Double Trouble
09-18-2015, 04:34 PM
#1
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Join Date: Mar 2015
Location: Denver, CO
Posts: 4,261
Double Trouble
Sometimes it's hard to know whether or not to post something. As a relative newcomer to sewing machines, I would be hesitant to claim any discovery. More likely it's so well known that no one talks about it. But I learned something new.
We recently worked on a machine that didn't want to turn It was a 2x rotary hook machine. The problem turned out to be in the bobbin hook assembly. In the process of thinking about it, it occurred to me that all 2x rotary bobbin hook machines have a built in liability.
The gear mechanism (bevel gears and shaft) that doubles the speed of the hook, also creates a mechanical advantage for the hook to stall the machine. Any problem with the hook mechanism can slow the machine twice as easily as in other parts of the machine (2:1 gear ratio). This means a jammed piece of thread might seem like two pieces. Dirt and dust may behave as if there were twice the amount. And oil or grease that has hardened for ten years, could seem like it had been twenty. If people have unusual difficulty with rotary bobbin hook areas, this could be why.
I'll certainly look first at the bobbin hook area of a 2x rotary if the machine doesn't turn easily in the future.
Am I one of the last to figure this out?
John
We recently worked on a machine that didn't want to turn It was a 2x rotary hook machine. The problem turned out to be in the bobbin hook assembly. In the process of thinking about it, it occurred to me that all 2x rotary bobbin hook machines have a built in liability.
The gear mechanism (bevel gears and shaft) that doubles the speed of the hook, also creates a mechanical advantage for the hook to stall the machine. Any problem with the hook mechanism can slow the machine twice as easily as in other parts of the machine (2:1 gear ratio). This means a jammed piece of thread might seem like two pieces. Dirt and dust may behave as if there were twice the amount. And oil or grease that has hardened for ten years, could seem like it had been twenty. If people have unusual difficulty with rotary bobbin hook areas, this could be why.
I'll certainly look first at the bobbin hook area of a 2x rotary if the machine doesn't turn easily in the future.
Am I one of the last to figure this out?
John
09-18-2015, 08:41 PM
#3
Super Member
Join Date: Feb 2012
Posts: 8,091
Gear driven rotary hook machines have no trouble driving the point of the hook right through fingers. 
[ATTACH=CONFIG]531055[/ATTACH]
I got the scar to prove it.
As for thread and debris jamming them up, that goes without saying. Gotta keep 'em clean.
Joe
[ATTACH=CONFIG]531055[/ATTACH]
I got the scar to prove it.
As for thread and debris jamming them up, that goes without saying. Gotta keep 'em clean.
Joe
09-19-2015, 10:55 AM
#4
Junior Member
Join Date: Oct 2011
Posts: 216
Mine went alongside the fingernail, into bone and broke off in finger. I had to demand they xray the finger because I knew the tip of the needle was still in there. They did and it was. Minor surgery to get it out. But I still get my finger too close sometimes.
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