New to Fusion 360 and trying to find a way to wrap a sketch to a cylinder

[davemooreracing]

I Need to copy this part but i cant figure out how its done. Can someone please point me to a tutorial . The part is a shift drum from a motorcycle transmission and is no longer made.

[etfrench]

This thread may help.  Also a search of the forum will give you quite a few threads on the subject.  Try text or sketch on cylinder or ring, etc. for search terms.

[TheCADWhisperer]

Have you laid out the displacement diagram?

[davemooreracing]

I have not heard that term yet can you point me to some info on how to do that?

[MRWakefield]

In this case it's a diagram showing how angular displacement of the drum is translated into linear displacement of the selector forks. You'll find some info on displacement diagrams in this Wikipedia article on cams. Just use your favourite search engine for more info.

[g-andresen]

Hi,

follow this principle:

günther

[TheCADWhisperer]

Be careful with any "solutions" posted here as they are likely not correct.

@g-andresen is not correct technique.

@davemooreracing Can you File>Export and then Attach the *.f3d file of just the cylindrical features without the slots?

[davemooreracing]

I sure will.

[davemooreracing]

Here it is.

[g-andresen]

Hi,

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@TheCADWhisperer wrote:

Be careful with any "solutions" posted here as they are likely not correct.

@g-andresen is not correct technique.

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is that a qualified hint without any indication as to why that should be?

günther

[TrippyLighting]

@g-andresen if you cut profiles, not perpendicular to the main axis of the cylinder you'll find that the more vertical the profiles get, the more the crosssection of the slot will get a trapezoidal form being wider at the top.

In this thread, using a completely different technique (before we had the sheet metal tools) I made a similar mistake.

However, @TheCADWhisperer and @michallach81 pointed out the inaccuracies and presented the proper method. I've not tried whether those techniques presented would work with a different displacement diagram.

[g-andresen]

Hi Peter,

In my professional life it was a NO GO to call a thing wrong without giving a reason.

günther

[TheCADWhisperer]

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@g-andresen wrote:

Hi Peter,

In my professional life it was a NO GO to call a thing wrong without giving a reason.

günther

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Unfortunately I did not have time to demonstrate the error, but this general problem has been near the top of the most misunderstood geometry questions across many 3D CAD softwares for many years (I first wrote a white paper on this 14 years ago, and I am sure that I was not the first to recognize the issues).

In my original response - I just wanted to make sure the OP did not select a "solution" without critical evaluation.

I will try to find time to demonstrate issue and solution today (or in the next few days - I have a lot of student work to get graded this last week of virtual school).  (I have posted here on the issues many times in the past.  Search on terms like Displacement Diagram, Cylindrical Cam.)

[michallach81]

To prove to yourself you can create a vertical line (parallel to cylinder axis) on a flatten SM part, then fold it to a cylinder. Any path other then a horizontal (perpendicular to cylinder axis) will be distorted. The only usable part of that workflow is the outer face of SM. Except for some specific and simple examples, the only tool that will work would be sweep solid, which F360 doesn't support.

(after few minutes of thinking... maybe sweeping a rectangle with a surface guide... but I would need to check it specifically)

[TheCADWhisperer]

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@michallach81 wrote:

(after few minutes of thinking... maybe sweeping a rectangle with a surface guide... but I would need to check it specifically)

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I have tried this and never got it to work.

There is way (far more complicated than most would imagine).

I will try to find time to generate an example file.

[michallach81]

The sample file is below, it looks like it could work.

Of course, I didn't care to adjust SM to the cylinder in a way that this would be easy to use example.

[TheCADWhisperer]

I edited your Sketch4 to enter a precise size of 10mm.

Then I placed the part in Autodesk Inventor with a Transitional Constraint between  a Ø10 pin and the slot.

I am seeing interference at various locations along the slot.

@davemooreracing 

Imagine this cylinder is the cutter that cuts the slot.  The tangent contact is continuously variable along the length of the slot. In the process of cutting the slot - the red interference shown in image would be removed by the cutter.

Then in you mechanism a slightly smaller diameter follower pin will smoothly follow the slot.

Notice in the image below that the continuously variable tangent location has moved.

But when the cutter tangents are at 6 and 12 o'clock or 3 and 9 o'clock there is no interference.

This example is pretty close to correct, so the interference is relatively minor, but I think we can get a solution that is closer to Sweep-Cut of a solid body (the "cutter" cylinder translating up/down while the cylindrical cam rotates).

[michallach81]

I would blame interference detection accuracy which must relay on the tessellated model to run calculations. Maybe there is a tool in Inventor like in F360 the DISPLAY DETAIL CONTROL. If there is such setting it to HIGH level should decrease the size of interference. It is less likely that it's caused by inaccuracies of modeling kernel. In principle this method work as long as we driving a cylindrical pin (or a drill/mill).

[TheCADWhisperer]

@davemooreracing 

I would like to create a video that answers this question once and for all.

Can you take a piece of paper 128.8mm (PI*41) and wrap it around the cylinder.

Then take a pencil and carefully transfer the edge of the slot (it is beveled, so won't be perfect, but the model will be parametrically adjustable).

Unwrap the paper tracing and attach image here.

From this I can create a displacement diagram and the resulting slot in the cylinder.

[chrisplyler]

What @TheCADWhisperer  is trying to point out is that if you're trying to cut a precise mechanical guide slot into the surface of a cylinder, and your intended method is to cut it on an unfolded sheet metal part and then refold the part, you should reconsider your intended method, because during the refold your precise, square cut will become NOT precise and square.

Now, this may not matter if you're cutting fluid passages, for example. But if you're expecting a pin to slot perfectly into the groove, it's not going to work out the way you imagined. It may be fine if your allowable tolerances are big enough, and the depth of the slot is low enough, but these are things that must be considered instead of just assuming there will be no distortion.