Perpendicular / Corner Loft

[Stuart]

How do I get this loft to be tangent to each perpendicular face? I want it to be smooth like a fillet on an edge.
I've selected tangent on the curved end.



If I select tangent on the rectangular end, I can't find any magnitude or angle that will make it smooth.

 

[HaroldL]

I think you need to add some guide curves. Can you upload the model or at least a similar sample for a demo?

 

[Stuart]

Here's a stripped down version of the part. I added a guide from the top edge, which worked in that area.

How do I guide the front corner? Do I make a guide from the corner to the top center?

 

[HaroldL]

I'm not sure the Loft tool will get what you want if you want the top to be radiused up to the square corners I think a different work flow will be needed.

Here's a screen shot of the part using a Revolve Cut along with a couple of Extrude Cuts to trim the top edge to a 4 mm radius.
The Revolve Cut is a Dual Angle so the angles can be edited to change where the Extrude Cuts are positioned around the edge.

Does that look like what you are trying to achieve?

 

[Stuart]

The revolve cut will get close to the desired shape, but the extrusion cuts remove the corner "point".

The corner portion is needed to mate/align with another block shaped part.

In the loft, I would've expected a 90 angle for the tangent would have given the correct result.

 

[Stuart]

This is how the part mates with the other part. Currently it's using a fillet, but I want it to be more of a domed shape that blends to the corner and tangent to the other part.

 

[NateLiquidGravity]

Here's what I would do to the one shown in the last post.
Before the fillet do two triangle cut extrusions - one for each direction.
Then fillet the resulting edges. Maybe using variable radius.
If that's not clear let me know and I'll make a model later.

 

[HaroldL]

Is this closer to what you want? I tried Nate's variable radius fillet on this and needed to start with the initial radius smaller than 4 mm. I then applied the two VR Fillets and ended with a revolve boss. Alibre choked on using a variable fillet with the same large radius as the initial revolve cut so the extra step was needed.




I also noticed that the display of odd lines made their appearance in this model. Don't know what causes them but it is odd.

 

[Stuart]

That's getting closer for the blend to the corner, but I want the overall shape to be more of a dome / elliptical arc so a fillet doesn't work. (A fillet is what I have now, but it's not the shape I want to end up with)

 

[NateLiquidGravity]

Ok I tried my idea and a variation of it and Alibre Design Just couldn't get fillets (variable or otherwise) to work right. I did get something fairly decent using every trick in the book.

 

[NateLiquidGravity]

A tiny variable fillet can clean up those outer edges. V24 file attached. If you can't open that let me know and I'll detail the dirty tricks.

 

[HaroldL]

Can you say how this part is going to be made, machined, molded or 3D printed?

Here's another workflow that gets maybe a little closer to what you want. It still doesn't transition to a point in the corners but it does leave the corner points.



In this example IF Alibre could loft between sketch 6 and sketch 7 and use sketch 8 as a guide curve I think that would give the results you want. The same thing would need to be done in the opposite direction with selective use of guide curves. I have had some success in the past creating Lofts similar to this but this one kills Alibre on every attempt. (If I had a seat of SolidWorks this wouldn't be too difficult to make with some surfacing tools. Just sayin'.)

You know, @Oldbelt usually has good results with Lofts, maybe he will show up with an example to put our efforts to shame.

 

[HaroldL]

Okay, here's my last attempt at this. My thought was to create the lofted bits first then build the rest of the part after. It seems that Alibre still has a problem creating a loft between sketches that have a different number of elements. In this case going from a 3 element sketch to a 4 element sketch. Even after editing the sketches for the curved/domed shape with multiple elements of an elliptical arc Alibre still failed to create two lofts with a smooth transition. I've pointed out the offending lofts in the uploaded image and the one on the right is the worst. Maybe Alibre Support can take a look at this part to see how it can be created.

 

[NateLiquidGravity]

Harold,
Did you check out what tricks I did to make lofts work (work being an opinion in this case)?

 

[HaroldL]

Nate, I haven't looked at your model yet, I was just focusing on how I envisioned this working. I will take a look though, I,m open to any "tricks of the trade" to add to my tool kit.

 

[NateLiquidGravity]

To best describe it I wanted to use the face to face loft but it doesn't work for me when the 2 faces share and edge and especially not for 3 faces. So I made a grove cut to separate the faces. Then later filled it in and removed any excess.

 

[Stuart]

Nate, you got pretty close.

I don't use lofts very much, partly because I get frustrated trying to get the effect I want.

In the loft dialog, what does the tangent angle setting do? I expected that since the tangent it produced was 90 degrees from what I wanted, I could change that setting to 90, but that doesn't help. And the magnitude setting makes even less sense to me. Varying it usually didn't show a change or pupped up an error.

 

[HaroldL]

To best describe it I wanted to use the face to face loft but it doesn't work for me when the 2 faces share and edge and especially not for 3 faces. So I made a grove cut to separate the faces. Then later filled it in and removed any excess.

Looks like your method worked out a lot better. I don't use the face to face loft much, mainly because it doesn't allow guide curves, so it's not in my train of thought when working on lofts.

 

[NateLiquidGravity]

In the loft dialog, what does the tangent angle setting do? I expected that since the tangent it produced was 90 degrees from what I wanted, I could change that setting to 90, but that doesn't help. And the magnitude setting makes even less sense to me. Varying it usually didn't show a change or pupped up an error.

The best as I could get your original using those settings: it needed to be -90° for the top's tangent setting which also made "love handles" on the sides of the rectangle which were unwanted. Potentially/maybe/with some tweaking - it could have been done that way and then chopped off the extra but I wasn't happy with the shape. As far as I can tell it's 100% trial and error getting the magnitude right. I will say this adventure makes me more aware of how badly Alibre needs to fix the error dialogs when previewing.

 

[Oldbelt]

Loft by 3 sections and a guide curve.
Can be supplied with further sections to improve the surface.
God luck Stuart.