3D Printed Pi Coaster Set: SolidWorks Sketch Picture Tool, TinkerCAD, and a Holder Lined With 36 Digits of Pi

I have always had a fascination for the symbol pi because of its infinite nature. Combining this fascination with functionality and 3D printing, I decided to design a pi themed coaster set. This Instructible showcases a 3D printed coaster set built around the most famous number in mathematics. The set has three pieces: a circular coaster base with a pi symbol recessed into it, a pi symbol insert that snaps into that recess, and a coaster holder whose entire exterior wall is made up of the first 36 digits of pi in raised text. This coaster set is used to remind the user of the significance of pi every time they place their drink down.

What makes this project interesting beyond the finished product is the design workflow behind it. I used two different CAD tools. I started with SolidWorks then transitioned to TinkerCAD. I started with SolidWorks because it was best suited for creating the precise pi symbol. I then continued my design on TinkerCAD because it made the design easier and simpler to manipulate than SolidWorks would have been. One of the most important lessons I have learned from 3D printing is that the best tool is the one that gets the job done cleanly and efficiently, not necessarily the most advanced one. Knowing when to switch tools is a real skill, and this project is a good example of that.

I also made a full video tutorial of the SolidWorks portion of this build, which you can find embedded in Step 2. If you are newer to SolidWorks, the video walks through every click from start to finish.

The actual coaster part of this design was made in two pieces. This makes it more accessible to 3D print for someone without a multi material 3D printer. It also prevents excess waste material as multi material printers create a lot of plastic waste.

Difficulty: Beginner to Intermediate Total print time: 5 hours 12 minutes Coaster diameter: 4 inches Holder outer diameter: 5.5 inches.

Materials:

1. Filament (I used Sunlu PLA in black and white)
2. Any two colors work; choose whatever combination you like

Software:

1. SolidWorks. Used to trace the pi symbol from a reference image
2. TinkerCAD. Free, browser based, no download required (tinkercad.com)
3. PrusaSlicer. Free download, or use your preferred slicer

Tools:

1. Any 3D printer with a build surface of at least 5.5 inches / ~140mm in one direction (I used a Prusa MK4S)
2. A computer with a browser for TinkerCAD
3. A computer with SolidWorks installed
4. If SolidWorks is not available you can use TinkerCAD for the full design (I explain an alternative approach in Step 2)

Approximate Print Times (on Prusa MK4S, 0.2mm layer height):

1. Pi symbol insert: ~10 minutes
2. Pi circle coaster base: ~37 minutes
3. Coaster holder with digits: ~4 hours 25 minutes
4. Total: approximately 5 hours 12 minutes

The first step is finding a clean reference image of the pi symbol. I searched online for a simple, high contrast pi symbol.

The image I found ended up being in JPEG format. JPEG images are not compatible with the sketch picture tool in SoldiWorks, therefore I had to convert it to a PNG format (I used CloudConvert.com)

To do this, go to CloudConvert.com or any other photo editor. Upload the image you have into the converter and click convert. Then wait a few seconds for the conversion to finish and download the new image as a PNG file.

When choosing your reference image, look for one that is solid black on a white background with no gradients, shadows, or decorative styling. Simple and bold will trace the easiest, saving you time during the outline.

This is the core SolidWorks step, and I have made a full video tutorial that covers this entire process from opening a new part file to exporting the finished STL. I highly recommend watching it alongside reading these instructions, especially if you are newer to SolidWorks.

1. Open a new Part file Launch SolidWorks. Click New Part

2. Select your sketch plane In the Feature Manager tree on the left, click Front Plane. Then click Sketch in the drop down.

3. Open the Sketch Picture tool In the top menu, go to Tools → Sketch Tools → Sketch Picture.

4. Import your PNG file A file browser will open. Navigate to your saved PNG and click Open. SolidWorks will place the image directly onto the Front Plane. Tip: Make sure the file is a PNG, SolidWorks does not accept JPEGs. See Step 1 for how to convert.

5. Resize the image Drag the blue arrow to be the width of the pi symbol, then set the dimension to be 4 inches.

6. Confirm and begin tracing Click the green checkmark to confirm the image placement. The image is now locked in your sketch and you are ready to trace over it in the next step.

If you do not have access to SolidWorks, you can skip this step and the next one entirely by downloading a free pi symbol STL from a site like Thingiverse or Printables and jumping directly to Step 4 in TinkerCAD. The SolidWorks workflow produces a cleaner, more precise result because you are tracing from your own reference, but the TinkerCAD-only path will still get you a great finished coaster.

With the image placed on your sketch plane, use SolidWorks sketch tools to trace the outline of the pi symbol directly on top of it. I used splines for the curved sections and straight lines for the horizontal crossbar.

In order to trace the pi symbol:

1. Open a new sketch Click Front Plane on the Feature Manager Tree and make a new sketch over the image.

2. Start with the curved edges Begin tracing at the outline of the pi symbol. Start with the curves first as they are easier to get right before filling in the straight edges around them. To draw a curve, use the Spline tool and click the two endpoints of the curve on either end of the arc. Try to use as few points as possible in order to ensure a smooth curve.

3. Adjust the curve shape Once you place your two endpoints, SolidWorks will create a straight line between the points. Use the handles that appear on the spline to drag and bend it until it matches the curve in the image underneath. Take your time here. Small adjustments to the handles make a big difference in how clean the final shape looks.

4. Add the straight edges Once all the curves are done, switch to the Line tool and trace the straight edges of the pi symbol, this includes the horizontal crossbar and the flat sections at the bottom of the legs. The reason to do these last is that you can snap the endpoints of your lines directly onto the endpoints of the curves you already drew, which closes the sketch cleanly.

5. Close the sketch Work your way around the full outline until every edge is connected and the sketch is fully closed. Once the sketch is closed you will see it turn from blue to black. You are now ready to extrude.

6. Extrude the pi symbol Exit the sketch and use Extruded Boss/Base to give it depth. I extruded mine to 0.2 inches.

Export this body as an STL file. Label it clearly because you will bring it into TinkerCAD in the next step.

Before jumping into TinkerCAD, it is worth explaining the design decision behind making the coaster as two separate pieces rather than one.

You could design this as a single piece and make a circle with a pi symbol raised or recessed into the surface. If you have a multi-color printer, that approach might seem appealing. But for anyone printing on a standard single extruder printer, a one piece design means the entire coaster prints in one color, and you lose the two tone contrast that makes the pi symbol pop visually.

Designing the coaster in two parts makes it more accessible to people with 3D printers and reduces filament waste as multi material printers can produce a lot of waste when changing colors.

Open TinkerCAD in your browser and start a new design. Import your pi symbol STL file using the Import button in the top right corner. TinkerCAD will place it on the workplane as a solid shape. Select it, and in the Shape panel on the right side, switch it from Solid to Hole. This converts it into a cutter that will subtract from whatever it is grouped with.

I decided to scale down the pi symbol in order to make the total size of the coaster 4 inches including the cylinder.I decided to make the pi symbol thickness 0.1 inches, width 2.5 inches and height 2.5 inches.

Next, drag a Cylinder from the Basic Shapes panel. Resize it to 4 inches in diameter and set the height to 0.20 inches (this is the most common size of a coaster). Using the align feature in the top right of TinkerCAD center the pi symbol hole with the cylinder. Then select both shapes together, and click Group. TinkerCAD subtracts the pi symbol from the cylinder, leaving you with a circular coaster that has a pi-shaped pocket in the surface.

I want to note here why I switched to TinkerCAD for this step instead of staying in SolidWorks. I could have created the circular base with the cutout in SolidWorks but it was easier to do in TinkerCAD. TinkerCAD's drag and drop approach to combining shapes and creating holes is faster for this specific task, and since TinkerCAD is free and browser based, it also makes this step more accessible to anyone following along who does not have SolidWorks. Using the right tool for the right job is a core part of good design practice, and that applies whether you are an engineer or a maker.

Export the grouped coaster base as an STL.

The holder is the showpiece of this project. The outer diameter is 5.25 inches because the inner portion that holds the coaster is 4.15 inches in diameter and the outer walls are 0.75 inches in order to maintain structural integrity. Standard coaster sets include 5 coasters, therefore I made the height of the walls 1 inch in order to hold all 5 coasters.

Start with a cylinder that is 0.1 inches thick and 5.25 inches in diameter. In order to reduce print time and material hollow the center by dragging a negative volume cylinder that is 3.5 inches in diameter. This still provides enough material to hold the coasters while significantly reducing print time and material.

I used TinkerCAD's Text tool for each individual digit. I typed each number, sized it to fit the wall height, and then manually rotated and positioned each one around the outside of the ring so they wrap continuously around the full circumference. I ended up using the first 36 digits of pi as they comfortably fit around the holder, but if you want to use more you can either increase the circumference of the holder or make the numbers smaller. The first 36 digits of pi are: 3.14159265358979323846264338327950288. I set the decimal point and each digit as a solid shape, raised 1 inch from the surface of the ring so they print as raised text making up the exterior wall.

Positioning 36 individual digits by hand does take patience. The trick is to figure out the angular spacing first. 360 degrees divided by 36 characters gives you 10 degrees per character. Then rotate each one by that increment from the last. Once they are all placed and you are happy with the spacing, group everything together and export as an STL.

I sliced all three parts separately in PrusaSlicer before sending them to the printer. My settings:

1. Layer height: 0.2mm for all three pieces
2. Infill: 5% for the holder, 5% for the coaster pieces
3. Supports: None (all three pieces print flat with no overhangs that need support)
4. Print orientation: Flat on the bed as designed

The pi symbol insert and the coaster base are essentially flat parts and need no support. The holder prints as a standing ring, and the raised digit text on the exterior prints cleanly without any supports at these wall heights.

Print each piece in the filament color of your choice. I used black for the pi symbol insert and the holder, and white for the coaster base, but this is completely up to you. Some great combinations to consider:

1. White base + black insert + black holder (what I made — clean and classic)
2. Black base + gold/yellow insert + black holder (bold and striking)
3. Navy blue base + white insert + navy holder (clean and minimal)
4. Red base + white insert + red holder (great for a Pi Day gift)

Print times on the Prusa MK4S at 0.2mm layer height:

1. Pi symbol insert: ~10 minutes
2. Coaster base: ~37 minutes
3. Coaster holder: ~4 hours 25 minutes

If the pi symbol insert fits tightly in the coaster base cutout, that is by design — it should snap in with slight pressure. If it is too tight to seat flush, a quick pass along the edges of the insert with a fine grit sandpaper or a small file will get the fit perfect.

Assembly is as simple as pressing the pi symbol insert into the cutout in the coaster base. It should sit flush with the surface of the coaster. Then place the assembled coaster inside the holder.

The holder can sit on a desk, a side table, or a coffee table, and the raised digits on the exterior are a great conversation starter. Anyone who picks it up to look at can read the first 36 digits of pi just by rotating it in their hand. The coaster itself functions exactly like a normal coaster.

Expanding the set: The same SolidWorks and TinkerCAD workflow works for any mathematical symbol. Euler's number (e), the golden ratio (φ), or the infinity symbol (∞) would all make great additions to the coaster set using the exact same process.

More digits: If you want more than 36 digits on your holder, simply increase the outer diameter of the holder to give yourself more circumference to work with or make the digits smaller. Then continue placing digits in TinkerCAD. The angular spacing calculation stays the same just divide 360 by however many characters you want.

Color swapping mid print: If you want to print the coasters as one piece but only have a single extruder 3D printer you can pause the print at a specific layer height and manually change the color during the print.

Sourcing SolidWorks: If you dont have access to SolidWorks you can create this whole project in TinkerCAD. Do this by finding a free STL file for the pi symbol on websites like Thingiverse or Printables

This project started as a Pi Day idea and turned into a genuine exercise in using multiple design tools together and understanding why each one earns its place in a workflow. SolidWorks gave me the precision to trace a clean pi symbol from a reference image. TinkerCAD gave me the speed and simplicity to build out the coaster base and holder without overcomplicating the process. And the Prusa MK4S brought it all to life in just over five hours of print time.