# Frame Testing & Ugly Protoype Frame



## jgrano (Dec 5, 2011)

Just curious if anyone tests their work either by fatigue testing of by impact? I'm trying to find a good DIY method for testing a frame I brazed together as part of an engineering project at school. I expect this first frame to fail pretty quickly as it's a single top tubed 29er and I really don't know much about brazing so I don't expect my initial work to be worthy.

I've been practicing more with brazing since I finished brazing the initial frame together the other night. Please pick apart if you're feeling like it. I know there are quite a few problems with my technique. But again first time doing this so be any insight would be greatly appreciated. 

The next frame will include a hinge we've machined similar to a Brompton/Dahon. Based on some FEA anaylsis in Solidworks everything should pass the base level CEN tests but that's assuming good brazing and is in the magical land of computer modeling.. The two faces of the hinge will be clamped together with a quick release and have locking channels.


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## mitzikatzi (Sep 9, 2008)

Looks like a slingshot bikes without the "cable"


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## edsterra (Mar 21, 2011)

Braze isn't glue, so all that metal blobed on the outside isn't doing a thing for you. The 'secret' of a solid braze joint is for the to parts to be absolutely clean and mate perfectly. Then be sure that the joint is heated all the way through to draw the brazing material in by capillary action. There should be minimal metal left on the outside. Quite an art form really.


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## jgrano (Dec 5, 2011)

It is best to put lots of flux on the inside of the joint as well not just the outside? I'll try to clean up the joints more on the next frame, these mostly with with no gap except the lower end of one chain stay. Also I wasn't sure how much was typically removed with filing or grinding after the process so I put it in a too thick. 

It is quite the art form, I've been trolling this forum and looking at lots of pictures on builders sites to get an idea of how it should look.. going to take a whole lot more practice since I have issues keeping the blob of brass under control.


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## TrailMaker (Sep 16, 2007)

Hey;

One of the simplest things to keep in mind is using gravity to your advantage as much as possible, both in the vertical and horizontal sense. It's a lot easier to get that _piano_ down a slight grade than up one. Until you get good enough to walk that blob of brass against gravity when needed, keep that in mind and set yourself up accordingly. Another is using the filler sparingly at first. Don't get a huge blob rolling around right off as it is harder to control. You can always go back and add more if the fillet is not large enough to suit your purpose. Where welding/brazing/soldering is concerned, given good fitment as a first rule, less is usually more.


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## jay_ntwr (Feb 15, 2008)

Without doing a free body diagram, it looks like the seat tube is going to be uber stressed right above the seatstays. You're counting on it to hold almost the whole front of the bike on since you omitted the DT and on top of that, the SS don't support it well. I'll bet just above the seatstays that the FEA plot lights up really hot.

BTW, would like to see your FEA results as well. Give us von Mises and deflection if you can.


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## Meriwether (Jul 26, 2007)

*Tube bike!*

If you haven't seen it already, check out the Retrotec "Tube" frame for comparison. Different enough, but still similar to your design.


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## jgrano (Dec 5, 2011)

Thanks for the tips regarding the amount of filler used. I kept adding it thinking some of it would have to form a good bond and I could file the rest down to make it look presentable. I had some difficulty with the stand at the shop and getting it to move where I needed to have the filler go. Hopefully this next frame will go a bit better.

Thanks for the info about the Retrotec it looks very similar, I'll have to pass it along to the rest of my group.

I dug up the previous versions FEA, we had a failure point at the dropouts which means we probably screwed up some dimensions.. Should have that corrected in a week or so. But the hot spots are around the TT & SS joint and will most likely fail there on this frame with fatigue or impact testing.


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## Blaster1200 (Feb 20, 2004)

FEA is only as good as the person programming the loads.


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## jay_ntwr (Feb 15, 2008)

jgrano said:


> I dug up the previous versions FEA, we had a failure point at the dropouts which means we probably screwed up some dimensions.. Should have that corrected in a week or so. But the hot spots are around the TT & SS joint and will most likely fail there on this frame with fatigue or impact testing.


If you look at your FEA model versus the as built, you've got an entirely different thing going on at the SS/TT/ST junction. Move those SS below the TT like the actual frame and re-do. I'd imagine you'll see it get a lot hotter.


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## unterhausen (Sep 28, 2008)

jay_ntwr said:


> If you look at your FEA model versus the as built, you've got an entirely different thing going on at the SS/TT/ST junction. Move those SS below the TT like the actual frame and re-do. I'd imagine you'll see it get a lot hotter.


my observation as well. I think that little vertical tube isn't going to be nearly as effective as the fea says it will be. That and the seat tube will fail in short order


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## TrailMaker (Sep 16, 2007)

Hey;

I like weird too, with a healthy dose of improbability in it for good measure, but I'd have tried to pick up at least 20% of that top tube with the "down tube." I'd have made that DT pretty stout too.


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## jgrano (Dec 5, 2011)

We're going to put the SS up in the middle of the TT junction where they are supposed to go with the next frame we build. I agree that it is most likely to fail thanks to to total lack of skill while building... This first one was mostly to learn how to miter tubes & put it together.

Another thing that has been kicked around is building in a much larger diameter gusset to the base of the hinge we 're installing in the next frame. Something along the lines of a 31.8mm OD to help transfer the stresses. One other slight change is in the dropouts, going to use breeezer style next time so we can get the angles right and not have such a bad joint at the dropout/SS.

Thanks for all the critiques. I'll keep posting progress, I know I have a long way to go.


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## jgrano (Dec 5, 2011)

Also a quick question about welding markers. Does anyone use these? I'm just trying to make sure with my lack of ability that I don't overheat the tubes and weaken them.


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## febikes (Jan 28, 2011)

What advantage to to see in this frame design vs. a traditional design? My guess is that for a similar level of strength and stiffness you are looking at a heavier frame. 

It would be interesting to see the FEA for a load involving twisting forces and/or pedaling forces. It seems many frames crack from the forces of pedaling. Also, on a mountain bike you will see forces from lots of other directions so the exact loads you program are key.

Coming back to the design, do you see this a better mousetrap or just an artistic bike? If it's just art and you are not going to ride much off road I would guess it will be fairly strong provided you some thick tubes. 

Good luck and keep the photos coming. It will be a neat looking machine.


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## Smokebikes (Feb 2, 2008)

Well.........just to join in. For "fun", I once built a bike using all square tubing DT, twin TT, CS, and SS, what resulted was a very flexy bike. :madman: My point is........square tubes make for flexy frames.......easy to build and interesting in design, but flexy.


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## Eric Malcolm (Dec 18, 2011)

I'll add my concerns. As a concept or 'art form' it is interesting and I hope you enjoyed the process as it is a challenge to learn from. However from an engineering point of view the flex that will be generated from the BB will make this design an unrideable proposition. The rear wheel will not follow the front wheel in the vertical axis due to the torque twist going through that top bar. This design should have had the conection to the seat tube approximately in the area that you would fit a front derailleur, a T-joint if you like with SS & CS connecting above and below and better able to resist the torque coming from the rear axle, BB, and head tube. A flawed design but fun trying.


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## jgrano (Dec 5, 2011)

As far as a reason to use a single top tube we were pushed to do something different by our professor. I don't really care for it and I know it's gonna ride like crap. It's more an exercise in developing a product, doing the "engineering" and manufacturing our design and performing some kind of testing to get out feet wet before we are let loose in industry.

I won't call it art because it's nothing but an academic exercise, what most builder do here is art. I don't want to get that confused. Hopefully I'll be using the T-slots jig we made to build up some fillet brazed frames for myself and friends to go ride for fun after the class is over.

Regarding the FEA we developed loads for pedaling based around a 160lb male of medium strength.. just trying to model the typical american. Once we update the design by adding an increased BB/TT gusset system I'll post those in the 3 cases we are testing, static, pedaling & braking. I might even leave in the crazy deformation scale SolidWorks likes to use to scare the crap out of you.


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## Blaster1200 (Feb 20, 2004)

I hope you're not trying to be too different, when you can just rip off the designs of others. :thumbsup:


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## unterhausen (Sep 28, 2008)

I think it may be impossible to build a frame in the diamond frame configuration that hasn't been tried before.

It's fairly easy to build a frame testing machine. There are videos out on the web suggesting how. In this case I would suspend from the dropouts and drop weights on the saddle


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## jgrano (Dec 5, 2011)

I'll post some pictures of the impact machine we are slapping together. Should be fun and atleast will be a good short video of the frame cracking all over the place. 

I'll put up some hinge pictures when we finish the machine work.. it's basically a ripoff of a Dahon & Brompton hinge hybrid with some additional reinforcement.


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## TrailMaker (Sep 16, 2007)

Hey;

You seem to have a good grasp of the point here. It's not really about the bike, at least at this point. It doesn't matter if it is not ideal. Even if it is a total failure, if you learned something, it is then a success! Think, apply, test, learn, repeat. :thumbsup:


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## jucasan (Mar 18, 2012)

Can anybody translate what BB/CC/SS/TT/ST stand for? IDEA: why not have a dictionary of parts, names and vocabulary about bikes.


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## j.m. (Mar 13, 2011)

Well.......if you knew what the tubes of a bike frame are called it's very self-explanatory.


It's CS btw, not CC.


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## Blaster1200 (Feb 20, 2004)

Hey, at least he didn't ask what mtb stands for. 


....yet.


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## unterhausen (Sep 28, 2008)

jucasan said:


> Can anybody translate what BB/CC/SS/TT/ST stand for? IDEA: why not have a dictionary of parts, names and vocabulary about bikes.


see this wikipedia article


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## MrCookie (Apr 24, 2005)

Unless you mean carbon copy...

The mono tube folder concept/product has been explored extensively by Bike Friday.


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## jgrano (Dec 5, 2011)

only in a 20"... not 29er/700c


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## jgrano (Dec 5, 2011)

Figure I should post some kind of update on the project. We ended up having to build a testing rig to try and mimic some of the tests you'd find in the CEN standards. Since we couldn't afford to buy a hydraulic servo motor to run a fatigue test we settled on impact & max load. 

Results from the standard impact test test with a 22.5kg drop @ 18cm was 3mm of deformation with an allowable range of 10mm.. so that worked I guess. We are going to increase the load but are a bit short on weights. I think something more along the lines of 70-100kg would be a better test.

The next test that was run was a max loading of the front end. In this case the frame handled a load of 1000lb before the dummy fork bent, not sure how a wall thickness of 1.6mm out did the dummy fork that had 8mm walls. Since the fork bent we couldn't keep increasing the load and had to stop. The only resulting damage to the frame was a slight ovalization of the head tube at the lower bearing race area.


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## jgrano (Dec 5, 2011)

Also should post some updated photos of the 2nd frame I've been putting together. This time we were able to integrate the hinge and get everything aligned a little better than the last time. I think my brazing skills are getting better but still suck. Using too much filler & possibly getting things a bit to hot.

Comparing this to the last frame we've switched out dropouts to use the breezer style to allow for better SS alignment. I've also scaled up the frame to fit me better since I'll be doing all the real riding.

Things I still need to do - SS have to be mitered and put in place, disc support brace & ISO mount. 

Having some kind of dilemma about how to route the rear brake cable, should I drill holes in the TT and route it through the hinge and out along the SS? I'm also going to put the cable stops on so I can get gears on the damn thing it I feel so inclined to build it up that way.. also considering the internal route with some stops on the SS.


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