The only thing better than a letter board is one you designed yourself.

I'm going to show you how to take a design from online, pull critical information, and expand on it. Specifically, we're going to make a letterboard as big as we want and then cookie cutter it with a state outline!

First things first, a huge shout out to FLOWALISTIK who designed the letter board we will use for reference. Once we make our own board, we'll also be able to use his letter prints to fill the board.

Supplies

Fusion 360
3D Printer

Step 1: Pull Reference Dimensions From STL

To start, we'll need information from one of Flowalistik's STLs.

You'll need to download one of his board files from the download page on Thingiverse

Once downloaded, we could try to get our information by measuring random points on the STL but we can't snap the cursor to exact locations so we can't get reliable info. We want these boards to work perfectly with his letters, so accuracy is very important.

Lucky for you, I know a great way to get precise measurements off any STL.

Upload the file to Fusion 360 by clicking the Upload button on the Data Panel
Open the file from your Data Panel
Go to your Bodies on the model tree and right-click MeshBody1 (aka your STL)
Select Mesh to BREP and click through the pop-up. This will create a new Body and hide the MeshBody. Note: There is a limit to how many faces your STL can have for this command, 10,000. It will easily work for this file, but a high density model, like 3D scans and sculptures can exceed Fusion's limit.
Once converted, make sure your model is the right scale. Lucky for us, Flowalistik is smart and named his boards with their overall dimensions, making scale checking simple.
Press the I key to bring up Measure, or select it in the Inspect toolbar. Click two corners on the board to see if it imported at the right scale.
You can see in my images that mine came in 10x the correct size. This is solved easily with the scale command. (Scaling 1/10 or 0.10)
After scaling, our model is ready for precise measurements with the Measure tool. You can see from my image that I can click the two corners of the raised feature and see it is exactly 3.175 mm wide. This is actually 1/8", which in my experience is rare to find in online STLs. Many people prefer to model in metric.

Step 2: Create Letter Board Base

This step is much simpler, we'll use the dimensions we pulled from the STL to sketch the profile and extrude it. This will give us our basic shape to customize later.

Start your sketch on the right plane. This way when it's extruded the ridged surface will face the front.
Draw a rectangle the desired height and thickness of your back piece (I went with about 5" tall and 1-3 mm thick)
At the bottom left of your rectangle, draw a square to match the dimensions of the STL, 3.175 mm (0.125 in)
Rectangular Pattern the square up, along your back, 6.35 mm (0.25 in)
Extrude all of the sketch. Don't worry too much about length, we'll be using a cookie cutter to trim away excess so it's safer to go long.

NOTE: You can see in my image that my extruding Direction is Symmetric. This is a good practice to make mirroring components simple in the future. Although it's not necessary for this project.

Step 3: Create State Outline

Now comes the good part, getting your custom shape. You can see that I went with the state outline of North Carolina, but you can pick anything you want! Just be sure it doesn't get too complicated. You can see on the coastline, along the right side of NC, that the features got a bit close and I can't actually put letters over there.

Find a picture of your shape and attach it as a Canvas in Fusion
Scale the canvas to match your base object in height.
Trace the outline with lines, arcs and splines.
Extrude the shape and select Intersection

Step 4: Add Border

With our outline cut out, the last step is to add a border to really show off our custom shape.

To do this we are going to flip our model around and sketch on the back face to keep things easy. Don't worry, we'll get the feature to the front during the extrude.

Start sketch on back face
Project the back face to your sketch (if not done automatically. This depends on your Preferences)
Offset the outline 1-2 mm
Extrude the new band
In the dialog box select, To Object and click one of the front faces
Next we'll raise the border 1 mm in the Offset box.
Select Join and OK

Step 5: Print Board & Letters

Your 3D model is now ready! To export, go to Tools tab and then 3D Print in the Make section. You'll want to select your model, which should be one body and deselect Send to 3D Print Utility.

With the letter board STL exported you'll simply need to load the file into your preferred slicer and send it along to your printer. If you're looking to do two colors, you have two options.

Pause the print and swap filament when you only have the border left. The downside to this is that you'll need to watch the print.
Create two print files. One that ends at the height of the letter lines and a second one that starts at that height. Be careful that you don't include brims, perimeters, or other special first layer features on the second print that starts above the bed.

I personally do the second method, using Simplify3D, but I know other software has nice features to Add Pause at Height.

For the letters you'll need to revisit Flowalistik Letter Board and download the files you need for your message. Simple! I would however recommend printing at a slower speed to ensure they come out flat and smooth.

Step 6: Next Steps

My favorite part of printing a letter board is being able to print more letters! No more using a "5" as an "S" or "0" for "O". So if your message is Super Sale on Lassos and slinkies this Saturday" you don't have to worry about a thing!

A few other things you can try out.

Custom Letters. Using the steps from this project you can also pull dimensions from the letters and make your own! Why not try a different language's alphabet or a different font. You could also make a signature block to put at the bottom of your board.
Mounting the board. This design is meant to be held up with Command Strips, but you can also make the base thicker and add slots for nails or hanging wire. OR Why not make a separate stand so it can live on a desk or table. It doesn't have to be printed either, maybe laser cutting would be a good choice.

There are so many possibilities. If you try any of them let me know! I'd love to see what y'all do with this.