How many springs does a Model M spacebar normally have?

[Justblair]

I was working again on my Model M122 tonight and had the plates apart (I bolt modded the thing recently).   I have never been that happy with the feel of the space bar which was sporting one spring. 

There was a spare barrel which does not have a corresponding contact on the membrane.  I had a couple of extra springs and decided to install one in the empty hole. 

i much prefer the feel of the space bar now that it has both springs fitted.  It feels much closer to the rest of the keys on the keyboard in terms of stiffness.  Is this how the keyboard was intended to be equipped?

[Parak]

Nope! The extra barrel just acts as an additional stabilizer to prevent excessive Y movement of the two sides, where the wire one is more for the Z direction.

[rowdy]

Both of mine only have one such spring each.

[Justblair]

Well in that case I can thoroughly recommend adding a spring in there to stiffen the space bar. Without it the space felt pretty anemic.

The barrel has the notches on the back to take a std spring and it's lever. But it might be possible to drop a spring from a disposable pen in there and just let the space bar hold it in place. Then you would not need to do a bolt mod.

[Parak]

There's nothing in the space bar that should be making substantial contact with said spring as it only sits slightly above the barrel top. The spacebar section for that barrel would only contact the spring at the very bottom of the keystroke, for insignificant effect. I'm suspecting that the feel improved simply because you reseated it.

[Justblair]

I  will have another look.. You may be right.

[Daniel Beardsmore]

I never was all that keen on Model M/Unicomp space bars. They do lack something, and especially on a Unicomp, they don't even click — you just get a limp thunk.

Many keyboards have a stronger switch for space bar — does anyone know why this is? Is the Model M or Unicomp space bar spring suitably stronger?

[ch_123]

Lexmark used that hole for a split space bar on some keyboards, but the hole is also present on older Model Ms. As has been pointed out, it acts a stabilizer for the full length space bar (I think there's two holes on the 122-key Model F too, most of the other Model Fs have a more elaborate stabilizer mechanism)

[dorkvader]

I strongly suspect that the smaller "left" spacebar is the same as the "code" key on a wheelwriter.

There is an extra empty barrel on the 122-key model F that you have to remember. I accidentally put a spring in there last time I put this SSK back together, and it had no effect on the spacebar (other than a slight rattle if you shook the keyboard of the hammer / spring knocking about.)

[Justblair]

There's nothing in the space bar that should be making substantial contact with said spring as it only sits slightly above the barrel top. The spacebar section for that barrel would only contact the spring at the very bottom of the keystroke, for insignificant effect. I'm suspecting that the feel improved simply because you reseated it.

You are correct that the extra spring will only affect the space bar at the bottom of the keystroke. I think though this is a good thing. The bar is on my keyboard floppy and normally bottoms out too easily. The spring in there seems to soften the bottoming out, even making it a tad easier to avoid it.

I have a plan to use an existing spare key to make the space more solid again... I will report back...

[Justblair]

That was quick.  I cut up a key stem from a spare key and tried it in the spare barrel.  U used a little hot glue to connect it to the space bar.  This means that the space bar was getting double the spring force back.  I am typing on it just now.

First impressions are that the spring force required is now too strong rather than too weak.  Feels like a little too much effort to type on now. 

On the positive side, I can tell you that the barrel in standard configuration does virtually no stabilisation.  The round section on the space bar moulding has too wide a circumference to contact the empty barrel in a meaningful way. With the extra key stem the space bar becomes more solid with less lateral movement.  I am thinking that I will probably keep the key stem but shorten the spring a little.   

If you have a spare key that you are not using you might want to try modifying the space bar to take advantage of the spare barrel.