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Creating a solid with a thickness from a loft
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* February 18, 2018, 10:00:25 PM
Hi Guys

I hope you can have a look at this for a customer of mine, I can't work it out but I am sure you will be able to help.
Below is a extract from an email he sent me and I have attached his example file.

"I want to create the ‘crack solid’ so I can subtract from the rail head model. However, I spent probable 30++ hours trying to ‘fix’ what might be reason why I cant get a 1) lofts to even work (found it, cant have two profile splines on the same Y space) and 2) creating a solid with real thickness from the loft. 2) still has me totally frustrated and I am think I am following the instructions “perfectly”(well at least I think I am?!)

I have included a sample of the file I am actually using. I have tried both 2015 (originally done in this version), and 2017 just purchased as I thought it might be a fault with 2015. Same problem either version.
I have deleted the content of many layers to get the file size down but left enough in to show the problem I am facing.

Open the file.

Make visible the Layers 1.1(front of cut rail piece)  and 1.2(back of cut rail piece). Start with a plan view looking at the rail cuts end on. Look for the colour spline lins. Put into  perspective view if you wish but you have to do it manualy as the Y plane is the height and Z is the depth (more on this later).
You will see each layer has a photograph of the cracked rail and you will see the 3D Spline by Fit Points conform to the crack.
Each slice of the rail and its associated spline(s) has a dedicated layer and everything on that layer is set to the correct depth of the rail slice.
I have included layers 8 to 12 with their respective  splines. Turn the filter layers (8 to 12) on (it turns on both front and back (n.1 and n.2 layers)
Turn off the layer 1.1 and 1.2 to make it easier to see.
Now you see the group of splines, colour coded as to which relates to what crack.
I then create a loft using the lofting facility for each group. Turn on ‘Curves’ layer to see the lofts.
that is as far as I can get.
I cant get shelling to work. Often reports with failed something like  “ cant shell, both side used (Is this an open shell?)”

Sample simple file of two 3D Splines to fit points and a loft between and I can create a solid and make it thick.
Realised that the orientation of the spline / loft might be the issue as it thickens in the vertical plane and mine are not orientated that way. So I converted by a 90 rotation in the x axis everything in the file to orientate the ‘standard’ way. Made no difference.
Tried some of my 2 spline cracks (maybe an issue with the complex larger cracks) but this made no difference – still cant do it)
Tried exploding and making a solid again, didn’t work and just made life more complex as every facet now needed to be computed and time passes ever so slow when this happens!
Tried the online TC manuals and blogs for Open Shel and similar but can find any reference to it before so I couldn’t help myself to fixing the problem)

I want to make the lofts a real solid (not an asic solid which I really think should be called a asic surface for these lofts!). I need each surface representing a crack to take on a thickness of eg 0.3mm. The intention then is take the rail head closed polyline (layer 0)  converted to a length of solid and then subtract the lofts (i.e. real cracks with a thickness) from the rail head leaving the rail head model riddled with cracks.
Why do I want to do this??
The rail head model is then inserted into our simulation software and we can then determine what is happening to the head stresses and ultrasonic beams when it hits the stress and cracks.

I just cant get the lofts into a real true solid."

I hope you guys can help. I will send him your replies.
Mindscape Australia.


* February 19, 2018, 02:05:16 AM
Natalie.  To be honest I'd be more surprised if it actually worked rather than not work,  some of the curvature of the lofts is way too tight to allow for 0.3mm shell, for example, with the firebrick colour profile, most profiles will loft and shell, but the sharp difference between the top two profiles prevents a 0.3 shell from working (it will shell at 0.005).

Often (in my opinion) if it will shell at a small figure (like 0.005) it simply means that there is too much curvature deviation or too tight bends for larger shells to be produced.   A few options are :-

Alter the profiles to reduce any sharp bends or tight alterations in curvature, though this would mean the cracks are not as accurate.  Or

Loft and shell as much as possible (example - on the firebrick loft and shell all, except not between the top two profiles), and figure out a different approach for getting the top two with thickness.  Or

Try creating as a solid to start with, thus eliminating the need for shelling. In the attached I used make copy, to copy the profiles by -0.3 mm in Y direction, joined them into closed profiles using line segments on each end. then lofted as a solid object,  this isn't strictly accurate, but I think whatever is done, it is going to be a compromise

Someone else may have a better solution.


February 19, 2018, 03:52:41 AM
Another method avoiding using the Shell tool is as follows:

1. Give the Splines the 0.3mm line thickness setup in there properties as per the attached.
2. Explode them all once (to get nodes point to snap to)
3. Trace over the outlines of these splines with two splines and two lines to cap the ends ensuring you set the workplane to the spline you are tracing. No need to worry about how many node points with this method.
4. Delete/move/or turn off the original splines you traced round.
5. Loft now ensuring the Compound Profile in activated before selecting the first profile.
6. Increase the Faceter Quality right up to 100 in the ACIS Properties.

It should loft nicely and follow the contours well..  ;)
« Last Edit: February 19, 2018, 03:56:43 AM by Darrel Durose »


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* February 19, 2018, 04:33:46 AM
Hi Natalie.  I used a similar scheme to Andy's and Darrel's, a little simplified: I selected the splines and copied them all in place, then node edit one copy of each, displacing all nodes except for the end vertices by whatever notional crack thickness it is.   Alternatively select all the splines, check "make copy" and enter delta y offset value, then node edit delta Y the end vertices minus the same value to connect them with the originals' end vertices.  I did one of them and subtracted a sphere to verify, 0.3 offset, no hitches. 
« Last Edit: February 19, 2018, 02:23:50 PM by murray dickinson »


* February 25, 2018, 08:36:47 PM
thanks Everyone, I will let you know how the client gets on.