Even some modern bling CNC can suck

OrangeRetro · Jan 4, 2009

Your explaination seems to make sense. The picture below shows the two pieces together. I reckon the right hand side probably cracked and the left hand side sheered with the force of the brake lever being pulled. If the initial crack happened durring that crash 6 months ago then the lever has held together well, its been used a hell of a lot this year. It just doesn't feel right though that it has been there that long and that such a slight impact would have damaged it in that way?

IbocProSX · Jan 4, 2009

Crack initiation maybe could be from a nick or scratch that could have happened in that crash as you suggest. And since you brought it up, if I were Hope that would be my answer.

But a classic failure mode is cracking initiating from CNC milling grooves (Onza HO brakes anyone?). And there's plenty CNC action in the sculpted surface of that master reservoir and clamp. Mind you, all Thomson stems and posts are machined proving it can be done. But the devil is in the detail of alloys selection, matching the tooling spec and cutting parameters to it, and then a rigorous QA/QC regime checking the production. I'm afraid all it takes is a little burr on the tooling.

Xesh · Jan 4, 2009

It may also be down to the fact that Hope just machined off a fraction too much metal from the clamp.

I remember bitd when Middleburn cranks used to crack on the left hand BB axle interface. All Middleburn did was to machine a fraction of a mil less metal from them to solve the problem (hence the bulge on the outside of the left arm near the taper).

Even some modern bling CNC can suck

OrangeRetro

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