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View Full Version : Tip: Using LWCAD to make curved bannisters that stay upright.



kopperdrake
05-06-2008, 11:17 AM
If you've tried to make extruded bannisters in LW then you know it can be a pain. Rail extrude rotates a cross section as it moves through the background path, which was always my main gripe.

If you have a length of straight bannister, followed by an arc that then leads into another section of straight bannister, the curved joining section between the two straight sections can be a pain to set up.

This technique, using LWCAD, lets you create, as far as we can tell here, any type of bannister cross section, and still have the profile running accurately through its entire length.

Step 1: Create the curve you want the bannister to follow - I tend to use LWCAD's arc and line tools, then convert to a LW curve once done.

Step 2: Extrude the LW curve in the Y axis as high as your bannister will be (say 100mm).

Step 3: Copy the resulting geometry into another layer and flip the polygons.

Step 4: Use LWCAD's Engraver tool and choose a profile that fits half of your bannister. If there's no profile you like make your own, but make sure you only model the one half of your bannister's cross-section.

Step 5: Repeat the above step on the flipped geometry in the other layer to create the other side of your bannister's cross-section - you'll have to use the Rotate 90 button in Engraver's numeric panel to rotate the second cross-section to match the first.

Step 6: Copy and paste the one layer into the other, merge points and job done - one perfect bannister extrusion. Try some funky corners which would make a grown carpenter cry and it seems to work!

clintonman
05-06-2008, 11:58 AM
Thanks for the tip. I had exactly that problem last month on a model using rail extrude.

hrgiger
05-06-2008, 12:09 PM
You could also create your curve in LW, then use LWCADs snapping tools to recreate the curve (not sure if you can snap to curves but you could freeze it if necessary), then just use profiler. This will avoid having to make the other side of the bannister. I would think this would be easier.

kopperdrake
05-06-2008, 12:25 PM
We tried Profiler but you have no control over the vertical lie of the profile as it moves through corners.

hrgiger
05-06-2008, 12:56 PM
Do you mean the angle by which the profile follows the curve? Because you can adjust that in the properties panel.

kopperdrake
05-06-2008, 04:21 PM
Nope - if you have more than two 'joints', as in the attachment, then your middle joints' start and end angles are at the whim of the two ends of your extrusion. Using the numerical rotation dialogue box as you show only lets you set by eye the rotation of the ends - all of the highlighted base polygons on the attached image are non-planar as they've all distorted slightly using Profiler. Using the Engraver method assures you of no twisting except at the corner joints, as if you'd made them by hand with real wood :)

hrgiger
05-06-2008, 05:26 PM
Easy enough. Split the curve between joints before running profiler. Then merge the two afterwards.

liquidpope
05-06-2008, 06:18 PM
Why not just use Modeler's multiple rail extrude?
Create your curve, copy it straight up, extrude. No rotation.

Maybe I missed something?

prospector
05-06-2008, 06:24 PM
Why not just use Modeler's multiple rail extrude?

That's what I use

kopperdrake
05-06-2008, 07:12 PM
Maybe I'm missing something...

hrgiger - if you do that can you get each of the sections to line up with the next nice and smooth? I struggle to get the rotate accurate with LWCAD on each end. The beginning end, no problem, the last end once it's gone through a 90 degree curve in it's heading and a pitch up of whatever (say 30 degrees) and you just can't get it to rest on the horizontal accurately.

Liquidpope/Prospector - LW's curves don't handle corners well if you want accuracy. From a straight bannister to a 90 degree curve there's always a small blip in the curve so you have to stick a small anchor point in before the curve begins and after it ends to hold the long straight in place. But that still gives a small glitch in the extrusion when you use it. Unless I'm missing something I can't see a way round it.

Call me fussy, but unless there's something obvious I can't see with your techniques then I stand by the original post for an accurate bannister with multiple curves where end and beginning is important. Totally open to all suggestions though - more methods the better :)

hrgiger
05-06-2008, 07:37 PM
That is true Kopper, unfortunately, I see no way to snap it into any kind of precision. What you can do however is to make sure your ends are closed on your profile. Then just use the bridge tool to connect the parts and then bandglue out the new lines that are formed. This will leave you pretty close to dead on and you don't have to worry about the ends where you joined being slightly askew. I can see the advantages of both techniques.