View Full Version : Rail extrude. Bad results

03-12-2006, 05:00 PM
Hi all. I have recently swapped over from Max to Lightwave and am having a bit of trouble with the Rail Extrude option. I am trying to extrude a basic hexagonal disc along a spline but I am getting terrible results.

The shape does not orientate itself along the spline (both with or without Orientation ticked in the extrude options) and the shape also seems to shrink as it goes along the spline. Besides this the shape suddenly rotates at some points along the extrusion and I also get faces flipping along sections of the extrusion as well.

I have tried all the suggested remedies, flipping the orientaation of the spline, the original poly or both, and I have also tried all possible variations of the options in the Rail Extrude tool. All to no avail. I am careful to place the hexagonal poly at the right point at the start of the spline.

Am I missing something??

ANY help would be greatly appreciated!!!!!

03-12-2006, 06:06 PM
I don't know about using a spline as a guide for Rail Extrude. I use the native LW Sketch Tool which will also draw a line. Then in a new layer create a disc ( or whatever } which you then align to your line ( your line should be in a background layer ). Selecting the Rail Extrude function brings up the panel where you can define its properties. One thing I did notice in the Rail Extrude panel is that you need to deselect the oriented checkbox to obtain a nice circular tube. I was also going to recommend Carl Meritt's AligntoRail plug-in ( as mentioned in LW's Getting Started Guide ) but the website seems to be no longer there. I checked Flay and they also have deleted this URL so if someone knows where to get this useful plug-in, it would make aligning your object to line a bit easier. And if anyone knows if Rail Extrude does work with splines-please chime in. I tried using a spline as a background guide layer but didn't get anything useful. Good learning!

03-12-2006, 06:37 PM
The most common problems I have when using Rail Extrude are:
shape is at the wrong end of the spline curve
extruded shape is inverted so I have to Flip the polys afterward
shape is too large to follow the tight curves defined in the spline,thereby
inverting the polys

Good Luck

03-12-2006, 07:02 PM
I am think some of your problems, may have to do with multiple splines. A single rail extrude only works with the splines merged in that rail. An example of this is using bezier curve which makes multiple splines to get those perfect 90 degree angles.
Any ways, you can select all the splines and hit shift-z to merge the splines.
Make sure your poly is facing away from the spline and the spline is creating starting at the poly and is traveling the opposite direction the poly is facing.
If either the poly or spline is wrong direction select it and hit the f key to flip it.
Hope this helps,

03-12-2006, 07:02 PM
Thanks for the help guys.

I figured out what I was doing wrong. I had several splines in the background layer. With just one spline the results are much cleaner.

I generally get good results now with splines made using the Spline Draw tool.


03-13-2006, 12:37 AM
Pictrix free script: 'C_First Contact'. Is highly recommended if you do rail extrude a lot. It saves time lining up the polygon with your spline.


03-13-2006, 12:45 AM
If you're on a pc you can try hairblade plugin. It will probably be the closest thing in lw to the loft thingie the max had when i looked at it last time (loong time ago).