From the design point of view, one of the many really neat things about the Grasshopper is the way that when you put a bobbin on the end of the motor shaft in order to wind thread onto it, doing so disconnects the drive to the motion i.e. your bobbin goes round but your needle no longer goes up and down when you start the machine.
Actually, let’s make that “should disconnect” the drive, because if you’ve just acquired a Grasshopper which has been seriously neglected, putting a bobbin on might not disconnect it. In fact, you might not even be able to get a bobbin on to the shaft …
I can’t with that machine, which is in a really sorry state. Apart from the surface rust, what’s stopping a bobbin sliding on to that shaft is shown in the picture below.
The wedge-shaped doohickey running along the top of the shaft in that photo is properly called the coupling key, and it’s that which is the problem. It’s seized solid. It can’t sink down into the groove it sits in, which is what it needs to do when you slide a bobbin onto the shaft.
Now, the best remedy for any problem with this particular bit of a Grasshopper depends upon three things – the precise cause, your expertise with things mechanical, and what tools and magic potions you have available. So I reckon the way forward here is to explain how the thing’s supposed to work, so that you can decide for yourself how best to proceed with your particular machine.
That’s what it’s supposed to look like, and here’s how it all works. The motor pulley and the gear wheel behind it are one and the same plastic moulding, so we can ignore the gear wheel part of it here and just talk about the pulley.
The pulley is actually free to rotate about the shaft, but it’s prevented from so doing by the coupling key, which sits in that slot in the motor shaft. Now, if you look again at that picture above, you’ll note that about halfway along the key, there’s a semi-circular depression in the shaft. That’s actually a round hole, in which sits the spring which pushes the key back up when you push down on it. It’s that key which locks the pulley to the shaft.
As photographed above, when the motor shaft turns, so does the pulley, because the coupling key has coupled them together. Push a bobbin onto the end of the shaft, and as you push it further on, it pushes the coupling key down into its slot. When the bobbin’s on as far as it’ll go, the drive to the motor pulley is disengaged, because what locks it to the shaft is the end of the key, which is now depressed into its slot by the bore of the bobbin.
If that doesn’t yet make any sense, it soon will …
In the picture above, the arrow is pointing to the end of a slot which runs along the bore of the pulley. And what you can’t see is that the far end of the coupling key engages with that slot. It’s confusing because there’s a notch in the coupling key just where it continues into the pulley, as will shortly become apparent.
Hopefully all will become clear when we take the motor pulley off, and to do that we first have to remove the circlip holding it in place. We then need to take off the flywheel, because otherwise the pulley won’t come off the end of the shaft.
As we slide the pulley off, you can see there the (worn) end of the slot in it, in which the coupling key engages. And when we take if off the end of the motor shaft, this is what we see …
There’s the coupling key pushed all the way up by the little spring under it, and you can now see the notch in it that I was on about earlier. It’s the bit of the key to the right of that notch which fits into the slot in the motor pulley and so locks the pulley to the shaft, in order to transmit the drive to the motion.
There’s your slot in which the end of the coupling key engages.
Now you can see why, apart from anything else, this all relies on the coupling key being free to retract completely into its slot in the motor shaft and to spring back up again when pressure is taken off it.
If the key won’t depress fully and return properly, you’re stuffed until you work out why and free it up so it does.
If you can get a bobbin on all the way but the motor pulley is still locked to the shaft, frankly your guess is as good as mine. All I can think of is corrosion of the shaft inside the pulley, or, and most likely, somebody who didn’t understand how it works has “modified” it …