On 26 Mar 2005 14:00:38 -0800, the inscrutable "Jason"
spake:
I picked up a 1951 Singer Featherweight sewing machine recently. It's
in great shape, except that even after applying lots of oil, the shaft
which rotates the bobbin assembly resists rotating through about half
its travel. Presumably this means the shaft is very slightly bent,
although I can't detect any distortion visibly. So, while I can still
turn it by hand, the motor isn't quite up to the task. Here's a photo;
the problem is the light shaft running down the middle:
Check for pieces of thread in the mechanism, Jason. If none,
disassemble each piece connected to that rod and run it through
the range of motion again, looking for the actual area which is
causing the binding.
When I picked up the old Universal machine (ca. 1930s), it was having
a hard time running. I adjusted the angle of the motor so it wasn't
pushing the armature into a worn bearing and it spun 3x faster. After
a quick oiling, it ran like a new machine. Five bucks well spent.
http://www.lunkwill.org/tmp/singer.jpg
As you can see in the photo, it's about a 1/2" dia shaft held in place
by two cast iron mounts at either end, with cast iron caps at either
end connecting to the bobbin assembly and motor rod. The caps are held
in place by about 1/10" dowel pins, which unsurprisingly can't be
pounded out.
That proves how seldom they went bad.
Here are the solutions I can think of, but I'd appreciate your
comments:
1. Remove the shaft by drilling out the dowel pins or perhaps by
careful heating of the caps with a torch to loosen the pins. Then
either:
a: turn the shaft on a lathe so it moves more freely. (How much play
might this introduce?)
b: cut a new shaft and make sure the caps end up at exactly the right
places. (Apparently, bobbin position and rotation needs to be rather
precise)
2. Leaving the shaft in the machine, heat the center of the shaft until
it just starts to become plastic, rotating the shaft continuously as it
cools, so that the mounts themselves ensure smooth rotation. Potential
problems would be twisting of the shaft causing the caps to be at the
wrong angles, and expansion of the shaft preventing any rotation while
it's hot.
3) Neither of the above. Ask a sewing machine repairman what he'd do,
then do that.
If you can't find one to talk to you, keep removing mechanisms from
the shaft until it turns freely and go from there. Those large old
shafts don't bend very easily and they're tougher than the brittle
cast iron around them. Chances are good that it's something else
that's bent, an addition to the shaft, if not a simple thread buildup.
If all else fails, try drilling out the pins and look for scoring. It
could have been run completely unoiled for 30 years.
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