Tuesday, January 19, 2016

Drawing a house in Autocad 3D Solids

I have become the magpie of CAD software, dabbling in, but never quite mastering Inventor, Solidworks, Vectorworks,Chief Architect, and so on.

The thing that strikes me with most of the architectural ones is that they provide a solution to a set problem, for instance, how to draw a roof.  Then you have a major struggle to make things like the fascia board to be in the correct position, which usually causes it to be buried in the roof.  I have just realised most users of this software just live with the approximations the software creates.  After all, does it really matter if the gutter is out of place by say 30mm?

You can draw a house using solids Autocad, but things like doors and windows can be a problem because you have to draw them each time, or have a library of pre drawn ones to stretch into place.
Or have a set of lisp routines to Africa to insert these.  Not impossible.

A unioned window frame is not that stretchable, but if you could live with a window made up of slabs, you could alter these using the properties of the slab. Then once things are fixed, union it all.

I have just got a job drawing houses in 2D, using Autocad LT.  The boss says he is not totally against 3D though, so this possibility is suddenly interesting.  In the meantime, I hope to learn the ropes using 2D.

Over the years I have made a few lisps to lighten the load:

1. Wind.lsp  This just draws a simple window, putting things on layers like "window" and "glass".
You can have only vertical mullions, so it is pretty limited.  On the other hand, is is fast.

2. Truss.lsp. 

The truss routine uses a dialog box called truss.dcl to draw a cross-sectional view of a roof truss. It inserts components such as GutterCopper in the process of drawing the truss.

It could be argued that the bracing is a bit unrealistic.

This is usually not a problem in New Zealand because the draftsman is only expected to
produce an approximation as the actual truss is redrawn anyway by the truss maker.

3. A set of routines to draw wooden windows.

Modelling The House in 3D
The technique used is to model the house carefully in 3D, then xref this into a blank drawing and then use the section command, and the flatshot command.

Bringing my recent try at this into Showcase turned out a bit strange: all the bricks decided not to lie the correct way! I tried drawing a brick as a block and laying them, but this was too long and involved, plus the mortar seems to be a problem. A cunning plan might be to draw a wall all as mortar and then stick 10mm thick bricks on top of this.  Which still does not solve the problem of trimming the bricks around a window. Maybe a super lisp routine might be needed.

The nice thing about Autocad is you know EXACTLY what you are modelling, and Autocad has a nice set of solids editing tools.

In this screenshot, you can see the model on the left, with the sections and flatshots on the right.

I brought this one into Showcase, from Autocad, all weatherboards are drawn, which came out with a bit of realism.