Tips for Modeling a Wooden Bike Frame in Fusion 360

[Snoopy_87]

Hi everyone,

I use Fusion 360 regularly, but mainly for fairly simple parts, so I’m not very experienced with advanced modeling techniques.

I’m currently working on a project to design a wooden bike frame. The frame is made up of four parts:

The main triangle, which is split into two halves (left and right) with a hollowed-out interior.

The two rear parts that hold the wheel.

I’d like to know what you think is the best approach to model this type of project in Fusion 360, keeping the following in mind:

The frame needs to be lightweight, so it should be hollowed inside. I also want to run cables through the frame.
I plan to make several prototypes, so I need to be able to easily tweak the geometry or adjust tube dimensions without redoing the whole model.

Here’s what I’ve tried so far:

Solid modeling: I create sketches for each tube end and connect them with lofts. But I struggle to get clean, smooth joints between the tubes.
T-spline: It looks good, but I find it hard to maintain precision. If I want to adjust a dimension by even 1 mm, it often turns into guesswork, which isn’t ideal.
Surfaces: I ran into the same issue as with solids—difficulties getting nice, smooth transitions between parts.

So I’m a bit lost between all these methods. Do you have any suggestions or workflows that you use for similar projects?

Thanks in advance for your help!

[Drewpan]

Hi,

I would first recommend reading the documentation for Loft, Spline, Sweep and those

type of more advanced modelling tools and doing any embedded tutorials. I would then

check out the Self Paced Learning pages.

It will depend a bit on exactly how "fussy" you are about what your joints look like.

Remember that your chosen fabrication material is timber and so you will be limited in

the joints that you can use. You will also be severely limited in the kind of timber you

can use to get the strength you need if you hollow out parts. Balsa is easy to shape and

fabricate with, but will a hollowed out tube of Balsa have the strength to hold a 100kg

person? What about the torque produced by the cranks by that person in Le Tour de

France climbing the Alps? You may need a much more robust timber like Oak - much

heavier than Balsa but more suitable to the forces involved in the design you want.

One method you can get "better" joints is to sculpt them with Lofts between the end of

a T type piece and the cross member. If you want an oval style joint then create a sketch

and project a surface onto the cross member. Use the intersection of the Surface and the

cross member as the end of the loft from the round base piece. Adjust shape with rails.

You can adjust the shape with rails. Remember that this is just a Surface right now but

you can use Thicken.

Cheers

Andrew

[TheCADWhisperer]

---

@Snoopy_87 wrote:

Here’s what I’ve tried so far:

---

@Snoopy_87 

Can you File>Export your *.f3d files to your local drive and then Attach it here to a Reply?

[TrippyLighting]

If you can share your modeling attempts, that would help.

For smooth transitions, lofts are the main tool. More complex geometry often requires surface modeling.

For example, here is a recent thread discussing how to model a head tube transition.

[Snoopy_87]

Hello,

Thanks for your replies! Unfortunately, I won't be home until Friday. I'll try the technique of @Drewpan for joining two tubes, and for joining the headtube, I'll test the method described in the link provided by @TrippyLighting .

I'll try all of this on Friday and will keep you posted !

Thanks

[Snoopy_87]

Hello,

I successfully completed the assembly of the headtube. I attempted to apply the similar method for the bottom bracket, but it doesn’t work as expected, as shown in the image below. What is the issue ?

Thanks

[TrippyLighting]

I personally would not call that geometry a success 😉

The surface transition aren't even tangential anywhere. A head tube like this is a very challenging area.

Mirroring a fit-point spline is not a good idea. When editing a mirrored spline is is possible to loose symmetry.

All of the things can be addressed, if you have a bit of patience and are willing to learn.

[Snoopy_87]

It's a success compared to my first attempt, but I agree with you, it's far from perfect.
What strategy would you recommend to improve my assembly?

When you mention the spline, do you mean the one I used in my sketch to define the shape of the tube, or the spline I used to create the joint ?

I'd like to learn how to create clean joints between tubes, but I'm a bit lost regarding where to find tutorials, documentation, or videos to help me to have a better understanding.

Thanks for your response.

[TrippyLighting]

---

@Snoopy_87 wrote:

It's a success compared to my first attempt, but I agree with you, it's far from perfect.
.

---

Firstly, thank you for naming your sketches and bodies. It makes it so much easier to find things and provide help.

I created a screencast mainly concerned with the sketch profiles you used for lofting.

1. use the simplest curves that represent the shapes you're after. Fit-point splines are sometimes really convenient, but in this case, I would use 3-degree control point splines for some or all of the loft profiles. Even the simplest fit-point spline with two endpoints is a 5-degree multi-span spline. In this case, a 3-degree control point spline with four control points will represent the shape well and is a single-span spline. It is easier to control the shape with the control points, and control point splines are also easier to fully constrain and dimension.

2. Only sketch half, then loft, and then mirror geometry.

[Snoopy_87]

Thank you very much for your time.

I have updated my project following your advice. The overall design is now much cleaner, as I have only sketched half of the design and the join are now tangente.

I've been reworking the junction at the head tube, refining my sketch to use only circles and 3-degree splines. I successfully completed the lower half of the junction, but encountered issues with the upper half. For the bottom section, there's a strange behavior: when I start to select a line  and then the other path (as shown in the image below), the surface patch doesn't generate. However, if I begin by selecting a specific line first (spline) and then the other one, the patch works correctly (see the image below).

 

 

Regarding the upper part of the head tube, when I select the chain of curves, nothing happens, there are no error messages displayed. Should I divide this top part into several smaller sections and create multiple surface patches? What would be the recommended strategy to achieve a clean and smooth junction?

Thank you!

[TrippyLighting]

---

@Snoopy_87 wrote:

Thank you very much for your time.

I have updated my project following your advice. The overall design is now much cleaner, as I have only sketched half of the design and the join are now tangente.

I've been reworking the junction at the head tube, refining my sketch to use only circles and 3-degree splines. I successfully completed the lower half of the junction, but encountered issues with the upper half. For the bottom section, there's a strange behavior: when I start to select a line  and then the other path (as shown in the image below), the surface patch doesn't generate. However, if I begin by selecting a specific line first (spline) and then the other one, the patch works correctly (see the image below).

 

 

Regarding the upper part of the head tube, when I select the chain of curves, nothing happens, there are no error messages displayed. Should I divide this top part into several smaller sections and create multiple surface patches? What would be the recommended strategy to achieve a clean and smooth junction?

Thank you!

---

[TrippyLighting]

You are trying to move to fast 😉

To achieve smooth junctions, in most cases  you need to loft between surface edges. Only then do you get the needed options for tangency (G1) and curvature continuity (G2).

That means you will need to tangency ribbons for some of the sketched curves.

I'll look at this in more detail later this week.

[TrippyLighting]

I think you/we should take a step back. Before discussing details about how we model "some geometry, we should discuss how you want the end result to look like.

I would also suggest that we focus on another area first. These 3-tube connections are difficult and often require patches, instead of lofts.

(Boundary) patches are a last-resort solution, at least in Fusion. They are difficult to control and often create problematic surfaces.

The top tube to seat tube connection will be a good exercise to discuss  good surface modeling techniques. The head tube connection with the top tube and down tube connection to it is a challenging area and should be reserved for later.

[Snoopy_87]

Hello,

The goal is to machine the bike frame out of wood. If the joints aren't perfect initially, I can machine an extra 1 mm and then sand it down to achieve a clean connection. I considered that if I'm unable to obtain smooth joints directly, I'll create a square at each joint and then sand it manually 😅. So, I don't necessarily expect perfect joints, but I would like to have nice  joins in order to better understand Fusion.

Today, I'll attempt to create a smooth lofted joint between the top tube and the seat tube.

Thanks !

[TrippyLighting]

The easiest, but ugliest one would be a simple constant radius fillet.

You could change that to a chord fillet and see if you like that better.

[TrippyLighting]

Attached is a version of how I would model this. I modified all of the tube profile sketches . They only include 2 curves. The arc on the top and a 5-degree 6-point control point spline. THis eliminated tangential connections within the profile sketches which helps later to create smooth surface transitions.

The glossy paint appearance was only applied to  judge reflective highlights and surface quality.

[TrippyLighting]

I had a go at the frame using a Sub-D approach in Blender. This can also be done in Fusion using T-Splines. Blender is just faster for me as I've used it for a long time.

The main goal was to prototype the design for the head tube connections. 

[Snoopy_87]

Wow, so nice the jonction of the saddle tube ! I try to do the same on my projet in order to understand the technique, and I managed to get the same result — I’m really happy! Thank you so much!

As for the head tube, I tried using the same technique as for the saddle tube, but I’m not getting good results. As you mentioned, I’ll use the T-Spline. So far, I’ve only created a penguin with T-Spline, so I still have a lot to learn to use it properly. I’ll do some tests this afternoon.

Your frame looks so nice on Blender.

Thanks for your time and help.

Best regards,

Dany

[TrippyLighting · Accepted solution]

Attached is the quad polygon mesh from Blender. You can import it into Fusion into your existing design using the process I describe in the video:

I'd be interested in seeing how you join the separate wood pieces before machining.

[Snoopy_87]

Hello,

I forgot to show you the final result. Thanks to your help, I was able to build my wooden bike, which I used to take part in a big race in my region 🙂 !!

Thank you very much for your advice.