A Two Cylinder Steam Engine

[romartin]

[SIZE=+2]A TWO CYLINDER VERTICAL STEAM ENGINE[/SIZE]

INTRODUCTION

I have resumed building the steam engine I had started when my encounter with HMEM caused me to embark on a fruitful interlude of tool building during which I learned much and for which I will always be grateful to HMEM and it's members.
This engine is a two cylinder version of the single cylinder steam engine which my brother and I built in 1956/7 when we were kids in the South African town of Eshowe in what was then known as Zululand and is now called Kwazulu. The pic below shows this 50+ year old engine for which no design drawings were ever produced. It was built entirely from scrap metal using our father's old 3.5" screw cutting lathe.

DESIGN OVERVIEW

In November of 2011, when planning a two cylinder version of this engine, I decided to develope a design which allowed an option to build a single cylinder version. The two versions have many parts in common. Like the original, all parts are intended to be built from stock metal; no castings are required. Unlike the original engine which used the imperial dimensions and standards then current in South Africa, the new design uses the metric units and standards current in my adopted patria Italy.

The design was modelled in 3D and construction drawings were extracted from the models. The drawings for all the parts and assemblies for both versions occupy a total of thirteen A4 pages. I will attach each drawings to the post which deals with the parts on it.

Below is a CAD generated image of the overall assembly for each of the versions. To give an idea of the size, the cylinder bores are 22 mm in diameter, the pistons have a 26 mm stroke, while the flywheel has a diameter of 72mm.

From here on I will refer only to the two cylinder version that I'm now building.

The design structures the engine into a number of assemblies. Here are the CAD images of their 3D models.

Base Assembly

Vertical Structure Assembly

Shaft Assembly

Cylinder Assembly
Two of these are required.

Inlet Piping Assembly

Exhaust Piping Assembly

When work got interrupted last year I had completed building the Base Assembly and the Vertical Structure Assembly and all parts of the Shaft Assembly with the exception of the Crank Shaft itself, the Bearings, the Flywheel and the Eccentrics. I had done some initial work on preparing the chunks of steel destined to become the Crank Shaft and the Flywheel.

WHAT'S NEXT?

My next posts on this thread will report on these completed parts and assemblies; unfortunately I did not take many photos while doing this work.
Then I'll move on with more detailed reports as the work for completing the engine proceeds.

 

[romartin]

[SIZE=+2]THE BASE ASSEMBLY[/SIZE]

DESIGN CONSIDERATIONS

The Base Assembly is composed of the Base itself plus the two Bearing Straps with their associated Oil Cups and bolts. The Base itself is fabricated by soldering together subparts made from sheet brass: two Sides from 5mm plate, two Faces, one Top and four Fixing Lugs from 3 mm plate.

Here are some extracts from the construction drawings, the two PDF files of which are attached to this post.

Base Side

Base Face

Base Top

BUILD APPROACH



The key points of the approach chosen for building the Base Assembly were as follows.

• Hold the subparts in position for soldering with small M2 brass screws; removing the heads of the screws after soldering.
• Before soldering, prepare to final size only those edges of the subparts which are part of a contact to be soldered. Leave excess material on all other edges and reduce them to final size after soldering.
• Using a single setup in the milling configuration of my lathe to perform final machining of the cut outs in the Top, of the tapped holes in the Top for the eight Pillars of the Vertical Structure, and of the tapped holes in the Sides for the Bearing Strap bolts. This is to ensure high precision in their relative positions and alignment.
• Prepare the Bearing Straps and their Bolts first, and then use a single lathe setup to machine the split holes for both the Bearings with the two Bearing Straps held in place on the Base with their own bolts. This is to ensure perfect alignment of the two Bearings. In this lathe setup, the Machine Vice holding the Base is mounted directly on the flat upper surface of the lathe's cross slide.

PHOTOS

Using the Filing Guide to make the rounded profile of the Fixing Lugs.

The subparts of the Base ready for soldering.

The assembled subparts of the Base in the oven for soldering.

The Base Assembly Parts

The finished Base Assembly.

WHAT'S NEXT?

The next post will report on the building of the Vertical Structure Assembly.

View attachment Base1 Assembly 1of1.pdf

View attachment Base2 Assembly 1of1.pdf

 

[canadianhorsepower]

nice work thanks for the drawing
Thm:

 

[romartin]

[SIZE=+2]THE VERTICAL STRUCTURE ASSEMBLY[/SIZE]

DESIGN CONSIDERATIONS

The Vertical Assembly is composed of two groups of 4 pillars which screw into the Base and together support at their top ends a horizontal platform on which the pair of Cylinder Assemblies will be mounted. Below the Platform, the rear two pillars of each group also support a subassembly for guiding and constraining the vertical oscillation of the Small End.

Here are some extracts from the construction drawings, the two PDF files of which are attached to this post.

Platform

Slide Upper Support

Slide Lower Support

Piston Slide

BUILD APPROACH




The making of the parts of the Vertical Structure Assembly did not present particular difficulties. Some points of the approach chosen were as follows.

• Use a single milling setup of the lathe to perform final machining of all the holes in the Platform. This ensures precision in their relative positions and alignment.
• For each of the Slide Supports, use a single milling setup of the lathe for boring and tapping all the holes. This ensures precision in their relative positions and alignment.

PHOTOS

The parts of the Vertical Assembly.

The Vertical Assembly. A temporary bolt is holding each of the Slides up against the lower face of the platform.

The Vertical Assembly mounted on the Base Assembly.

WHAT'S NEXT?

The next post will report on the parts of the Shaft Assembly which were completed last winter.

View attachment Vertical Structure1 Assembly 1of1.pdf

View attachment Vertical Structure2 Assembly 1of1.pdf

 

[romartin]

[SIZE=+2]THE SHAFT ASSEMBLY - 1. Conrod and Eccrod Units[/SIZE]

DESIGN CONSIDERATIONS



The Shaft Assembly is composed of:

• the Crank Shaft itself,
• the Flywheel,
• the two Eccentrics,
• the two Bearings,
• the two Connecting Rod Units with their Big and Small Ends,
• the two Eccentic Rod Units with their Eccentric Straps and Links.

The three PDF files with the construction drawongs of these parts are attached to this post. However reporting on their builds will require several posts.

This post reports on the Connecting Rod Unit and the Eccentric Rod Unit which were completed last winter and for which I do not have photos of the build process.

Here are some extracts from the construction drawings.

Connecting Rod Big End

Connecting Rod Small End

Eccentric Rod Straps

Eccentric Rod Link

BUILD APPROACH

The making of the parts of the Connecting Rod Unit and the Eccentric Rod Unit was fairly straight foreward but required care owing to their small size.

The approach for making the Big Ends may be of interest. First the M2 bolts and nuts for holding the upper and lower straps together were made from 5mm bar mild steel stock. Then both Big Ends were done together with a single chunk of 18mm bronze bar. At a certain point the lower halves of the straps were cut away from the bronze chunk, and the contact surfaces of both upper and lower straps were milled flat. The lower halves were then fixed with the bolts back onto the upper halves which were still part of the bronze chunk, thus allowing final turning of the 7mm bores and their outer faces.

A similar approach was followed for the Eccentric Straps.

PHOTOS

The Connecting Rod Unit. One Unit is assembled and one is shown as disassembled parts.

The Eccentric Rod Unit. One Unit is assembled and one is shown as disassembled parts.

WHAT'S NEXT?

The next post will report on the building of the Bearings and the Crank Shaft.

View attachment Shaft1 Assembly 1of2.pdf

View attachment Shaft1 Assembly 2of2.pdf

View attachment Shaft2 Assembly 1of1.pdf

 

[aarggh]

Loving this build Ian! Thanks for putting the files and pics up for everyone, very generous.

cheers, Ian (yes, another one!)

 

[romartin]

That you Luc and Aarggh! I'm enjoying doing it!

 

[romartin]

[SIZE=+2]THE SHAFT ASSEMBLY - 2 Bearings and Crank Shaft[/SIZE]

This post reports on the recently completed building of the Bearings and the Crank Shaft. These parts are part of the Shaft Assembly, the three construction drawings of which were attached to the previous post. Making the Crank Shaft has been by far the biggest challenge so far!

Here are some extracts from the construction drawings.

Crank Shaft Bearing

Crank Shaft

BUILD APPROACH


The key aspects of the approach chosen for the Crank Shaft and its bearings were as follows.

• Make the Bearings before the Crank Shaft, finishing their bores with a 7mm reamer. Then fir the crank shaft to the bearings.
• Machine the Crank Shaft from the solid. This approach was decided after some trials to test the feasibility of building it up from separately prepared disks and bars. My attempt to silver solder the trial pieces of steel failed - the steel oxidised before reaching the fusion temperature of the solder. I suspect that this may be due to the presence of lead in the steel.
• Facilitate precision in the positions of the crank pins relative to the center of the shaft via two narrow flats milled along the length of the solid bar. These flats were used twice:
  • posioning the solid bar in the Machine Vice for drilling the center holes for machining the crank pins;
  • positioning the Crank Shaft in the Machine Vice for milling the profile of the cutouts in the crank disks.
• Attempt to avoid where possible the need to transmit torque to the point being turned through the finished crank pins. In other words attempt to orient the part so that the section to be turned was near to the dog or chuck.

BUILD LOG

The Bearings

The Bearings were turned together from 18mm phosphor bronze bar. Their bores were finshed to size with a 7mm reamer.

Preparing the Crank Shaft Chunk

Intial machining from bar stock produced a steel cylinder of diameter 38mm (2mm oversize) and length 127.5mm (final size) with the two shallow flats milled along most of the length and with three center holes at each end - one at the center and one on the axis of ecah crank pin. This cylinder also had eight shallow grooves around it to mark the edges of the four crank disks. I regret that I have no photos of this machining nor of it's product.

Machining the Crank Pins

Following removal of a modest amount of metal from all sections of the shaft with the exception of the disks themselves, I started the long task of making the two crank pins. The following three photo show the machining of the second crank pin. The shaft is mounted between centers along the axis of the pin and therefore turns with a marked eccentricity.


To reach into the depth of the crank the cutting edge of the tools had to project almost 30mm from the front face of their tool holders. The whole job was done with the spindle turning at 63 rpm. The 6mm space between the inner faces of the crank disks was gradually deepened in a series of nearly 30 "steps" each of which deepened the slot by 1mm. Each step consisted of three substeps:

• Use a small threading tool to make a V sided slot 1mm deep and aboy 3 mm wide at the center of the slot.
• Use a left shouldered knife tool to widen the slot up to the disk on the left of the slot. This was done in four passes of 0.25mm each.
• Use a right shouldered knife tool to widen the slot up to the disk on the right of the slot. Again this was done in four passes of 0.25mm each.

Every ten or so steps, the inner faces of the disks being formed were faced off using the appropriate knife tool. This process was of course repeated at the end. The final step was special in that the cuts were very light with frequent checks for fit with the bore of the corresponding Big End.

Each of these steps took about 20 minutes. Thus the turning of each crank pin took around 10 hours. Interestingly, this 10 hour process required almost 100 tool changes! Without my new QCTP it would have been very tiresome!

The following photo shows the three tools used during this process. They were resharpened frequently. Note that the holders of the knife tools hold the tool with a small horizontal angle (1 degree). This enabled me to do all the tool swapping without having to adjsut the angle of the QCTP itself.

Rough turning the sections of shaft

Once the two Crank Pins were completed there was no further need for their center holes and so the excess material from the shaft sections could be removed. Almost all of this metal (of which there was a surprising amount) was removed by holding the work firmly in the 3-jaw chuck near to where the material was being removed. For the two end sections, the thin disk left in the jaws of the chuck was cut away with a hacksaw. For the middle section, the chuck jaws were holding the work by one of the pairs of crank disks.

Here is the crank shaft at the end of this rough removal of material. The shaft sections are still oversize by about 1mm and, having been turned in the chuck and not between centers, are not perfectly concentric with the center holes. The crank disks are still too thick by about 0.5mm. Note too that the diameter of the crank disks is still 2mm oversize and that the flats in correspondance with the crank pins are still there.

Milling the crank disk cutouts

This process was done with the lathe in its milling configuration, using a 12mm end mill in the 3-jaw chuck. The work was done with four different setups, one for each side of each pair of crank disks. The flats on the rims of the crank disks were used to ensure that the orientation of the disk being machined was correct. The curved section of the profile was machined in a series of small steps: X was increased by 0.1mm (just under 0.004") and Z was decreased by the appropriate amount to follow the 8mm radius. The resulting stepped surface was then smoothed carefully by hand with a small flat file.

The attached pdf file shows the Excel page with the detailed instructions I had with me in the shop while doing the job.

Final turning of the disk rims and the sections of shaft

At this point I could finally mount the crank shaft between centers for the finishing cuts on all the cylindrical surfaces along the main axis ie the three shaft sections and rims of the four disks. No particular issues here except to take light cuts (max 0.25mm) with sharp tools, and to avoid squeezing the shaft tightly between the centers - just tight enough to have no side movement. Notice the rubber band holding the dog to the driving pin of the faceplate.

Finished Crank Shaft

The photos show the finished crank shaft first on its own and then mounted in the Bearings on the Base Assembly.

WHAT'S NEXT?
The next part on my plate is the Flywheel.

View attachment CrankDiscCutouts.pdf

 

[romartin]

[SIZE=+2]THE SHAFT ASSEMBLY - 3 Flywheel[/SIZE]

This post reports on the build of the Flywheel and the associated fixing screw. They are part of the Shaft Assembly, the three construction drawings of which were attached to the first post about the Shaft Assembly.

Here are some extracts from the construction drawings.

BUILD APPROACH


The key aspects of the approach chosen for the Flywheel were as follows.

• Machine the flywheel from a single 18mm slice cut from a 75mm bar of AVP (Pb) steel.
• Hold the slice in the 3-jaw chuck to machine one face and the bore.
• Then use a custom mandrel to hold the slice via the bore to machine the other face and the rim.
• If necessary, make a custom extension for the 3mm first and second taps to allow use of the tap guide. Then drill and tap the fixing screw hole through the boss by holding the flywheel in the machine vice directly bolted to the upper face of the cross slide, using the bore through the boss to ensure that the axis of the bore is at the same height as the axis of the lathe spindle.
• Make the grub screw in brass to avoid damage to the Crank Shaft.

BUILD LOG

Rough Machining

This photo shows a moment of the process of the initial rough machining the slice. First the raw slice was neld in the 3-jaw chuck by the outer surface of the rim to rough machine the exposed face including the boss, the 3mm recess and the rim edge, leaving an excess of less than 0.5mm.

Then the slice was reversed in the chuck, this time holding it by the inner surface of the rim. In this setup the outer surface of the rim and the second face, including the 3mm recess, the boss and the rim edge were rough machined again leaving about 0.5mm of excess.
Here is the slice at the end of the rough machining. At this point the slice is ready for finish machining.

Finish Machining

Holding the Flywheel in the 3-jaw chuck by the outer surface of the rim, the exposed face was finish machined to final size. Then an initial 6.5mm hole drilled through the boss was bored to final size with very light cuts until a smooth fit with no wobble on the Crank Shaft was achieved.

Next a custom mandrel was fashioned on the end of piece of 12mm steel rod held in the 3-jaw chuck.

Without removing the mandrel from the chuck, the flywheel was mounted on it with the unfinished face exposed so that it, and the outer surface of the rim could be finish machined to final size.

Drilling and Tapping the hole for the Fixing Screw

Before starting the job I made a jig to increase the length of the shank of the 3mm taps.

Then the flywheel was mounted in the machine vice which was itself mounted directly on the upper face of the lathe's cross slide. The height of the flywheel was positioned with the help of the tail stock center.

The 10 degree angle for the Machine Vice was set with the help of a carpenters angle guage. Then, after milling a small flat on the boss and starting with a center drill, the hole for the Fixing Screw was dilled and tapped.

Making the Fixing Screw

The Fixing Screw was machined from a short scrap of 6mm brass rod. The photo shows the final step of cutting the screwdriver slot in the head using the slotting saw I have built for my QCTP.

Finished Flywheel

The photo shows the finished flywheel with its brass Fixing Screw.

WHAT'S NEXT?

The next parts on my plate are the last ones to complete the Shaft Assembly, namely the two Eccentrics and their grubscrews.

 

[canadianhorsepower]

Nice work thanks again for the drawing.

one question why did you go 90 degree instead of 180 for crank pin

 

[romartin]

Thank you Luc.
Your question. Since the cylinders are double acting (ie live steam pushes the pistons on their up strokes and on their down strokes), the 90 degree angle between the cranks ensures that the engine will start itself whatever the angle of the crank shaft and that it has no dead spots. Furthermore the power is more evenly transmitted to the crank shaft because when one piston is at the top (or the bottom) and is therefore doing no useful pushing, the other one is in midstroke and is therefore doing its maximum useful pushing.

 

[romartin]

I gave a quick answer to Luc's question in my previous post but the old grey wheels continued turning! I'm refering to the advantage of the 90 degree angle between the cranks of evening out the transfer of energy from the steam to the crank shaft. I came up with a simple, and approximate model.

The torque on the crank shaft poduced by a single piston as it move from TDC to BDC (Top/Bottom Dead center) will roughly follow the first half of a sine wave - ie it will start at 0, rise to a maximum value (say 1) when the crank is at 90 degrees and then fall back to zero. The same curve will then be followed again on the upstroke from BDC to YDC. The overall curve for a complete 360 degree cycle therefore looks like a two humped camel or a rectified sinewave. Not surprisingly, the repetition period of this waveform is 180 degress.

The torque on the crank shaft from a two cylinder engine with the cranks at 180 degrees will be simply twice that of the single cyllnder i.e. it will start at zero, rise to 2 when the crank shaft is at 90 degrees, fall back to 0 at 180 degrees, rise again to 2 at 370 degress and fall back to zero at 360 degrees. The repetition period remains 180 degrees.

When the cranks are placed at 90 degrees with respect to each other, the analysis is a bit more complex. We have to add one of these repeating camels to itself shifted to the right by 90 degrees. A sinewave shifted by 90 degrees is a cosine wave. So the resulting waveform is the sum of a rectified sine and a rectified cosine. The resulting wave is a hump which starts at 1, rises to a peak of 1.41 (square root of 2) at 45 degrees, then falls back to 1 at 90 degrees and then repeats itself another three times to complete a full 360 degree cycle. The shape of the hump is the middle half of a sine wave (i.e. from 45 degrees to 135 degrees).

So the smoothing effect on the torque applied to the Crank Shaft derives from two effects:

• Smaller Excursion: the amplitude of the torque varies between 1 and 1.414 instead of from 0 to 2
• Higher Frequency: the repetition frequency of the torque waveform is doubled from 2 per cycle to 4 per cycle

Math
Trig formula: sin(A+B) = sinAcosB + CosAsinB
With B = 45 degrees so that cosB = sinB = 1/sqroot(2)
and so we get sinA + cosA = sqroot(2)sin(A+45)

 

[romartin]

[SIZE=+2]THE SHAFT ASSEMBLY - 4 Eccentrics[/SIZE]

This post reports on the build of the two Eccentrics and their associated fixing grubscrews. They are the last remaining parts of the Shaft Assembly, the three construction drawings of which were attached to the first post about the Shaft Assembly. At the end, the present post also shows the Shaft Assembly put together from all its parts, and the Shaft Assembly integrated with the Base Assembly and the Vertical Structure Assembly.

DESIGN CONSIDERATIONS

Here are some extracts of the Eccentric from the construction drawings.

There are differences with respect to the drawings attached to the earlier post; they derive from my decision to increase the diameter of the grubscrews from M2 to M3:

• the diameter of the bosses is increased from 12 mm to 14 mm.
• the width of the bosses is increased from 4 mm to 5 mm.
• the grubscrews are threaded M3 with an overall length 5.5 mm.

BUILD APPROACH


The key aspects of the approach chosen for the Eccentrics were as follows.

• Machine the Eccentrics together from a single length of 20mm AVP steel bar stock.
• Hold the bar in the 3-jaw chuck to machine the external (ie eccentric) profile including the 1mm wide slots, checking the fit with the corresonding Eccentric Straps.
• Mount the bar in the 4 jaw chuck using the dial indicator to check that the center of external profile is offset from the lathe axis by exactly 2mm. Use this setup to machine the 14mm diameter bosses and the 7mm diameter bores of both eccentrics.
• With the bar still in the 4-jaw, use the electric drill in its cross slide holder to drill and tap the cross holes for the fixing screws.
• Make the two grub screws in brass to avoid damage to the Crank Shaft.

BUILD LOG

Here is the bar with a 26mm length turned to the finished size of 18mm.

These pics show the bar with the first of the two 1mm grooves and then with the two Eccentric Straps mounted in place to check their fits. The grooves were made with a special bit ground on the end of a 2 x 8 parting tool. During this process I discovered that the protruding lip in one of the Straps was a bit wider than 1 mm. I took the easy way out of widening the groove of one of Eccentrics.

Below you see a stage of the setting up of the bar in the 4-jaw chuck with the help of two small chuck keys and my Dial Indicator mounted on the QCTP. (This is one of the tricks I learned from an HMEM member.) I need two small keys because the handle of the chuck's main key is too long to turn except when inserted into the topmost tooth.

The boss of the first Eccentric has been turned to its final 14 mm diameter and the boring of the 7 mm hole is in progress. Boring started after drilling with a center drill, a 3mm drill and a 6.5 mm drill.

The next pic shows the setup for drilling the hole for the grubscrew of the first Eccentric. The electric drill is held by it's neck in a holder which I made at least 14 years ago and which bolts onto the upper surface of the lathe's cross slide. Unfortunately my plan to use this setup also for tapping with my usual tap guide proved impratical; there was insufficient space available even with the cross slide fully wound back. I decided to do the tapping of the holes later using my lathe's milling setup and using the holes to position the Eccentrics in the Machine Vice.

Below you see the first Eccentric being parted off with a freshly sharpened 2mm parting tool under power feed.

This is the milling setup for tapping the holes for the M3 grubscrews using my usual tapping guide.

Below you see the two finished Eccentrics with their brass grubscrews.

COMPLETED SHAFT ASSEMBLY

At this point I had completed all the parts of the Shaft Assembly, so I could assemble it for a snap. Here it is. The fit of the parts is still a bit tight.

I could not resist the temptation to integrate the three finished assemblies. Here is a pic of the new Shaft Assembly integrated with the Base Assembly and the Vertical Structure Assembly.

WHAT'S NEXT?

My next objective is to make the two Cylinder Assemblies. I still have to choose the approach and get some of the material.

 

[Gerry Sweetland]

What a wonderful way to show and document your build! I wish I could express myself so eloquently.
I have been building Elmer's #11 and have been taking photos as I go thinking that I may post a build log. I was thinking that I would supply solid models and or drawings too (even G code if it would be useful to others), then I stumble on to your excellent build log.
Thank you for the inspiration and looking forward to the rest of your build.
Gerry

 

[romartin]

Thank you Gerry!

 

[romartin]

[SIZE=+2]THE CYLINDER ASSEMBLY - 1. Introduction[/SIZE]
INTRODUCTION

This post contains some preliminary considerations on the design of the Cylinder Assembly. The three construction drawings are attached to this post. Here are some extracts of the Cylinder Assembly from these drawings, showing viewS of the 3-D CAD model. The first one shows a front and a rear view of the Assembly, showing the various units and parts of which it is assembled. I use the term unit to mean a part which is assembled in a non-reversable manner (like soldering or glueing) from simpler parts.

The image below shows a section though the Cylinder Assembly in the XZ plane at Y = 0, clearly showing the Piston, the Slide Valve, and the passages for the steam linking the Steam Chest with the cylinder and the Exhaust.

For people who have not yet met this Slide Valve, here is a brief description of the way it works.
The first point worth noting is that it is the pressure of the steam in the Steam Chest which keeps the Slide Valve pressed up against the flat surface of the Cylinder Face.
The Slide Valve makes a vertical oscillation which it receives from the associated Eccentric on the Crank Shaft. This vertical motion of the Slide Valve alternately exposes one end of the cylinder to the live steam in the Steam Chest while, via the hollow in the face sliding on the Cylinder Face, connecting the other end of the Cylinder to the Exhaust outlet. In the above image, the Piston is shown in it's highest position. Since the Eccentric which moves the valve is fixed to the Shaft at 90 degrees with respect to the crank pin which moves the Piston, the Slide Valve is in the middle of it's oscillation and is moving downward. In this position it is blocking both the upper and the lower steam ports on the Cylinder Face. The downward movement of the Slide Valve will progressively expose the upper steam port to the live steam in the Steam Chest and connect the lower port to the exhaust outlet. When the Piston is in the middle of it's downward movement, the Slide Valve will be at the bottom of its movement with the upper steam port fully exposed to the live steam and the lower steam port fully connected to the Exhaust. The Piston continues it's downward movement but the Slide Valve starts moving upward so that when the Piston reaches the bottom of it's excursion, the Slide Valve is again in the middle of its excursion and is therefore agin blocking both steam ports. And so on....

DESIGN CONSIDERATIONS

Symmetries



I had an initial objective that the Cylinder Assembly for the single cylinder engine and the two Cylinder Assemblies for the double cylinder engine all have the same design. Note however that in the two cylinder version of the engine the two cylinder assemblies are not identical; they are mirror reflections of each other because while the steam chest is on the left of one and on the right on the other, they both have the inlet and exhaust nippls to the rear. So the design objective became that the component parts of the Cylinder Assembly have certain symmetries so that the two mirror reflections can be assembled from the same set of parts. What symmetries are required?

• Cylinder Unit: The threaded bolt holes in the upper and lower rims of the Cylinder must line up with the holes in the Platform when the Cylinder Unit is rotated 180 degrees about a vertical axis and when it is rotated 180 degrees about a horizontal axis parallel to the crank shaft. The first symmetry ensures that the Cylinder Unit can be mounted with the Steam Chest to the left or to the right. The second symetry ensures that the exhaust nipple can be at the rear or in front.
• the Steam Chest: The left half and the right half of the Steam Chest must be mirror reflections of each other. This symmetry ensures that the Steam Chest can be to the right or to the left of the Cylinder and that, in both cases, it can be oriented so that inlet nipple is at the rear or at the front.

In my first stab at the cylinder design the cylinder flanges were fixed with five equally spaces bolts as did the original engine made over 50 years ago. But I had to change this to be six equally spaced bolts in order to satify the symmetry requirement.

In practical terms, these requirements for symmetries imply a need for special attention to precision when making the parts. For example for a Cylinder Unit to allow either of the cylinder ends to be at the bottom means that both ends must be perfectly square to the cylinder bore.

Steam Passages



The two steam passages linking the Steam Chest to the top and bottom of the cylinder are each composed of three sections:

• A horizontal slot, called a steam port, with a height of 2mm, milled right through the Cylinder Face.
• A vertical slot 3mm wide milled into the outside of the cylinder wall.
• A horizontal hole drilled from the end of the vertical slot right through the cylinder wall.

All three sections of the passages are machined before the Cylinder, the Cylinder face and the Exhaust Nipple are soldered together to form the Cylinder Unit.

Bolting of Cylinder Assy to Platform

In the two 3D views one can see that the bolts holding the lower flange to the cylinder aappear to be too long. This is because the same bolts pass through six matching holes in the Platform part of the Vertical Assembly. The rearmost of the six bolts is even longer than the others; this is because it also passes through the Slide Upper Support to hold it up against the lower face of the Platform.
A consequence of this choice of bolting is that it is the tapped bolt holes in the cylinder walls which determine the angle in the horizontal plane of the cylinder relative to the Platform. It is therefore important that these holes be precisely positioned.

WHAT'S NEXT?

For me, the most challenging part of the Cylinder Assembly seems to be the Cylinder Unit both because of the precision required and because I'm always a bit nervous when there is silver soldering to be done. However before starting this adventure I shall put a somewhat irksome chore behind me, namely making the 20 M2 bolts required for each Cylinder Assembly!

View attachment Cylinder Assembly 1of3.pdf

View attachment Cylinder Assembly 2of3.pdf

View attachment Cylinder Assembly 3of3.pdf

 

[lennardhme]

Great series. looking forward to more.
many thanks.

 

[Swifty]

Amazing job Ian, just goes to show what can be produced using only a lathe with a milling attachment.

Paul.

 

[romartin]

Thank you Lennardhme and Paul.

 

[romartin]

Hey Gerry have you started posting a build log of your Elmer #11?