Le Wed 25 June 2014
In the ROV development project it is necessary to produce accurate 2D drawings of the panels that will be cut by scroll-saw or laser cutter. In order to do that TurboCAD is the best tool I have to hand to produce line work accurately. Unfortunately TurboCAD Deluxe 11 is a little bit limited in the useful import (and export) formats that it has available. The only ones of use are; 3DS, DWG, and DXF.
While Blender does an OK job on the 3DS it is not that good and certainly not good enough for TurboCAD. Blender 2.49 had an exporter for DXFs and DWGs but it seldom worked well - the later versions don't have working versions either. So an intermediate format was required so that another tool could be used to produce higher quality versions of the DXFs or DWGs that TurboCAD would accept.
Here is the successful series of steps used to create a pdf at 1:1 scale using the Blender model of the ROV as the basis. The outline below assumes a good working knowledge of Blender.
- In Blender, lay out all of the panels flat ie. parallel to the z-plane, but not overlapping. They do not need to be movd to the z=0 plan. It pays to lay things out as they might appear on the final drawing, but this is not essential.
- Join all of the meshes into one mesh. In Edit mode flatten everything in the z-direction by using a scale z=0. Remove all the double vertices. This small step has advantages later when you get to TurboCAD because you won't have to create a new working plane and TurboCAD automatically lays it out flat on the z=0 plane ready for tracing over.
- Export the mesh as an STL. This preserves the scale of the objects.
- In Meshlab, import the STL.
- Eyeball it to see that it is all OK.
- Export it as a DXF
- Open the DXF and then save your new document in the TurboCAD format.
- The shapes are all one object so this makes it easy to handle them.
- The document units are probably imperial, so go to the Document settings and change them to Metric. Nothing else will change but all of a sudden your 100 inch object will be 100 millimeters instead and will be the correct size.
- Create a new layer and appropriate name and a nice light colour.
- Put your imported object into that layer and switch back to the 0 layer to begin tracing over the object.
- Trace around the shapes snapping to the Vertices. Using polylines, lines, two edge point circles, and 3-point curves, you can quickly create the object outlines. You may want to lock the original mesh layer to avoid shifting it - although the risk is small and the undo is good.
- Turn the shapes created into closed polylines, and if they have any holes in them turn them into groups. Name the groups and objects with useful names. Turning off the Mesh layer from time to time can help seeing what you are doing and selecting the elements when joining them or grouping them.
- Set the pen thickness at the layer level to be 0.5mm or so otherwise you may not get a line when the drawing is finally turned into a pdf. Do this before you group the elements.
- In the Paper Space set up the paper size and printout size to be A3.
- In the model Space create a view (or views) to capture the bits you want on your drawing.
- In the Paper Space create a new viewport and direct it to the view you have just created.
- In the Viewport properties set the scale to 1:1 (or whatever scale you want)
- Pull and push around your drawing elements in the Model Space until they fit into your viewport in the Paper Space. You may need to recreate your Views and Viewport a few times as you fine tune it.
- Add any labels and dimensions in the Paper Space on a new layer. I have found it pays to add a 100mm long rectangle into the Paper Space pages to provide a check that the printer has not automatically scaled your drawing to something other than what you wanted.
- Print the new image as a pdf. Make sure any automatic scaling is turned off when you print.