Half Scale Domestic "Stovepipe" build

[Jasonb]

Well with the Benson out of the way I suppose I should start to write up the next project which is as the title says a half scale model of a Domestic “Stovepipe” or frost proof hit and miss engine, the name comes from the fact that the hopper is sheet metal not cast which was prone to crack if left in a barn or around the farm full of water in cold weather. This is an old catalogue picture of what the finished engine should look like

This kit is one of the original Dick Shelley produced ones but you can now buy them from Bob Herder. As you can see there are quite a few pieces and being half scale its quite a hefty model, the parts as shown below weigh it at about 55lbs. To get an idea of size the flywheels finish up at 7.2” dia.

As is my usual way I have several projects on the go at the same time and started to do the odd little bit of this engine between other things. Rather than tackle one of the castings first I thought I would get some of the smaller items out of the way so decides to make rather than buy all the fixings. The drawings specify 1/4x20, 10-24 and 5-40 for most of the threads so I substituted ¼ Whitworth, 2BA and 5BA and came out with this little pile.

Once I started properly the first item to get worked on was the main engine casting which is really the crankcase. A light skim was taken off the upper surfaces to give a stable base so that the casting could be clamped upside down and the foot machined flat, the edges trued up so future references could be taken from them and at the same time a recess cut to take a brass plate to form the fuel tank within the base.

With that done the casting was bolted right way up to the mill table and the flat pockets to take the bearing caps machined and bolt holes to hold them tapped. The bearing caps were also machined at this time so they would be ready for when the bearings needed boring.
The casting was then upended and the flange that holds the cylinder faced, bored and the fixing holes drilled to the correct PCD using the DRO to work out the locations.

Due to the way the base pattern is split the fuel feed boss needs to be machined round . I free handed it with a ½” slot drill that had had the corners rounded off so it left a “cast” fillet at the base of the boss. As a guide to the freehand cutting the bit of hex stock is screwed into the pipe thread and an ali ring left loose on the shank, as the edge of the mill touches the ali it starts to turn, that’s when you stop feeding in the cutter and move a little further round the boss.
The mould halves were also a bit out of line so the casting was shimmed slightly off true and the end milled flat, the effect of the shim is to maintain the draught angle. The surface will be textured a bit later so it looks cast.

The last major item for now on the base is to bore the two bearing housings so the bearing caps were fixed on with socket screws for now and the casting set on its side. The centre point was then picked out and the majority of the waste drilled out before changing to a boring head to take it out to 0.812 ready to accept the bearings.

And here it is with a few other surfaces faced to size, holes added and you can just see the two little pins in the bottom of the bearing housings that stop the bearings rotating.

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The bearings were finished off with some brass covers to the oil boxes with springs & screws to keep them in place

That will do for now, next I will deal with the crankshaft.

Jason

 

[b.lindsey]

Nice start Jason. Should make a beautiful engine too....will look forward to following along.

Bill

 

[vcutajar]

I will be following your build also. 55lbs, that is heavy.

Vince

 

[lazylathe]

You must have a motto "No rest for the wicked" hung up in your workshop!

Another great start to a great looking engine!
Will be tagging along for this journey!!

Andrew

 

[Don1966]

Jason I would follow any of your builds, your work is superb. You are already off to a good start keep all of those photos coming.

Don

 

[Blogwitch]

Very nice start to an interesting project Jason.

It is refreshing to see easy to read text and large pictures together.

Nice one


John

 

[deverett]

Jason

You know I will be watching avidly!

Dave
The Emerald Isle

 

[cfellows]

Looks like a fun build, Jason. I'll be following along.

Chuck

 

[rhitee93]

I have my pencil and notepad ready...

 

[SBWHART]

An interesting engine Jason look forward to folllowing your thread

Stew

 

[Jasonb]

Thanks for all the encouraging comments so far.

Don, there are plenty of photos to come (about 60 at the moment) it’s the words to go with them that take a while.

John Bogs, English was never my best subject so easy writing equals easy to read and we can all understand pictures

So back to the build. As this is a good size engine with a capacity at 79cc or 4.8cu.in it will have quite a kick when it “hits” so rather than a built up crank shaft I opted for cutting from solid.

A length of 1”x2” Flat bar was squared up on the ends to give a length of 10 ¾”. This was then blued and some basic layout done to make sure that I knew which bits where waste and what had to remain.

Next the blank was clamped vertically to an angle plate and an edge finder used to locate the mill over the end, The DRO was then used to position the three centres needed and also a hole to be tapped to take a stud to drive the crank in the lathe, this was repeated on the other end.

The waste was then removed by stitch drilling. I used a ¼” split point stub drill as they don’t need a centre or spot drill to start when doing this sort of work as I left a 1/16” clearance to the line and also being shorter they don’t wander into the previous hole. I just used the hand wheel scale to give me 0.25” steps as its quicker than the DRO which I tend to have set up to more decimal places.

While drilling it was actually possible to see the two ends of the crank starting to curl away from me as the tensions within the cold rolled steel were released and the stitching opened up, I had made allowance for this. It was then just a case of 4 short saw cuts where the drill had been kept clear of the vice jaws and the waste fell out.

With the burrs removed the crank went back into the mill and the webs were milled to thickness and a bit of excess removed from their length.

It was then over to the lathe were the first job was to round the ends of the webs. Rather than go straight in and start the pin I took a few roughing cuts of the shafts to get rid of some excess metal so things would not be quite so out of balance when the pin was turned enabling a higher speed to be used.

Here the pin has been finished and the inside edges of the webs machined to width. This was done with a combination of parting tool and left & right hand indexible bits. For the last couple of cuts I changed from a 0.4mm corner radius on the tip to 0.8mm, this helps eliminate stress raisers in the corners.

The next shot shows one end completed, note the bit of ali under the dog screw to save marking the finished surface. The other end has had the drive lug cut off and is about to be machined. You will also see that a disc of steel was machined to a snug fit between the webs, cross drilled to take a retaining zip tie and a bit of hot glue to make sure it did not move about. This allows the tailstock centre to be brought up tight without the risk of deforming the crank.

And this is the finished item save for a bit of clean up to remove the tool marks on the web sides

That’s enough for now, quite a bit for one part so I will leave you with a few shots of the state of play so far.

Jason

 

[mh121]

Excellent work as usual Jason, I will be following this build as I have looked at this kit myself.

Cheers,
MartinH

 

[smfr]

Great looking crankshaft. What kind of tool did you use for the center journal and the insides of the throws?

 

[ZAPJACK]

Nice job on the crankshaft :bow: :bow:
LeZap

 

[Jasonb]

For the throws I have a tool similar to this but it's double sides so I can flip it over to get the other hand, I've not seen them for sale anywhere I got mine at a show from JB cutting tools (no relation). I don't much care for this shape of insert and mostly use CCMT ones but the more pointed one is a thicker shank to the rest I have so it was more rigid with the long overhang

For the actual journal I got most of it out with the tool above and then the final 10thou was done by going back and forth with a parting tool like this taking 0.001 cuts and feeding in while traversing.

 

[moconnor]

Hello Jason,

Thanks so much for sharing your work with us. I look forward to each one of your posts because I learn something about modelmaking every time. Your efforts of documenting your work are greatly appreciated.

I am curious about how the crankshaft is located between the main bearings though. Not just on your engine, but on several model hit-n-miss engines that I have seen so far, there are flanged bearings that look similar to what you see in an automotive engine to control thrust and crankshaft end play. But, the main journals have no 'thrust surfaces' - like a thrust bearing journal on an automotive crankshaft, instead the journals have these short shoulders like the design of your engine does. I just wonder why they don't use a taller shoulder on the crankshaft to match the height of the flanged bearing? Does the crankshaft just 'float' between the main journals? I suppose that if everything is straight and all the forces are at right angles to the axis of the crankshaft, it should just float between the bearings. Of course, a hit-n-miss engine like this has a single cylinder and wouldn't have the axial thrust from a clutch like an auto engine may have. But, why not have a taller shoulder to match the flanged bearing? Any thoughts? How much end play does the drawing call out on the assembled engine?

Come to think of it, many steam engine models are similar- like most (all?) in the Stuart line. If you had a marine application, the propeller shaft would certainly apply an axial force that could use the extra oil film that a taller shoulder on the crankshaft would provide. Although, I imagine that a substantial thrust bearing would be used on the propeller shaft before it is coupled to the engine.

Thanks again Jason. I will be following your build 'with notebook at the ready' like many others here.

Kind regards,
Mike

 

[Jasonb]

There is actually a bit more to come off the diameter of those flanges they are still the stock size but they will end up about twice the width of the 1/16" shoulder on the crankshaft.

There is no endplay specified just a note to say machine the thickness of the flanges to centre the crank in the engine, there is quite a bit of sideways play available on the little end/inside of piston so any misalignment will be lost there.

The sideways movement of the crank is also stopped by the flywheels which bear against the other end of the bearings as they are a fraction longer than the bearing housings so once its all together there will be maybe 0.001" of float, just enough for a smooth rotating crank.

I suppose this type of location is fine as most of these engines and stationary steam engines had little or no end loads so there is no need for a large thrust surface.

J

 

[Don1966]

Jason thank you for those excellent photos, i have never done a crank and you have inspired me to do so, just to see if I can do it. Your documentation to detail is the greatest. Keep um coming.

Don

 

[moconnor]

Hello Jason,

Thanks for answering my numerous questions, I appreciate it. Looking forward to your progress on this engine with keen interest.

Kind regards,
Mike

 

[Jasonb]

Staying with this end of the engine the next piece to be tackled was the splash guard , this is an alloy casting and needed very little machining, just the bolting flange and a couple of bolt holes plus a hole for a drip feed oiler. It did need quite a bit of hand work to remove the casting part line but I’m happy with how it looks now.

And here it is in position, it’s only held by the two bolts at the cylinder end and just notches over the base casting at the other so I have to resist the temptation to pick the engine up by this part.

With the crank complete I could start to make the parts that fit onto it and bore them to the correct fit. First up was the pulley. I did not use the bronze casting supplied as the pulley face will be left as bare metal so CI will look right. Also did the brass spacer ring and here they are along with one of the supplied timing gears.

Next up were the flywheels, luckily these have a substantial boss either side of the hub so I was able to hold by that carefully while the opposite side was cleaned up, the flywheel was then held by the cleaned up boss in the 3 jaw with centre support which allowed the face and both sides of the rim to be machined all in one setting along with the bore so no risk of eccentricity. The final job was to recess the faces and remove the unwanted boss on one side of each as the same casting is used but the wheels are handed.

I still have to cut the keyways and fit dummy bolts as the cast in ones were quite poor, pic to follow.

The engine was originally supplied with either an ugly looking cast silencer (muffler) or a cylindrical steel one. The model is supplied with the cast one in alloy or drawings to fabricate the steel item which is what I opted for.

Luckily a quick rummage found some suitable dia steel tube so that was faced to length and the required number of holes drilled. I did not have a lot of 2.5” dia steel in stock for the end plates so used ¼” plate, here you can see the tubes and the initial machining of the plates before they were rounded off.

To cut the 3/8” pipe thread on the nipple I opted for my set of pipe dies and ratchet stock as this gives plenty of leverage.

This is the finished item, the curved socket was silver soldered into the end plate and the malleable iron elbow was bought in.

J