Modelling Tubular Motorcycle Frame

[Anonymous]

Hi all,

I use Inventor quite a bit in my work, but i've never done 3D sketches. I'm trying to model the frame for a WW2 motorbike i'm building a replica of. I was planning on drawing the centreline of the frame using a 3D sketch and sweeping the cross-section of the tube. I've watched a number of online tutorials on the subject but none of them seem to cover pipework in true three-dimensions, they cover modelling pipe in X, Y, Z directions but not like i need to do go in all three axes at once, and how to then restrain it. As you can see from the picture its quite a complex set of curves, especially for something produced in a hurry in wartime conditions. Can anyone help please?

Thanks, Richard.

kelly.young has embedded your image for clarity.

[kelly.young]

Hello @Anonymous Do you have side, top, and front view dimensions? If you do, you can use 3D Sketch > Draw > Intersection Curve.

A different approach is to create points in space with 2D sketches, then use 3D Sketch to draw between them and use 3D Sketch > Draw > Bend at whatever radius you like. 

Once you have the 3D Sketch you can insert it into an Assembly and use as a Skeleton for Frame Generator. 

Frame Generator Overview

Skeletal Modeling

Please select the Accept as Solution button if a post solves your issue or answers your question.

[dan_inv09]

Do you have that piece?

Because it looks to me like if you were to lay it on the left side (opposite the kickstand lug sticking out to the right) that it might actually be flat. (It looks like there may be a little curve ahead of the seat post, but that could be an optical illusion or damage - now maybe you want to be like the Russians who copied the B-29 right down to patches over bullet holes.)

Whatever it is, it's probably best to lay it out the way you measure it. You can use 2D sketches on planes to create points for a 3D sketch.

What is it? All the frames I'm finding with Google are much more complex than that one.

[TheCADWhisperer]

See attached file.

My made-up dimensions look a little wonky compared to your image, but this should get you started.

If you have a direct Side View and Top View you simply need to project the intersection curve for the two views.

[Anonymous]

Some fantastic replies thanks very much.

I like the idea of plotting the points on 2D places and then joining them up.

@TheCADWhisperer - thanks very much for the effort you've gone to in creating that template. Would it be possible using the technique you've used to have a different curve in plan for the top and bottom tubes? I presume the radius' at each end would then have to match up the tubes coming in at slightly different angles.

To answer Dans question, its called a Welbike originally made by a company called Excelsior. They were built to fold up and be dropped by parachute in aluminium canisters along with airborne troops. I'm trying to make as accurate a replica as possible. I have best part of three original engines and a few other original parts, but complete original bikes are too expensive for me to justify. I collect and restore WW2 military vehicles for a hobby, so this would join my fleet.

[TheCADWhisperer]

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@Anonymouswrote:

 Would it be possible using the technique you've used to have a different curve in plan for the top and bottom tubes?

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Yes.

[dan_inv09]

I saw just one of those in my search and didn't look close enough - I assumed you must have had something bigger in mind.

I found some other photos of just the frame, and it really does look to me like it's bent in one plane. Not that you should stop learning how 3D sketches work, that still might be easier if you're modeling the whole frame as one piece rather than a welded assembly.

(Those are really neat but, personally, for dropable bikes I think it's hard to top the French Airborne's Vespa Recoiless Rifle squads.)

[Anonymous]

That looks like one of the Indian frames that are quite abundant on eBay, they're not very accurate replicas.

I thought i had it just now plotting points on 2D planes and joining them up with 3D curves but the radius at the front was the last piece of the puzzle and i couldn't get it to tie up. See attached. Also couldn't find a way to add bends between the subsequent 3D sketches.

I've taken dimensions from three originals and the top and bottom tubes are definately different in plan, also shown by the line drawing attached.

kelly.young has embedded your image for clarity.

[kelly.young]

Hello @Anonymous just wanted to check in and see how your frame is coming along and that you found a good workflow. 

Did you end up using Frame Generator or just Sweep along a 3D Sketch/2D Sketches?

Please select the Accept as Solution button if a post solves your issue or answers your question.