Geared horizontal twin engine

[Brian Rupnow]

Oh!!--I do love it so, when a plan starts to come together. No major pieces made today that show, but about 8 or 10 that don't, and they are all required to make this thing run.

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[Brian Rupnow]

Today has been designated "Connecting Rod Day". Since I'm dealing with a bit of Cabin fever due to Covid and winter, I'll do a complete run-thru on this subject. Con rods for internal combustion engines all look basically the same, except for size. Con rods for steam engines come in a few different shapes, and there is a bit of "mechanical art" involved in a steam engine connecting rod.

 

[Brian Rupnow]

I had a length of 1/2" square brass that I will make the con rods from. These rods will be turned between centers, not held in a chuck. As a consequence of this, the exact centers are marked out by using the handy little 45 degree angle tool in the picture. The material (as per my hand sketch) is made 0.2" longer on each ends to allow for center punch marks. The material has been coated with layout dye, and the point at which major diameter differences occur they have a line scribed around them. After establishing the exact center of each end, the pieces get a good center punch mark, so they can be turned between centers using a lathe dog.

 

[Tim Wescott]

I'm drooling over your handy 45 degree angle tool. BTW.

 

[Brian Rupnow]

I have a couple of old lathe dogs that hardly ever get used. If this was something super critical, I would remove the chuck and put a dead center into the tapered socket in the end of the spindle, however for what I'm doing, I simply chuck up a piece of cold rolled with the one end turned to the specified angle. The other end is supported by a dead center in the tailstock chuck. I do have a live center, but on short pieces like I am doing here, it takes up too much space. I will put a dab of grease on the end of that tailstock dead center, and the turn the round portion of the conrod down to 0.25" diameter over it's full length. I know that the drawing specs out 0.236" diameter, but I'm going to make it a bit heavier.

 

[Brian Rupnow]

Eventually, the round area of the shaft will get worked down to .250" diameter. This will require left hand cutters, right hand cutters, and possibly even parting off tools to work the 1/2" square brass down to 0.250' diameter. This is trickier than it sounds, because as the diameter reduces, the part wants to spring away from the cutting tool, then dig in when it rebounds. All you can do to prevent that is to take progressively smaller depth cuts and use really sharp tooling. Since I have machined away the black center mark, I will restore that mark with my black marker, then set my compound rest over two degrees and work from the center out towards the ends. When one side is completed, I set the compound rest over two degrees in the other direction and working from the center machine out towards the other end. Note that the last two cuts must be made with the topslide, not the normal lead screw.

 

[Brian Rupnow]

And here is the con rod with a 4 degree included angle running from the center out towards the rectangular ends.

 

[ajoeiam]

Today has been designated "Connecting Rod Day". Since I'm dealing with a bit of Cabin fever due to Covid and winter, I'll do a complete run-thru on this subject. Con rods for internal combustion engines all look basically the same, except for size. Con rods for steam engines come in a few different shapes, and there is a bit of "mechanical art" involved in a steam engine connecting rod.
snip

You left a bit of a tease when you indicated that IC engine con rods are quite similar but no information on con rods in a steam engine other than mentioned that a 'few different shapes' are used. Would you have any docs or urls that you would care to point the curious to?

TIA

 

[Brian Rupnow]

And con-rod day comes to a close!! It was a long but successful day, with many interruptions. In the end, at the close of the day, I have one finished con rod, installed. Tomorrow, I hope to have the other one.

 

[werowance]

that looks really nice. the rod just barely clears on the bottom (a hair is good as a mile) which makes it look nice

on another note. if you ever get bored and want to describe in more detail the procedure to cut an ecentric circle or offset circle on another circle, ill try to listen and hopefully understand it. doing it on a 4 jaw and measuring the offset is what eludes me. even more so when there are multiple ecentrics on a single base circle and not just one

 

[Steamchick]

I'm drooling over your handy 45 degree angle tool. BTW.

The "Engineer's centre square"
Apprentices used to make them, now the Chinese may them for just a couple of £...
I have one my Father made - as an apprentice.
Bigger ones cost more...
https://www.ebay.co.uk/itm/RDGTOOLS...5MM-MEASURING-ENGINEERING-TOOLS-/350538498265Also: Search for "45degree centre finder"... and find many forms of the same principle.
Very useful on round, hex, square material, also on cast material, where a series of scribed lines can give a pattern that will "surround" the centre of the casting...
Apprenticeships were a very good way to learn.... very thorough, and guided by experts - as this website holds.
K2

 

[Steamchick]

I have a couple of old lathe dogs that hardly ever get used. If this was something super critical, I would remove the chuck and put a dead center into the tapered socket in the end of the spindle, however for what I'm doing, I simply chuck up a piece of cold rolled with the one end turned to the specified angle. The other end is supported by a dead center in the tailstock chuck. I do have a live center, but on short pieces like I am doing here, it takes up too much space. I will put a dab of grease on the end of that tailstock dead center, and the turn the round portion of the conrod down to 0.25" diameter over it's full length. I know that the drawing specs out 0.236" diameter, but I'm going to make it a bit heavier.

Thanks Brian for explaining such a simple alternative to stripping off the chuck to fit a centre. And also the use of a dead centre in the drill chuck in the tail-stock to give more clearance.... A problem I had yesterday and did the same thing!
K2

 

[Steamchick]

that looks really nice. the rod just barely clears on the bottom (a hair is good as a mile) which makes it look nice

on another note. if you ever get bored and want to describe in more detail the procedure to cut an ecentric circle or offset circle on another circle, ill try to listen and hopefully understand it. doing it on a 4 jaw and measuring the offset is what eludes me. even more so when there are multiple ecentrics on a single base circle and not just one

I once used a small 3 jaw self-centring chuck offset in a large 4-jaw chuck to machine big-end journals on a 180 degree twin big-end crank-shaft: It worked - same off-set: interesting set-up, but the imbalance was horrendous and I could only run the lathe at a very slow speed.
The better alternative is to make a simple block with clamp screw to take the round stock and mount eccentrically in the 4 jaw chuck - or on a face plate - when normal turning of the eccentrics can easily be achieved. Using a face plate gives scope to add a balance weight for the eccentric material, for better (smoother) running of the lathe. Returning the "eccentrically turned" stock to the self-centring 3-jaw chuck or collets - or between centres - will then be appropriate for machining main journals.
But "better men than I" can teach us all better methods...
K2

 

[Brian Rupnow]

Both connecting rods are finished and installed. They fit and everything still goes round and round----but---what a pig to get into place!!! The original design was for one piece connecting rods, and they went into place with no difficulty on the single cylinder popcorn engine. However, with twin cylinders, there is simply no good/easy way of installing them. I have changed the detail drawing of the con rods, so that they now have bolt on end caps. this will make it a lot easier for the next person to build this engine.

 

[Brian Rupnow]

Slide valve actuator rods and ends are finished (mostly) and in place. That's all for today folks. good wife is calling me for supper!!

 

[Steamchick]

Hi Brian. I am enjoying your build - and tutorial (including cat and Wife notes!). In trying to understand your remark about the assembly of con-rods... is the problem simply that you need to address the big-end of con-rod to crank-pin laterally to rod axis, while the cross-head only permits axial motion? I guess you hand to assemble the cylinder with con-rod and cross-head and then fit this assembly to the crank? A lesson in "design for assembly" that I didn't spot earlier. I must try harder!
But when I worked for a major automotive factory we actually did this sort of thing - because in the total cost game it was the best solution. In the 1980s, I was fascinated by the assembly of a carburettor to manifold where 1 nut with difficult access was wrapped with a spiral of string, held on the end of the stud, then the string pulled to wind the nut onto the stud. Poor design overcome by assembly skill? There were many examples like this.
Keep up the good work,
K2

 

[Brian Rupnow]

This morning I'm setting here dreaming up an intake manifold for this engine to get air into it. Rather than just hooking an air-line onto a hose barb, I want this engine to have a control valve to govern the air flow. I had to reach back about 10 or 12 years to my steam donkey engine and have a look at the air control valve I designed and built for it, because it worked very well. This new air intake control valve looks totally different rom the steam donkey engine valve, but it has all the same guts in it.

 

[Steamchick]

Hi Brian,
I'm curious to know "the guts"! - I'll not be surprised if you have them in your CAD - even exploded!
K2

 

[Steamchick]

1. Will the Throttle be controlled by a "maritime" type of wheel and linkage? - or just a simple knob for the finger and thumb? - I suggest "Maritime", as this engine reminds me of the configurations for Side paddle-wheel boats where the engine was sited low, but the crank was situated higher - in line for the paddles.
2. While I think of it, I'll bet you have some clever scheme for linking cylinder drain valves? - Or are they "not required" on this if only an "Air" engine?
3. Another odd question: What do you plan for timing when designing and Air engine instead of steam? - I.E. how much (crank angle) advance on the eccentric - and how much cut-off do you set on the valve? I'm asking because I understand steam can have an earlier cut-off than if the engine is just used for air, but the Lead of the eccentric is just to do with engine speed, and may be different depending on the number of cylinders? I've not read anything that I can remember on this so unsure of the subject! So please excuse if a "stupid" question.

Ta, K2

 

[Brian Rupnow]

The vertical lever swings 90 degrees to provide full pressure to the both engines. Since I only run these engines on air, they don't require cylinder drain valves, but those are easily added if someone wishes to run on live steam. To time an air engine you put the piston at top dead center, then with the set-screws on the eccentric hubs unlocked, you turn the eccentric hubs until the slide control valve is at mid travel, then lock up the set screws. If you want opposite rotation you set the piston at bottom dead center before doing this.