Needing help drawing fan blades using loft tool with rails

[mgianzero]

I'm a newbie to mechanical CAD work, never mind Fusion 360.  I'm attempting to make a fan with complicated blades - they are twisted in many directions with a distinct profile on each edge.  I've gotten the general blade bend I wish, but now I'm struggling to trim the leading and trailing edges of the blades using a specific profile I want.  

Ideally, I was hoping to using the loft tool to not only define the basic shape of my blades, but to also define my leading and trailing blade edges with no success. I attempted to do the trailing edge using a revolving cut and leading edge with a fillet.  Not exactly what I want, not to mention, seems more complicated than it needs to be.   How would I do this?

I've attached a pic of my fan as well as the Fusion 360 file to show my problem.

Any help is very much appreciated.  Thanks everyone!

Marc

[davebYYPCU]

Reviewed your file, your file appears to be the same as the picture, 

so far its a good job, unless you are looking for airfoils on the blades themselves.

so you have said, I am this far, not happy, but we have no idea what you did want.

A loft rail, close to that LE fillet profile will cause you trouble, the trailing edge will be OK.

Need more information to be able to help....

[mgianzero]

Well, actually the fan blades do have a bit of an airfoil profile to it, though not much.  I haven't seen much in the way of tutorials regarding airfoils for odd shaped blades such as these.

Here's a side picture of the fan blades (although it's upside down).  See the leading and trailing edge profiles?  What's an easy way to do this?  Are you are saying it's too hard to use rails with loft command?  

My way of using a revolving cut to make the edges is hard to tweak since the blades are at a constantly changing angle.  Perhaps I need to learn how to project a profile on these blades before cutting them.

Marc

[laughingcreek]

IF (a big if) you want the airfoil cross section to remain the same, you could build the blade with a sweep.  See attached. look at the sketch names, they should help understand the drawing.  play with the shape by moving points around.

Using loft to create the entire blade will give you a lot of control over the final shape.  You do have to create really clean geometry to get it to work right.

[mgianzero]

Wow, this is great!  But, unfortunately, this is all new to me, so I think I have more questions than answers now.  If you don't mind, I'd like to ask a few things.  Perhaps maybe a video (if possible) would help explain this better to me.

Your blade actually looks quite close to what I'm looking for.  But here are my questions  ...

1)  How exactly did you draw this without using any new construction planes?  I always seemed to be running into problems because I could not draw in the direction or plane(s) that I wanted to.  I'm also kinda new to "projection" so I'm guessing you got around this using that technique.  Again, I'm pretty new to all of this, but really appreciate your time here.

2)  Why does sweep serve more my purpose than loft?  I'm kinda confused as to the reasons why to choose one over the other.

3)  My picture does not really show it, but my blades are all rounded off at their ends, so the airfoil would also need to be rounded from the periphery.  I included a picture for you to see.  It's a pretty complex fan blade.  Would this best be done by revolving a cut through the blade once the airfoil is drawn?  Again, I'd need to see the steps of how to do this.

I really appreciate everyone's time here.  I sometimes understand things better through example (whether it be a file or a video) so I can play around with it, like you did for me.

Thanks again for all the help so far!

Marc

[davebYYPCU]

The green blade is Swept with a profile and 2 rails.  It may not suit the purpose because as the rails spread apart, the profile gets scaled, not suitable in some cases.

Read the timeline, step by step, to see how it is constructed.

The Trailing edge was created with an Intersection Curve, under the Project Menu.  Select front view and top view curves to get the 3d curve.

That is how you would make the Leading and Trailing edge curve for your blade.

In your case we place the airfoils inside the hub and outside the shroud, on offset planes, but the green blade is on the origin plane for demonstration.

You are likely to need Loft because in the real world, the inside airfoil is generally fatter than the tip foil, and Loft will do it, and as Alex said, it's a big If, to get away with the Sweep.

We would join to the hub, and cut with the shroud.

A small top and bottom fillet on the ends of the blade would probably suffice.

Another tip off topic, your hub could have been made with one Revolve, instead of the holes you have used.

Many ways to do things, let us know if your stuck....

[laughingcreek · Accepted solution]

hey @mgianzero-

A few answers to your questions-

-I got away with not creating new planes because, as dave said, I was able to take advantage of the existing origin planes since there wasn't anything else to deal with.  When ever possible I use the origin planes and try to not create new ones.  But sometimes you do need a new construction plan.  They aren't hard to create and we can help you here if you have a specific example of where you need one.

-In this instance I used the "project-Intersect curve" to get the trailing edge.  The "Project/Include" commands are very use full, and I would suggest getting to know them very well if you want to do any kind of lofting.  This thread has some screen casts for projecting.

https://forums.autodesk.com/t5/fusion-360-design-validate/how-to-use-the-project-command-in-sketch/m...

The intersect curve is a good way to tame a 3d curve and get it to do what you want.

-I suggest sweep because it is by far easier to execute than a loft.  Loft will give you a lot more control over the final shape, at the expense of being more finicky about the input curves. But if sweep doesn't get you where you need to go, well . . .

-could you sketch on some of the pictures where you talking about being rounded off at the ends?  Happy to give example of this once I understand.

on the topic of lofting and airfoils, you may want to look at this other ongoing conversation I'm having about a wing-

https://forums.autodesk.com/t5/fusion-360-design-validate/loft-function-bug/td-p/7340505

(It isn't a bug)

Dave is right about there being lots of factors in airfoil design.  Airplane wings of course do taper off.  They have to because of loading and some pretty weird turbulence that can happen at wing tips.  I don't think fan blades necessary do though.  some do, some don't.  Yours don't look like they do.  They look like they mostly just twist (another way to control loading without changing the cross-section), as is the case with many axial fans. Turbulence would be dealt with by the shroud.

But is optimizing design your intent here, or trying to replicate your part "as is"? (replicating is going to be easier)

[mgianzero]

Okay.  I took your advice and attempted to use the loft command over the sweep command because I want to distinctly define my start and end airfoil profiles.  According to your comments, a sweep would distort the profile, which is not exactly what I want.  I'm moving very slowly but please bare with me.

The way I found to create my outer airfoil was to draw some rails from above ahead of time and construct a "plane at an angle" to draw this profile.  I didn't fully do this right as I had trouble projecting my trailing rail from the top down perpendicular to this newly created plane, so I guess I still need help with that.  I just projected a couple of points using "project include 3D geometry" and drew my new trailing rail in 3D space.  Did I do that right?

Also, ideally this outer profile would be circular in shape, but I guess I need to create that effect by cutting it with a shroud.  Laughingcreek was asking about what I meant by rounding off the ends of my blades - in post #5 above I submitted an image of this from upside down (shows the blades more clearly from that angle).  I'm not sure how I'm going to deal with that right now.  Like I said, I'm moving slowly.  And, to answer your question about whether I am trying to reproduce this design exactly or not - yes I am.  This has been an old fan for years that works, so we are trying to replicate it - but with todays technology of 3D printing and newer materials, we will then experiment with possible changes to it.  Maybe do some flow studies on it (Autodesk CFD?) to see how it looks - who knows.  RIght now I mostly learning Fusion 360 as you can see here and it's been fun so far with everyone's help!

Here's my new design with loft.  So what do you think?  Comments?

[mgianzero]

Actually, here is a closeup of one of the blades.  As you can see, both ends of the blades are turned a bit, so my airfoil profile at the origin would have to change quite a bit to get me where I need to go.  Baby steps.

[davebYYPCU · Accepted solution]

You are on the right track, this part is not a beginners project by any means,

I see you are using the canvass, but because you have the original part, you could take more accurate photos, to guide you with the shapes.

Loft will get your blades very close, compared to the Sweep.

With your old file, and the canvass I could get from the thread, I have done another example file, 

Best to learn by reading the timeline, step by step, then with right mouse clicks, edit the features and you can see the settings.

After making the blade, I made the hub, with one casting cut out for the slots, then pattern for the slot and the blades in same operation.

so the hard part is developing the shape of the TE and LE, rails, which I did with Top and Front curves to generate the Intersection Curve.

Happy to answer questions....

[mgianzero]

This is absolutely amazing what you did here!  It will take me some time to digest as I'm sure I will have some questions.

Thanks again!

Marc

[mgianzero]

davebYYPCU -

I do have a few preliminary questions so far  ...

I noticed you used some of my pictures as the canvas to make measurements to make your drawings.  One of the reasons I did not do this is because I found a lot of the measurements would be off a bit from accuracy when doing it this way.  For example, it is true the the outermost diameter of the hub is 165mm with roughly a 4mm thickness.  However, the inside collar diameter (one with a 3-bolt pattern) is actually about 62mm when yours measures to be about 53mm.  

What causes this?  Does this have to do with attempting a sketch on top of a 2-dimensional picture?  How can one get a more accurate picture to trace from?  The camera lens for the picture of the entire fan from below was taken at about 12in (or 300mm) from the closest, bottom most lip.

Marc

[davebYYPCU]

Gooday Marc

I did the canvass / trace as an example, I also had the original file to measure the hub particulars

so I made the inside bottom view of the canvas 165mm diameter, you will see that the centre of the photo is distorted from the sketch, but that doesn't matter too much.

The best for you is to measure the real object and copy those sizes into the file, making the canvass a secondary source of information.

If taking pics, you want the camera as close to square to the object you are focusing on, as you can get it,

I am told, position the camera as far away as possible, and use telephoto zoom in to frame the pic, for least distortion.

To make the boss a new size, edit with a dimension, but don't delete...

if the blade turns out to be too short, edit the layout sketch line (the tip rib is tied to that line, (again move, don't delete it)),

and all the file should update, 

ask away, happy to answer the questions....

[mgianzero]

davebYYPCU

So why do you have two two sets of sketches for the tip rib and the base rib?  What exactly are you doing here?

Also, I take it that you mean by the comment "if the blade turns out to be too short, edit the layout sketch line (the tip rib is tied to that line)" that you mean to move the perpendicular line at the tip of the blade on your second sketch labeled "Tip Rib" in order to lengthen the blade tips, correct?

Is there any easy way to make the blades longer in length, not just the tips?  Because if I pull the outer circle defining the outer edge of the blades in sketch "Top Layout", it does not also pull the blade rails with them.  I guess I should assign these points so that they move together.  I'm assuming it would involve something like using the coincident constraint somehow.

I'm also still slowly going through your sketch and learning how your projected these points in 3D to make it all go together.  I'm learning slowly.

Marc

[davebYYPCU]

Gooday Marc

There are two sets of ribs, see below...

this comes from my guesstimate of the blade shapes, from your file, and canvasses, there was nothing concrete to give me those shapes.

You are now highlighting my quick but not consice modelling, if I did it over, it would be neater, but at the time, it was see if it can be done, with what I have got

I sort of bulldozer my way to getting the blade, not pretty.  Reading between the lines you will see I have stuff that can't be deleted that lets me proceed to next stage, etc.

I was not knowing at the time, I needed the rails before the profiles to make the loft work, the rails didn't line up with the early ribs, by not much.

The second set of ribs come from projected (purple) points off the rails. Project > Intersect them into the second rib sketches.

To make the blade longer, you can't go very far before things will break, the length of the 3d rails will be the main drama.

the early ribs are built on a Plane at angle from the layout sketch "chord" lines, moving them out may break things, not sure.

See how you go...

[mgianzero]

davebYYPCU -

I'm really trying hard to fully understand what you did to create this loft, but I'm just confused.  Would it be too much to ask to "clean up" the example you gave me to show me just the pertinent steps  to make this loft? 

You said you needed to create the 3D rails first but then it looks in your Fusion file that you first created the profiles.  But then you changed those profiles before you lofted it, but I can't seem to delete the unnecessary profiles.  I just really want the basic steps to create this fan blade - I don't really care about the hub features at this time.

Also, how exactly did you use the Project command to create your 3D rails?  I imagine you used some sort of selection process using the Project -> Include 3D Geometry, but I'm not exactly sure what you projected where.  Again, I new to this stuff and the Project command, although I have watch a few videos, I am still learning what form of Project to use and when to use it.

Sorry for all the questions.

Marc

[laughingcreek · Accepted solution]

Project\intersecting curve.  Maybe the best thing since sliced bread?

take two, 2d curves at right angles to each other and project into a third sketch to create a 3d curve.  Like cutting a profile on a block of wood on a bandsaw from the top and from the side to start a carving.

[laughingcreek]

The difficulties your having with loft is one of the reasons I suggested using a sweep instead, because it's much more forgiving in terms of guide curve placement.

With sweep you can still twist the blade, and curve it along it's length, and even do a certain amount of scaling and stretching (or not).  Are you certain the cross section of your air foil changes that much?  It's going to be fatter right at the hub  of course, but try measuring the thickness at the middle along it's length and near the end and see if it's really changing.

[davebYYPCU]

Put the screencast together to explain a bit better, as Alex shows, it is not include 3d Geometry but Project > Intersecting curves

Might help, 

[mgianzero]

davebYYPCU and laughcreek (Alex) -

Guys, I'd really like to thank you for all your help.  But, I guess I've gotten really overwhelmed with using loft for my purposes.  Dave, although you put together this screencast, I was still overwhelmed with the multiple canvas's that you used with old and new profiles. 

So, while you were making this screencast (which I still need to digest), I went back to Alex's simple airfoil design (that was originally drawn with sweep) and tried to make it work with loft and I continually get the error "the selected rail does not touch all of the profiles" but I do not understand why.  I made a rail through the "Profile -> Intersection curve" option.  But I cannot select this one rail (blade trailing edge) , but only the other one (blade leading edge).

I will attach this file as my attempt for someone to explain to me why loft has failed here.  I really want to use loft over sweep since it is important to have the control of the blade profiles like I wish.  I would also really like to become more facile with using the loft command any ways.

Thanks again for your time!

Marc