How to Make a 3D Sign with a CNC Machine


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Making a sign seems to be almost a write of passage among CNCists. I decided to share some of my own sign making ideas and tribulations in the hopes that someone might find them useful.

Like most everything else on the Cerebral Meltdown site, this page will focus on methods which can be done using cheap, or even free, software. Although there is professional software designed to do exactly what we are trying to do here, it costs an arm and a leg to buy.

Preparations

Software

If you haven’t already, download and install the free version of Google Sketchup.

You will also need to download and install CamBam+. (There are other options, of course, but I personally am using CamBam) There are two versions of CamBam. The first is an earlier beta version and is free. CamBam+, however, isn’t free, and costs about $150 to buy.

There isn’t currently any free software available for generating 3D toolpaths that I know of, but $150 for CamBam+ is a pretty reasonable price. There is also a trial version available so that you can see if you like it.

Plugins

In addition to the above software, you will also need to find a way to export STL files from Sketchup.

There are actually a few different ways you can export STL files from Sketchup. The easiest is to use one of the two plugins that I wrote about on the How To Export STL Files From Google Sketchup page.  Note: For this projects, I used the Su2stl.rb plug-in.

Another more roundabout way is to use the method that I wrote about on the Sketchup to CNC page.

Making a 3D Sign in Sketchup

Making 3D objects is one of the most challenging things you can do with a CNC, and, of course, one of the most time consuming. Although there isn’t much that can be done about the length of time it takes to cut out the sign itself, there are a few tricks for shortening the design time.

One such trick is to utilize the models in the vast Sketchup 3D warehouse to form the base of your own work.

Now, you can of course make you own models from scratch, but doing so can add many hours to the project. The model I did for this tutorial, for example, would have taken me all day to design if I had to make all of the parts from scratch.

Make the Frame

For this sign, I started by making a simple frame. This isn’t absolutely necessary, but it does help give a better idea of how it will look finished. The dimensions are entirely up to you, but mine is 8″ x 8″ x 0.75″. Keep in mind that bigger signs take longer to cut out.

pushedsquare

Pick out Models at the 3D Warehouse

Note: Sketchup’s 3D Warehouse can be found by going to “file” on the menu bar and clicking on “3D Warehouse >> Get Models.” The models found in the 3D Warehouse can then be downloaded straight into Sketchup.

After drawing the frame, I next started searching for user created models in Sketchup’s 3D Warehouse that I thought would fit well into this project. Below is a picture of the models after I downloaded them into Sketchup.

misctools

Tip: Some people seem to be really egotistical about their models. You download them only to find out that they are scaled up much bigger than you’d like. In fact, you may have to zoom out a couple of light years just to find them. Once you do, you can scale them down to a more useable size.

Rescale and Align the Models

In the picture below, you can see that I both rescaled the tools and arranged them into a pattern that I liked. Also, notice that I found it easier to align the tools onto a copy of the inside of the frame instead of actually inside of the frame.

toolslayedout

Notice that the models are situated so that they are laying halfway down through the square face.

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The next thing I did was move everything into the frame.

toolsinset

Preparing for the Model Export 1

Here is a side shot of the frame with the tools inside it. The important thing here is to make sure that they aren’t sticking out above the top of the frame. The reason why is because the top of the frame represents the top of the stock. Anything above that is just open air.

Also notice that I moved the entire frame down so that the top of it is at ground level, z = 0.

sideshot

Preparing the Model for Export 2

The next thing I did was explode all of the small groups. Depending on the complexity of your model, Sketchup may freeze up and think for awhile when doing this step.

Note: You can tell a model is grouped if it is surrounded by a blue box when you click on it. (Right click >> Explode to ungroup.)

After the small groups were exploded, I then selected all of the tools and regrouped them into one single group (Right click >> Make Group).

The reason I did this is because the model doesn’t always export correctly when there are groups inside of groups.

Export the Model

The next thing you need to do is export the model to a STL file. How exactly you do this depends on which of the three methods mentioned at the beginning of this tutorial you use.

Keep in mind that it can take a looong time to export a model if it has a lot of intricate detail. The model I made here is one such example. I didn’t use a stopwatch, but I’d say that it took between 15-20 minutes to export it.

The Model in CamBam+

Here is the model loaded into CamBam+. It looks pretty good from this angle.

img2A

Let’s see what it looks like after generating some toolpaths.
Hmmm, that’s not right. Notice that there seems to be a strange hump running diagonally across the frame starting at the upper left corner.

It is not uncommon to have unexplained phenomenon such as this in the exported model. These sorts of things can usually be fixed, but it might take a little bit of experimenting in the original Sketchup model to get it right.

img2C

Second Try

So, here we are back at the original model. To try and clean it up a little more for the second export attempt, I first decided to delete the frame because it wasn’t really necessary.

I next copied and pasted the entire model into a fresh Sketchup model.

I then double checked to make sure that the model didn’t contain more than one group. It turns out that it did, so I made sure that the group was exploded before continuing. (I forgot to check underneath the frame the first time)

[bad]

Finally, I deleted the faces that the tools were embedded inside (left) and redrew them (right). I believe that this is what actually fixed the problem.(You might try reversing the faces too by right clicking a face and going to “Reverse Faces”.)

img23 img18

And here we are back in CamBam+ after exporting the file from Sketchup again. (Which took another 15-20 minutes of waiting.)

It looks a lot better this time. Everything is where it is supposed to be, and there isn’t any unexplained geometry to cause trouble.

Note: These aren’t my final toolpaths. I did these just to see how the model looked.

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The End (of the beginning)

There is, believe it or not, still a lot more to say about making 3D signs with a CNC machine. In fact, this barely scratches the surface. For example, the toolpaths still need to be generated, and, although I called this thing a sign, there isn’t actually any text in it.

These things will have to wait until later though because this page is already long enough. Wait tight though because there is more to come.

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