TypewriterGuy wrote:

^ WOAH! You gotta wonder what happened to it...

Time and neglect happened to it. Not a rare set of issues to come across when you look at enough typewriters.

TypewriterGuy wrote:

Mech, was it the century 10?

No, it was a Royal KHM that I recently cleaned up:
https://myoldtypewriter.wordpress.com/2015/06/17/the-foster-typewriter-royal-khm/

Years of disuse caused most of its problems - the mainspring was paralyzed with congealed grease. I suppose the drawband slipped off and got jammed under the carriage after the mainspring stopped moving.


 

freck wrote:

Okay, so the carriage rolls smoothly when I press on the carriage release levers, and the drawband seems perfectly functional. I'm guessing it must be an issue with the mainspring, but I have no idea where to find that/how I would fix it. Any more help from you wonderful people?

Though I am unfamiliar with Underwoods, here is what I would do if I had a machine with your symptoms.

I would first rule out a problem with the escapement. Facing the typewriter, pull the left carriage knob gently to the left and type or hit the space bar with your right hand.  Does the carriage advance a space with each key struck? If the carriage doesn't move when operating in this fashion (which simulates the pull of an intact and well-tensioned drawband), then you may have an escapement issue.

If the carriage does advance a space with each key stroke, I would take a look at the mainspring.  The mainspring may lack tension, be gummed up or even be broken.

I believe this is your mainspring drum (I have highlighted the area on your picture from a different post). 



Though I am unfamiliar with the Underwood 6, you should be able to see and access the drum from the top by moving the carriage all the way over to the right (if you are facing the machine).  This is what the mainspring drum looks like with the carriage moved all the way over to the right. (picture from the Royal KHM typewriter I recently worked on):



This is the view from the top back of the machine.  The drawband in this case is a thick woven strap.  Yours may look like a waxed string or thick twine.

Here is a link to mainspring information and diagrams for several types of typewriters including the Underwood that may be helpful to you in visualizing the set-up:
http://archive.hnsa.org/doc/typewriter/index.htm#pg16

Facing the machine, I would test the mainspring by holding the drawband securely with one hand so that it doesn't slip off its anchoring point at the right end of the carriage and gently rocking the mainspring a small distance to the right.  Does the mainspring zip back when you let go? Does it have a weak zing or does it moves stiffly if at all?