Drawing complex radii

[craig.james.r]

Hello everyone, 

Apologies for the post - I've been trying to resolve this workflow, but have just hit 'ignorance brick wall' after 'ignorance brick wall'. 

I'm modelling a shotgun barrel, as per the attached drawing. Where I've run aground is modelling the radius' / fillet /  that I've circled in yellow in the attached .jpg.

I'd anyone has any suggestions or guidance on how it might be done, that would be greatly appreciated. 

Cheers!

James

[laughingcreek]

You can revolve that.  see attached.

FYI-the way you have your loft set up results in a messy surface.  Here's a curvature comb applied to your barrel. yikes-

[craig.james.r]

Thanks for the solution - I figured that a revolve was the solution, but I just couldn't quite set it up. Could you spare an explanation in a bit more depth about how you set it up and executed it?

As for the curvature comb, was taking my measurements off a specific barrel which explains some of the grubbiness there. 

Cheers!

James

[TheCADWhisperer]

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@craig.james.r wrote:

As for the curvature comb, was taking my measurements off a specific barrel which explains some of the grubbiness there. 

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Rather than Loft - I would try to closely represent the real world manufacturing process - Revolve.

One Sketch and no extraneous work planes.

Edit:  Oops. I see that was already suggested by @laughingcreek .

[laughingcreek · Accepted solution]

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@craig.james.r wrote:

Thanks for the solution - I figured that a revolve was the solution, but I just couldn't quite set it up. Could you spare an explanation in a bit more depth about how you set it up and executed it?...

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Fist sketch is used with the first revolve to make the barrel.

After building the shroud area, the profile with the arc in the second sketch is revolved as a cut using the same axis as the revolve for the barrel.  I over built the profile so it would catch all of the shroud as the cut went around the barrel. 

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As for the curvature comb, was taking my measurements off a specific barrel which explains some of the grubbiness there. 

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It's a common misconception that more points on a spline, or more profiles in a loft equals more accurate.  You want to use as few data points as possible.  every profile introduces the possibility for error, which just gets magnified as more are added.  as an illustration, if you where to sight down the length of your actual shotgun barrel and/or run your fingers along it's length, I would hazard to guess that it would be pretty dang smooth and not have an undulating surface.   As modeled, you barrel wouldn't be like that.  you would feel/see ripples along it's length.  Here is your barrel with a curvature map analysis-

 here's mine-

I'm missing some important geometry of course, particularly at the breach end, but this is the type of thing your going for.

[craig.james.r]

Thank you so much for the very thorough solution - it is really helpful - learning to see the objects as manufactured items - that are made by tools with their specific shapes and processes - is a work in progress. Feedback like this is of immense assistance. 

Absolutely take your point on the barrel loft too. I'm making the fore end for this barrel by hand, and wanted an accurate representation of the barrel dimensions as they are, variations and all. This was as much to understand the tolerances in the historic manufacturing process, as well as answering the question for myself 'how can I draw this?'. 

Anyways, again - thanks so much - I really appreciate your help - it has been tremendously useful. 

[craig.james.r]

Thanks for the input - it's really helpful. The lofting on this drawing represents 1950s English barrel making, warts and all, hence the variation. The principle of 'less lofts' is one that I'll take on board tho'.