Hi everyone,

I have already made the cylinder block for a two cylinder, double acting steam engine. I have just read through "Steam Engine Number One" and found that and many other posts useful. And I have watched just about everything I can find on YouTube and read Wikipedia. I am doing this whole project with a lathe and decided to use piston valves which came into fashion about 1900 instead of the slide D valves used before that.

I am not an engineer because I failed to get into engineering school and became a doctor instead . My father taught engineering at Te Puke High School in New Zealand and I was in his class for 4 years doing engineering theory, workshop practice and technical drawing in the early 1960's.

When Dad died recently he left me a lot of tools and a lathe that he bought from the school: A 1955 Boxford Model A. I now have that set up in my car garage. I do have a propane-oxygen welding torch. It is adequate but there is no spare space for more equipment. I do not have a compressor but think I will need one to test the steam engine. I use an old propane tank flushed out and filled with compressed air at the petrol station (NOT recommended). I have made about 32 YouTube videos about how to use and overhaul the lathe. (under the name evan-e-cent or evanecent : Youtube.com/user/evanecent see Playlists on steam engines and using an engineers lathe).

My first project was to build a Hero steam engine (designed by the Greeks 2000 years ago) and calculate its power output and efficiency documented at http://www.HeroSteamEngine.com. (there are some numerical errors in the text shown on the video.)

On the same web site I wrote software for working out what gears to use in the gear train to cut any thread, metric or imperial, and to calculate feed rates (see HeroSteamEgine.com/RideTheGearTrain).

I built a model of a gold-mining quartz stamper battery and that worked out very well, but is not on YouTube yet. (see my wife's web site http://www.KaeLewis.com for a video of a small battery). The plan is to possibly use the steam engine to drive this battery.

Edited By Evan Lewis on 17/11/2020 12:54:15

The valve piston works exactly the same way as a D slide valve and the cross section of the piston assembly is exactly the same as the cross section of a D valve. It consists of two pistons, each 9mm long with only 5mm space between them. Steam galleries 6.5mm diameter were drilled from the ends of the cylinder block, straight across the valve cylinder and into the steam gallery described above. Then the holes in the end of the block were tapped and blocked off with 8mm stainless steel grub screws. That is why the 6.5 mm drill was chosen.

The biggest flaw with this design is that the steam galleries are too small. And the large mass of brass will take a long time to heat up resulting in condensation. A third problem is that I have read that you should not use brass with steam because it will corrode. I am not sure how quickly that occurs and wether it is really a problem for a model.

The diameter of the ducts is restricted by the limits of the valving system. I was surprised at how precisely this has to be made so that the inlet and exhaust valves do not open at the same time. Usually slots are used to increase the steam flow. At one stage in the design process I was going to have two sets of these galleries for each piston but forgot about that when I actually came to make it! See photo. Since the holes are 6.5mm and the valve pistons 9mm there is 2.5 mm total overlap giving 1.25 mm steam lap and 1.25mm exhaust lap but i have not been able to find any documentation on how to design the lap. It may be too much? When the main piston is at the mid-point of the cylinder the valve pistons occlude with inlet and exhaust ports.

I have not decided on rings for the pistons. I was just going to manage without rings but that may not be wise, so I think I will use O-rings but could use some tips and tricks to work out how deep to cut the grooves. Should I have rings on the valve pistons – they would have to pass over numerous port holes and might get torn up? Also the valve pistons would ideally be sealed along their whole length.

Also I have not worked out how to seal the glands that the con rods pass through. O-rings here too? Placed inside the bearing surfaces?

So now I plan to bolt flat plates on each end of the brass bar as a frame with a brass plate for the floor screwed onto the under side of the walls. These walls will support the crankshaft. Then I will place additional 3 walls between the cylinders and mount brass bars 5x20mm across the tops of the 5 walls to make a T shape 100 mm long for the cross heads to slide on.

The cross-heads will be about 10mm thick (is weight a concern?) with grooves milled down the side. I do not have a mill but have a milling attachment for the lathe. (Otherwise it could be made from 3 plates screwed together.) The connecting rod will screw into the crosshead and the "swing rod" which connects to the crank shaft will require a wrist joint.

I plan to have double eccentrics for each cylinder so that they can be connected to a C-shaped slot controller to provide forward and reverse and variable power. But in the first instance I will just use one of them to make it a bit simpler until I am sure it will work.

I do have some scrap bronze and all the bearings and cross heads will be made from that.

I also have some interesting scrap I got from a scrap dealer in NZ. This is 80mm diameter solid round bar about 500mm long which he gave me. It was attached to a plate 100mmx10mm and the same length and I was able to remove it. It appears to be very hard magnetic stainless steel but the Menz Shed has an electric hacksaw which will cut off disks.

At first I assumed I would be able to make the crankshaft out of a single block but with 36mm swing it is too big. I can just fit the 80mm bar into my chucks but cannot set an offset to turn the bearings for the big ends. So I have decided that I will have to cutoff and face 3 disks and drill holes to place shafts for the big ends. I do not know how they will be kept in place. Probably pins drilled across the holes. Any suggestions here would be helpful. I think that threading these joints would not be sufficiently accurate or rigid. Can it even be done?

Any advice that you can offer would be greatly appreciated!

Thanks for the tip GL. The brass block shown in the photo above is the only part that I have made so far. The rest is in my head and some rough sketches. Since you requested visual representation I have added my sketches here but they are VERY rough.

This is a photo showing the cylinder boring process with the block of brass (covered in engineers ink) mounted using 3 bolts on the compound slide.

Incidentally you can see the DC treadmill motor I just installed with variable speed control 2.5 HP at 4700 RPM motor speed.

This 3D sketch shows the cylinder block, two main pistons near the center and two valve pistons towards the sides. Steam ducts are shown for the piston on the right. Intake and exhaust galleries are not shown here.

Sketch #2 includes the cross head and crankshaft. It top left I sketched two types of cross-head slider and plan to use the design to the right. Probably made of bronze.

The following is an image I took from an animation in Wikipedia and this has been the basis of my design. I altered the slide valve to make it look more like a pair of pistons. The gap in shaft shouldn't be there! I said the valve pistons would be 180 degrees out of phase with the main piston, but this is adjustable and an approximation.

This is the end view showing the "walls" between all 4 cylinders with a brass bar on the top to act as slider surfaces for the cross-head. The 4 cross heads will be about 25mm square and 10mm thick with grooves cut down the edges to run on the brass slider.

Plan view showing the walls and the brass sliders will be mounted on top and screwed to the walls. I have reduced the thickness of the walls to 5mm aluminum bar.

VERY rough sketches.

Steam galleries:

PLAN VIEW:

Side walls and internal "Walls" which support brass sliders (20x5mm brass bars) centered on the cylinder axes:

END VIEW

Showing the walls and slider bars

Rough 3D Sketch

Possible cross-head sliders shown at top left. 

3D Sketch – an early version

PHOTO of the brass block covered with engineers blue, mounted with 3 bolts on the compound slide of the Boxford A lathe. This uses a purpose built boring bar holder in the 4-jaw chuck. The position of the boring tool is fairly easily and accurately adjusted with a dial gauge.

Note: You can the motor I installed recently. It is a 180 volt DC motor out of a treadmill with a Chinese pulse width modulator HQ-SXPWM-X speed controller.  It is very nice to use!

PHOTO of the finished brass cylinder block. That is all I have made so far.

Yes it seems spooky and a bit weird for Newbies. I could not see how to make an album which was required for the camera icon above, but the icon next to it allowed me to link to photos on my web site and they showed up on my posts.

Anyway I finally found my way to albums and created one by uploading the same photos. For those having trouble seeing them I will display them again using the album!

Edited By Evan Lewis on 19/11/2020 00:11:25

I have the option of making the pistons from bronze or stainless steel. They will of course be running in the brass cylinders. Which material should I use?

I also have 1/4 inch brass rods for con-rods but I see model kit sets often use stainless. I am thinking of turning down to 6mm so that I can use a 6mm reamer for the con-rod bearings.

Thanks to you both again. Last night I threaded an 8mm brass bar, tapped the passage hole and glued it in with superglue. I considered cutting a keyway groove down the side but decided to drill it afterwards. we will se how that goes! I like your idea of a plain rod with a flat on the side best. I still have 3 more to do so I will try that. Yes, the link should be very helpful.

I don't have the material for the crankshaft yet. I would like to make it from stainless so that it doesn't rust. It is much harder to work with. Am I asking fro trouble?