3D Printed Engine Days 4-6

So there has been a lot of trial and error over the past few days. Nothing more than what was expected, but there have been a lot of changes made as I began printing.

On Day 4, I made the changes I was planning on making, namely making the bottom removeable and shrinking the height of the container. Now the bottom of the piston container has teeth on the end of it that should lock in with teeth on the container walls. Additionally, the wall height was shrunk from 5 cm to 3 cm. The power piston walls were reduced to 2 cm. This also meant adjusting the most of the rest of the objects, since they depend on how far the pistons can move.

I ended the day with much fine tuning of the object’s measurements. This takes a deceptively long time. I also dealt with a bug that deleted all my parts from the assembly…twice. For some reason running the engine caused the program to malfunction and remove all the parts. I fixed it by redoing the entire assembly.

I began printing on Day 5. I headed over to Small Hall to use the Makerbot Replicator in the Makerspace. To my surprise, I couldn’t get into the room. Luckily, a faculty member let me in, and I learned that I only have weekday swipe access.

That would turn out not to matter very much, since I have no need to return to the makerspace for the remainder of my project. The printer issue that I wrote about in my first blog is still not resolved. I troubleshooted for a few hours, but I don’t have the technical expertise (or confidence) to take apart the printer in the way that seems to be required.

Thankfully, Swem is awesome. They have portable 3D printers that can be checked out of the front desk. After a couple minutes, I walked out of the library with two cubic feet of printer strapped to my back.

My new printer is an Ultimaker 2 Go, which is smaller and less sophisticated than the Makerbot Replicator I planned on using. It should get the job done, but I may have to shrink some of my designs so it can handle them. We’ll see. It does work, which is a big win over the Makerbot.

After calibrating it, loading the filament, and doing a test print, I began printing my own objects. The first one I printed was the crankshaft. I learned two things from that print. First, 2 mm is too small a diameter for my purposes. Second, the printer doesn’t seem to be very good at printing a cylinder that was lying down. I doubled the diameter, stood the crankshaft up, and tried again. This print took longer since there were more layers, but it came out quite nicely.

The new crankshaft

Day 6 was a busy day. I spent it printing and adjusting. First I doubled the diameter of the pin that would connect the pistons to the cylinders. While that was going, I doubled the diameter of all holes and cylinders from 2 mm to 4 mm. I then printed the power piston. However, the pin would not fit through the holes in the piston since the print was not fine enough. So I quickly increased the diameter of the hole to 5 mm and printed again.

The original power piston

The pin

This fit excellently, but I made a mistake that would cost me several prints. I did not adjust every hole at this moment, but I would later assume I had. So I printed a cylinder with a 4 mm hole that wouldn’t fit the pin. I also learned from this print that I would have to round the ends of the cylinders or they would be unable to rotate freely. Both the power and displacement cylinders printed nicely the second time.

The power cylinder (right) and displacement cylinder (left), and yes, they are not actually cylinders

I next printed the tower, and again fell victim to the same mistake. So I printed again with a 5 mm hole. Then, I printed the displacement piston. This was my largest print yet, so I took some steps to speed it up. I made it hollow and increased the layer width beyond the recommended amount. This ended poorly, as the result was a flimsy and fragile piston…with too small a pinhole. Not wanting to waste so much plastic, I printed a replacement top for it and broke off the current holes. I also reinforced the bottom by covering it in masking tape. With all these parts printed, I had a working model of the engine, without the container.

The tower with the 5 mm hole

The displacement piston with the taped bottom and new top

Rotating the engine

Next I need to print the container and flywheel, and make adjustments to the rest of the design as necessary.

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