Many of the pieces for this engine are easy to machine and require no explanation, but some are a bit more difficult. My intention here is to describe the more complicated pieces and the machining steps I used to complete them. My methods aren’t the only way to machine the engine, but if they worked for me, they should work for you as well. I’ll be documenting this project in several parts:

Part 1: The Cylinder
Part 2: The Piston, Valve, and Connecting Rod
Part 3: The Flywheel
Part 4: The Ball Bearing Support and Spirit Burner

So let’s get on with it.

Part 1: The Cylinder

Jan recommends using “pearlitic cast iron” or stainless steel for the cylinder, piston, and valve. I’d recommend trying to get cast iron if you’ve never worked with it before. It’s different than steel and very messy to turn, but I think that it’s properties lend itself well to the cylinder design. For one thing making the cylinder, piston, and valve from cast iron helps with lubrication because cast iron rubbing against cast iron is somewhat self-lubricating. With a flame eater engine you don’t want to use oil to lubricate the cylinder because it will eventually burn away and gum up the cylinder. Another benefit of cast iron is the fact that it was easy to cut the fins with a parting tool. The cast iron chips were short and broke away easily unlike steel, which often produces long springy chips that bind in between the two halves of the piece being parted off (or in this case between the fins).  In my opinion it would have been a little more difficult and taken more time to cut the fins in a steel cylinder. Whichever you choose, be sure to make all three parts out of the same material. If you make the valve and piston out of steel and the cylinder out of cast iron (or vice versa) they won’t expand and contract at the same rate leading to either a sloppy fit, or too tight a fit once the engine heats up during use.

Step 1a: Turn OD

Center drill the cylinder and support with a live center (or lubricated dead center). Note: other than lubricating the dead center, don’t use lubricant when cutting cast iron – it should be turned dry. Turn part to the desired OD but leave .001 extra to polish to size. I used 400, 800, 1200, and finally 2000 grit sand paper to get literally a mirror finish on the cylinder. Note: the picture below shows the part unsupported and with the cylinder hole already bored, you’ll be boring the hole next.

Step 1b: Drill/Bore/Ream ID

Remove the center drill and drill the hole to within .010 of final size, then bore to .001 or .002 of final size, and ream to final size (ream if you’ve got a reamer, if not you can always lap the cylinder instead). I drilled the hole in stages, about 1″ deep at a time. I drilled a .250 hole an inch deep, then I swapped the .250 for a .500 drill and pecked until that drill bottomed out at about an inch deep. Then I’d go back to the .250 drill and make the hole deeper by another inch or so. Drilling the hole in steps like this is safer than trying to drill the hole to depth in one plunge. If I tried to drill 3″ deep with a .250 drill bit the bit would likely break. But it’s fine in one inch increments. Remember to “peck” with the drill – plunge .050 or so and then retract the drill to clear away chips – then plunge another .050. The larger the bit the deeper you can plunge without clearing chips, but watch carefully. If chips stop coming out of the hole on their own they are building up inside and will eventually bind the drill causing it to spin in the chuck or break. Avoid that.

Once you’ve got the cylinder drilled out to within .010 of the final size for the entire depth of the cylinder, move on to boring. Boring will ensure that the hole is concentric and uniform in diameter across the entire depth. Take very light cuts with a quality boring bar. If you’ve got a reamer of the proper size use it. But don’t ream more than .001 or .002 and try to ream the hole all at once in one continuous plunge while turing the work at a slow speed. Don’t ream the hole multiple times or the hole will likely turn out oversized. Don’t ever run the lathe in reverse with a reamer in place – you’ll dull or chip the flutes on the reamer.

If you don’t have a reamer or your hole ends up slightly under or over the desired size, don’t worry. You’ll be turning the piston and valve to fit.

Step 2: Cut the Fins

This step really spooked me. So much so that I set the part aside for weeks avoiding this step. Don’t let it scare you -especially if you’re using cast iron. It’s not as bad as parting off because you’re not plunging the parting tool all the way to the center of the part. I turned the part at a fairly fast RPM, 500 maybe? I can’t remember for sure. And I plunged the parting tool very slowly into the part to the desired depth. I made sure that the parting tool didn’t stick out any further than it had to for clearance – thus avoiding unnecessary overhang. I used a dial indicator with a mag base to accurately space the fins. Be sure to support the part with a center to help with chatter. Once you’ve got the fins cut, part off the cylinder leaving an extra .005 or so of length so that you can face and polish the newly parted end.

Step 3: Mill the Large Flat

Support the part in the mill vise and mill the flat. I have a horizontal mill, so I’m using a vise within a vise to support the part parallel to the end mill. Remember to use some sort of packing. Aluminum shim or card stock (I’m using an old business card). Take light cuts of .005 to .010 – deeper if you’re using a larger end mill and have a more robust mill. But be careful not to put to much cutting force on the part – it could cause it to shift or rotate spoiling all your work. Take your time.

I used the knee to keep track of the depth of the flat, but you can also use a multi-anvil micrometer (with the cylindrical anvil inserted) to measure from the ID of the hole to the flat to double check your knee measurements.

Step 4: Cut the Two Small Flats

This step is pretty simple, but I thought it was worth mentioning the use of a square to ensure that the two small flats are at a 90 degree angle to the larger flat. The angle isn’t critical (89 or 91 would be fine) but it’s nice to have a way to get it very close.

Here’s a finished flat.

Step 5: Drill and Tap for 2x Cylinder Supports

You want to be very careful on this step not to drill too deep. If you drill into the cylinder bore, you’ve scrapped your part. One way to make sure you don’t drill too deeply is to use the knee on your mill. I’ll show you another method using a drill press and a plug gage.

Position the part so that the drill bit is just touching the surface of the flat (note: you should have already center drilled). Then use a plug gage with a diameter that matches the depth of hole you wish to drill. Position the plug gage between the nut and the stop on your drill press depth stop and turn the nut until it’s contacting the plug gage. Then remove the plug gage. Now when you plunge your hole the nut will contact the stop after plunging to the depth set by the plug gage. Now tap your holes using a plug and bottoming tap.

Step 6: Mill the Intake Slot

This is pretty self explanatory, but I would recommend using an undersized end mill. If you use a 3mm end mill from the start, your slot will be 3mm+ and ugly. I used a 7/64″ end mill and plunged the slot to depth and length using multiple passes along the centerline of the slot. Then I widened the slot from .109 to the 3mm (.118) width by taking a bit off of the top and bottom of the slot.

Here’s another view.

Step 7: Drill for the Valve Push Rod

This was another step that concerned me – but drilling the 4mm hole turned out to be a piece of cake because each gap between fins allowed for chip clearance. I could have plunged the entire hole all at once, but I didn’t.

Step 8: Bronze Bushings

Making the bronze bushings was easy. Turn the speed up to a fast speed appropriate for bronze of that diameter and use a sharp tool. I was able to turn the bushings unsupported using light cuts (.005) and a sharp tangential tool holder from Eccentric Engineering. I’ve worked with bronze in the past when I replaced the bearings on my Atlas mill and the bronze chipped away in dusty flakes. With my new tangential tool holder the bronze made long spiral chips and had a beautiful finish. Coincidence? No. Get yourself a tangential tool holder. You won’t regret it.

Once you’ve turned the OD and drilled the ID, part the bushins off and press them in. They are small enough to be pressed with a quality vise. However, as a general rule I’d recommend you avoid using your vise as an arbor press. It’s a bad habit that can lead to a busted vise casting. Add an arbor press to your tool list. Harbor Freight sells them and they are much cheaper than a new AngLock-style vise.

Step 9: Fixing a Rookie Mistake

By now you should be finished with your cylinder. But I wasn’t. I mentioned at the beginning of this post that I’ve been working on this project for over a year now and I turned most of the parts that I could make on the lathe months ago. Unfortunately I substituted a 5M thread for a 4M thread on the cylinder supports and completely forgot. Months later when it came time to make the cylinder I went ahead and tapped the holes for a 5m thread, not a 4m. The result can be seen below. Obviously the support legs didn’t fit. I fixed them by re-chucking them and drilling them out for a 5m set screw – which I inserted upside down and secured with lock-tite. It’s upside down because the support has a hole all the way through – so I’d have access to the set screw using a hex wrench if I ever needed a little extra force to remove the support legs from the cylinder.

I’m including my mistake so that you guys can learn from it.

Lesson learned: Never change a part without making a change to all mating parts on the blueprints.

But I also thought it would be an opportunity to show you that some parts can be made without using a die. I could have easily made these supports using a 5m tap and set screw from the start – totally avoiding the need to purchase a 5m die. Since I normally work in inches and not mm, this would have saved me a few dollars. I have a complete set of taps and dies up to 1″, but up until this project I didn’t own any metric taps or dies. So this little engine has actually been a bit more expensive than I had hoped. But that’s ok. And of course you can usually use the nearest inch equivalent when tapping holes of a non-critical dimension. I just didn’t want to. I wanted to use this project as a chance to practice working with metric measurements.

Well, that’s about it for the cylinder. Next I’ll be documenting the steps for making the piston, valve, and connecting rod.

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I asked Jan to pick his most simple designs in each of 3 categories, Stirling, Flame Eater, and IC.  This set of plans is for his most simple IC design, a pressure controlled 2-stroke engine. If you’d like to see the other two designs shared by Jan, they can be found here: Jan’s Coffee Cup Stirling Engine and Jan’s Flame Sucker. And of course, all of Jan’s other engines can be found by visiting his site, which is written in both English and Dutch.

Here’s an animation and a description of the principle behind Jan’s masterpiece (excerpt from Jan’s site):

A ball valve only opens when the pressure below the ball is higher then above the ball. For the upper valve this is only the case, and for a very short time, when the piston reaches the exhaust port. The pressed gas mix below the piston and between the two ball valves is injected then, filling the cylinder and pushing out the remaining burned gases. Before and shortly after that moment the pressure above the ball in the upper valve is always higher then below the ball. When the piston is moving upwards there is an overpressure above the ball (gas mix compression) and a lower atmospheric pressure  of the sucked-in fresh gas mix below the ball. When the piston is moving downwards there is a high overpressure above the ball due to the combustion (power stroke) and a much lower overpressure of the compressed fresh gas mix below the ball. So also during that power stroke the upper ball valve keeps closed until the piston opens the exhaust port.

So the timing of the process is exactly right and automatically controlled by the alternating pressures in the system. That is why I called this engine the “Pressure controlled Two-stroke”.

Here’s a video of the engine in action:

For more information on this engine (including construction tips and trouble shooting) please visit Jan’s website. Jan also has many other engines on his site and he shares his plans freely with anyone by request.

I’d like to say Thank You one more time to Jan Ridders for sharing multiple sets of plans with this site. By sharing your plans you’ve helped this site grow.

[nms: stirling engine]

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If you’re looking for a simple engine to build that runs on compressed air, here’s a nice set of plans for you. Here’s what Rob had to say about his plans:

“This was the semester long project we did in class for Machine Tool Technology at the University of Central Missouri . I would like to hook the engine up to something and do tests.

The base is made out of a 3/4 in thick aluminum and the body and cylinder is mild steel. The flywheel and crank is made out of brass. I used most tools that you would use with metals. Vertical mill, horizontal mill, metal lathe, drill press and grinding machine, thread tap. I even machined the threads on the wrist pin.”

- Rob K.

Here’s a video of the little engine in action:

Thanks for sharing your plans Rob!

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Here’s a set of plans for a nifty little two stroke engine submitted by Shane W., a sophomore studying Mechanical Engineering at the University of North Carolina at Charlotte.

Here’s what Shane had to say about his project:

“This is a two stroke internal combustion engine that I designed for a design class. Though the design is unique and engineered by me, much inspiration was taken from an engine from the 50′s called “The Little Dragon.”

Engines are not exactly simple to make or design, but this one is designed to be as easy as possible to construct, using standard size stock to minimize machining. In fact I was able to build it and get it running with the experience from building a simple air engine and nothing else.

Most of the tolerances are a little tighter than necessary, particularly the bore of the cylinder. You can get away with it being a couple thousandths off.

It runs on 30% nitromethane fuel mixed with castor oil. The plans don’t exactly follow any standard, though they lean toward ansi. In the drawings for the cylinder, con-rod, and piston I used hidden lines to represent tool paths. I don’t have drawings for the needle valve, though many are easily obtainable online, or a pre-made one can be purchased.

- Shane”

Thanks for submitting your plans Shane! Be sure to visit Shane’s site to check out his other projects and to see a video of this little engine in action!

Would you like to have your project featured on this site? If so, do what Shane did and click the “Submit Your Plans” tab at the top of the page.

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Back in February I posted plans for a Coffee Cup Stirling Engine by Jan Ridders, which have proved quite popular with more than 500 downloads to date.

Since the first engine went over so well with everyone, I thought it was about time for another. These plans are for a “Flame Eater” engine (AKA a Flame Sucker or Vacuum Engine).

The working principal is nicely illustrated by the animation below, but you really need to visit Jan’s site for the whole story on how this engine works, and what makes Jan’s design so special.

Here’s a short video of Jan’s Flame Eater in action:

If you decide to tackle this little engine, be sure to visit Jans site for lots great information on the theory, design, and construction of this great little engine.

Thanks Jan for contributing your plans!

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Material: various
Units (mm)

As luck would have it, I came across a site by a fellow from Florida named Ernie. Ernie is an accomplished machinist and hobbiest who will happily share his engine plans with others upon request. I asked Ernie for a set of plans for his internal gear engine and he quickly fired a set off to me via e-mail.

In his email Ernie recommended that I visit the site of a machinist that Ernie considered to be of truly exceptional talent – a man from the Netherlands named Jan Ridders.  Now, I had just finished admiring Ernie’s work, so if there was a machinist out their that produced work that Ernie admired, it was definitely worth a look.

I was amazed. Jan’s website documents several of his projects, most of which are engines, all of which are amazing. And again, as luck would have it, Jan is also willing to share his plans with his visitors upon requets. I quickly emailed Jan and mentioned that I had set up projectsinmetal.com and I asked him if he would be willing to donate a few plans for my visitors to enjoy. He agreed.

Because this site is focused on offering plans suitable for the beginner, I asked Jan for his most simple, straightforward set of plans for each of his 3 categories. Stirling Engines, Internal Combustion (IC) Engines, and Flame Eaters. Obviously all three plans would be considered advanced projects by anyone new to the hobby, and therefor they will all be listed under the “Advanced” category on this site.

Below is the PDF file that Jan provided for his “easiest and most reliable” stirling engine – the Coffee Cup Stirling Engine. Here’s a video of a few different versions of this engine in action:

Be sure to visit Jan’s website for more inspiration!

And if you don’t have enough materials in your scrap bin to build a stirling from scratch, they’re are tons of great kits on Ebay and books on Amazon to get you started. Just look below. Be aware, however, that most kits on Ebay aren’t ready to assemble, they just save you the time of gathering up all the necessary materials. Usually machining is still required to complete the kit . . . which is kinda the whole point.

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