One of the 3D modeling tools that I use for designing plywood furniture is SketchUp. The goal is to have the plywood cut by a CNC router. The software I’ve been using to create the g-code for the router is VCarve. Here’s the process I’ve been using to get the 3D model from SketchUp into VCarve.
In the instructions below, I’m working on Windows 8.1. The SketchUp version is SketchUp Pro 2013, 13.0.4812. The VCarve version is Pro 7.012.
What you’ll be doing in SketchUp is taking your 3D model and converting it to a 2D representation. Then exporting the 2D to the DWG format that VCarve can read. Here’s the workflow.
The first step is to create your 3D model in SketchUp. Here's mine for a workbench. Each piece of wood is a component in SketchUp.
Initial 3D Model in SketchUp
As a quality check, you should check the integrity of all of the components by using the Solid Inspector add-on. You can find this tool by searching in the Extension Warehouse within SketchUp. When installed its at the bottom of the Tools pulldown menu. The tool ensures that all of your 3D components are fully enclosed and have no stray entities.
Solid Inspector Add-On
In SketchUp, you need to get all of your pieces from your 3D model layed out flat. To do this, I made a copy of my original file and named this one Workbench-sheets. In my original file, I had put the 3D model on a layer called Workbench. I created a copy of the model. I put the copy on a new layer,Components. Then I turned off the layer Model, so I only had one copy of the model on the screen. This way, I can still see my model assembled in 3D and simultaneously see the pieces layed out flat. I selected this whole model and used another plug-in. This plug-in is called Center on Origin and is created by Chris Fullmer. It is also available in the Extension Warehouse.
Center on Origin
Then I rotated the pieces that were not already flat 90 degrees to make them flat. I had to do two rotations. One for the components that needed to be rotated about the X axis. The other for the components that needed to be rotated about the Y axis. I also re-ran Center on Origin to get everything at the same level again. I also moved all of the pieces down .375″. As my plywood is 3/4″, moving it down half of that thickness puts the top of all of the pieces on the XY plane for Z = 0.
Flattened at Origin
The next step is to lay out all of the pieces so they are not overlapping. You want to keep them all on the same XY plane. So you're moving them in the X and Y directions. But they are not changing their Z position. You don't have to worry about fitting them together on a plywood sheet in SketchUp. That will happen in VCarve.
Flattened and Spaced Out
Now its time to export the model to a format that VCarve can read. To prepare the view to export, set the view by selecting the Camera pull-down menu. Select Standard Views, then Top. Turn on Parallel Projection, also in the Camera pull-down menu. And then Zoom Extents so that all of the pieces of your model are in view.
Model and View Prepared for Exporting
Next, its time to export the file so that it can be read by VCarve. If your dimensions exceed 100 inches overall, you won't be able to export as PDF or EPS as SketchUp exports in those formats cannot exceed 100 inches in either the X or Y direction. As a workaround, you can scale down your export and then scale it back it up again within VCarve. My model does exceed 100 inches. Instead of doing the workaround, I'm exporting to DWG. So, go to the File pull-down menu and select Exportand then 2D Graphic. I'm doing a 2D export here because on the router, the only work I'll be doing is cutting lines. VCarve does not need a 3D model to do that. In the Export 2D Graphic dialog box, select AutoCAD DWG File (*.dwg) under Export type. Under Options, check that it is Full Scale. And then click Export. You're now done with SketchUp, so you can close the application. Next, open up VCarve. Select Open an existing file from the Startup Tasks. Select the DWG that you just exported from SketchUp and click Open. You're now at the Job Setup screen. Here, you'll define the wood sheets you'll be using. One thing to note is that in VCarve, the plywood sheets should be landscape. The plywood I'll be using is 3/4" thick 4' x 8' sheets. The screenshot shows the setup settings for that.
Now you have your model in VCarve. First thing to do is a quality check and clean-up. In the Edit pull-down menu, click on Select All Duplicate Vectors. If everything is clean, you'll get the message No duplicate vectors in design. If the command highlights duplicate vectors, you should delete the duplicates. And another clean-up step is to ensure that your vectors are joined and closed. For example in many DWG imports, a rectangle becomes four separate lines. VCarve will not see the rectangle; it will just see the lines. To fix this, select all the objects in VCarve and use the Join Vectorscommand.
The last clean-up step is to convert the arc segments from the DWG format into curves. You do this by selecting all objects. Then use the Fit Curves to Vectors function.
Fitting Curves to Vectors
You are now able to edit your model and set it up for milling.
So, that’s the process I use to get from SketchUp to VCarve.
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