Straightening Singer Featherweight bobbin shaft

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:
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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.
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.
-J
Reply to
Jason
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I don't think that application of heat is a good idea. You stated you can't visibly see any distortion. Are you sure the resistance is caused by the shaft and not in another part of the bobbin assy.? What type of metal is the shaft? You might want to speak with someone who is familiar with restoring old sewing machines.
-Tom
Reply to
TT
On 26 Mar 2005 14:00:38 -0800, the inscrutable "Jason" spake:
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. ;)
That proves how seldom they went bad.
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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Reply to
Larry Jaques
If you have a lathe, you probably have a dial indicator. I would verify that the shaft is indeed bent with the indicator - if not, then a little investigation is in order as to all the components connected to the shaft - do they all operate freely? If the shaft is slightly bent, I would suspect that it would be binding 360 degrees, not just half of its rotation. You may be able to place the bend close to the "cast base plate" and gently pry to straighten - checking over and over with the indicator to know how much correction you are gaining. Ken.
Reply to
Ken Sterling
Can you lap it in with some fine valve grinding compound?
Tom
Reply to
Tm
Check into the Featherweight Fanatics newsgroup.
"If you would like to join our daily discussions, please send an e-mail message to snipped-for-privacy@ttsw.com"
Several knowledgable and helpful folks follow and contribute to that group. One is a guy named Jim Sorrell, who has bee repairing and restoring these machines for many years. We've dealt with Jim and would recommend him highly.
Reply to
Don Foreman
Thanks for the ideas. I disconnected the shaft from all the other parts, so I'm sure it's the shaft and sleeves. I'll ask on the sewing machine lists and see what I come up with, but it looks like the shaft itself will need to be repaired or replaced.
-J
Reply to
Jason
On 27 Mar 2005 01:00:11 -0800, the inscrutable "Jason" spake:
If it's slightly scored from lack of oil, you can probably get by with a honing (or reaming) of the cast iron bearings and a quick crocusing of the shaft itself. That one pin looked to have a head on it, so prying it out with a wedge may be a possibility. G'luck!
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Reply to
Larry Jaques
Jason, Be interested in knowing how this all turned out...... Ken.
Reply to
Ken Sterling
The friendly university machinist helped me force out one of the dowel pins, which are indeed tapered. I put one end of the shaft in a drill press, and using a clamped pencil as a dial indicator noted perhaps a millimeter of wobble at the bottom, then ran out of time for today.
The bobbin-side end cap was ground in places on the face next to the bearing, so that seems to account for most of the resistance, although it still doesn't turn as smoothly as I'd like even without the end cap forced against the bearing.
The machinist pointed out the tapered cuts down into each end face of the shaft, and it seemed like he was saying they're useful for checking straightness and whatnot. But I can't figure how to use them for that -- seems to me like I'd just clamp one end in the lathe and use a dial indicator at the other end. (As you can see, I've reached the extent of my true-Machinist skills)
Anyway, it seems like the options now are some combination of turning down the shaft, grinding down a bit of the end cap so it doesn't bind, and just manufacturing a new shaft. There are some scratches in the journaled shaft surfaces; the machinist kept pointing out the journaled surface -- is there some trick to producing such a surface on a lathe?
Also, I suspect the end caps are cast iron. All I can tell from Google is that it's possible to grind cast iron, but it's different from dealing with normal steel.
As to machining a new shaft, the biggest trick seems like it would be measuring the angles for the dowel pins, since they're offset by a few dozen degrees. First I'd have to get the other pin out, which doesn't seem possible by pounding (even with heating); he said that'd entail end-milling out the pounded up pin end before I could drill it -- that just means milling it flat, right? Once the pin is out it seems like I could line up one end so the drill sinks through the hole, then note the table rotation required to sink through the other hole in order to get the angle. But I'm hoping it won't come to that -- I think with just a tiny amount of reduction, the shaft will go from finger-turnable-with-a-little-effort to free-spinning, and hopefully that won't cause noticeable errors in the sewing stitch.
Thanks for your comments! I think that unless fine sandpaper and maybe the suggested valve grinding compound fix up the shaft, I'll have to talk one of my engineering buddies into an exchange of food for machine-shop tutoring. :)
-J
Reply to
Jason
From A retired Sewing Machine Mechanic. 1st the machine is old hwnce it will be worn, there will be no need to "Lap" or anything like that. From 25 yeard of experiance the trouble will be in the Bobbin Race. Remove that and if the Race itself is mot a "Mirror" finish that's the problem. Forget all the bearings it won't be there. First Put the Bobbin into the machine, then hold the Bobbin with your finger tips as best you can. Turn the hand wheel backwards and forwards slightly is the Bobbin in your finger tips shudders at all it is the problem. When you do this action the Bobbin should remain stationary and you should feel a smooth movement. To rectify this remove the Bobbin Case not the part that you put the spool into the Case that remains in the machine, and polish it with "Rouge" (I'm not sure what you call it in the US) If the outer ring of the Case Bobbin Case not the part that you put the spool into, the Case that remains in the machine, Sorry but it's a bit difficult to explain hope you can figure it out "Kiwi" Jack
Reply to
Jack
Thanks for everyone's suggestions! After unhooking everything from the shaft (bobbin end and pushrod end), it was still tight. Filing down the cap at the pushrod end where it meets the bearing seems to have done the trick.
I've got it stitching now, although the needle broke when I hooked up the motor. The needle was old and bent, and I had noticed it hitting the side of the hole in the table. That and the take-up spring doesn't seem to be quite right. But hopefully with a little more tinkering she'll be right.
(My gf's birthday was yesterday, BTW, and she loved it! :)
-J
Reply to
Jason

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