Saturday 22 October 2011

KHM: tab problem solved

The grime inside isn't doing any harm - it has taken 74 years to build up. I reckon that's part of its heritage and I'm positive I'd do more damage removing it than leaving it alone

I have figured out the solution to the sticky tab illustrated in my previous post

Removing the left-hand rear dust cover reveals the motor and what I'd originally thought was a retaining collar for the clockwork motor's spindle. At second glance (and in better light) I spotted a worm gear. A drop of oil and a trial and error turn in both directions and voila! No more sticky tabs and enough pulling power wound into the spring for the carriage to move briskly along to the set tab. If I hadn't had all the covers off again for a more thorough cleaning of the paintwork, I'd probably never have spotted that worm gear.  

I hope this is of help to any other Royalists (aristocrats? typocrats?) with sluggish carriages. This fix took two full rotations of the motor spindle to load the spring sufficiently. To save straining yourself with heavy carriage returns or stressing any parts, slightly over-wind the spring first and then gradually slacken it off until there's just enough tension.

7 comments:

  1. Jolly good show, old man! :D

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  2. Hello. I'm curious if you know how to fix my issue. I had the same problem with the carriage not advancing on my KHM, but (and here's the kicker) it only happened when the right hand ribbon was engaged. If it was set to engage the left hand ribbon, the carriage moves like a dream! I adjusted the tension like you suggested but it still hangs up on the right hand ribbon setting and now it's just a bit too strong on the left hand ribbon setting. I've tried cleaning the cogs and rods thinking some gunk built up in the worm gear or something, but I can't figure out for the life of me why the issue only exists when the right hand ribbon is engaged. I can work around it, but for a machine with automatic spool reverse, I kind of want it to work.

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  3. Hello. I'm curious if you know how to fix my issue. I had the same problem with the carriage not advancing on my KHM, but (and here's the kicker) it only happened when the right hand ribbon was engaged. If it was set to engage the left hand ribbon, the carriage moves like a dream! I adjusted the tension like you suggested but it still hangs up on the right hand ribbon setting and now it's just a bit too strong on the left hand ribbon setting. I've tried cleaning the cogs and rods thinking some gunk built up in the worm gear or something, but I can't figure out for the life of me why the issue only exists when the right hand ribbon is engaged. I can work around it, but for a machine with automatic spool reverse, I kind of want it to work.

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    1. I'm afraid I can't help but a niggling thought tells me that the best way of replicating this might be to wind the ribbons the 'wrong' way round. The KHM threads differently from most machines (though Corona 4s are like this too) in that the feed and take-up sides of the spools are nearest the keyboard rather than the platen. Undue tension in the ribbon may be preventing the carriage from moving. That's probably not it, but worth checking the obvious first.

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  4. Ahhh, yeah. I thought of that. The problem occurs even when there's no ribbon. My only guess is that when the ribbon is set to spool to the left, the worm gear is at a pretty straight angle to the tension belt, where it connects and is turned. When it's set to spool to the right, the worm gear drops to engage the gear below, which puts it at a slight angle on the tension belt side. I'm wondering if maybe the knuckle in the worm gear rod (sorry, I don't know all the technical terms :P) has some build up inside that makes the rotation at this slight angle a bit more sticky. It's not a ton, but just enough to stop the carriage from advancing every once and a while (typically at the start and end of a line).

    If I figure it out, I'll be sure to let you know. Thanks for your thoughts, though!

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