Loft help please

[conjured2018]

HI, part attached is called transition made up of six 1.5 inch parts. I am trying to smooth out rough spots in the loft. Most of body is smooth except the top right as image lies. I want to get rid of all ripples, and seams. I dont know what the black lines are and can not edit them. I have put rails on body successfully except in this area. I get rail does not touch all profiles error.

In sketch menu the 2 profiles for loft are call big_t and small_t. The sketch for rails is called rails. Please any advice on loft and rails is needed. End goal is to make this body smooth without any ripples or seams. I split body this to 6 bodies. Then cam each 1, stack laminate to build body up with plywood. When ripples are in design the part comes out with the ripples which I have to grind to smooth surface. I want part to come out and not have to grind down.

thank you as always. 

Much appreciation to @seth.madore  for showing me how to rough part and then finish. JR

[TrippyLighting]

There are a few things to know when designing with lofts.

1. Lofts create NURBS surfaces. The shape of a NURBS surface is controlled by a quadrilateral mesh of control points (CVs). That means if you design a loft in Fusion 360 it usually helps if the 2 loft profiles have the same number of control points. That is particularly true for control point splines, but also helps with fit point splines. Otherwise Fusion 360 will make approximations.

2. While cyclical NURBS surfaces theoretically can be created, I am not aware of a CAD software that would do this, so there will always be at least one seam indicating the end/start of the surface. If designed correctly, e.g. if the profiles and rails are curvature continuous (G2) or at least tangent (G1) there will be no visible seam in the end product.

Your profiles consist of many curve segments of which many are not even tangent so there will definitely be seams. 

Also, the two profile are dissimilar enough that Fusion 360 will need to make different NURBS patches to achieve the overall shape.

[conjured2018]

thanks Peter, are you saying I should clean up to profiles then create control points in precise places that make sense? On tangent, I do not understand how to make the rails tangent. And I thought this too be wrong because some of my rails destroy the loft at times, error saying a rail can not be tangent or something like that,

please describe how to make a control point. And please describe how to make splines tangent. Thank you, JR

[conjured2018]

error is rails can not be tangent to profiles. So I am missing the tangent concept. JR

[TrippyLighting]

Before I start making recommendations I would ask you to explain in detail what you want to achieve.

IMHO you are skipping some essentials and move into areas far to advanced for your current skill level.

For example,  none of your sketches are properly dimensioned or constrained.

The individual sketch objects within each profile are not tangent with each other. that alone will create different surface patches that will then also not be tangent to the next one.

As a general guideline, if you cannot imagine the exact geometry the loft is supposed to great the loft tool will likely not create a good result, or any result at all. 

[TheCADWhisperer · Accepted solution]

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@conjured2018 wrote:

 On tangent, I do not understand how to make the rails tangent.

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What is this all about? Dimensions?

What are the lines for?

Is this the curve that you really want?

What are the lines for?

What are these lines for?

Where are the logical dimensions?

Design Intent?

?

Do you have examples of prior projects of increasing complexity that you completed leading up to this project?

[conjured2018]

I want a smooth transition from big t to small t that can be milled. I know
exactly what I want.
I do not see dimensioning and constraining my parts important. All parts
are contoured.
Is this critical?

The part posted is very close. I just want to remove ripple as described.

Please tell me how to make rails tangent and tangent to what. When I try
this it errs. Thx Jr

I

[conjured2018]

attached is earlier trans version.Please note that this one has straight edges. My attempt in new version is to round off these edges to make loft smoother. This has worked yet I have on area I can not fix. This area, top right in original upload will not take rails. I get rails do not touch profiles area.

And I have tried to tangent the points you showed but it makes sketch unusable. I just used the body as template for sketch.

How do I dimension this multi curved body?

[conjured2018]

I went back to sketch and fixed the 2 areas, I was successful in moving a point around and then doing tangent. Body is now smooth. Thanks, JR