Pen Mold Visualizer

So you've found a model for a 3D printed pen mold that looks interesting. But what will it look like on a finished pen? It would be a shame to print the mold, cast the resin, cut and drill the blank, glue up a tube, turn the pen, then discover it doesn't look at all like you had hoped. Isn't there some (relatively) easy way to visualize the mold design on the finished pen while it's still a model?

Well, yes! And this Instructable will show you one way to do that using Tinkercad.

This is presented in Tinkercad because it's free to everyone, but the method would work as well in any modeling software. To work through the exercise you will need a 3D pen blank model and a Tinkercad account, or your preferred modeling software.

The video shows the entire process from start to finish. Feel free to skip the steps and just watch that.

Here's an overview step-by-step:

1. Make a working copy of the model.
2. Make an object in a contrasting color to represent resin.
3. Make a die to cut away all of the mold and resin that extends beyond the finished barrel size.
4. Apply the die to the resin and the mold.
5. Combine the resin and mold.
6. Reduce the resin diameter slightly to help with the visualization.
7. Repeat as desired to simulate pens of various sizes.

The first thing to do is make a working copy of the mold model. This makes it easy to delete the working copy and start over without having to reload the project from scratch.

In this case I used a model in which the design was separate from the outer mold so I just copied the design. But if the model you use comes in a single monolithic part that's fine too.

After cutting away parts of the mold it can be difficult to visually pick out the parts that form the outer edges. The cut-away view lets us "see" all the way to the center of the pen which is useful only if the plan is to use clear resin, which we are not. So let's cast some virtual resin! The good news is there's no weighing or measuring, curing is instantaneous, it's free and there's an undo button.

Pick a color that will contrast with the mold color and make a cylinder that is large enough to fill in the mold. The height and width don't need to be exact, so long as the resin is larger in diameter than the pen barrel to be simulated. Also, the resin should be as long or longer than the mold. Once the cylinder has the right dimensions, rotate it 90 degrees so it is parallel with the mold.

When this step is complete there should be the original mold and the virtual resin side by side as shown in the photo. It is important to keep the resin and the mold separate for now.

Next we will create a die that will cut away everything larger than the finished pen barrel that is being modeled. This is done by creating a negative space cylinder with a hole down the center.

First, drag a cylinder and a cylinder hole to the workplane. The solid cylinder must be large enough in diameter to completely enclose the mold or the resin (whichever is larger). In this case the mold was 27.4mm tall and wide. The diagonal for a square of that size is 40 so the die must be at least 40mm in diameter. No harm in guessing large here.

Next, make the hole cylinder the diameter of the pen barrel being simulated. In the video I simulated a Slimline pen with a finished barrel 8mm in diameter. Since this represents the finished barrel of the pen, be sure to make the outside as smooth as possible. I do this by setting Segments and Sides as high as they go.

Now center the two cylinders onto each other so they are concentric with the hole in the middle. Rotate them 90 degrees so they are parallel with the resin and the mold. Combine the two shapes so they become a thick-walled pipe, then use the Hole button to make the whole shape a hole. Congratulations, you just made a die!

Finally, before proceeding to the next step, make a copy of the die. We'll need one for the resin and one for the mold.

To cut the pen barrel, select one of the two die objects and select the mold object. With those two shapes selected, use the alignment tool to center the die on the mold so the two objects are concentric. Center on all three axes and merge the two objects.

The photo shows the mold complete and ready to apply the same process to the resin.

After completing the same steps on the resin object, you should now see on your screen two cylinders - mold and resin - whose diameter matches the finished pen barrel.

Now comes the fun part. Select the resin and the mold objects and use the alignment tool to center them on each other on all three axes. Voila! This is your finished pen barrel.

There's one slight problem, though. When Tinkercad renders two surfaces that are in the same plane, they shimmer. While we can more or less see the shape of the pen at this stage, the shimmer is a bit annoying. We'll make one final adjustment in the next step to fix that.

Important! Do not merge the resin and mold objects. Once they merge they become one color and that defeats the purpose of the modeling exercise. Keep the resin and mold as discrete objects so they retain their contrasting colors.

To make the shimmer stop, the mold needs to stand a bit proud of the resin, which is an easy fix. First, select the resin object and check the "Shapes" indicator to make sure the mold was not accidentally included. Next reduce the height and width to .1mm less than the nominal diameter.

I say "nominal" because Tinkercad always seems to round up by .01mm during the die cutting step. Because of this the resin and mold are now 8.01mm diameter instead of 8.0mm. While that's an interesting effect it has no functional impact and can be ignored. Just select the resin and set the height and width to 7.9mm to make the mold stand out a bit.

The dimension changes are always anchored to a side and that side will still shimmer. So the last step is to select the mold and resin objects and use the alignment tool once again to center them on all three axes.

Congratulations! You can now see what a pen with an 8mm barrel would look like with that mold. Feel free to zoom and swing the camera around to look at it from all sides. The mold I used always looks about the same from above but the pattern rendered on the side changes considerably as the pen barrel diameter varies.

Although it's possible to backtrack and change the hole size to simulate a different pen profile, making a copy is better because the two models can then be viewed side by side.It doesn't take any longer to make a copy than it does to backtrack and redo the model so there's no down side.

1. First, select the resin and mold objects together and make a copy. Drag the completed barrel to one side and move the copy to the center.
2. Next, separate the resin from the mold.
3. Ungroup the resin to reveal the die.
4. Ungroup the die to reveal the central hole.
5. Select the hole and change the height and width to the new pen barrel size.
6. Center the hole on the cylinder since changing the dimensions will move it. IMPORTANT! Check the "Shapes" indicator to make sure that the resin was not accidentally selected.
7. Making sure the Shapes indicator says '2' merge the hole and the cylinder to create the pipe.
8. Click "Hole" to make the pipe into the die.
9. Merge the die with the resin object.
10. Do the same steps for the mold object.
11. Rejoin the resin and the mold.
12. Reduce the resin .1mm less than the mold diameter.

You now have two pen models of different sizes. In the video I picked 8mm and 12mm to make a noticeable change in the pattern revealed.

Make as many copies as you like. For the demo I simulated 8mm to 16mm pen barrels in 1mm increments. The 16mm barrel models a Guardian pen. The 14mm would be a Guardian Jr. or a Cigar pen. Lots of pens come in around 12mm - Vesper, Duraclick, Compson, etc. Down in the 8mm to 9mm range are Slimlines, Concava and so on.

The second photo compares the visualization on a 12mm barrel with a finished Compson pen.

Resin sticks to a lot of stuff but one thing it doesn't stick to so well is plastic. The first time I made a pen from a 3D printed mold I tried turning it the day after I cast it hoping the softer resin would be easier to turn. Good thing I had a full-face shield on because one of the large outer diagonal resin chunks came loose and hit me. If I'd been wearing goggles it would have cut my face, or at least left an impressive bruise.

I don't know whether the adhesion improves as the resin cures, or whether PETG would have been a better choice than PLA. But when working with 3D printed pen molds it's probably a good idea to assume that any plastic/resin combination is going to be sketchy, wear full safety gear, and take light cuts. As Dr. Mom says, "you could put an eye out with that thing!"

In the photo one and a half of the sides separated while truing a blank. The chunk that hit my face shield rattled me a bit and I forgot to get a photo of that.