Testing the wheels with their connecting rods.

After turning the wheels and axles, making the hornblocks, axle boxes, and coupling rods, there are now enough parts to assemble and test. See the video at the end of this page. 

First, the axles were glued to the left wheels 

In SolidWorks, a measurement was taken of the height of the crank pin to the top of the milling table, where the wheels are positioned in the T-slot. A support bar was then made on which the crank pins can rest while the axle and wheels are in the table's groove. The height of these support bars ensures that the cranks are set at 90 degrees.

There is about a minute before the Loctite 648 glue begins to cure. This is enough time to check that the wheels and axle are aligned in the T-slot groove, and both crank pins are resting on the top of these support brass rods.

Leave it for a few hours, before the next set of wheels is glued. 

The crank pins are straightforward, but the right side have a right-handed screw thread, and the left side have a left-handed thread.

On the rear axle, a small eccentric is needed to drive the mechanical lubricator

A simple straightforward turning job. Drilling and reaming was done in the milling machine. 

With this centre locator, a line can be scribed on the excenter. Knowing the diameter of the hole (16mm), a piece of 8 mm rod is used to position the excenter so the middle can be marked. 

This line is needed to align the drill and tap for making an M4 threaded hole for the grub screw.

Tapping, done by hand.

The planned position for the mechanical lubricator under the footplate.

All wheels are glued to their axles. 

The day after, the motion could be assembled and tested. The 0.02 mm play on the bearing bushes made it hard to assemble, and the motion was too stiff. Although it was possible to rotate the wheels without binding, it wasn't smooth. If left like that, running on an uneven track would be difficult. So, the play was increased to 0.05 mm with a hand reamer.

Now everything is moving fine. 

The locknuts for the crank pins, with the dummy cotter pins.  

This is also the first test of my specially made rolling road. After years of testing my locomotives by simply putting them on wooden blocks, I decided to make a rolling road. My son has one for his 5" gauge 'City of Truro' class loco, which he used to demonstrate the loco under its own steam at an exhibition.

The City of Truro demonstrated at the Oisterwijk op Stoom event, last September.

Klick here to see photos of this event

The drawing has been updated. With the aid of photos and a small sketch, I finally got the height of the tender correct. It's only 7.5 mm higher, but it makes a difference and looks more like the historic black-and-white photographs of the real loco. 

Connecting rods

 The connecting rods connect the three axles, so the steam engine's power is evenly distributed on the track. They are made from cold-drawn mild steel and are fully machined. They were usually forged for full-scale locos, before being milled to shape and having a ground finish. 

There were two versions of these rods. With and without flutes  (the recess in the middle, to reduce weight). The locomotive I'm building, no 5361, will have the non-fluted (plain) connecting rods.

With the band saw the bar is cut to length. 

Because the steel was cold-drawn, they were annealed. This relieves the tension of the steel, so it stays reasonably straight after machining.

The middle part of the rods is cut away with the shaping machine. 

The pre-machining is done.

The bearing holes are drilled and reamed in the milling machine. 

Then I wanted to use the CNC-milling machine for the outer contour of the rods, but the machine showed a fault. The Y-axis was not moving constantly and didn't get to the home-position.

It turned out that one of the flexible couplings between the motor and ball screw axle was broken. 

No new one could be bought easily on a Sunday, so a new one had to be made. 

With some quick measurements, a sketch was made and a new part could be turned and milled.

And ready to continue the work on the connection rods.

The outer contour was programmed directly from the SolidWorks drawing. The CAM software calculates the toolpath using the DXF file.

It is a small milling machine, so light cuts have to be taken. Although it takes some time to mill the rods, the result is good and much faster than sawing, chain-drilling, and filing by hand, as I used to do when making these kinds of rods for the 3½" 'Mona' locomotive in the '80s.

The recess for the coupling pin between the rear and front rods is milled in the conventional milling machine. 

For this machine, I have many more tool holders and different cutters. The slitting cutter was used for the 4 mm groove.

The sides were cut with a 16 mm endmill.

With files and sandpaper the rods were worked, so that no machine marks were visible. 

This was done with almost rods on British locomotives. Appearance was even in the days of steam important.  

A quick test fitting and check.

Bearing bushes turned from bronze. 

The oil holes were centred on the milling machine.

They are press-fit size (+0.02mm)....

....and pressed home in the vice. 

Small top nuts are turned and the hexagonal shape is cut with a dividing head. 

Almost finished. 

A small bearing bush is also fitted between the two rods.

This knuckle joint needed, so the sprung axles can move up and down in their hornblocks, without binding the motion. 

The connecting pin has a simple screw to hold in place.

The retaining or locking pin is only a dummy one. This would be impracticable for a working live steam model. Disassembling or assembling would become a tiresome job. Especially when this is needed to be done at a steam event at a model engineering society. 😐