Change the end of an extrusion.

[kevin_steegmann]

Hi,

I'm having trouble getting two tubes that intersect each other to join seamlessly. I want to model two extrusions where one with a slightly larger size meets the side of a round tube (see attached screenshot). Viewed from the top it should look like a parable but I'm stuck on how to modify the joint. I've tried using filet, chamfer and draft. Both chamfer and draft throw errors and draft just extends the leading edge around the round tube.

[davebYYPCU]

You can do that type of intersection with Loft.

you will need an ellipse drawn on a plane with angle, parallel to the axis of the cylinder.

Your top view sketch being rails.

Might help...

[kevin_steegmann]

Thanks for the suggestion. That did the trick to get the sides right but now I'm unable to add the filets at the top and bottom. The error says "can't add at the requested size". Changing the size doesn't have any effect. Any ideas?

[jeff_strater]

You may have to use variable radius fillet to make it succeed.  Can you share your model here, so we can try some things out?

Jeff

[kevin_steegmann]

There's nothing secret in it.

here's the link: https://myhub.autodesk360.com/ue286af75/g/live_review/SHabee1QT1a327cf2b7a6bc789f3382bcf5d?sessionID...

[jeff_strater]

Thanks, @kevin_steegmann.  The link you sent me was for a Live Review session.  I'd like to be able to download the model.  So, can you share the design using one of the techniques here:  How-to-share-a-Fusion-360-design?

Thanks!

[kevin_steegmann]

OK. How about this:

http://a360.co/2DaSpad

[jeff_strater]

Thanks, @kevin_steegmann, that's what I needed!

I think there is a Fillet UI bug here that I have not completely figured out.  Sometimes I cannot select the edges:

 other times, I am able to create the fillet just fine (at 1mm):

The method that does seem to work reliably, though, is to pre-select the edges:

 Is that consistent with the problems you are having?  

Jeff

[kevin_steegmann]

Thanks Jeff. I haven't actually had any problems selecting edges. The problem I'm having is getting a filet at all. I hadn't tried one as small as 1mm because it is too small for my purposes. If you look at the screenshot in the original post, the filet has a 10 mm radius. After your post, I tried smaller filets and worked my way up but I can't get any bigger than 2 mm, which is too small (at least on the top and bottom).

One thing I did notice about the edge is that it is not symmetrical. Viewed from the top, the right side has more segments than the left side. The edge going around the bottom and up the left side is continuous. The right side is broken into several parts. The sketch from which it is extruded/lofted is symmetrical. This makes making variable fillets to compensate for the shallower side impossible.

https://knowledge.autodesk.com/support/fusion-360/getting-started/caas/screencast/Main/Details/a8ac7...

[jeff_strater]

Yeah, you are probably going to have a hard time with this fillet, to be honest, because of the nature of the geometry involved.  Unfortunately, variable radius fillet can only work on one edge at a time, and I had some problems getting that to work.  The best I was able to do is to use "Chord Length" fillet, and get to 5:

The reason why the geometry is not topologically symmetric is because Loft creates a seam edge:

and this gets propagated into the resulting body.  There's no real way around this, unfortunately.

[kevin_steegmann]

Thanks Jeff,

That's really frustrating. The fact that the loft is not symmetrical lead me to check the sketch onto which it is proected. I found the error but the loft is still not symmetrical. I tried to change the length but that only made things worse. 

Do you think it would work if I went back to the original model (straight extrusion) and added bullet-shaped caps to the sides?

[kevin_steegmann · Accepted solution]

Success! Instead of using the loft function I drew a profile on a plane at the end of the extrusion and revolved it. Together with the variable fillet, I am happy with this even if it isn't perfect.