Part 3 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. A double sized version can be found here. Drawings can be downloaded for personal use only.

This one is built to Julius’ metric drawings.

I made both rocker shafts (item 35) from 12mm silver steel.  I also made some spacers that go on the rocker shaft. These are items 36 (2 off), item 50 and item 51.  Wanted to make them from 303 stainless but could not get a short piece.  Was offered 304 or 316 instead and made them from 316.

Ed: at this point Vince Vince started working in England for some months. Away from his workshop he decided to get to grips with CAD (Fusion 360). This was his first attempt at CAD!

Wanted to do something easy on return so I chose items 40 and 41 which are the rocker shaft arm centre spacers.  I would have liked to do them with 303 stainless but my usual supplier refused to cut me a piece but he was able to cut me a piece from 316.

Machined to length and drilled and reamed a 12mm hole.

Next I needed to drill two 3mm through holes in each spacer.  That's where the problem started.  I am not looking forward to drilling the 3mm through holes especially in the longer spacer which is 46.5mm long.  I am afraid that the holes might wander.  So I drilled both spacers half way through.  Then I put one in the vice, inserted two 3mm pins and a 12mm shaft.
Flipped the other spacer and put it on the other spacer and using the DRO just marked the position of the holes.
A little clean up and I can say that these two spacers are finished.
Started work on the vibrating arms in aluminium instead of BMS.  I found a piece of aluminium which might be enough for both of them.  As I was not very sure, I printed two copies just to check it out.
They fit just right.  So I squared it out and brought the thickness down to 12mm by flycutting.  Applied some blue and marked the arms out.  Drilled and reamed all the holes.
Milled out some slots.
Milled the round ends on the rotary table.
And reduced the size of the arms in the middle part.
Here they are nearly finished.
Cleaned up the vibrating arms and made two brass bushes for the small end.
Pressed them in using the vice and fitted them on the rocker shaft to see how they fit.
Working on item 37, the Piston Rocker Arms,  I used exactly the same method I used for the Vibrating Arms. The only thing different is milling out the required slot. On the plans it calls for the length of the slot to be 19mm but I decided to do it 17mm instead.  And this is where I made a boo-boo. I was milling the slot in the second arm when I got distracted and over-enthusiatic with the X-axis handwheel.  I overshot the 17mm line.  I thought I was going to scrap it but after some measurements it was nearly 19mm.  So I decided to leave it at 19mm.

Piston Rocker Arms are finished.

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