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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! https://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.

https://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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Old 06-22-21, 04:44 AM
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hello dear all


one question. Can i get the data from a bike while watching the foto!?
In other words. I want to "gather" the data form the geometry - while only having the foto.

eg. the foto from wheel2Nut !?

is this possible!?

Let us take this bike in this posting here.
Can i gather all the geometrical data with this foto!?

look forward to hear from you

regads

Originally Posted by WheelNut2 View Post
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! https://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.
Attachment 434850
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Old 06-22-21, 07:18 AM
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As a practical matter, I don't think it would be very good. Wheel2nut's picture is at some odd angle to the centerline of the frame. If it was square to the frame, then you would have a better chance. But you still are fighting lens distortion.

There are programs that try to make a 3d scan from pictures, I have no idea how successful they are. I would start there. But that's a real rabbit hole.
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Old 06-22-21, 08:48 AM
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Fancy drawings and diagrams are rarely reflected in the final product when it comes to frame building. Especially when people are experimenting for the first time.
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Old 06-22-21, 09:10 AM
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I'm always impressed when I see someone with a full size frame drawing. But the thought of finding a place for a full sized drafting table gives me hives. I used to draft out portions of the frame. It's less than fully satisfying. I think bikecad has saved me more than what it cost, it's nice to be able to move things around and make sure everything fits.

I noticed the new version of bikecad will export freecad drawings. Freecad has been getting better recently, I can't talk myself into learning it though. Stuck on solidworks. Although now I'm curious if you could get freecad to spit out a full size drawing that you could get printed at kinkos
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Old 06-22-21, 09:12 AM
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I can speak to the value of Bike Cad for my hobby work. I purchased the pro level a number of years ago and am very glad I did. While only a couple of dozen frames have been produced with Bike Cad design I have drawn up many more dozens that never got past my tinkering on the monitor. If one plans to keep doing this stuff the investment will be used over and over. I have had a couple (3 or 4?) updates for my Bike Cad at no additional cost and have sought help from Brent directly a few times. I find the rider fitting features a great way to review fitting decisions and the ability to plug in components and check their relationships with the frame a big help. Andy
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Old 06-23-21, 05:20 AM
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Originally Posted by unterhausen View Post
I noticed the new version of bikecad will export freecad drawings. Freecad has been getting better recently, I can't talk myself into learning it though. Stuck on solidworks. Although now I'm curious if you could get freecad to spit out a full size drawing that you could get printed at kinkos
FreeCad is what I use for 3d modeling and now for 2d sketches for the plasma table. It has the ability to export models and sketches in a large number of different formats, so you could surely export in a format that you could print out. If you are coming from another modeling program like Solidworks, the learning curve would not be very steep. It uses the same basics as any other parametric modeling program. There is a guy on Youtube that does videos where he compares FreeCad to other programs by modeling the same object in both programs to see the differences.
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Old 06-23-21, 08:33 AM
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That's really interesting you use freecad for useful objects. I have to try it, most of my home projects are not all that complex.
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Old 06-24-21, 05:42 AM
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Originally Posted by unterhausen View Post
That's really interesting you use freecad for useful objects. I have to try it, most of my home projects are not all that complex.
It's very powerful software and can do almost anything that Fusion360 or Solidworks can do. It's nothing like Sketchup or Blender or any of the other beginner friendly programs. Joko Engineering on YouTube has some good tutorial videos and comparisons to other modeling software. The latest stable version is 0.19.
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Old 06-24-21, 06:55 AM
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Looks like I'm already subscribed to Joko Engineering, probably because of linuxcnc

On edit: I guess I had the most recent stable and upgraded it. Hopefully not too much of a mistake. I am designing some tubing benders in solidworks, I'll have to see if I can do it in freecad

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Old 06-24-21, 03:07 PM
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I know this is a pretty caveman alternative, but have you considered a spreadsheet? Mine has one nice feature, it is super fast to use, at least for the old-school type frames I like, using tubes, and a fairly standard diamond-frame shape. Change a few parameters like frame size, TT length, STA, HTA, BB drop... hit Print, bring it over to the milling machine to start cutting tubes, in usually less than 5 minutes, sometimes under 1 min. If there are a lot of parameters to change it can take longer, but one of the things it does is save designs to recall later, so I can pick a saved design to start with as a template, one that shares all the main data like tube diameters, wheel sizes, dropout brand etc.

It doesn't give you a drawing at all, but I feel those are mostly of value to the customer the FB shouldn't need one. It outputs all the things I need, like front-center, F.wheel toe clearance/overlap, R.wheel clearance at the seat tube, steering trail, and of course tube cut lengths.

I have not tried BikeCAD, so maybe it is just as fast to use as my spreadsheet. Anyone fluent in BikeCAD want to comment? Can you call up a saved design, change a few things and have everything update itself instantly, ready to start cutting tubes in 5 minutes? Maybe I'll try it, but I am somewhat poor and also just a cheap bastard by nature. Don't even own Excel, I use LibreOffice Calc (free and compatible with Excel files). BikeCAD is $500, right? If all that gets me is a pretty drawing, I can live without that.

Long boring history explaining why I don't just upload my spreadsheet here; skip unless interested:
An ex-employer had a very basic version made for them in maybe 1986-88, that I added to over the years I worked for them, making it more adaptable to different frame styles (sloping TT, bi-ovalized tubes, extended head tubes, even tandems and a stem-design tab) and I added a ton of macros, like to choose your dropout brand/model from a menu, add in your suspension travel to see the angle changes, that sort of thing.

Then in '94 I quit that place, went to work at a shop that used AutoCAD to draw frames in 2d, which was OK but too slow. It wasn't parametric, you had to draw every tube and centerline and then dimension everything yourself. Just using AutoCAD as an "electric pencil". I missed the old spreadsheet and wanted my own, so I derived all the trig functions and wrote one in Excel, from scratch, not one bit of theirs in mine (I didn't take a copy of theirs with me). This one was never really finished, but all the important (to me) functions are working. No tandems or stem design, no menus for choosing dropout brands or suspension travel, or a few other refinements that are in the old one.

I shared this one freely on forums and such for a while, around 1997-8, until my ex-employer got wind of it and threatened to sue me because mine was "too much like theirs". Duh, it's a bike frame spreadsheet, how different could it be? I don't think any such lawsuit would have had any merit, but I couldn't afford a lawyer, so I stopped sharing it.

That was over 20 years ago and the partner who threatened me has retired. The other partner is still in the biz, but he may have no problem with me sharing my half-assed partly-done spreadsheet. I could ask him, if there's anyone here who's interested. Or if anyone wants to make their own spreadsheet, I can give you my trig formulas for the cut lengths, clearances and such so you don't need to derive them from scratch.

Caveat: I am no Excel expert, nor a mathematician. I learned just enough trig and Excel to make this spreadsheet, and then I promptly forgot it all. (Use it or lose it.) The math may contain errors, though I think I did compare its output to what I got in AutoCAD I just don't remember for sure. If there are errors they must be very small, because I have built a few frames from it and they came out as OK as I am able to discern. The partner that sent me the nasty-gram (lawsuit threat) couldn't resist razzing me over what he said was an error in mine, seemingly unaware that by doing so he admitted that mine was not a copy of theirs, weakening his case. Maybe I used a tangent somewhere instead of a sine, which are close in value for small angles, causing a tiny error, something like that. Or maybe mine is correct and theirs is the one that's wrong, wouldn't surprise me.

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Old 06-25-21, 02:28 AM
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Nice work to do it with a spreadsheet! I wrote mine in Python. It does render a scale drawing (more for sanity checking) and mitre templates. You save the bike design (in an .ini file) and then it produces output like the below, which I print out, along with the mitre templates, and take to the garage. That's everything I need. It's basically all 2D but does a bit of 3D on the rear-triangle to check the fit of the tyre and chainrings.

On the first frame there was a lot of careful double and triple checking of everything before I cut any tubes but I now just trust it.

BikeCAD looks good but there comes a point where there's just too much detail and it's easier just to match up the fiddly physical parts like dropouts and bridge tubes and things in the real world-- put them where you want them and make sharpie marks etc instead of trying to encode them into the computer as well. And although I can write a bit of code I never get on well with those complicated GUIs that CAD programs have.

Mitres
======
Rendered to tt_ht.png
Top Tube to Head Tube Mitres at (10.00, 23.35, 36.71) from tube top
Rendered to tt_st.png
Top Tube to Seat Tube Mitres at (39.28, 52.56, 65.84) from tube top
Rendered to dt_st.png
Down Tube to Seat Tube Mitres at (577.73, 594.41, 611.09) from tube top
Rendered to dt_ht.png
Down Tube to Head Tube Mitres at (94.68, 111.19, 127.70) from tube top
Rendered to st_bb.png
Rendered to dt_bb.png
Rendered to cs_bb.png
Rendered to lss_st.png
Rendered to rss_st.png
Rendered diagram to side_view.png

Front Triangle
==============

Tube Cuts
---------
Head Tube cut square 140.70
Top tube length between outside mitres: 522.14
Top tube length between inside mitres: 522.63
Seat Tube length from top to BB mitre (at side of frame): 583.00
Down Tube length from inside ST mitre to inside HT mitre: 584.88
Down Tube length from inside BB mitre to inside HT mitre: 596.17
Offset between DT/BB mitre and DT/ST mitre on DT inside centreline: 11.29
Down Tube length from outside BB mitre to outside HT mitre: 579.66
Down Tube length centre to centre: 620.60

Other Metrics
-------------
Stack: 557.97
Reach: 383.89
Trail: 62.18
Front Centre: 593.90
Rear Centre: 420.15
Wheelbase: 998.54
Wheel flop: 18.27mm axle drop over 90 degrees
BB height (ground to centre of BB): 267.00
Pedal clearance: 82.00
Min steerer length threaded: 157.70
Min steerer length threadless: 192.70
Angle between ST and DT: 59.01deg
Angle between DT and HT: 119.99deg
Angle between ST and TT: 73.00deg
Angle between TT and HT: 108.00deg
Chainring radii: 97.02
Approx total mass excluding dropouts: 1.95kg
Flexural Rigidity of Down Tube: 1034.94Nm^2
Approx deflection of Down Tube under 100kg load in centre: 4.72mm
Flexural Rigidity of Seat Tube: 1351.06Nm^2
Approx deflection of Seat Tube under 100kg load in centre: 3.31mm
Flexural Rigidity of Top Tube: 719.20Nm^2
Approx deflection of Top Tube under 100kg load in centre: 4.85mm

Rear Triangle
=============

Tube Cuts
---------
Chain Stay length from inside mitre to dropout: 365.33
Chain Stay length from outside mitre to dropout: 362.50
Seat Stay length centre-centre: 501.91
Seat Stay length from inside mitre to dropout: 474.21
Seat Stay length from outside mitre to dropout: 487.91
Angle between CS and BB: 97.25deg
Angle between CS and dropout: 172.75deg
Angle between SS and ST: 45.61deg
Angle between CS and ST: 63.52deg
Angle between CS centre-line and horizontal: 9.71deg
Rendered chainstays to chainstays.png
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Old 06-25-21, 12:46 PM
  #23  
Nessism
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I used rattleCAD to design my last steel tubed frame. It was easy to use and free. Highly recommended. It won't help you define carbon lay ups and what have you but it does a great job with geometry and for round tube builders, it's pretty much all you need. When mitering and cutting tubes I lay the tubes on top of the drawing and compare against the full size drawing I had printed. One caution: after printing measure the drawing to make sure the scaling is correct. I had to print a couple of times to correct scaling problems.

Prior to using rattleCAD I made a full size drawing by drawing it myself. I didn't do the rear triangle other than figure the axle point, just the front triangle. It's easy and fun to draw. Again, lay the frame on the drawing during construction to make sure you don't stray off the design too much. Good fun.
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Old 06-25-21, 05:52 PM
  #24  
JohnDThompson 
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Originally Posted by bulgie View Post
I know this is a pretty caveman alternative, but have you considered a spreadsheet? Mine has one nice feature, it is super fast to use, at least for the old-school type frames I like, using tubes, and a fairly standard diamond-frame shape.
That's what I've done, using Martin Manning's Exel-based "Bicycle Geometry 101." I don't have Excel, but it works fine in gnumeric or LibreOffice.
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Old 06-26-21, 09:58 AM
  #25  
Cynikal 
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Originally Posted by JohnDThompson View Post
That's what I've done, using Martin Manning's Exel-based "Bicycle Geometry 101." I don't have Excel, but it works fine in gnumeric or LibreOffice.
I was always blown away at this speadsheet and it's ability to draw out the frame. I haven't use it since rattlecad, I should play around with it again.
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