unterhausen

I think you will be disappointed, but maybe there are engineering schools that are different than Penn State. Although I suspect you are familiar with not being able to get any work done without a charge number. All the bicycle related experiments that I have thought about doing would require enough specialized mounting that I haven't pursued it. I sometimes wish some of the machines I built were still around, lots of potential there for bike experiments. But we needed the room, so they are gone.

Although taking a hammer to some eyelets is pretty interesting, so I might go ahead and do that.

One thing I found in one of my fatigue experiments is that having loose bolts leads to early failures. I never did too much work on that, but I did find some literature about it that agreed. Unfortunately, I haven't been able to find that paper again. But if there is any constant on rack mounting, it's that people often fail to tighten rack bolts enough and they come loose. So any time you hit a bump, there is a big impact. This isn't good for the frame, bolt or the rack.

Okay, so there have been people that looked at it https://www.google.com/search?q=loos...hrome&ie=UTF-8

branko_76 

A wood glue joint is often stronger than the wood itself. Is this also true for a brazed joint?

gugie 

That makes complete sense. I've started eliminating threaded fender connections with clearance holes and nylok nuts on bolts. I don't think I've ever had one of those come loose on me. But those are low stress connections. Rack bolts take a lot more stress. Being vigilant with checking their tightness is something you can't control with customers.

jackbombay

For my first attempt at brazing I brazed a canti stud to an old chain stay, and then I tried to remove it with a large hammer, the chain stay ended up a mangled mess and the canti stud was never failed in any way at all.

Also, brass can be built up to a fairly large fillet, or it can be be a very small fillet, how much brass is used will affect the strength. For my canti stud destructive testing the fillet was actually pretty minimal.

Salamandrine 

This thread has moved in some new and interesting directions.

I have pretty limited brazing experience. It is limited to doing some simple repairs, ie replacing dropouts, in the back of one of the bike shops where I used to work. One of the other mechanics there who was also a framebuilder taught me. What I remember from this is that most failures from brazing are likely to be the result of insufficient cleaning, not enough flux, etc. The actual brass is pretty strong, especially with a good fillet. I'd be interested to see what fails first in some destructive testing too. As I already pointed out, I think part of the reason I never ran across a broken eyelet in the old days is that the racks would break before the eyelet. Perhaps the answer to this question then is, yes, brazed on eyelets are fine, just be sure and use a Pletscher rack with them. Also, probably most people that toured used bikes with forged on eyelets for the rack, and knew which eyelet to use.

I also remember my Blackburn rack as being pretty tough. Hard to imagine breaking it. I wonder if the original flavor Blackburns were heat treated? Mine was the old original style non-adjustable type. It would have been very easy to bring the cost down by not heat treating at some point. None would have been the wise, and production cost would go way down, but the racks would be ~ half as strong.

For sure. In fact I wanted to get up to the PNW this summer to visit some old friends, but given the situation, it's going to have to wait till next year. Also, As I Recall more Correctly, I think I added about a day per decade to that tour, much like how fast I was BITD , but it was still around 3 weeks. We burned up a couple bottles of fuel.

Cycle Tourist

...or use the eyelet to support both the rack and fender. The rack first and the light fenders attached outboard. I circumvented the US on such a set up front and back with absolutely no issue. If your adding canti bosses anyway though I'd add the extra eyelets. I like the idea of filing a little extra contact area though. Why not?

dsbrantjr

Files + patience are a very under-rated combination.

79pmooney

My '73 Competition. Brazed on bits being the DT shifter stop (I saw the lack of braze underneath and had further investigation done) and bits like the main tubes to the corresponding lugs. Little stuff like that. Dave Levy worked in braze like it was a freshly jigged frame. Also found a couple of cracked tubes - at the lugs. Said the paint held it together.

gugie 

Destructive testing is something that new members of the Blue Flame Union are encouraged to do. Braze some scrap bits together, try to break them. When I started making stem mounted decaleurs, I wanted to make sure they were strong enough. I made a few "blanks" and bent the bits to see if the braze would hold.



If you look closely, even though the one on the right didn't break off, there's a crack in the braze. I tightened up interface hole, did a few more, now I'm satisfied that the design, properly executed is stronger than it needs to be.

jackbombay

I've been a fan of destructive testing for a long time!

You did end up with a crack in the brass on one of those joints but you really had to beat on it to get that to happen, its crazy how strong such a small amount of brass is!

unterhausen

Okay, I did a two part experiment on this. Let's just say I'm not going to be using any brazed on eyelets for rack mount use. Hourglass or bottle cage mounts should be fine. The eyelets I used are thick, so bending them would be pretty difficult.

I had a piece of angle iron and brazed on two eyelets. One was just cleaned up, no filing. The other, I filed a shallow groove. I held the other leg of the angle iron and beat on the eyelets on their sides. They both broke off with a few hits, not really that much difference, 4 or 5 maybe?. Then I noticed there wasn't full penetration on the grooved one, so I brazed another eyelet in the groove (should go find the two first victims). This time the eyelet bent over fairly far before it broke off.

My conclusion is you need more surface area.

Having said all this, most eyelets would never see loading like this and would work fine for years. Unless it got hit wrong.

Salamandrine 

Thanks guys for taking the time to do actual destructive testing. Real world tests are more valuable than theory alone.

I suspect building up a large and non traditional level of brass fillet would enhance the strength of a brazed on eyelet, if one were to needed to carry a rack. It's pretty easy to break stuff in shear.

gugie 

That's an Admiral Hopper!

unterhausen

my fillets weren't particularly large. I might try this again with a deeper groove and more brass.