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Tuesday , July 7 2015
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Home > Engines > Building a Flame Eater (Vacuum) Engine – Part 1: The Cylinder

Building a Flame Eater (Vacuum) Engine – Part 1: The Cylinder

I’ve been working on Jan Ridders’ “Flame Eater” engine for over a year now. When I first started I didn’t have a mill (nor a plan as to how I would complete the project without a mill) but I started on the engine anyway. Eventually I turned just about every piece that could be turned and then hit a wall. Without a mill I could go no further. So the project got shelved for months while I searched for, purchased, and restored and Atlas MFC mill. A few weeks ago I finished my mill restoration and it was time to get back to my little Flame Eater.

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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About Tyler

Tyler is a hobby machinist and 3D printing aficionado. He teaches computer programming and web development at Highline College near Seattle. Tyler founded Projects In Metal in 2008 because he was frustrated by the lack of free plans available for hobby machinists.