Continuing the small fixes and adjustments on the Underwood Champion portable typewriter; now for the carriage. From what I've read, the Underwood 'Typemaster' portable should be capable of being a fine and smooth writing machine, so 'adjustments' is probably the way to get there.
In addition to the individual key-pressures still being very un-even, the carriage-shift felt very heavy, as did the carriage return. Almost as if everything was adjusted to the maximum - similar to Helen Howes' assessment of how the top-tension is near-always found on old sewing-machines.
Measuring the shift-key force, this machine needed 450 gram force (gf) or 4.5N to move the carriage. That definitely feels too heavy and probably is too heavy. Measuring some other portables for the force needed on the keys to shift, there's quite some variation. As expected, a Corona Speedline is the lightest, with the Champion indeed the heaviest. The 400 gf value for the Remington Portable 2 is probably mostly due to dirt gumming-up the mechanism - this had significant hysteresis; a delta of 200 gf for the returning movement whereas the other machines generally were in the 50 gf range.
Having established that it really was too high, first read up on how to adjust this force in the Ames' service manual on Underwood portables. The weight of the carriage is compensated by a shift-balance torsion-spring. The manual has a small paragraph about adjusting this shift-balance spring.
So - this tension should not be disturbed. That sounded a bit worrying - in a "here be dragons"-style worrying. Also the need to form the free end of the spring (a pretty stiff, strong spring) was notable. However, when then comparing the drawings in the manual (1944 printing) with the parts on the actual machine (1939 manufacture) this paragraph becomes clearer and probably makes sense.
The drawing shows the spring is held on the shaft without an adjustment ratchet - the actual '39 machine however has an extra, teethed collar on the shaft with an adjustment ratchet mounted on the spring. Maybe the Ames drawing was simplified, or quite possibly the design was changed by Underwood some time after 1939 to leave out the shift-balance adjusting ratchet.
Either way; by adjusting the spring, the force on the shift-key can be readily adjusted to taste. Note that this is only changing the net-force and not the mass of the carriage that needs to be moved. With a heavier carriage, a heavier shift will be needed for fast typing. Otherwise the carriage will not have returned to lowercase before the next character is typed. Myself preferring a lighter machine and taking it a bit slower, the shift-balance spring was wound up a few notches to counter the weight of the carriage.
The ratchet that is fixed to the spring is held by a set-screw. This set-screw needs to be removed completely, as it depends on where the ratchet-collar ends-up in what threaded hole it needs to be mounted again (to always permit screw-driver access).
With the set screw removed, the spring-mounted collar can be pushed out of its engagement with the fixed collar on the shaft and rotated. This really can not be done by hand, but will need the firm grip of a pair of pliers. The 'posed' image below shows the parallel-beak pliers that were used for this. (Best practice would be using some protection (card/wood) to prevent marring the spring, but this machine's pretty rough already so skipped that - luckily it didn't scratch.)
Firmly held with the pliers, the shift-balance spring was wound-up only a few ratchet-notches at a time. As always when working with springs - it's important to not let go halfway the process! Move the ratchet back in engagement carefully whilst keeping a firm hold of the spring. Only then let go.
When shifting-key force is at the desired value, re-mount the set-screw and tighten lightly.
Net-result of the operation is a carriage that will now shift with 250 gf on the shift-key. This I found is a pleasant, 'light' shift. With this balance, the carriage still drops down snappily, but with perhaps a bit less of an impressive thump on its stops. (Although it probably is too light to work reliably for fast typists.)
The further adjustment of the carriage is of course the drawband-tension. This also was very heavy, from 500 to over 800 gf over a return-motion! Adjusting this force is fortunately a very easy affair and exactly as was described in the Ames service manual.
With a newly light and snappy carriage, the Champion is starting to show potential :-)
Congratulations on the tension adjustment. Those torsion springs are the worst part of those typewriters. I find them really difficult when adding pressure which requires moving opposite the ratchet.ReplyDelete
Very scientific approach! I'm impressed.ReplyDelete
Thanks for this! I just had to make the same adjustment--but my machine has the torsion spring with no ratchet (1947). It matched your snippet of the manual perfectly.ReplyDelete
Glad it was useful :-)Delete