After purchasing a fresh sponge bar for the Toyota K747 I started to put it through its paces. It knits stockinette beautifully, so I started working through the tuck stitches.
At first I couldn’t get the I and II buttons to stay in place at all. After some disassembly and a lot of oil, we got things moving again and it works great. But I quickly noticed that the 3rd needle selector wasn’t working. So I started to disassemble the machine to figure out why.
With the top cover off you can see some of the neat mechanisms in there. The zigzag gear (right) physically moves the needle selector up or down the needle bed. This means if you have a simple shifting pattern like a zigzag or checkerboard, you don’t need a punch card at all. You can just move the zigzag back and forth with each row.
Each of the blue needle selector levers rotates down to catch a small lever on the bottom of the machine. When these levers are caught, they cause the corresponding shafts (anyone know what these are really called?) to raise, which then push the needle butts forward. The small red lever releases the needle selectors.
Getting into the machine was a little tricky, you have to remove the card and zigzag knobs to access all the screws. Thankfully there’s a useful diagram in the K747 service manual. With the knobs removed, you can see the discoloration of the plastic over the years.
I had to fully remove the needle bed from the machine casing to get at the needle selector levers. Unfortunately by that time my hands were absolutely covered in grease so I couldn’t take many pictures. But once I got it out, I could flip it over and see the problem part:
The two little tangs on the bottom of the 3rd needle selector have somehow broken off, though I’m really not sure how. Unfortunately disassembly/repair of that part of the machine isn’t covered in the service manual. I see two options going forward: 1) I can carefully disassemble the needle selector mechanism, 3D print a replacement lever, and pray to God that I can get it all back together again, or 2) Fashion some replacement tangs with Sugru and hope they stay in place.
Since option 2 doesn’t require completely disassembling the machine, I’m going to try that first. There are a lot of little springs and I’m not sure I have the dexterity to get them all back in place again. I’d also like to better document the machine teardown, so sometime in the new year I’ll recruit an assistant and take apart / photograph the whole thing.
In the meantime the machine works great, and I can come up with plenty of patterns that avoid the 3rd needle selector.