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  1. #1
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    Can anyone design me a frame?

    G'day,

    I recently had a fit done and now have some bio mech measurements for what I need my bike to be. However, I'm having some trouble translating that into a frame design that actually makes sense. Basically, I don't know what I'm doing at all. Just fooling around with Bikecad isn't going to get me anywhere.

    Anyone mind giving me some pointers or even a quick design? Would be greatly appreciated, cheers.

  2. #2
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    Why won't playing with Bikecad get you anywhere?

    Isn't a frame design that makes sense part of what you'd pay your framebuilder for?

    Did the fitting not tell you a seat height etc. and reach to shoot for? Put your ass where it needs to be and your hands where they need to be with relation to the BB and connect the dots from there.

    I believe a previous edition of the Paterak manual is available for free download and should cover a bit of frame design in it or at least explain how to generate a full scale drawing.

  3. #3
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    It's relatively simple, at least to get your basic design on paper.

    1) You need to know the parameters of the kind of frame you want. You can find these by looking at the numbers for non-extreme versions of the kind of frame you want to make. What is typical head tube and seat tube angles, and what is the BB drop. Wheel size, real with inflated actual tires. Fork with offset.

    2) Seat tube - Assume you have determined the typical ride on your wheel size is say 73 degrees, 73 degree, and 80mm drop. You presumably have ridden a bike before and have one that feels like a good fit, and you have been doing recent fit work. So you should for starters know what seat height and tube angle are. Now you buy the actual seat post, and seat you want to use, and you look at those and determine whether the best position for them, the seat centered on the post with adjustment room, in a structurally beneficial position, will fit over your seat post angle of your fit bike at the same angle. In other words, if the bike riding style and your fit numbers both yell 73 degree, you still want to match that up sensibly with a seat post (what offset) to be sure that the seat ass contact point relative to your existing fit, is actually a 73 degree seat tube angle in the real world. Where your ass hits the seat relative to the BB is the real issue, how you get there depends a little on the parts. This seat/bb relationship thing is bio-mechanical to some extent, does not vary all that much from bike to bike, except if it is a bike type with super laid bad cruiser style, or say time trial style. I could ride a 72-73 tube depending on seat, for just about any normal riding I do. But your philosophy might vary.

    3 - Head tube- So once you have you seat tube on the diagram you need your front end. So in your fit , and prior bike experience you should have some idea in mind of a reach number. Again, whatever it is needs to be massaged for the actual parts you will be using: the real bars, a stem proportional to your frame - we aren't going to use a stem to make the frame right; taking into account the head tube angle, and how that affects fit, etc... So once you have that position worked out, you should know where the top end of you head tube needs to be. The lower end will depend on the fork you will be using, and the stack height of your headset, real wheel size. Again, if you are using parts, these need to be real numbers, based on parts you have on hand. This will work out far better than guessing.

    4 - Stand over - OK, so you know your HT, your ST. You know your BB because it is a function of ST position, wheel size and BB drop. Next you need to know what a reasonable stand over is, and you get that from your fit work, previous bikes owned, etc.... This will determine the rear end of the top tube, and the front end was established with the HT work, and joinery offsets.

    5 - You connect the downtube by drawing it centered on the BB and a workable amount above the base of the HT, and that depends on type of joinery. The lugs will define it, or weld size, or fillet size.

    6 - Rear Triangle - You now have the front triangle. The rear triangle comes from absorbing the CS lenght of the average type of bike you are building, that will determine how far back you place the rear wheel relative to the BB. Do your research. I try not to get too carried away with extremism here, I don't think the average rider need to have the rear wheel rubbing up against the BB.

    The Seat stay position is determined by your rear wheel position, the drops actually used, and in hand, and the type of joinery you are using at the seat tube.

    You're done. Except you never are. You need to keep going around the design spiral, working the design as a whole, and integrating real numbers as more parts become available.

    You might say, well I don't know x or y number, offset, parameter. Well design is all about knowing where everything goes, putting numbers on it, and having your own opinion about it. You just need to do the work. One thing you can do is scale nice side views of existing bikes in your interest segment and draw them, and keep files, over time you will learn what kind of stuff goes where. Do this with your existing rides, some day they may be gone, but you will still possibly want to know the numbers. These don't need to be beautiful drawings, just so long as they locate the basic parameters.

    I'm sure BikeCad, is a useful tool, but I like doing drawings in 2d CAD with parts files that I have accumulated that are real parts. And I own the results and don't pay any fees. For one thing, when you do that, you need to draw out these parts (mostly dead simple), and learn more about the parts and how they go together, than if you use pre-digested stuff. I would probably use BC if I was producing proposals for clients.
    Last edited by NoReg; 03-17-11 at 12:16 PM.

  4. #4
    Map maker cbchess's Avatar
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    http://sourceforge.net/projects/rattlecad/

    download this, much better than bike CAD free version.

    starts with a template and you can tweak the numbers to fit your specs , but be careful it is all connected! So one change will affect lots of measurements

  5. #5
    Senior Member GrayJay's Avatar
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    Quote Originally Posted by cbchess View Post
    http://sourceforge.net/projects/rattlecad/

    download this, much better than bike CAD free version.

    starts with a template and you can tweak the numbers to fit your specs , but be careful it is all connected! So one change will affect lots of measurements
    Thanks for the suggestion, I downloaded and am playing with rattlecad. Is there a source for project files (bikes) beyond just the two generic road/MTB templates provided in the download? Anyone have project files they would like to share?

  6. #6
    Senior Member mudboy's Avatar
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    Quote Originally Posted by GrayJay View Post
    Thanks for the suggestion, I downloaded and am playing with rattlecad. Is there a source for project files (bikes) beyond just the two generic road/MTB templates provided in the download? Anyone have project files they would like to share?
    That's kind of like going to Nike and saying "design me a pair of shoes" without telling them what you'll be using them for, the size/width of your foot, etc.

    For starter, it would be helpful to know:
    * Height
    * Weight
    * inseam/femur/various other lengths
    * riding experience
    * Athleticism & flexibility
    * Intended use of bike
    * Intended tire width
    * Intended to use fenders/racks/panniers/etc.
    * Will the bike be carrying a load beyond the rider

    Now, there are certainly good (hate to call them "standard") starting points beyond frame size, i.e. 73 parallel, 415mm stay length, 50mm rake, 70mm BB drop, but even these things vary greatly between builders.

    Pete
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  7. #7
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    I was hopeful with rattlecad, but I didn't find it would do what I wanted, so I went back to straight CAD. I can't remember what the problem was, but it wouldn't either draw the bike I needed, or allow me to built it the way I need, output wise.

    What do you want the design for? If you are building your own bike, won't you need to at the very least need to know what it is going to look like?

  8. #8
    Senior Member schooner's Avatar
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    Pretty much every bike company website has geometries that you can look at. You look at a few of them and you will start to see some similarities and you can go from there. I will hope that you know what size bike you have now, did your fit change that drastically? If not, start with a basic frame design, and see what changing up the top tube or seat tube do to the rest of the design.
    Honestly though, the Paterek manual is free and that will give you the basics of how all this stuff ties together, so you can do it yourself.
    If you still want someone here to do the work for you, you really need to provide a lot more information. What are you on now? What did the fit tell you was wrong with it? What do you like about your current bike? What do you want to change about your current bike? What kind of riding will you do 90% of the time? What other things do you want it to be able to handle for that other 10%? See where I'm going with this?

  9. #9
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    Did not know the software, is great! THanks!

  10. #10
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    That's how I felt when I first took it out for a spin. I mean, anyway, I need like 4 numbers to build a bike.

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