I must have a very short attention span because when I am undertaking a longer project, I seem to frequently take time out to make something that doesn't take too much effort. For my latest quickie, I have chosen a design from 1928.
I take my hats off to model engineers of yesteryear - not only did they not have the range of machinery that we enjoy these days, but their drawings left a lot to be desired. This is the one and only drawing for the engine now being built:
Where are the dimensions? Only by reading carefully through the narrative can a few important dimensions be found. Still a lot of personal interpretation required. The authors must have assumed model engineers of the day would have loads of experience, probably because the vast majority came from some sort of engineering background.
So, to start cutting metal. When this design was current, steel was the metal of choice for structural parts, so I followed suit. The drawing suggested 1/16 plate, which seemed rather flimsy. I used 3/32 because I had two suitable pieces. After getting them squared up, the required holes were drilled in both plates. The crank bearing hole was drilled separately. Note how I angled the parallels so that the drill missed them when drilling the holes near the edge.
The frame sides are slanted, and as my hacksawing skills are none too good, I used a sawing guide consisting of a couple of pieces of HSS clamped to the frame plates.
One piece of HSS in the vice, the 2 plates (which had been super-glued together) and then the second piece. One clamp lined up the 2 guides and 2 more clamps held everything together. The mk.1 eyeball played an important part in getting things lined up.
When secure, the assembly was upended in the vice for sawing the first side.
First saw cut
When the second saw cut had been completed, the two plate sides were filed up. They were then mounted on the rotary table to machine the curved top. For flat or odd shaped jobs on the RT, I have a square plate with strategic tapped holes for clamping that takes the place of the chuck.
As an aside, I bought the swan-neck clamps some years ago, but this is one of the few times that they have ever been used. Traditional flat clamps are a lot easier to use, but I was determined to make them earn their keep here.
The completed frame plates
Next were the crank bearing and lock nut. A couple of left-over bits of brass were turned to a press fit at either end of the bearing housing and the nut was a thin slice from some hex bar.
The two frames were separated by warming them to destroy the glue bond. And then the crank bearing was tried for fit in the frame.
The engine frames are held together by tie rods threaded at each end and the model is held to the base by bolts passing through the centre of the tie rods. The tie rods were held in a collet, turned and threaded. A length stop in the mandrel ensured both parts came out to an acceptably accurate length between shoulders and thread length.
To drill the cross holes, I held the tie rods in the vice and used a small slot drill to create a flat for the drill to start and a land for the hold down screw heads. The vice length stop was used to help counteract any sideways force from the slot drill, there not being much metal within the jaws.
The tie rods
The top of the frames are bridged by the trunnion rod, which is shouldered so that it doesn't slide sideways through the frames. This is a more secure way than the original which relied upon the external fittings only to locate it. One end was threaded for the steam(air) fitting, the other end was left plain for the reversing lever.
Now time for a trial assembly
Dave
The Emerald Isle
I take my hats off to model engineers of yesteryear - not only did they not have the range of machinery that we enjoy these days, but their drawings left a lot to be desired. This is the one and only drawing for the engine now being built:
Where are the dimensions? Only by reading carefully through the narrative can a few important dimensions be found. Still a lot of personal interpretation required. The authors must have assumed model engineers of the day would have loads of experience, probably because the vast majority came from some sort of engineering background.
So, to start cutting metal. When this design was current, steel was the metal of choice for structural parts, so I followed suit. The drawing suggested 1/16 plate, which seemed rather flimsy. I used 3/32 because I had two suitable pieces. After getting them squared up, the required holes were drilled in both plates. The crank bearing hole was drilled separately. Note how I angled the parallels so that the drill missed them when drilling the holes near the edge.
The frame sides are slanted, and as my hacksawing skills are none too good, I used a sawing guide consisting of a couple of pieces of HSS clamped to the frame plates.
One piece of HSS in the vice, the 2 plates (which had been super-glued together) and then the second piece. One clamp lined up the 2 guides and 2 more clamps held everything together. The mk.1 eyeball played an important part in getting things lined up.
When secure, the assembly was upended in the vice for sawing the first side.
First saw cut
When the second saw cut had been completed, the two plate sides were filed up. They were then mounted on the rotary table to machine the curved top. For flat or odd shaped jobs on the RT, I have a square plate with strategic tapped holes for clamping that takes the place of the chuck.
As an aside, I bought the swan-neck clamps some years ago, but this is one of the few times that they have ever been used. Traditional flat clamps are a lot easier to use, but I was determined to make them earn their keep here.
The completed frame plates
Next were the crank bearing and lock nut. A couple of left-over bits of brass were turned to a press fit at either end of the bearing housing and the nut was a thin slice from some hex bar.
The two frames were separated by warming them to destroy the glue bond. And then the crank bearing was tried for fit in the frame.
The engine frames are held together by tie rods threaded at each end and the model is held to the base by bolts passing through the centre of the tie rods. The tie rods were held in a collet, turned and threaded. A length stop in the mandrel ensured both parts came out to an acceptably accurate length between shoulders and thread length.
To drill the cross holes, I held the tie rods in the vice and used a small slot drill to create a flat for the drill to start and a land for the hold down screw heads. The vice length stop was used to help counteract any sideways force from the slot drill, there not being much metal within the jaws.
The tie rods
The top of the frames are bridged by the trunnion rod, which is shouldered so that it doesn't slide sideways through the frames. This is a more secure way than the original which relied upon the external fittings only to locate it. One end was threaded for the steam(air) fitting, the other end was left plain for the reversing lever.
Now time for a trial assembly
Dave
The Emerald Isle
