Monday, October 25, 2010

Sewing Machine Repair Adventure

It was a dark and stormy night.....
Well, not really, but it *has* been raining on-and-off here the last week or so.
Anyway.....My wife came out of the bedroom the other night, and told me her sewing machine "Wasn't pulling the fabric in", so I went in to take a look. I pushed on the foot pedal and heard the "Ziiiing" of an unloaded motor, and saw that the needle wasn't going up and down. Hmmmm.....has to be a broken belt, so I took the top cover off to inspect things. The first thing I noticed (besides the belt being all chewed up!) was that there must have been a full spool of different colored threads wrapped around the inside of the hand wheel mechanism. She has the operating manual for it, but other than how to thread it and set up what kind of stitch you wanted, and where to put the occasional drop of oil, it was pretty useless. So, since I had the model number (Singer 5107), off I went to Google to see what I could find. I found a free parts list, and paid $12 for the complete service manual, and started calling around this morning for the belt. Several places were closed Mondays, or the phone was disconnected (and the phone numbers were from Singer's website!), and a couple told me "Servicing MUST Be Done By Qualified Professionals!" in a rather rude tone. Geezz....I helped keep my Mom's Singer running when I was a kid, and repaired several other Singers for various girlfriends and their Moms over the years, and have mechanical skills that are just a notch or two above "Normal For A Guy", so I wrote off those places pretty quickly. I finally found a place over in Norwalk that not only had the parts, but was very friendly is suggesting other normal wear-and-tear items that would be nice to get. Got the belt, a "Bobbin Winder Ring" (looks like a slot-car tire), and a couple of spare light bulbs for $12 total, less than the price of just the belt at the only other place that would talk to me. He wanted $24, and it was "Special Order, Pay In Full Before We Order It, NOT Returnable, and It'll Take 3-to-5 Days To Get It".
Got the belt installed, cleaned out big bunches of lint, old grease, and thread scraps, scrubbed the machine inside and out, oiled it in all the places the manual said to, tightened up all the hardware on the table it mounts to and waited for my wife to get home.
She was thrilled, and said it looked like a new machine.
20 minutes later she came back out and said "Honey, it's not working right".
Uh-Oh.....Probably should have tried to run it before I bolted it back into the table! Figured out I had the belt tension set too tight, but it was still binding about half-way through the cycle it runs to make one complete stitch.
Now, if you've ever had a sewing machine apart you'll probably know what I'm talking about. There's one main shaft driven by the motor that runs through the entire "Top End" of the machine, and runs the needle up-and-down, and has the cam assemblies that move the needle back-and-forth to make different stitches. Take the top cover off and watch one run, and it should be obvious how it does things like make the needle go up-and-down. The tricky part is what you don't see....all the stuff underneath, where the "Bobbin Case" goes, and the mechanism that moves the little fabric grabber up-and-down and forwards-backwards to pull the fabric through. I *NEVER* worked on that stuff because when I worked on sewing machines before, it was consider Black Magic that took "Special Service Tools" to adjust, and woe betide the Young Wizard Mechanic who messed up Mom's machine trying to learn it!
But I digress.....
On one end of the main shaft in the upper part of the machine, right by the hand wheel, is a crank throw, and a connecting rod running down into the nether regions that makes all the little Magic Parts go up-and-down, and back-and-forth. It's a pretty clever collection of shafts, cams, bevel gears, and cranks that takes the up-and-down motion from that connecting rod I mentioned, and turns it into a back-and-forth half-revolution of the bottom mainshaft, which also moves the cams and bevel gears, and makes the fabric grabber work.
Now was the time I was glad I had the Service Manual! With the connecting rod disconnected from the upper mainshaft, and moved aside so it wouldn't catch on the crank throw, the machine ran perfectly, nice and fast and quiet. So, I pulled the machine out of the table, and took it into the living room table where I could sit down and turn the machine over to look at the bottom. I found several things that were causing the lower mainshaft to bind up at one particular point in its rotation. These was some dried out caked grease that had to be cleaned out, and under a cover was a set of bevel gears, with more dried out grease, and a loose set screw that held one of the bevel gears in place. These are "Half Bevel Gears", as they're not a complete gear, but only one sector of it, and it had slipped enough that it was running out of teeth and hitting the solid part. And the housing that holds the Bobbin Case was packed full of old lint and other debris that caused a lot of drag on the entire mechanism. After I cleaned everything out, and reset the timing of the gears, it turned over smoothly. I then reconnected the top part of the connecting rod, crossed my fingers, and plugged it back in and pressed the pedal.
The machine ran smoothly, pulled the fabric through like it's supposed to, and made correct, tight stitches without skipping any, which made my sweetie giggle like a school girl. She still has to adjust the thread tension, as I kinda screwed up the adjustment by grabbing the knob accidentally and turning it.
I'll post some links on the subject of "How Do I Fix My Sewing Machine" on Tuesday.

How Sewing Machines Work
Secret Life of Machines: The Sewing Machine, Part 1
Secret Life of Machines: The Sewing Machine, Part2
Secret Life of Machines: The Sewing Machine, Part 3
Animation of Needle and Bobbin to produce Lock-Stitch


  1. At the USPS we had some ancient string bundlers or "tie out machines" that would wrap two strands of string around whatever you wanted to tie shut, then tie a knot and cut the string. Bunn made 'em back when dirt was new.

    I thought I was pretty clever keeping those things running and it was generally for reasons like you mentioned - old string fragments and grease buildup.

    But, those machines were pretty simple compared to a sewing machine!

  2. Yep, I've worked on very old machinery that was kept running tip-top shape by careful maintenance. Back when I was an Industrial Controls Engineer, the place I worked for would fix just about anything that had an electrical motor in it. I've worked on motor control panels from the 1880's, when they were just learning to build motors! Slate back-panels with brass studs and fabric covered wiring, oil/pneumatic dashpots for timers, and stepper-relay driven "logic". It was amazing to see this ancient stuff still operating, and doing it's job just fine, thank you.


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