Coil Spring Winder Tool

Custom tool to wind a seatbelt spring safely.

TL;DR

I was repairing the seatbelt rewind springs on the Celica when one fully unwound. Winding it back by hand cut up my hands and got me nowhere after half an hour. I modeled a small 3-part mould with a crank in CAD, printed it, and finished the job in about five minutes.

Loose seatbelt spring

Seatbelt springs store a lot of energy in a thin steel ribbon. Once one is loose, you need to coil it tight again and lock it before you put the retractor back together. Doing that with bare hands is slow, and the ribbon edges are sharp. I wanted something that held the coil in place while I cranked, then let me zip-tie it so it couldn’t spring open on the bench.

First attempt

The first version could wind the spring, but it couldn’t let me tie the coil safely afterward. I added a push block meant to raise the coil a few millimeters so a zip tie could go around the outside. On the desk that sounded fine. In practice I couldn’t get a tie around it, and the spring blew open on me twice.

Time for a redesign.

Second try: zip-tie slots

Same basic idea: a three-part constraining mould, a slit for the ribbon, and a crank. The middle tang of the spring sits in the crank slit, the rest of the coil feeds through the mould slit, and the whole stack bolts together with M3 hardware.

The useful change is five slot cutouts through the mould. You push zip ties through those slots so they grab only the coil, not the tool. Five is probably overkill. Two might be enough. I value my fingers more than three zip ties.

How to use it

1. Put the crank through the top piece and the middle piece
2. Seat the coil’s center tang in the crank slit
3. Pass the steel ribbon through the mould slit
4. Add the bottom piece and screw the mould together
5. Crank, and push ribbon in as needed when it bunches

In action

The seatbelt went back together in a few minutes of cranking. The tool is still in the box for the next spring that gets away from me.