This started out as an idea a friend had. She runs a pre-school and was looking for new activities for the kids to do, and one of the things that she wanted was a marble run that she could reconfigure so the kids wouldn't get bored with it. The pre-school has a metal fence around it, so the first thought that came to mind was magnets. If you're attaching this to a solid sheet of metal, the magnets should be enough on their own. With the perforated metal fence, they didn't quite have the holding power needed, so I added a place to add a screw-in hook. After a few iterations in Fusion 360, we came up with a design that's pretty quick to 3D print and works great.

Step 1: Step 1: 3D Printing the Endcaps

I've attached the .STL files for the endcaps assuming 2" schedule 40 PVC pipe (that's what you'll find at Home Depot, etc). I found it easiest to print out with the slots for the pipes facing up. Print out one right endcap and one left endcap for each segment you plan to build. And don't forget to do different colors if you have that option.

While you're on the 3D printer, I would also recommend printing out the drill guide. While not necessary, it will make drilling the large holes in the PVC pipe (in Step 3) much smoother and safer.

The endcap was designed in Fusion 360, and if you're interested in a different pipe size, this is a great introductory project to help learn Fusion 360 and sketches. It took one main sketch (I've included an screen capture of this sketch) to get 90% of the design done with just a couple of extrude commands from this sketch. Then you just need the holes in the back for the mounting screw and the hook, and you're good to go. If you're interested in a walk-through of the process to create the endcap in Fusion360, please leave a comment.

Step 2: Step 2: Cutting the PVC Pipe

You can pick up PVC pipe at any hardware store or home center. The standard length that the pipes are sold in is 10', but most places will cut it for you. There are places that will sell it by the foot, but make sure to check the price. My neighborhood hardware store wanted more per foot than Home Depot wanted for an entire 10' pipe.

To cut the PVC pipe to length, it used my miter saw with a 32 tooth general-purpose blade.

To cut the pipe in half length-wise, I used the bandsaw. And to make the pieces easier to handle, I cut everything to length first, so that I wasn't trying to feed a 10' piece of pipe through the bandsaw. This also meant that I had a pair of sections for each length, but this was fine for me.

To start, I used a stock centerfinder to mark opposite sides of the pipe. I also marked down one side of the pipe so that I could make sure that the blade didn't start to wander and make sure that the pipe wasn't rotating as I was feeding it into the saw. (And just to be a perfectionist, I made the line through the writing on the pipe so that I could hide the writing at the back of each section of track.) I then moved the fence of the bandsaw until both marks were lined up with the blade so that I knew I was cutting the pipe in half. Make sure that you lower the upper blade guide to just above the pipe so that you minimize blade wander.

Step 3: Step 3: Drilling the Holes

To drill the large hole at the end of the pipe, I used a 1 7/8" Forstner bit in my drill press. But before I did that, I inserted the pipe half into the drill guide and used a 3/32" drill bit to drill what will become the hole for the endcap mounting screw. I then screwed in a #4 sheetmetal screw part-way through that hole to keep the drill guide and pipe locked together.

From the top side, I then drilled the large hole. As you are going through the sides of the pipe, the drill bit will chatter, so use a slow, steady rate to keep the drill bit from catching.

Step 4: Step 4: Assembly of the Pipe Sections

Grab two endcaps (a left and a right) and a section of pipe. You'll also need two magnets and two 1" long #4 sheet metal screws. For the magnets, I used part number 5685K31 from McMaster-Carr (http://www.mcmaster.com/#5685k31/), with a diameter of 1 15/64". You can find similar magnets at your local hardware store. If you're not planning to use hooks, the diameter of the magnet won't matter. If you are planning to use hooks, then make sure the magnet that you choose won't block the hole for the hook. For the screws, I found that sheet metal screws went into the 3d printed endcaps much easier that wood screws, but wood screws can work as well.

Put the endcaps on the pipe and then place the assembly on a flat work space upside down. This makes sure that the tops of the end caps are aligned, which makes sure the backs are aligned. This ensures that both magnets will attach evenly to your wall. There's some wiggle room for the pipe to rotate in the endcap. I did this in case the pipe wasn't perfectly cut in half. But this also means that the endcaps can be misaligned if you don't make sure they're even.

First, attach the endcap to the end with the big hole. Even though you already drilled through the pipe in the previous step, I still used a 3/32" drill bit to drill the mounting hole through the endcap through the pipe. This just cleans up the hole from the 3D printing making sure it's the right diameter and that your screw will go in cleanly. Now feed your screw through the mounting hole on the magnet and then into the mounting hole on the endcap and tighten. Pay attention that the screw goes in straight or you can end up cracking your endcap. Once the magnet is attached, you can insert the screw-in hook if you're using them. I used a 1" long square screw hook that I picked up at my local ACE hardware store (#52385). Repeat the process for the other end.

For each pair of pipes with a given length, I put the big hole on the right for one and on the left for the other to allow the balls to go back and forth once the whole ball run is assembled.

Step 5: Step 5: Construct Your Ball/marble Run!

Once all your track segments are assembled, it's time for it all to come together. Let your imagination go wild and create a maze. Recruit some small test subjects to send the balls down the track. Then it's time to mix it up and reconfigure the tracks and keep the fun going.