Trouble using LOFT!

[Anonymous]

Hi all,

In summary, I am trying to loft between two "lobes". Each pair of lobes is on a different work plane (see image below). The left lobe of one pair should loft with the left lobe of the other pair, and the same thing between the right lobes should occur. However, I'm having trouble completing what I thought would be a farily straightforward task.

The inner design of lobes was drawn with multiple lines between imported points from excel (using the spline function to better approximate the desired shape). The resulting closed loop was then offset 0.5mm outwards (this was done in all four lobes), however, different numbers of lines were used in each (maybe a reason for my problem...?)

I have attached the Inventor file - any and all help is appreciated!

Thanks in advance,

JR

Edited by
Discussion_Admin

[Anonymous]

I have tried extruding each closed sketch out a tiny amount and then using the rail loft, but then it says it can't loft due to self-intersecting surfaces. Any idea why this happens?

[Curtis_Waguespack]

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@jr12714 wrote:

Hi all,

In summary, I am trying to loft between two "lobes". Each pair of lobes is on a different work plane (see image below). The left lobe of one pair should loft with the left lobe of the other pair, and the same thing between the right lobes should occur. However, I'm having trouble completing what I thought would be a farily straightforward task.

The inner design of lobes was drawn with multiple lines between imported points from excel (using the spline function to better approximate the desired shape). The resulting closed loop was then offset 0.5mm outwards (this was done in all four lobes), however, different numbers of lines were used in each (maybe a reason for my problem...?)

I have attached the Inventor file - any and all help is appreciated!

Thanks in advance,

JR 

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Hi jr12714,

I can't tell from your description what the trouble is. Are you getting the two lofts, but not liking the results, or are you having trouble selecting the profiles?

I took a quick look and I think the different numbers of lines were the cause of the "ugly" results I got, but I was able to create two criss crossing lofts. You can manaully map the loft results (see the last tab in the Loft dialog) , or  you can add some rails for it to follow, etc. in order to get smother results. But I  think would likely start over and simplify the sketches.

What is this object and what do the sketch points correspond to? Maybe knowing that would help in coming up with a better approach. Also, can one of these loft be created and the other just copied and rotated into place using the Circular Pattern tool, or are they really two different shapes?

I hope this helps.
Best of luck to you in all of your Inventor pursuits,
Curtis
http://inventortrenches.blogspot.com

[JDMather]

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@jr12714 wrote:

The inner design of lobes was drawn with multiple lines between imported points from excel (using the spline function to better approximate the desired shape).  

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It is unclear to me what you are attempting to do.

Do you have any prior experience with Loft command?

Did you sketch these splines, or did you set Inventor to automatically create them on import of the Excel points?

It appears that you are missing Tangents and the splines are not even on the points?

Can you attach the original Excel file(s) here?

Are you sure you intended to use Control Vertex Splines, or did you intend to use Interpolation Splines?

What manufacturing process will be used to make the part?

[Anonymous]

What is this object and what do the sketch points correspond to? Maybe knowing that would help in coming up with a better approach.

It represents the internal geometry of a pipe obtained from a CT scan. I used ImageJ to extract point which describe the geometry and then imported the points (only the points) into inventor. From there I fitted interpolation splines as best I could to come up with a geometry as close to the internal geometry of the pipe as I could. I'm not sure what that shape is called. I would love to just use a few parameters and simplify that geometry without the need for importing points, but I'm not sure how to design a simplified shape that has similar features...

Also, can one of these loft be created and the other just copied and rotated into place using the Circular Pattern tool, or are they really two different shapes?

Yes, this could be done. I'm just a beginner at Inventor and I'm trying to best describe the design I scanned... How did you manage to loft between the two sketches? Curious as to what "ugly" results you obtained!

[Anonymous]

Thanks for your reply, below are my answers. This is my first time in the forum, so apologies if I am not able to fully describe the problem.

Do you have any prior experience with Loft command?

I do not - any pointers as to how I could perform this would be more than welcome.

Did you sketch these splines, or did you set Inventor to automatically createthem on import of the Excel points?

It appears that you are missing Tangents and the splines are not even on the points?

Can you attach the original Excel file(s) here?

I sketched them myself using the interpolation spline feature to best match the internal geometry than I was hoping to get out. I believe I used the control vertex spline once because it provided a better approximation to the geometry I wanted. If it would help, I could post the excel points!

What manufacturing process will be used to make the part?

This part will not be manufactured. It's for an acoustic analysis on COMSOL. Manufacturing issues do not need to be considered!

Thanks!

[JDMather]

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@jr12714 wrote:

I could post the excel points!

What manufacturing process will be used to make the part? 

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Yes, post the Excel file(s).

Inventor can be set to automatically create the splines for you.

It is a common misconception that more points equates to better curve.

The reason I asked about manufacturing process is that I would strategically remove points to use as few as possible required to get a smooth curve with acceptable tolerance.  My guess is that at least half (if not far more) of your points can be removed.  And if possible, replace splines with lines and tangent arcs.

Also, I suspect you will get better results with only the inside curves Shelled to the outside rather than using Offset of the sketches.

[Anonymous]

Also, the lobe lofts are not meant to criss cross... they are meant to be parallel tubes. I'm sorry if I didn't explain this correctly. Did you employ the area/rail/centreline loft? Would you mind explaining the steps you took to loft between the two sketches?

[Curtis_Waguespack]

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@jr12714 wrote:

Yes, this could be done. I'm just a beginner at Inventor and I'm trying to best describe the design I scanned... How did you manage to loft between the two sketches? Curious as to what "ugly" results you obtained!

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Hi jr12714,

This is as far as I went (see attached).

I hope this helps.
Best of luck to you in all of your Inventor pursuits,
Curtis
http://inventortrenches.blogspot.com

[JDMather]

I didn't take time to clean up the curves (other than to recreate them), but maybe something like this is what you are after?

[Anonymous]

Thank-you for your reply.

I have attached the excel file - coordinates for the two lobes of cross section 1 is in sheet 1 and for the lobes of cross section two is in sheet 2. The distance between the two working planes is 58.627mm. Every time I wanted to import points, I'd copy those values onto a new excel sheet so that the X coordinates started a A1 and the Y coordinates at B1. That file is just where I have all my info summarised.

I did not use all of the points for the interpolation. They were included mostly for me to ensure that the spline would be ok-ish as it crossed about 1/5 of the total number of points I imported.

I was aware Inventor could do the splines for me, but wasn't sure how accurate it would be in comparison to mine. How would this simplify my lofting? I believe what i have should still be able to be lofted. I have just never used loft, but despite the videos and tutorials I have found, I have not been able to get this one to work thus far.

Have you tried to loft the sketches I attached in my original post?

Regards,

jr

Edited by
Discussion_Admin

[Curtis_Waguespack]

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@jr12714 wrote:
Also, the lobe lofts are not meant to criss cross... they are meant to be parallel tubes. I'm sorry if I didn't explain this correctly. Did you employ the area/rail/centreline loft? Would you mind explaining the steps you took to loft between the two sketches?

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re: criss cross

yep, i miss-read this the first time

re: Would you mind explaining the steps you took to loft between the two sketches?

Select the bottom sketch from the browser, then click the profile in the graphics area, then click the Click To Add in the Loft dialog, then repeat for the upper sketch. I was not able to select the "loop", but instead just the overall profile, which told me enough about the sketches to decide not to go much futher.

Q: If you had clean geometry in the bottom sketch, could you project that sketch up to the plane in order to create the top profile, or do they need to match the scan data for top and scan data for bottom?

I hope this helps.
Best of luck to you in all of your Inventor pursuits,
Curtis
http://inventortrenches.blogspot.com

[Anonymous]

Hi JDMather,

This is perfect. How were you able to get this result? Would you mind clarifying some of the steps you took? I see you used both loft and shell - I have never used shell before. Also, did you import the points with Inventor automatically fitting a single spline?

Would love to get information on how this was done, as it's exactly what I'd be looking to do myself!

[JDMather]

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@jr12714 wrote:
...

Have you tried to loft the sketches I attached in my original post?

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No, I didn't bother as they didn't look like good quality curves to me.  Did you check the file that I did attach?

[Anonymous]

Hi Curtis,

I appreciate you taking your time. That is what I was expecting to obtain, except that I was hoping the pipe would be hollow. I believe JDMather obtained a more simple and working version of what I have been attempting to do for the past few hours. I really appreciate your help.

Thanks so much,

Jr

[Anonymous]

I understand. It's my first time importing points into Inventor. I thought it would be best to interpolate between them myself. Your result looks much better and exactly what I hope to obtain myself. Not sure if you saw my previous reply to your post as it was posted at the same time as this post of yours, so was hoping to bring attention to it through this reply.

Thank-you again, and look forward to hearing back from you!

[JDMather]

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@jr12714 wrote:
Thank-you again, and look forward to hearing back from you!

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Well, I am off to bed.  If you don't figure out what I did, and reproduce on the other side - post back tomorrow.

Good luck!

[Anonymous]

Homework! ha I appreciate it. I will try to figure out and get back to you. Hope it's ok that I accept it as a solution once I get it working myself? Not sure what the procedure is here as it's my first forum post!

I'll post back tomorrow if I can't get it to work!

Good night!

[JDMather]

Actually, Curtis wrote the book on using Inventor and his bedtime is 3hrs or so away.  He will probably post back to ight.

[Curtis_Waguespack]

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@Anonymous wrote:

Actually, Curtis wrote the book on using Inventor and his bedtime is 3hrs or so away.  He will probably post back to ight.

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Hi jr12714, 

I'm working late tonight, but about to give up too... but now that JDmather is in bed, let's talk about him!

So attached is my Area loft example for this. Notice that I've only used the scan data to use as a guide. As JDMather mentioned sometimes simplifying the scan data is the best bet. I don't have a great deal of experience with this kind of thing, but from what I have I've learned that using the data to generate actual geometry is generally not what we want to do (although we always start out trying). Instead we bring it in and use it as a guide to create a more refined result.

Anyway, maybe this example will give you some ideas, I didn't make any attempt to stick real close to the exact scan points, as this is just for example. You might find that in your case you have to hold more true to the actual scan data, in which case JDMather's example will be closer to how you want to proceed, but in any case don't feel you must be a slave to all of those little data points if you don't have to.

I hope this helps.
Best of luck to you in all of your Inventor pursuits,
Curtis
http://inventortrenches.blogspot.com