I think I first saw the image below of this engine when it came up on Pintrest and it caught my eye. A bit more digging about with Google showed that it originated from the 1905 edition of "Scientific American" and was listed under Amateur Mechanics as a "Simple Single-Acting Steam Engine"

I manages to find another engraving that showed an end view and side view sectioned through the cylinder with a couple of other details of the valve but that was too grainy to be of much use. There was also a basic description of the engine and some key sizes. One feature was the use of brass tubes for the cylinder and piston that would telescope together thus saving having to bore the cylinder and machine a piston on a treadle lathe that it was assumed most amateurs at the time would have.

It was said to be approx 1/20 HP and had a bore of 1.5" x stroke of 2" and an 8" flywheel. I set about drawing it up to suit some thick wall brass tube that I had for the cylinder and that dictated that I use a 19mm bore so my metric design is about half size. I also altered some of the construction methods suggested and also added a bit more elaborate detail so that I would not make it too quickly.

For example the text suggests that the plate supporting the cylinder be sandwiched between two threaded rings with the threads being hand chased and the assembly then being soft soldered together. I opted to make the plate and the two rings as one then fix to the cylinder with Loctite. Strangely it suggests the cylinder head is a casting with what looked like cored passages, I opted for an inserted sleeve to form the ports for the rocking valve's spindle to rotate in. Rather than brass on brass I went for a piston machined from steel.

Edited By JasonB on 29/05/2023 17:00:35

As I mentioned in the opening post I wanted to add a bit more detail and ornamentation and the rather plain flat plate of the original engines base was the first candidate for that. I have had a couple of images of this engine in my "future projects" file and likes the edge detail it featured.

So after milling some 5mm plate down to size and drilling the various holes I started by using a 10mm cutter to do the recesses along the edges

After that the plate was held upside down and a dovetail cutter used to chamfer the edges to a height of 4mm which left a small 1mm vertical edge around what would be the bottom.

I deliberated for some time on whether to stick with parallel columns or to taper them, in the end straight won so it was just a case of turning spigots on each end that were threaded M4. Two bases were turned with a bit more decoration to the profile and then parted off over length.

The feet were attached to the longer bottom spigots with Loctite and once set were faced back to give the finished length from underside of base to the shoulder at the top of column

For the cylinder support a piece of 8mm flat bar was held in the 4-jaw and bored to 22mm then the integral upper collar formed by turning 2mm off the face of the bar.

I took the option to profile and drill the two holes on the CNC but it could also be done easily enough with a rotary table. .

An old arbor was reused to hold the work while the thickness was reduced to 4mm leaving just the lower collar standing proud by 2mm.

Edited By JasonB on 30/05/2023 18:33:23

The piece of thick wall brass tube that I had came out at 22.7mm by the time the chrome plating had been skimmed off so I opted to use a M22 x 0.5mm thread for the gland nut that seals the end of the piston (no rings). I opted to make the female thread first and rather than single point cut it I took the opertunity to have ago a thread milling on the CNC. So an odd bar end of 1" brass was held in a 3-jaw chuck, the end milled flat and then the threading size and smaller clearance hole were bored with the CNC followed by thread milling.

With the internals done I cut a test make thread on the opposite end of the stock and screwed the gland nut onto that to do the remaining turning, the final operation was to use one wheel of a diamond knurl to add a rope type knurl to a half round bead that had previously been turned.

With sufficient length sticking out of the chuck the chrome was turned off the other end of the tube and then a 12mm length reduced to 22mm dia which gave a shallow shoulder to locate against the cylinder support plate. Following that the thread was cut, I find it easier to run the lathe backwards and bring the tool in from the far side, that way I can cut at several hundred rpm and not have to worry about overrunning the length of thread if I don't stop the lathe when required

After checking the fit of the thread using the gland nut as a gauge I bored out the tube to the desired 19mm diameter. It was then sawn off and the top faced back to final length.

A piece of 20mm leaded steel was turned to fit the cylinder and then bored out to 17mm to leave a 1mm wall thickness, sawn off, faced to length and a 3mm hole put into the top ready to receive the small end yoke.

Rod, the short notes in the original article do mention "mandrel drawn" brass tube so sounds like something similar.

At this stage I was enjoying the building so much that I did not take as many photos as I could have done but there is nothing too special about most of the remaining parts.

The crank disc was roughed out and then a RCGT 06 button insert used to finish the back edge and give a nice large fillet to the protruding boss and then the hole was spotted, drilled 5.8mm with a stub drill and reamed 6mm before sawing the disc off of the piece of steel bar. It was then Loctited onto a length of 6mm precision ground mild steel and once that had gone off the front face was turned to final thickness thus ensuring the face was perpendicular to the shafts axis.

The bearing supports that can also be seen in the photo above were turned from 12mm leaded steel using a ball turner to form the top and a 1mm radius tool to turn the tapered column so it blended in nicely to the ball. Moving over to the mill 3mm was taken off opposite faces and an 8mm hole drilled and reamed through to take the bearing. Back into the lathe a parting tool was used to form a 3mm dia spigot that could be threaded once cut off for a nut to hold the support to the base

Bearings were simple turning and reaming from Colphos and loctited into place after which the oil hole was drilled through

After turning the OD of the eccentric a 1mm parting insert was used to cut a central groove to retain the strap

After which the stock was held in the small 4-jaw and clocked to give the desired throw before turning the spigot, spotting, drilling, reaming and then cut off

After tapping for a M3 grub screw the eccentric was mounted on a 6mm bar so the sawn face could be turned back to the final 5mm thickness

A piece of brass was square dup and then milled to 5mm thickness before boring to size using the eccentric to gauge the fit.

The outside profile was done on the CNC but could quite easily be done on a rotary table or even with filing buttons depending on what you have available.

The eccentric rad was just 2mm dia steel threaded at both ends and the end that screws into the strap had a small spigot turned to locate in the groove of the eccentric

For the top end of the rod I kept the ball shaped theme going when making the rod eye.

Before I continue the build some new information has surfaced which puts the original article at a some what earlier date of 1881 (Thanks Pat)

The last few parts comprise the head and valve assembly.

As mentioned at the start the article calls for a cast head with passages cast in though the detail was not really clear enough to see exactly what was intended and the overall shape was quite boxy. I drew up something a bit more appealing to my eye and used the CNC to translate that image into cast iron. Without removing the partially machined head from the 5C block I transferred to the manual mill to drill and ream for the sleeve and drill & tap the inlet exhaust pipe connections.

Some more doodling with Alibre came up with a valve design that I thought would work, here is a section through the head. There is an inserted sleeve that has what would be the port faces on a slide valve engine milled into it, drilled passages down into the cylinder. There is then a stainless steel spindle with a flat milled onto it that will open and close the ports and connect the open one to the cylinder as it is rocked by the eccentric rod.

This is the sleeve with the larger exhaust slot on the left

Once the sleeve had been Loctited into the head the two holes were drilled

This pic shows the valve spindle having had it's flat milled a 1mm hole was drilled through it's spigot and the actuation arm so they could be pinned together

From an early stage I had decided to leave this engine in bare metal which I did with the exception of the "cast" surface of the flywheel which was done in a Rustoleum cast iron effect paint. I did think of bead blasting it but it would have been prone to rust so went with the paint. A piece of mahogany that I took out of a clients 110yr old house provided the base.