DIY Singer 66 Belt

August 2020 · 5 minute read

The ancient belt that came with my Singer 66 snapped today. I knew it was only a matter of time, so I had been thinking about various ideas for replacing it. It felt right to make a new one; it didn’t feel right to buy one. This machine has lasted 97 years in wonderful running condition. I wanted to believe that it could keep working for another couple thousand regardless of the existence of its manufacturer. That said, my solution isn’t perfect and I’ve only been using it for about a day. I’ll try to remember to update this post over time as I see how it performs. For now I’m happy enough with how it works that I’m using it. TLDR: My machine is a treadle-powered 1927 Singer 66 in an open side cabinet #24. The solution I ended up with was an approximately 68.5” length of 1/8” low-stretch polyester cord. After threading it through its path, I sewed the ends together with polyester thread. After engaging it to make sure the fit was right, I used ~4.5” pieces of duct tape, torn lengthwise into thirds, to wrap the belt at intervals to increase the traction and prevent slippage. This seems to work fairly well; I was sewing some kind of PVA-backed material today and I was able to use the treadle to get through it. Adding duct tape to the rest of the belt would likely increase the traction further, but once the material gets thick enough to require it I might prefer using the handwheel anyway. The original belt was made of leather and badly dried out, as is common with these machines (I needed to replace the belt on my motor-driven 66–18 as well). The belt measured approximately 67.5” long (I found that the paracord belt had to be almost an inch longer, 68.5”), with a diameter of approximately 1/5”. It was sewn together with thread when I got it; I re-sewed it with polyester thread and it lasted for a few days. I had joked about replacing it with Ethernet cable, which seems to match the diameter and provide a nice grippy surface. I still think that might work, but I’m not sure how I’d join the ends. When re-sewing the belt, I broke two needles, bent one, and hurt a couple of fingers; I wanted to avoid repeating the experience if possible.

worn original belt. Dried, cracked leather with duct tape over closing stitches

worn original belt. Dried, cracked leather with duct tape over closing stitches

I decided to try 1/8” paracord first. It’s visibly thinner than the leather and very smooth, but I figured that duct tape would make up the difference in both. I’ve heard that the belts are sometimes joined with metal staples. I tried using dressmakers’ pins but they tended to pull apart under the strain. It’s notable that so far the paracord fibers (fused at the end) have never been the things that failed.

bent dressmaker's pin used as a staple in the end of a piece of paracord

When I was researching this machine before buying it, I wasn’t able to find a clear image of the treadle online. The #43 cabinet is not the classic cast-iron treadle base I usually think of; it’s a wooden cabinet with a flywheel mounted into the bottom-right side. I was a little disappointed that it wasn’t the classic one, but now that I’m used to it I think I like it better. I love the idea of human-powered machines and this treadle-and-flywheel arrangement is pretty compact, extremely robust, and would be fairly easy to remove and reinstall in a different device.

detail showing the structure of the treadle in the bottom-right corner of the case

Treadle arrangement in #43 cabinet. I got you, past Raphael.

The following images show the belt path I’ve been using, which seems to work well. I’ve found that sewing the belt together is a time consuming and annoying operation, so it’s worth checking twice that the belt is threaded correctly before closing it.

Top of belt path showing belt passing around handwheel, inside bobbin winder

Note the paracord traveling inside the bobbin winder. The belt must be threaded through before closing; there isn’t enough clearance to fit it afterwards.

belt path showing belt passing through holes in machine mounting plate, front and back

Front and rear holes for the belt to pass through

Underside. Note that the back of the belt needs to pass through its own opening, far right at the back of the case.

Underside. Note that the back of the belt needs to pass through its own opening, far right at the back of the case.

The back of the belt needs to come forward this way, on the underside of the axle and inside the wheel frame.

The back of the belt needs to come forward this way, on the underside of the axle and inside the wheel frame.

The front of the belt passes down through this “shifter” loop, then joins the other side. This is the correct orientation for the shifter during operation. When you want to close up the machine, you pull the trigger at right while running the treadle, and it disengages the belt. To re-engage the belt, you simply open the machine and run the treadle a few times with the shifter in this resting position. The manual advises leaving the machine un-tensioned to avoid wearing out the belt.

The front of the belt passes down through this “shifter” loop, then joins the other side. This is the correct orientation for the shifter during operation. When you want to close up the machine, you pull the trigger at right while running the treadle, and it disengages the belt. To re-engage the belt, you simply open the machine and run the treadle a few times with the shifter in this resting position. The manual advises leaving the machine un-tensioned to avoid wearing out the belt.

Detail of the belt ends joined with polyester thread. The very ends of the paracord are fused lumps of plastic, and so far have not seemed to notice any strain from the thread.

Detail of the belt ends joined with polyester thread. The very ends of the paracord are fused lumps of plastic, and so far have not seemed to notice any strain from the thread.

I couldn’t really think of a good way to illustrate the tension that I eventually went with. This shows that at the “right” tension (without duct tape on the paracord) I could just get the belt to slip if I yanked up on it suddenly. If the belt is too tight, the flywheel will stop every time the treadle rocks forward and backward, making the belt slip and / or the machine reverse, causing a jam.

I couldn’t really think of a good way to illustrate the tension that I eventually went with. This shows that at the “right” tension (without duct tape on the paracord) I could just get the belt to slip if I yanked up on it suddenly. If the belt is too tight, the flywheel will stop every time the treadle rocks forward and backward, making the belt slip and / or the machine reverse, causing a jam.

After the belt was installed and I was happy with the tension, I added duct tape every few inches to improve traction. I found that it was easiest to sit at the machine and add the tape in sections about this length. I found that 1/3 the width of the duct tape was enough to fully wrap the cord without adding too much bulk. The duct tape I used was pretty thin; the fibers were clearly visible on the roll. I don’t think thicker, stiffer tape would be very good for this.

After the belt was installed and I was happy with the tension, I added duct tape every few inches to improve traction. I found that it was easiest to sit at the machine and add the tape in sections about this length. I found that 1/3 the width of the duct tape was enough to fully wrap the cord without adding too much bulk. The duct tape I used was pretty thin; the fibers were clearly visible on the roll. I don’t think thicker, stiffer tape would be very good for this.