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Drafting, CADing, building

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Drafting, CADing, building

Old 02-08-15, 04:39 AM
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PiLigand
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Drafting, CADing, building

So I'm an engineer, and my interests can get away from me sometimes. I've been playing around with different drafting and modeling softwares a lot recently. I'm curious, Has anyone started here in designing a bike frame?

It's a lot of go-through, but I've been thinking more and more that I'd like to draft a frame from the ground up on my computer, order some negatives, and then try to wrap it in carbon. Absolutely in a "fun project" kind of way. This isn't really to save money, time, design, etc. Has anyone done this or part of it?

TIA!
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Old 02-08-15, 12:09 PM
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I take it that, "order some negatives" means have someone make open molds for you? If I'm right, that's a pretty expensive proposition. I drafted a fork in solidworks a couple of weeks back, when I finally got to where I wanted to be, it crashed.
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Old 02-09-15, 12:10 PM
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For an all carbon frame, not that common. People playing around with solidworks, very common. Back when the chopper craze was all over, there were guys getting solidworks, and coming back with awesome drawings, after playing with the program for a few evenings. It was sorta annoying. I met a guy at a party who was an architect, and took a university course in CAD, and said he couldn't draw a square. But after Solidworks, everyone was an expert, in fact the pictures looked so great you had to be careful not to buy into stuff that had not the slightest iota of common sense in it.

I design frames in simple 2 d cad. All I really need are the angles between the tubes, and the lengths between the saddles of the notches. I use tube mitering programs, or fixtures to get the actual parts from that. A lot of people don't make their own forks, because of high end racing, carbon, forks, and suspension forks. But if one does the parts and dimensions pretty much take over. The same thing can be true of rear ends which can be bought either as bolt or weld on parts, or even when made up, the tubes or benders, kinda make it a 2.5D process.

The nearest thing to what you are doing, that was done by an amateur was that guy who made female molds by 3D printing, and then laid carbon into them. He was making lugs in carbon for carbon tubes. At the pro level there was that project where they 3D printed a whole frame in Ti.

There are packages for Bike Cad, one called BikeCAD, and another called Rattlecad. They are mainly for tube builders, and I have never thought they offered much that simple 2D did not. BikeCAD is sorta an enterprise solution, though, for frame builders. You rent it or something. Never much liked the sound of it.

If it isn't just a fantasy exercise, CAD, often ends up writing checks that the builder side of things will not want to have to cover. One can do all kinds of great looking things that are a nighmare to build. Doubtless present company knows this, but it is worth keeping in mind.

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Old 02-09-15, 05:12 PM
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bikecad is a good investment if you are going to make frames. Not so sure about solidworks at $5k or whatever the minimum license is nowadays. Sometimes I figure I could make money with it, but I'm not sure.
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Old 02-12-15, 11:15 PM
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Originally Posted by unterhausen View Post
bikecad is a good investment if you are going to make frames. Not so sure about solidworks at $5k or whatever the minimum license is nowadays. Sometimes I figure I could make money with it, but I'm not sure.
For a metallic tubed frame a 2D CAD program is enough, even if you want to Know tire clearances etc.

If you want to do a developed surface CAD model and hand it off for mold machining, then something like Solidworks would get you to the machine shop doorstep, but I don't see it being cheap enough unless you have moonlighting machining time access.
Trouble with a bike frame is that the exterior surface will only get you so far, plenty of interior assembly surfaces, and that means you are controlling the interior and exterior at the same time... Not cheap in my observation.

Be sure you understand bike geometry first, or copy an existing you like for the major angles and dimensions.
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Old 02-17-15, 09:48 PM
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Hey PiLigand, cool project idea!
I'm an industrial design student and I've been building a frame as a side project this semester. I did a model of the bike in Rhino3D first so I could visualize everything and figure out my dimensions, and do renders to figure out my paint scheme and such. My frame was lugged steel though, so no molds involved. (I've attached a image of one of the renders for reference)

I don't know too much about the practicalities of building a one-off carbon frame, but I imagine you might be able to build molds out of MDF, cheap hardwood, or foam if there isn't too much pressure involved. The machining time for any softer material will be a lot less and if you keep the mold fairly simple you could probably get the molds cut on a fairly basic CNC. Looking at the procedure used by the big manufacturers looks pretty tough since you need to inflate carbon into the mold cavity. Laying up the carbon by hand over top of a foam core ala fiberglass and then vacuum bagging the parts would probably be a lot easier to do without expensive tooling.

There is a composite bike build on Sheldon Brown's website: How I Made a Carbon Fiber/Epoxy Composite Bike in my Garage, by Damon Rinard
He used a foam core with layers of carbon and epoxy built up on top of it. He used electrical tape to wrap the carbon/epoxy during curing! So, obviously this can be done on a budget, lol.

Also, check out OUR KITS | HERObike they are bamboo bikes with hand wrapped carbon "lugs" that builders can do at home. Very simple and perhaps a source of techniques for home carbon layup. Also, note that they use aluminum head tubes and bottom brackets with carbon/bamboo affixes to them.

Also, check out this post on instructables! http://www.instructables.com/id/How-...-bam/?ALLSTEPS
Quite a good process overview...it doesn't really look any harder than building with steel (easy to say at least, haha!). You could probably have a foam core CNC'd so the dimensions are perfect. You could add complex details by hand after machining too, since foam is so easy to work.
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Old 02-18-15, 10:58 AM
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I haven't seen any how-to's about open mold composite frames on the internet. Just tube-to-tube. I have thought about making molds, but getting to a frame from that point is a big step
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Old 03-19-15, 04:21 PM
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Originally Posted by MassiveD View Post
For an all carbon frame, not that common. People playing around with solidworks, very common. Back when the chopper craze was all over, there were guys getting solidworks, and coming back with awesome drawings, after playing with the program for a few evenings. It was sorta annoying. I met a guy at a party who was an architect, and took a university course in CAD, and said he couldn't draw a square. But after Solidworks, everyone was an expert, in fact the pictures looked so great you had to be careful not to buy into stuff that had not the slightest iota of common sense in it.

I design frames in simple 2 d cad. All I really need are the angles between the tubes, and the lengths between the saddles of the notches. I use tube mitering programs, or fixtures to get the actual parts from that. A lot of people don't make their own forks, because of high end racing, carbon, forks, and suspension forks. But if one does the parts and dimensions pretty much take over. The same thing can be true of rear ends which can be bought either as bolt or weld on parts, or even when made up, the tubes or benders, kinda make it a 2.5D process.

The nearest thing to what you are doing, that was done by an amateur was that guy who made female molds by 3D printing, and then laid carbon into them. He was making lugs in carbon for carbon tubes. At the pro level there was that project where they 3D printed a whole frame in Ti.

There are packages for Bike Cad, one called BikeCAD, and another called Rattlecad. They are mainly for tube builders, and I have never thought they offered much that simple 2D did not. BikeCAD is sorta an enterprise solution, though, for frame builders. You rent it or something. Never much liked the sound of it.

If it isn't just a fantasy exercise, CAD, often ends up writing checks that the builder side of things will not want to have to cover. One can do all kinds of great looking things that are a nighmare to build. Doubtless present company knows this, but it is worth keeping in mind.
In carbon frame design, isn't there a lot more to it than tubes and lengths? Aren't carbon fabric selection, layering, layup angles, and designing/selecting tube joining strategies and designs also critical? I saw a lot of carbon composite structure design in my career, and the implementation details took a LOT of time. I would think home carbon composite design is "fraught with peril."
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Old 03-19-15, 07:43 PM
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I looked into building a carbon frame in the early '80s, and what is clearly still true is that if you take a naive approach, steel is better. Not that carbon isn't better in optimized designs, but if you are just going to randomly throw material at a bike frame shaped object, you might as well use steel. Carbon just isn't that much better that you can ignore fundamental issues of stress and strain
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Old 03-21-15, 01:43 AM
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Originally Posted by Road Fan View Post
In carbon frame design, isn't there a lot more to it than tubes and lengths? Aren't carbon fabric selection, layering, layup angles, and designing/selecting tube joining strategies and designs also critical? I saw a lot of carbon composite structure design in my career, and the implementation details took a LOT of time. I would think home carbon composite design is "fraught with peril."
There is a lot more to it than tubes, that is a reference to building standard steel. Though carbon tubes could be similar.

Monocoque to build a perfect bike would probably be involved, but there isn't a lot of that going around. Take the example of all these bamboo bikes folks are making. Some are even joined with hemp string. When you consider the inherent strength of something like a carbon monocoque frame, just making the parts stiff enough to support themselves, not oil can. Exactly how much weaker than bamboo held together with string would one expect them to be?

There is a process as a non-engineer i use a lot. I call it managing. As an extreme example, imagine you want to make a time trial bike frame and you are not too fussy about the weight, the main gain would be aero. A hobby thing. You have some idea what commercial frames in carbon are coming in at. You then try to do your best to distribute the fiber where it will do the most good. Yeah, a lot of finite element analysis, prototypes with built in stress cells, and real engineering would help. But that is how a lot of stuff gets built. And also why occasionally something embarrassing like a nose falling off an America's Cup boat also happens.
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Old 03-21-15, 01:58 AM
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If you're looking for a free package that you can fiddle with to get an idea in your head of what you're after, I've found this to be reasonable.

http://www.openscad.org/

One thing about it is that it's a programming language. You model the components of the bike piece by piece and use binary operations/transformations to combine the pieces or put them in place.

I'll admit SolidWorks is nice, and the open source world is yet to come up with an interface that's as intuitive. I've been fiddling with OpenSCAD though for building a bicycle trailer and so far I've been able to model a lot of detail.



The wheels shown are modelled off the Giant SXC2 wheelset I have spare. A downside to SolidWorks is there isn't an easy way to generate 2D plans, but given you can spin the model around in 3D space, you can then turn to a 2D CAD package and re-draw it out, having gotten the model pretty much figured out.
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