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Complex Lofting Question

22 REPLIES 22
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Message 1 of 23
HomeMadeSin
453 Views, 22 Replies

Complex Lofting Question

I have a need to form what is known as a Francis vane impeller (double curvature). Lucky me, huh? Anyway, I understand the loft method for generating a shape from multiple planar sketches, but how on earth can you generate a 3D sketch on a non-planar surface??? As far as I can tell, 3D sketch is only for sweeps. A couple of good similar examples of what I'm trying to do would be either a propeller for a airplane or a boat if you were trying to do the lofting outward, STARTING (I repeat - STARTING) from the hub surface which for both of these objects are curves....Thanks in advance.

Troy Zellers
22 REPLIES 22
Message 2 of 23
jptutt
in reply to: HomeMadeSin

Though probably not identical to your design, the Autodesk Inventor 5 Essentials Courseware has an example of creating a fan blade using the loft feature. See Chapter 7 (7-5 through 7-9
Message 3 of 23
Anonymous
in reply to: HomeMadeSin

Centrifugal pump. eh? You have a profile of the
shape or a way to determine it? If you want to email me the profile, I'll give
it a shot.

Larry

 

 


style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
I
have a need to form what is known as a Francis vane impeller (double
curvature). Lucky me, huh? Anyway, I understand the loft method for generating
a shape from multiple planar sketches, but how on earth can you generate a 3D
sketch on a non-planar surface??? As far as I can tell, 3D sketch is only for
sweeps. A couple of good similar examples of what I'm trying to do would be
either a propeller for a airplane or a boat if you were trying to do the
lofting outward, STARTING (I repeat - STARTING) from the hub surface which for
both of these objects are curves....Thanks in advance.

Troy Zellers

Message 4 of 23
HomeMadeSin
in reply to: HomeMadeSin

Yeah. It is easy to be impressed with the simple lofts and extrusions, etc when they demonstrate the software. I was. But I have yet to see the complex shapes of pumps, turbines, etc easily demonstrated.

As it stands right now, I only have the profile of the bottom edge of the vane,not the top. I was trying to see if I could project the 2D profile onto the curved impeller shroud first. If I could do that, then I could do the same on the other shroud and have two non-planar (or 3D) "sketches" to serve as the beginning and terminating loft points.

I'm having to scan the original hand-drawn drawing, convert to vector, import into AutoCAD and re-trace via polylines and then import the AutoCAD profile into Inventor. I'm sure there is an easier way, but I haven't found one yet.
Message 5 of 23
Anonymous
in reply to: HomeMadeSin

Search customer files for this example.  An
excellent treatment on lofting.

 

 


size=2>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>




Newsgroups: autodesk.autocad.customer-files

Sent: Thursday, October 24, 2002 7:06 PM

Subject: Propeller R6 update



Here's that prop Kent. I updated (re-drew) it in
R6.

~Larry

 


size=2><<<<<<<<<<<<<<<<<<<<<<<<<<<

 

 

 

-tom


style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
I
have a need to form what is known as a Francis vane impeller (double
curvature). Lucky me, huh? Anyway, I understand the loft method for generating
a shape from multiple planar sketches, but how on earth can you generate a 3D
sketch on a non-planar surface??? As far as I can tell, 3D sketch is only for
sweeps. A couple of good similar examples of what I'm trying to do would be
either a propeller for a airplane or a boat if you were trying to do the
lofting outward, STARTING (I repeat - STARTING) from the hub surface which for
both of these objects are curves....Thanks in advance.

Troy Zellers

Message 6 of 23
HomeMadeSin
in reply to: HomeMadeSin

Pardon the dumb question, but is there a way to get to the customer files in www mode? I used to do all newsgroup, but had problems with the laptop had to reformat a few times. So I've procrastinated in setting it back up. Besides, I haven't figured out newsgroups from behind a firewall at work so I have to do them after hours via dial-up (yuk).
Message 7 of 23
HomeMadeSin
in reply to: HomeMadeSin

Duhhhhh. Nevermind, I found it. sorry.
Message 8 of 23
HomeMadeSin
in reply to: HomeMadeSin

Ok. I found the file and downloaded it. I agree it is a excellent treatment of lofting, however, all of the sketches are planar. This is easy. I'm talking about establishing a sketch ON A CURVED surface and using it as loft ...er plane..

Any ideas?
Message 9 of 23
Anonymous
in reply to: HomeMadeSin

All sketches in IV are going to be planar. (at
least in my experience)  I'm not sure about the new
surface capabilities of IV6; maybe something to look at there.  I
suggested the propblade because it seemed to have some unique lofting. 
More food for thought than an exact example.  I could  have
been more specific. 

 

I have allways used planar profiles on our fan
blades and  I'am constanly repeating to my self, "it's only a
fan".

 

As a possibility - MDTs surfacing and stitching if
you have the patience.

 

 

 

-Tom


style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
Ok.
I found the file and downloaded it. I agree it is a excellent treatment of
lofting, however, all of the sketches are planar. This is easy. I'm talking
about establishing a sketch ON A CURVED surface and using it as loft ...er
plane..

Any ideas?

Message 10 of 23
HomeMadeSin
in reply to: HomeMadeSin

Thanks Tom.

Frankly, this is one of my fears (that Inventor isn't set-up - yet - to do this type of feature). I just couldn't face learning P/E. Besides, at another pump manufacturer, the P/E guys didn't tackle this issue either - they "faked" it for visual purposes, not actual dimensions.

I would try MDT.....something else to learn.
Troy Zellers
Message 11 of 23
Anonymous
in reply to: HomeMadeSin

I think it can be done. I posted an airplane prop
awhile back as did Jeff. I'd probably do it another way now but I'll see if I
can make an example file tomorrow and post it.

~Larry


style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
Thanks
Tom.

Frankly, this is one of my fears (that Inventor isn't set-up - yet - to do
this type of feature). I just couldn't face learning P/E. Besides, at another
pump manufacturer, the P/E guys didn't tackle this issue either - they "faked"
it for visual purposes, not actual dimensions.

I would try MDT.....something else to learn.
Troy
Zellers

Message 12 of 23
Anonymous
in reply to: HomeMadeSin

is there a reason you can start below the curved
surfaces?


style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
I
have a need to form what is known as a Francis vane impeller (double
curvature). Lucky me, huh? Anyway, I understand the loft method for generating
a shape from multiple planar sketches, but how on earth can you generate a 3D
sketch on a non-planar surface??? As far as I can tell, 3D sketch is only for
sweeps. A couple of good similar examples of what I'm trying to do would be
either a propeller for a airplane or a boat if you were trying to do the
lofting outward, STARTING (I repeat - STARTING) from the hub surface which for
both of these objects are curves....Thanks in advance.

Troy Zellers

Message 13 of 23
HomeMadeSin
in reply to: HomeMadeSin

Matt:

I'm re-creating a part from a hand-drawn file dating back to 1967. I would have to imagine that many face the same issues with converting old 2D to 3D drawings.

At any rate, either old and redrawn or new design, it is necessary to define the lower edge of the vane and the upper edge and loft between if no intermediate sections are available (they aren't in my case). The problem is the lower surface that applies to the lower edge or profile of the vane is curved, so a planar sketch beneath the curved surface would allow me to generate a vane, but it would be completely different than the actual piece.

It seems the correct way to do it (if programmed) is to create a 3D sketch (actually 2) and loft between. Then the difference between the actual part and the 3D model would be how the loft was done (computer versus pattern maker). I could live with that. Unfortunately, the tools in IV don't seem to accomodate 3D sketches used for lofts or the creation of a 3D sketch via a 2D sketch projected on a surface (not a planar surface). Until then, I'll have to do what I am doing: sending the actual vane to a 3D scanner and input into 3D file (the vendor uses Solidworks) and drop the "dumb" file into the overall drawing. It is a work around that I hope is not permanent (rev. 7???)
Message 14 of 23
Anonymous
in reply to: HomeMadeSin

I think this problem is the same one we were trying
to solve in "Barrel Groove..." We were trying to loft or sweep to get a cam slot
around a barrel. The best answer I saw involved a coil, but that probably won't
help here. Anyway, check out that thread in here and CF for help.


 

 


style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
Matt:

I'm re-creating a part from a hand-drawn file dating back to 1967. I would
have to imagine that many face the same issues with converting old 2D to 3D
drawings.

At any rate, either old and redrawn or new design, it is necessary to
define the lower edge of the vane and the upper edge and loft between if no
intermediate sections are available (they aren't in my case). The problem is
the lower surface that applies to the lower edge or profile of the vane is
curved, so a planar sketch beneath the curved surface would allow me to
generate a vane, but it would be completely different than the actual piece.

It seems the correct way to do it (if programmed) is to create a 3D sketch
(actually 2) and loft between. Then the difference between the actual part and
the 3D model would be how the loft was done (computer versus pattern maker). I
could live with that. Unfortunately, the tools in IV don't seem to accomodate
3D sketches used for lofts or the creation of a 3D sketch via a 2D sketch
projected on a surface (not a planar surface). Until then, I'll have to do
what I am doing: sending the actual vane to a 3D scanner and input into 3D
file (the vendor uses Solidworks) and drop the "dumb" file into the overall
drawing. It is a work around that I hope is not permanent (rev.
7???)

Message 15 of 23
Anonymous
in reply to: HomeMadeSin

See CF "impeller (IV6)" for a quick attempt. Might be something useful in it
for you.

Jeff
====================
"HomeMadeSin" wrote in message
news:f129fe2.-1@WebX.maYIadrTaRb...
I have a need to form what is known as a Francis vane impeller (double
curvature). Lucky me, huh? Anyway, I understand the loft method for generating
a shape from multiple planar sketches, but how on earth can you generate a 3D
sketch on a non-planar surface??? As far as I can tell, 3D sketch is only for
sweeps. A couple of good similar examples of what I'm trying to do would be
either a propeller for a airplane or a boat if you were trying to do the
lofting outward, STARTING (I repeat - STARTING) from the hub surface which for
both of these objects are curves....Thanks in advance.
Troy Zellers
Message 16 of 23
HomeMadeSin
in reply to: HomeMadeSin

Wow. I mean wow! That's a sweet looking part. I guess Inventor can handle it, but it will take me a good while to figure out how you actually made the vane and if I can do it with what little info (2D drawing) I have. Thanks!

Troy Zellers
Message 17 of 23
SeanS
in reply to: HomeMadeSin

If I understand you correctly, you are trying to loft a profile consisting of two complex curves (i.e. the high and low pressure sides of the blade) in a radial direction from the hub out to the outer circumference. Correct?

Why is it necessary to start and end with curved profile sketches as opposed to planar ones (which could be inside the hub diameter, and outside the actual blade diameter, respectively) which are then cut to size?

Can someone tell me how to access that sample impeller blade file (I am using WWW interface)?

I have created boat propellor blades using Inventor, by creating a coil (thin rectangular helix) to define the high pressure side of the blade, cutting the blade shape axially, and then tweaking the edges.

If you can use any 3D path (and my understanding of Inventor might be a bit off here, so bear with me) as a rail for a loft, could you not use a helical path as a loft rail? I don't know if that would help in your case...

If you know what the starting loft profile would be in 3D at your hub, could you not create a work plane parallel to the hub axis, intersecting the leading and trailing points on your 3D profile, then project that profile to the work plane, and use the new sketch to define your loft?

Just brainstorming out loud...

-Sean
Message 18 of 23
Anonymous
in reply to: HomeMadeSin

From the FAQ Sean posts weekly

WEBBASED CF:
http://discussion.autodesk.com/WebX?14@67.Wd6TaaEbdXF^1@.ee940b5

NTTP CF:
news://discussion.autodesk.com/autodesk.autocad.customer-files


--
Kent Keller
Member of the Autodesk Discussion Forum Moderator Program

http://www.MyMcad.com/KWiK/Mcad.htm

"SeanS" wrote in message
> Can someone tell me how to access that sample impeller blade file (I am
using WWW interface)?
>
Message 19 of 23
Anonymous
in reply to: HomeMadeSin

I posted a more coherent version of the vane in CF that might be a little
easier to follow.

Good luck with it,
Jeff
====================

"HomeMadeSin" wrote in message
news:f129fe2.14@WebX.maYIadrTaRb...
Wow. I mean wow! That's a sweet looking part. I guess Inventor can handle it,
but it will take me a good while to figure out how you actually made the vane
and if I can do it with what little info (2D drawing) I have. Thanks!
Troy Zellers
Message 20 of 23
Anonymous
in reply to: HomeMadeSin

Well, got hung up yesterday, but I see Jeff
jumped in there. ... Nice job Jeff! ... I went ahead and did a Silver
Tongue as an example of another way to do curvy curves. It's under
Jeff's.

~Larry


style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
Thanks
Tom.

Frankly, this is one of my fears (that Inventor isn't set-up - yet - to do
this type of feature). I just couldn't face learning P/E. Besides, at another
pump manufacturer, the P/E guys didn't tackle this issue either - they "faked"
it for visual purposes, not actual dimensions.

I would try MDT.....something else to learn.
Troy
Zellers

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