Part 7: Ease of Seat Adjustment

Ease of Seat Adjustment

The ease and speed of adjusting seat width is the heart and soul of this design and the most significant claim of my pending patent. The mechanism is simple. There are two spring plungers, one for each seat half. To adjust width, you pull one plunger, slide that half to a new position, and release the plunger so it locks. Then you repeat on the other side.

After I unboxed the prototypes, the first thing I did—before mounting a seat—was adjust the width. They shipped in the narrowest position. I pulled a plunger and slid one half out to the widest position. It moved fairly easily and snapped into place when I let go. I did the same on the other half with the same result. With both halves now at the widest position, I tried to slide them back to narrow. That took more force than sliding out. I saw the same pattern on the other two prototypes, though not quite as stiff as the first. I made a note and decided to ride it before tearing anything down.

On my first test ride I changed width five times. I could make the adjustment, but I was not satisfied with the force it took. Back at the bench I disassembled the seat to see why sliding from widest to narrowest felt harder.

I found two issues. First, there was flashing inside the square opening in one of the seat halves. Flashing is a thin bit of extra material from molding. Second, the end edges of the guide rail were square and sharp. The flashing was making contact with the rail in both directions, which added friction. The force was worse going from widest to narrowest because the edge of the rail was being pushed into the flashing.  

I took all three prototypes apart, removed the flashing where needed, and filed a small chamfer on the ends of each guide rail. After reassembly the halves slid much easier and locked cleanly.

For production, the guide rails will ship with rounded ends. We are also adding a step to inspect for flashing.

A note on prototype materials. The prototype bases were cast nylon made in a silicone mold. That is a common choice for prototypes because it saves cost. For production we plan to use injection-molded polypropylene. The injection molds are a significant investment, but the process is controlled and repeatable. The materials are different, but for our design both provide the structure integrity we need. We will test first articles from the injection molds and ride them before we approve anything. 

Takeaway
Quick, tool-free width change is only useful if it feels smooth and locks positively. Finding and fixing those small friction points made the mechanism easy to use the way I intended: pull, slide, click, ride.