by Vince Cutajar

The USS Monitor was an ‘ironclad’ steam ship which famously saw service in the Civil War in the early 1860s. The ship's engine was designed by John Ericsson as a "vibrating side-lever engine." He had created similar engines before and decided to use the design again because of its advantage for a small, low-riding warship.

Most steam engines of the time had vertical pistons, which occupied a lot of space and made them vulnerable to enemy fire because they were partially above the waterline. In contrast, the Monitor's 30-ton, 400 horsepower engine had pistons that moved horizontally, which reduced the height of the engine and allowed it to be mounted below the waterline.

Although a successful fighting ship the Monitor was not stable in rough seas due to its formidable rotating turret and sank in the early hours of January 1, 1863.

The engine was recovered from the Monitor's wreck site in 2001. It is now resting upside-down in an alkaline solution to inhibit corrosion. Over the coming years, conservators will continue to clean and separate the many different pieces of the engine to preserve them properly.

The first model Monitor was shown at Harrogate in 2014 by Brian Stephenson to the design of Bob Middleton. It was built without castings, like Bob’s other designs. Julius de Waal has produced these CAD drawings for both metric and imperial (see here) versions. Drawings can be downloaded for personal use only.

This one is built to Julius’ metric drawings.

I like to start a project with something simple which does not have to fit with something else.  Item 4 was a good candidate for this.  It is the outrigger top plate and two are required.  I am using 6mm thick and 50mm wide flat bar for these.  Started by getting the length to size.

Started getting the width down from 50mm to 45mm by milling both sides.
Continued on the two parts by drilling all the holes.
These should have been 4mm holes but I made them 3mm.  I think if I made them 4mm then the bolt heads would have been too close to the edge.  I still need to round off the corners and I also need to countersink one of the holes.  Cleaned up the top and bottom surfaces with sandpaper. I had to  decide which surface is going to be the top surface and then countersink the hole.
I cheated a bit and had the frames laser cut.  Made from 3mm mild steel and cost me 58 Euro.  I could not resist it.  Needed to de-burr it a little and wipe them with an oily rag to protect against rust. All the 4mm holes have been reduced to 3mm on the frames also.

Next was item 3 which is the outrigger base frame.  Two of these are required.  These are 25 x 25mm and I actually found aluminium bar stock of this size, but by the time I would clean up the sides from all the dents and scratches, the finished size would be much smaller.  Next size up that my supplier had was 30 x 30mm! So I had to spend some quality time with the mill bringing it down to size. 

Bringing the length down to 130mm.
Drilled and tapped the 3mm holes in the outrigger base frames and countersunk the hole in the outrigger top plate so that I can fit them together.
Drilled and tapped the 3mm holes in the sides of the outrigger base frames.  This is the setup I used to hold it on the mill table.
The cylinder mounting plates were made using aluminium flat bar 12mm thick and 25mm wide.  Cleaned up all the sides with sandpaper and took a skim cut to the top of the plate to make sure it is flat. Also used this face as the datum for the 3mm tapped holes.
Next up was to make the slots in the outrigger base frame. 
Used 0.5mm DOC per pass using a new carbide cutter. The plans called for a depth of 13mm but I made it 13.5mm to give me some extra sideways adjustment just in case I need it.
Trial fit with the inner frames.
Next the spacers that go between the frames.  These are items 5 and 6.  I would have liked to make them from 8mm stainless steel but did not have that size and so made them from BMS instead.
Fitted in place.
That finishes the infrastructure on the model.

Part one here  Part two Part three  Part four Part five Part six Part seven Part eight Part nine Part 10 Part 11 Part 12 Part 13 Part 14 Part 15 Part 16 Part 17