indigo.girl wrote:

A little progress. I followed your advice Repartee and sprayed with WD40

Nooooooo!    That particular product excites some strong feelings so you might want to wash it off with the mixture I suggested.  I think the charge involves the residue it leaves behind... I will let others specify its evil nature!

and gave it some jiggling. I have been able to get some movement and in fact can now manually get the fingers to walk along the ribbon wheel and for the Y-shaped thing to move up and down (sorry for the lack of names but its where the type heads go to when keys are pressed!). I have taken a video and you can see what I mean. I have disconnected the space bar and am mimicking the movement using a screw driver. Now when I press any key it all moves but it will not reset so the next key does nothing. Its as if I am missing some kind of spring to pull it back each time. Any ideas what part should pull the mechanism back each time in between key strokes.

Great video.  The "Y-shaped thing" is the so-called ribbon vibrator, which allows the thing to put ink on the paper but get out of the way again so you can see the letters you just typed. I was wondering if my hope that if the ribbon advance mechanism were working - and as it turns out the ribbon vibrator also -- that the escapement might be actuated and advance the carriage.  But darned if you don't have the carriage off so can't tell.

Yes, the finger mechanism is extremely clever, like many mechanical things found in a typewriter, and in an open machine like the Underwood 3/5 easier to understand them!  My favorite cleverness writ large is the horrendous looking mechanism on the back of old Remingtons involved in adjusting the mainspring -- looks like part of a medieval instrument of torture but turns out to be a very large escapement!  One you don't want your fingers near in operation.

Sorry I can't be of more concrete help, earliest I could find my example might be next weekend -- yes I am that far gone in the hobby that entire standard typewriters are misplaced.  You are adventurous and this is obviously not your first tear down of a mechanism, just possibly your first typewriter.  You did not know about the cultural taboo against WD-40 so I hope will be forgiven. 

Update: I have solved the lack of carriage and ribbon movement when pressing keys. The escapement was not jammed but two things needed adjusting. I found a very useful document on the internet with the escapement movement described https://archive.hnsa.org/doc/typewriter/part2.htm

1) As the key was pressed the heel of the type bar was pushing the universal bar back but this was not coming into contact with the Trip adjusting screw on the Escapement rocker. The screw was not screwed in far enough - once lengthened the universal bar pushed the escapement rocker back. This in turn then moves the loose dog away from the teeth of the wheel allowing it to trip.

2) Once tripped there was no forward tension to return the universal bar back to its original position. A spring on the U-bar spring support was not stretched enough. The spring support can be lengthen to increase tension. This was enough to pull the universal bar back to start position. Here is a short vid showing the U-bar springing back and forth. Plus a photo of the spring support that I made longer.

https://youtu.be/-0btYOrVHRE

https://drive.google.com/open?id=0BwmrHl56AGVZazFhb3Fkb0t3VGc

Once reassembled the carriage and ribbon advances by one position with each key pressed. Unfortunately there's still a bit of work to do as the type face does not hit the paper (comes close but not enough). I'm hoping this will be a small adjustment. Any ideas of how to adjust this?