehow when ready for retirement (might have the damn thing today for all we know). Unfortunately, that is almost impossible for us unless someone wants to the be the "buckling spring tycoon". We can control spring length easily by clipping coils, but it takes a pretty healthy dive to change coil spacing and wire ID/OD. Each run of a unique spring is several hundred dollars, even for one, if paying a supplier. We were lucky enough to have the Model F "end game" dimensions as a starting point (60-65g), and still missed the math when trying something "lighter", with help from consultants by around 3.6% on our 50-55g goal (ended up with 40-45g). ALL spring producers will be VERY good at telling when the spring would naturally buckle under load. They struggle when the spring is meant to be fired by outside shear tension at some distance (paddle being diverted breaking the perpendicular plane) along with load since that is an abnormal act in almost every situation of normal spring usage aside from our need.
All that said... I am very confident we got the math right after trying once and being off about getting a 50-50g in a typical compression spring of known length. If we keep the same ID, I think we can nail other attributes like changing length or OD... but if we change designs altogether (like rectangular), it is going to be random luck to get it right. Not trying to be Debbie Downer, but LOTS experimentation/deep pockets/hyper-brighter minds will be needed.
For our MF^2, where we want Cherry MX mounts, I have a shorter spring that should buckle at 50-55g spec'd since we need ~1.2mm shorter key stem length to be desirable. We have ran by 3 others that have better guesses than me as to whether it actually works, and they agree it does. Even with that, it's a leap when it comes time to produce it since machine tolerance is always questionable. I just want to make sure others are aware of the road you are going down in this space if you take it on. I hope you do, but be prepared to have hiccups anytime you change a proven design. Ellipse is finding that even mimicking it, let alone altering, was difficult. It's just is an odd switch, and the dimensions are certainly touchy