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krautfed

How can I fix this loft?

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krautfed

I'm self learning Inventor and I can't figure this one out. I showed a friend and he said I need more sections, which I'm not 100% understanding... the loft is like a spline and while more sections would constrict the splines more, they still wont be perfect.

 

Is there a good tutorial out there regarding the transition tab of the loft tool?

 

I'm trying to loft the following front of a model airplane. I want the loft to follow the red lines. The red arrows point to the spline part of the loft taht its off.

 

loft_transition.jpg

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JD Mather

You forgot to zip and attach the file here. (pretty pictures aren't very useful)

I do not see any rails selected.

There are several tutorials in my signature.

 

Oh, and you are correct - extra sections in a loft like extra points in a spline do not necessarily result in better geometry. Usually just the opposite.

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shift1313

on the right side of your loft dialog box, if you click in the rails box where it says click to add, then select your red lines as rails you should be better off. There are certain conditions your rails need to meet in order to be used but it appears as though your rails go through your sketches so im thinking you might be okay.

 

if you dont want to use rails you can also check out the conditions and transitions tabs and set your loft at angles coming into and going out of your sections.

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JD Mather
Be gentle!

 

Start with the ALL of the tutorials in my signature. Then come back to this one. There are many problems.

 

Also, students can download the latest Inventor for free from http://engineersrule.org

 

many others can download Inventor LT for free from http://labs.autodesk.com

 

It would be easier to communicate in latest version as files are not backward compatible.

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shift1313

your sketches are a little "off" but i think you have the right idea. You can do 3 separate lofts and get the shape close without using rails, but to actually get the shape you will need to setup rails and they will need to have verticies on your fuselage profiles. right now your "guides" are close but they do not touch.

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shift1313

i did a few to show you.

 

As far as i know, jd will correct me if i am wrong. your rails each need to be their own sketch. Also your rails need to be coincident with your cross sections or they are not valid to be used as rails. I am not sure if you can have rails in inventor go through multiple cross sections but i will assume you can.

fuse2.jpg

fuse3.jpg

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JD Mather
...your rails each need to be their own sketch. Also your rails need to be coincident with your cross sections or they are not valid to be used as rails. I am not sure if you can have rails in inventor go through multiple cross sections but i will assume you can.

 

You are correct on all counts (later versions do not require that rails be in different sketches, but if I recall v7 did have that limitation).

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shift1313

the one i used above was version 10 but it did have that limitation, but like you mentioned, i dont recall having that issue in 09.

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JD Mather
the one i used above was version 10 but it did have that limitation, but like you mentioned, i dont recall having that issue in 09.

 

There is a little trick that trips a lot of people.

Sometimes (usually) if there is more than one profile in a sketch the first pick only picks the sketch to use - a second pick is required to tell Inventor which portion of the sketch to use in the loft feature.

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shift1313

good to know, thanks:) im probably going to pick your brain on a few things here once i do a little more searching on the subject. Id like to know more about breaking links, projecting geometry etc,

 

for instance in this case projecting or including geometry for a 3d sketch so the constraints can be added. I would like to include geometry but only for construction purposes. Is there an option to use lines in sketch only for construction purposes. I thought ive seen convert to/from construction but in Inv10 I was using this morning it wasnt there.

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JD Mather
Is there an option to use lines in sketch only for construction purposes. I thought ive seen convert to/from construction but in Inv10 I was using this morning it wasnt there.

 

Select the entities and there is a construction toggle upper right corner of screen.

construction.png

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shift1313

perfect, thanks jd! hopefully that helps this thread and i didnt clutter it up.

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shift1313

kraut, in my earlier post i said i wasnt sure if you could have a rail go through multiple cross sections. The answer is yes you can. Just make sure it is coincident with every cross section

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krautfed

Thanks everyone. I realize that my original sketches are flawed big time.

 

One question, how can I constrain two seperate sketches on two seperate planes? For instance, I want to make sure my rails are touching my "section" sketch.

 

PS - I'm still going through the tutorials.

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JD Mather
Thanks everyone. I realize that my original sketches are flawed big time.

 

One question, how can I constrain two seperate sketches on two seperate planes? For instance, I want to make sure my rails are touching my "section" sketch.

 

PS - I'm still going through the tutorials.

 

 

You Project Geometry a connection point from one sketch into the next sketch.

 

With your splines you will want to reduce the number of point nodes. Contrary to popular belief more nodes is not more accurate. You want as few as possible that will still result in desired curve.

 

Even a two point spline can be transformed from a straight line into a complex (but very smooth) curve. This is getting into more advanced stuff than is covered in my tutorials.

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krautfed

Thanks. I've gone back and am trying to create a loft, using 100% sketch drawn, dimensioned, and constrained items... however I still can't get rails to work. I think it may be the Project Geometry.

 

I appreciate you being helpful to a new guy. :oops:

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shift1313

if you want to upload another zip file id be happy to take a look when i have time

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shift1313

okay so here is your issue with the rails. Above we stated that you need rails to be on separate sketches for older version of inventor, and the projected geometry is going to need to be converted to a reference. You can see in the pic i attached that all the red lines are on a single sketch. what i did was edit your sketch 5. I left the top spline there but i changed all the other lines to construction lines.

 

Your bottom two lines will not work as rails. you need to redraw that for it to work. I redrew it and overlaid your line so you could see. the issue is that you have two separate lines for your bottom rail and there is a sharp corner between them.

 

Try using a different sketch plane for each rail(top and bottom) and make sure that whatever projected geometry you use that you select the construction button that (edit: jd posted a few posts up) to convert it to a construction line only.

fuse4.jpg

fuse5.jpg

fuse6.jpg

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