Re: machine so hot the white plastic in the bottom of the bobbin case melted!
A lot of it has to do with how the machine works. That little gouged out bit on the back of a needle, called the scarf, is where the hook passes to grab the thread and make a stitch. It is VERY close to the needle when it does this. If something pulls the needle just a tiny bit to the back it can hit the hook, or more often, the hook race itself. The needle breaks. No buggy, just put in a new needle. Except that there is a pit in the hook race where it hit. Most people never give it a second thought until the trouble starts.toggle quoted messageShow quoted text
I once sold a 6500 to a quilter who was learning to free motion quilt. She came back several times complaining about her "lemon" machine. Each time the hook race was damaged from a needle strike, probably because she was moving the fabric while the needle was in it. I polished the hook 3 or 4 times, then replaced the hook race at my expense. Shortly after that it came in again. She had been in a class and her machine was breaking the thread constantly while all the other brands were fine - an obvious lemon. I threw in the towel and gave her back her money. The hook race looked like a cheese grater. I replaced it and sold it as a used machine. The new owner loved it and never had a single problem with this "lemon".
The hook is second only to the needle in the importance of making a stitch. Early machines with oscillating hooks sustained as much or more damage as our modern rotary machines. The difference is that the oscillating hooks are easily removed and polished, and cheap to replace if it comes to that. The rotary hook system requires a thin edge for proper operation. Because the bobbin case is help in place by a magnet, the hook race must be made of very soft aluminum. Needle strikes cause far more damage to them.
There's no need to sew in fear because of this. While take-up lever escapes make a lot of noise, they don't normally cause damage if you stop and fix it. (High school kids NEVER stop after threading wrong - they destroy an enormous number of hook races!) The big damage happens when the thread gets caught during a long embroidery, pulling the needle into the hook. Or sewing with the wrong settings, pushing, pulling or other atrocities. (I could always tell when a new customer had never sewn on a Janome before - one hand grabbing the fabric at the back of the machine, the other grabbing the front and pulling it through while sewing. This is a recipe for disaster and we had to retrain a lot of people who had sewn most of their lives on cheap Walmart machines.
It's easy to check for hook damage. Take an old stocking or pantyhose and wipe it around the hook race with the bobbin case removed. If it snags, you've got a burr. If the machine makes a horrible loud squawking noise while sewing, you've got a burr. If the thread keeps breaking, you make have a burr that is cutting it. Usually you can see the burr with a magnifying glass. A good mechanic can polish out the small ones, but sometimes a new hook race is required. I did replacements for $100, which basically covered the parts, with the labor being free. That's one of the reasons we did not retire rich!
Hook damage can seem like the thread came out of the take-up lever if the stitch gets caught in a notch on the hook race and does not release. In 3 or 4 stitches of this you will get wads of thread on the bottom, lots of clunking, and maybe even the bobbin case popping up and spinning. If this happens, open the door and check the take-up. If it's still threaded, you may have hook race trouble.
Topstitch needles have a larger eye, but this should not change the sound much. If your needle is making a popping sound, it's dull and should be replaced.
--- In firstname.lastname@example.org, "gbmko" <gbmko@...> wrote: