One of the great aspects about the time that we live in is the availability of technology to make things. I needed a #219 sprocket that didn't exist. 219 driver sprockets range from 11T to 18T. 219 driven sprockets range from 64T to 93T. To get my reduction where I want it on my mid bike drives I need a 40T 219 driven. I'd also like the center to fit a five bolt freewheel. Doesn't exist.
Here is my new 40T sprocket in the gap of what was previously available:
It's laser cut from .135" stainless steel, fits the freewheel down to .001" and the finish on the teeth is better than it needs to be. This is going to be a great part:
But as always seems to be the case with me, the first pass had to have a problem. I've designed pulleys in the past and have gotten used to that. This is my first sprocket. When I looked up the sprocket diameter for a 40T 219 sprocket I assumed that "sprocket diameter" meant the outside of the sprocket. No. It means the diameter of the center line of the chain. The 219 chain doesn't fit this pretty part. So I carefully measured the roller diameter and pin to pin distance of a 219 chain and went back to my sprocket drawing.
Luckily the tooth profile was correct so all I had to do was plot the chain roller diameters and pin spacing on the correct diameter. I resized the 40T tooth profile and everything fits like a glove.
So back to the laser cutter on Monday. I know that sometimes it's difficult to understand why projects take as long as they do. If I knew everything going into them they would go a lot faster.
I plan to use the lessons learned from making this secondary reduction sprocket to make freehub final drive sprockets. My plan is to design and laser cut cogs from 16T to at least 34T and then fit them on a steel freehub with spacers to create six speed spacing. Six speeds is more than we need but the derailleur will shift better with more steps from 16T to 34T and with any luck at all it will be possible to use a six speed indexed shifter instead of a friction shifter. We shall see.