My First Engine

My first automotive engine rebuild was actually decades ago, but this is something different - my first engine built from scratch! Not very big, and not really able to do useful work, but it's an engine, and I made it from a small pile of aluminum, brass and steel. It's powered by air:

Just to prove that it is a working engine and not just a static display, here's a brief video of it running, complete with a "blooper":

I built the engine in the 6-week Metal Machining class at the Make717 makerspace, working about 2 hours each Tuesday. The class is taught by Phil Oles, a generous and astonishingly patient man with a lot of machining experience. Students work one or two at a time, using the mill and lathe to make the parts to a high level of precision. In that class/lab environment, I didn't take time to set up photos of the process - take the class to see how it's done!

However, there were a couple of operations I did at the Grant St. Garage, and I'll share them here. Phil knows that I'm a woodworker and that I have my own lathe and mill, and he challenged me to "get fancy" with my base. The result is what you see above - a round base, mounted on a wooden platform. The wood was just a piece of ash that was lying around, cut to size, routed with an ogee edge profile. and sprayed with polyurethane. The round base was the interesting learning experience!

I started with a chunk of 2.25" round aluminum I bought as scrap last January at the Cabin Fever Expo. It's great that the premiere model engineering expo for the East Coast is very local to us - it was in York this year, and will be in Lebanon next year. Here's what the raw material looked like, next to a finished piece after truing everything up on the lathe. I used my metal-cutting band saw to slice off the base, and then "faced" the cut side to make it pretty and parallel to the other side.

The next task was to drill holes very precisely to match the holes already drilled and tapped in the upright of the engine. The holes were exactly 1.5" on center. I mean exactly - I used the controls of the mill to accomplish that, and later checked them at exactly 1.500 inches. I needed two holes to mount the upright, and two more at the same spacing to mount the engine to the wooden base. Here's the finished underside - the two screws are holding the upright in place, and the threaded holes are how I attached the wooden base.

The problem was how to precisely locate those holes on a round piece. After some deliberation, I decided to use my edge finder to locate the flat surface of the vise, which is obviously tangent to the round stock. The edge finder lights up when it touches, and then it's exactly 0.100" from the edge.

Since I had previously measured the diameter of the base, I could easily use the mill controls to move exactly half that distance (the radius), minus that 0.100". Then the edge finder could be moved to the edge of the work. Since I just moved it to align with the center, I knew that the point it touched would be the farthest point from the center. Moving the radius plus 0.100" aligned with the center. I put a pointed rod in the chuck, just to double-check that it aligned with the center - easy to see, because  the lathe leaves faint concentric circles on the work, too faint to see here, but I could easily see them:

On my tiny mill, I have to use a dial with marks that I must count, 0.050" per turn. That means that holes 1.5" apart require exactly 30 full turns of the handwheel - easy to goof up. At Make717, it's a lot easier, because their mill has a DRO - a digital readout - that lets you start at zero and move to 1.500. These photos are definitely not to scale - the ring on the handwheel of my lathe is less than 2" in diameter.

After it was all together and the test video above was shot, Phil challenged me to one more enhancement. He pointed out that a brass spacer on the rotating shaft would help locate the assembly and keep things working well. I made that today, using brass that I had bought on that same trip to  Cabin Fever. I mounted it in the lathe, cleaned it up, and center drilled to a size of 15/64", which is 1/64" smaller than the desired 1/4" size:

The reason I didn't drill to 1/4" is that drills are not very precise - they drill an oversized hole that is not quite round. On an application where you want a perfect fit, you use a tool called a reamer. It removes a tiny bit of material (that last 64th of an inch) to make a perfect round hole that is very precise in size. In fact, the reamer I have for a 1/4" hole is exactly 0.250", and you can buy them in 0.249" or 0.251" for under- or over-sized shafts.

Reamers are a bit fragile, and require a slow speed on the lathe. At Make717, that is accomplished by simply pressing a button, but on my old workhorse, you have to open a cover, loosen a hard-to-reach bolt to move a belt tensioner, and then move the belt to a different set of pulleys:

Once that was done, I gently reamed that hole to a precise size:

Phil suggested a good technique for determining the thickness of the spacer - use the shank of a drill bit, testing various sizes until you get a sliding fit. In my case, that number was 7/32". You can see  that friction is holding the bit in place, but it's still easy to slide out.

My first attempt at parting off the spacer to the exact dimension yielded one that was too thin, so I made another, cut it too thick, and then used the mill to take off a tiny bit at a time. Cut and test, cut and test, until I had a perfect fit. You can see the spacer between the flywheel and the upright below:

Such a rewarding project. I started down this path of learning some machining techniques because I wanted to improve my woodworking precision, but I wound up with a rewarding new hobby to boot!