Originally Posted by
guy153
My point is really just that the "burden of proof" is on the guy drilling the holes. When I make a fork I buy the blades from Reynolds on the assumption that they've done the math and they're strong enough for the intended purpose, even if they are light. If I plan to make modifications to the design like removing material it's up to me to work out whether that is going to be OK. The same if I was making something less well-known than a bicycle-- I would have to work out what tubes to use and estimate the safety margin.
These links might be some places to start, but it seems like quite a complex problem. Especially if you have a bolt on both sides squeezing the tube. That will add some residual stress, which will be in tension in some places (the front and back of the tube I guess) and this might lead to fatigue.
Intuitively it just feels like something I would want to avoid because a fork failure is so unpleasant. If it was somewhere else on the frame experimenting a bit more might be justified.
https://www.fracturemechanics.org/hole.html
https://www.physicsforums.com/thread...weaker.952298/
Yeah, those are 100% fair points, and that first link is actually pretty darn good.
Forget about the hole for a second as it is proving to be a distraction; have you seen any resource measuring the amount of load a fork experiences along it's length? Interestingly enough steel forks tend to break/bend much higher because while that area has more metal it is also the one experiencing the most stress due to leverage. Well that and at the drop casting but those are due to material defects, too hard/brittle of a casting.
In any event; it may feel to go against logic but drilling a hole on the lower part of the fork, where there is less metal, should also be less of a toll on the overall strength of the fork as this area experience smaller loads. Drilling holes on the upper part of the fork ought to be of more concern.
Chances are I'm not going to do it on this project but I may start chucking dead steel forks in a pile and eventually test these assumptions. Basically rig the forks so I can crush them on both a hydraulic press and under sudden shock, see where they like to break even with a hole on them.