Making my own parts

[capner2112]

I was thinking that, so I'll opt for something like that similar to Hollowtech's design. Would it be wise to pocket out the inner side of the cranks making it a "U-beam?" Weight savings isn't critical, but worth thinking about.

[xerxes]

What are you trying to acheive, what's the objective of making your own cranks and chainring?

The one bolt chainring fixing is like those on old American style one piece cranks. It was a lousy system and was never designed with looks or performance in mind, only to be easy and cheap to manufacture.

If you're making something yourself, surely you want to make something better than what's available "off the shelf" now, not something merely adequate and most closely related to a 50 year old design that was only ever intended to be cheap and easy to make. :S

[nfmisso]

(08-27-2012, 08:38 PM)capner2112 Wrote:  I was thinking that, so I'll opt for something like that similar to Hollowtech's design. Would it be wise to pocket out the inner side of the cranks making it a "U-beam?" Weight savings isn't critical, but worth thinking about.

A 'U" is very poor in torsion - which is very important for cranks - think about the load thru the crank when you have the pedals at 9 and 3 (horizontal)

[capner2112]

Xerxes- The objective for me is experience. I'm not an engineer and have never made my own drivetrain parts. Since I have an interest in the bicycle industry, I'm still green with knowledge and don't really know how to break in, so I need to start somewhere. Going with the single-bolt design is like training wheels. I could have easily just picked stuff off the shelf long ago, but for me this is worth it.

[xerxes]

OK, fair enought, but I wonder if the crankset is the right place to start. It's probably one of the most highly stressed components on a bicycle and even the big boys get it wrong on occassion, I remember reading about a particular model of Campagnolo cranks that were prone to failure, it was eventially traced to a radius between the crank and the spider on the drive side being too tight, causing a stress riser, from which a crack propagated, leading to eventual failure.

As I mentioned earlier, quite a few bicycle components are now forged for added strength. There was a fashion for CNC machined MTB components in the 90s, all available in a range of pretty anodized colours and costing 3 times the price of more run of the mill Shimano components. Unfortunately they seemed to suffer failures at 3 times the rate as well. I'm thinking in particular of Hope hubs, lovely to look at, but I've seen quite a few failed Hope hubs, but not many Shimano ones.

[capner2112]

I see your point and where you're coming from with concern. I picked the crankset because it's what I needed to complete this bike, and I passed on making the BB because it was cheaper. Performance-wise, I'll be the only one really using these cranks, and if I make more I will probably do a spider. There's so much variety to pick from in terms of components, and when someone gets it right it's hard to keep up (like Shimano and Campi). There's other component's I'm planning to make also, so no sense in overloading myself.

[capner2112]

Here's a long awaited update to this project, namely the sprocket. I found some engineering data on how to properly design the toothform and since I'm not an engineer yet I really can't say if it'll work for this application (the information came the Standard Handbook of Chains textbook I viewed online). All of the information can be found in the below image.

[attachment=3906]


xerxes- Ever since you put the thought in my head and considering I haven't moved past design, it's worth redesigning the drive-side crankarm to accommodate a spider versus a single pin. The benefit is it removes the need for the mating boss and bore get it concentric so long as my bolt pattern is concentric. I'll see how things work out.