I have been riding my Raleigh XXIX for 5 years and have wanting to make a chainring for it. I have all of the tools, but it has been hard to get around to it while keeping up with the regular jobs. I finally got one done this week. Took it for a spin this morning.
It's a 33T to replace the one Truvativ ring that came on the bike originally.
I don't have a gram scale. I put it on my postal scale and it weighs somewhere between 40-50 grams. I didn't put much effort into making it light. Just wanted to try out the tooth profile. It worked fine on a quick 6-mile ride this morning.
This one is machined out of 1/8" thick (3mm) 6061 material that I had on the shelf. I did it in two setups on my Fadal CNC mill. I ran the mounting holes, teeth and center bore in one operation and flipped it over to cut the step and ramp on the teeth on the other side. So it is very concentric: no runout. The teeth are machined to 2mm thickness. I will probably redo it with thicker teeth for the wider chain on my SS.
What I learned so far: I need more clearance to mount the ring easily without removing the crank arm. I was barely able to get it over the spider. So cutouts are necessary.
I don't have a gram scale. I put it on my postal scale and it weighs somewhere between 40-50 grams. I didn't put much effort into making it light. Just wanted to try out the tooth profile. It worked fine on a quick 6-mile ride this morning.
This one is machined out of 1/8" thick (3mm) 6061 material that I had on the shelf. I did it in two setups on my Fadal CNC mill. I ran the mounting holes, teeth and center bore in one operation and flipped it over to cut the step and ramp on the teeth on the other side. So it is very concentric: no runout. The teeth are machined to 2mm thickness. I will probably redo it with thicker teeth for the wider chain on my SS.
What I learned so far: I need more clearance to mount the ring easily without removing the crank arm. I was barely able to get it over the spider. So cutouts are necessary.
I intend to get there before too long. I will not sell anything that I don't already have made. I know how that turns out. I need to get some 7075 material for strength and longevity.
Math and CAD. I used my old standby BobCAD V17. The software is 15 years old, but it's quick and efficient. For more complex stuff like fork crowns and 3D hot rod parts, I use a newer version of BobCAD.
I will check into coatings that will hold up once I get some 7075. This piece is just a test mule to check geometry and function. I really want to see how long 6061 will last, just for fun.
I've been talking to a friend that makes parts to see about getting some custom chainrings made. Let us know when you get around to selling these... I'd be up for buying one for my SS.
I did a similar design years ago. It turned out to be too weak, and collapsed under heavy load.
I did a revised version later where I did the cutouts pretty much the same, but with an end mill with a radius from both sides, and left a thin wall in the center. That one worked well.
Later I started using a mix of aluminum and composites, as that seems to offer a better weight to strength ratio.
Soon I'll have to make some more, as I'm about to be out of rings. I guess I'll look in the direction of the Hope design, but with carbon in the mix.
I did a similar design years ago. It turned out to be too weak, and collapsed under heavy load.
I did a revised version later where I did the cutouts pretty much the same, but with an end mill with a radius from both sides, and left a thin wall in the center. That one worked well.
I'll ask my drawing guy if there is a shortcut, and post it if he has something up the sleeve.
I couldn't make a CAD drawing if my life depended on it. He is on the other hand quite good.
When I made mine, I just had the numbers on a Post-It. Not the way it's going to be in the future. Made like 3 or 4 that way.
I could hardly imagine 2.5mm would be an issue with a 3/32" chain. I have made mine 2.4 as I recall. The height/ squareness, is a matter of entry/exit angle of the chain.
In a cad system, the easy way is to draw a chain on the smallest rear you intend to use it with. Then you can see if the edges collides on entry/exit.
Are you cutting these from sheet stock or off the end of a billet?
Reason I ask if sheet stock where are you getting your supplies. I need a new supplier for making skid pans for Moto Trials bikes! Mine has stopped stocking sheet aluminum, I guess the race car business dropped off for him.
On another note, love your designs so far, the bash guard is beefy and should handle a lot of abuse. :thumbsup:
Thanks. I have just been using 1/8" 6061 sheet that I have on the shelf. I am having trouble finding a supplier for thin 7075 sheet. At least an affordable one.
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