Advice in how to tackle Loft with complex 3d curve

[Drewpan]

Hi All,

My current project is for a ducted fan and I am creating the blades. I can get a very nice

standard loft with profiles and simple rails. The problem is creating a very complex 3d

curve to replace these standard rails. Things were going a little slow but forward when

the person came back and said they had an STL file of a similar "Rolls Royce Turbine Blade".

I only have basic experience when it comes to IMPORTING an STL and manipulating it but

I am confident I can turn it into a usable solid. The blade profile will be very different to

this STL but I do want to use the leading and trailing edges of this model to re-create the

curves to use as rails. How would I do this?

It is a complex 3d curve so I cannot just bang down a plane and create the curve with a

projection. Is it possible to use the edges of the STL model as my rails? How do I create

a 3D sketch from the STL so I can use this line as the rail?

Any other advice on how to reproduce these curves would be appreciated.

I don't yet have the STL, otherwise I would attach it. The blade profile is a

simple 3 point spline.

I can't post my design file as I don't have permission to share.

Cheers

Andrew

[laughingcreek]

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@Drewpan wrote:... they had an STL ...I am confident I can turn it into a usable solid. ...

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I'm skeptical you can turn the stl into a "usable solid" by any means other than using it as a visual reference only to model the object from scratch.   That's the case for 95% of the stl's we see here.  that goes up to 99.99% if it was created by scanning.

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It is a complex 3d curve so I cannot just bang down a plane and create the curve with a

projection. Is it possible to use the edges of the STL model as my rails? How do I create

a 3D sketch from the STL so I can use this line as the rail?...

---

unlikely you will be able to use the edge of the stl for rails.  I create most curves of this natures by using the "intersection curve" type projection.  (actually, I use extruded surfaces and use the resulting edge because it use to create a cleaner curve, but a recent update to fusion improved the curve quality of projected curves.  it looks promising, but I haven't fully tested it.  try intersect curves first b/c it's less tedious, and if the curves aren't great then fall back to the tried and true surface technique.)

[wersy · Accepted solution]

I would draw splines from top view and side view of the leading edge and the trailing edge.
Then ceate intersection of them.

[davebYYPCU]

Looks like a third or fourth intermediate profiles, with appropriate tilt, will get a wavy loft without rails, but catch 22, you can then snap rails to the profiles.

Might help...

[wersy]

In this caseI used cross sections and 3D Splines.

[wersy]

Have you made any progress in the meantime?
This is the way I would do it in your case. First create the rails via intersection lines. Then fit the profiles into the rails.

[Drewpan]

Hi All,

Not made any progress yet as I had to rework the Wing Airfoils but 3D printing now.

Next thing is to return to the Fan blades. Will have a shot tomorrow and post again.

Had a week of lessons on how to practically design airfoils by eye. Scary stuff. I know

basic airfoil design theory but a mm of thickness and a 0.5mm scoop out and a bit of

twist - wow this guy knows his stuff. He could explain why and the effect of every minor

change and did it by simply looking at the airfoil section.

Cheers

Andrew

[Drewpan]

Hi All,

So I have the STL now. What I need to do is extract the curve of the edges so that I can run

a different airfoil up those edges as rails for a loft.

Front view

Left View

Left Front View

Top View

I have tried a few different ways to create intersecting surfaces but just cannot

get it to click. I have an actual 3d printed blade that I have cut in half. Not only

are the leading and trailing edge different and not the same width, but there is 

a big twist also.

It would be nice if I could just take a snapshot of the wireframe view and turn it

into a 3d sketch. The wireframe is exactly what I need.

I am beginning to think manually doing cross sections and the rails might have

to be it.

All this trouble over two lines.

Cheers

Andrew

[davebYYPCU · Accepted solution]

Create > Mesh Section Sketch.  Moving the selection marker to where you may need it.

Do not use Fit Curves to sketch, because the default curves' curve comb is atrocious.

When you have these sketches created, you can place 2 point splines as chord curves.  3d sketch and snap splines to the spline points.

I agree that the rail curves will be needed for Loft control.

3d Spline handles can only be edited / moved with Move Tool.  (Splines will turn blue)

Might help...

[wersy]

The uploaded stl is just this.

[davebYYPCU]

I got the Australian version no trouble.

[wersy]

It is difficult to find the leading and traing edge when they are rounded.
I tried to find the supposed points on the triangular surface.
The resulting 3D splines can thus not be precise.

[Drewpan]

Hi All,

Ok. Making some progress. I have managed to get something fairly close to the leading edge curve.

My trailing edge is way out. I have used the intersecting surface method. The mistake I had made

was trying to intersect surfaces and not change them into bodies with thickness first. Still a bit of

a work in progress. I will let you know how I am going. Used the wrong surface for the trailing edge

so will re-do it.

Chers

Andrew

[davebYYPCU]

The mistake I had made was trying to intersect surfaces and not change them into bodies with thickness first.  

No, that would be another mistake.

Develope the surfaces and use them to Surface > Modify > Trim each other. 

Trim will remove the offcut, and you will only need one body (front / back) to reference when done.

Much simpler to snap splines to 4 end points and then manipulate the handles.

I found the file confusing as the midpoint of the flat stand is not close to the Origin, in 2 directions. 

Flush with and around the Origin, makes Offset planes easy to understand the geometry.

Not obvious question, are the (airfoils) profiles in the STL, the ones you want to use?

Might help...

[Drewpan]

Hi All,

Continuing to make very slow progress on this. Have a quite odd issue right now

using intersecting surfaces method. Both surfaces are at right angles to each

other. When I thicken them up to 0.001mm and try to create the curve with a

combine cut intersection, what I get is a body that I can use as a rail, but there

is a strange artefact on it.

As you can see from the shadow - what is this ribbon hanging off of the rail?

This is not a graphics issue, the software has calculated it as there. The combine

cut intersect should not logically create it.

I have thickened the surfaces to 0.01mm and it disappears.

Any thoughts?

Otherwise I am crawling forward but haven't cracked it quite yet due to having

lost time making modifications to the wing.

Cheers

Andrew

[wersy]

Intersection curve should go with just curves.

Can you upload your file?

[davebYYPCU]

Display Detail Control, will fix the graphics, for the display anomaly.  Set to High.

Might help...

[Drewpan]

Hi All,

Unfortunately cannot upload the file. It worked with a 0.01mm thickness, I can use

that.

Cheers

Andrew

[laughingcreek · Accepted solution]

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@Drewpan wrote:... Both surfaces are at right angles to each

other. When I thicken them up to 0.001mm and try to create the curve with a

combine cut intersection, what I get is a body that I can use as a rail, but there

is a strange artefact on it.......

---

thickening up your surfaces by minute amounts is your problem.  this isn't how the intersecting surface's technique works.  you just create surfaces, and then use the edge of a resulting surface for your rail.

[Drewpan]

Hi All,

Success.

Prototype 3d printed fairly well of the RR Blade shown here. As you

can see in the Browser Tree I had a few practices before I got to this

point.

Next step is create a custom 3D leading and trailing edge from what

I have learned here, replace the airfoils with what the guy wants then

mount them onto the hub. I just hope that when I do a few cross check

calculations that the tips will not melt or explode when the balanced

titanium version spins at 20,000rpm. In a DUCTED FAN! I thought that

only turbines went that fast but he insists he has the appropriate fan

motor ready to go. The blades are 140mm so the fan will be about 300mm

when done.

Thank you so much for your help guys. I have learned a great deal about

fusion and practical engineering with this project. I will let you know how

it goes when I find out.

Cheers

Andrew