Cilinder covers, slide bars and crossheads

 The crosshead and slide bar are straightforward jobs on the milling machine and shaper. Only some care is needed to work to close tolerances, so they have a nice sliding fit.

The cylinder covers are turned from brass bar. This is fine, although bronze would be better of course. The glands, however, will be made of bronze.

My small roller‑bearing tool is very useful for ‘straightening’ the thin disk in the chuck before turning the other side. With the chuck running slowly, the bearing is pressed against the cylinder cover, pushing the part back into the jaws until it runs true. After that, the chuck can be tightened securely.

Machining the rear cover on the rotary table to ensure accurate bolt‑circle spacing and a perfectly concentric profile.

Tapping M3 for the slide bars. 

A small recess was machined on the back side to provide wide access to the steam ports, ensuring an unrestricted steam flow.

The slide bars are made from 5 mm thick cold‑drawn steel. Only the width has to be reduced to 14 mm. With a tolerance of −0.02 mm, measurements with the micrometer are essential, before taking the final light finishing cut. 

The oil holes are drilled with a 1 mm drill. Their positions are taken from a photo of the original locomotive.

This is the real engine as it appeared in 2005, still in its black livery with red inner frames. The GER version had yellow inner frames.

II wanted to use cast iron for the crosshead, but I didn’t have any suitable material in stock. What I did have was an old brake shoe from a German BR23, bought many years ago at the Hermeskeil Dampflokmuseum.  

It had been lying around ever since, so I decided to cut it up to provide a source of cast iron — recycling it into a new part for  this model steam locomotive.😃

Cast iron slides well on steel, has a low tendency to seize under poor lubrication, and is a fine material to machine. But starting with a brake shoe is quite a job, as the raw casting needs a lot of preparation before any accurate machining can begin.

The shaper was put to use to square up a block from the off‑cut.

To my surprise, I found that a piece of steel had been cast into the iron.

I have no idea why this piece of steel was cast in; perhaps it served as a wear insert or reinforcement, but it’s impossible for me to tell for sure.

Final shaping was done on the milling machine in several steps.

A first test fit on the slide bars went perfectly, with a smooth, even movement along the full travel.

Milling a 6 mm hole for the connecting pin.

The M2 thread was carefully drilled and tapped, taking light pressure to avoid breaking the small tap.

The top cover plate was also made from the same cast iron.

A small lid on top of the oil reservoir was made from steel bar.

With four small rivets (glued in with Loctite), the top cover was secured.

The same locomotive in 2022, restored to its correct GER livery, complete with yellow inner frames.

Cilinder drain cocks

After the cilinders were finished, there are several ways to continue. I opted for making the cilinder and steam chest draincocks.

An underside view in Solidworks of the drain cocks.

The steam chest was drilled and tapped for the drain cock, oil check valve and steam inlet. 

Milling, drilling and reaming the bracket, that will operate the drains. Done in several set-up's on the milling machine. 

Using two stainless‑steel screws, it is mounted to the underside of the steam chest. This design eliminates the need for additional holes in the frame and allows the complete cylinder block assembly, including the drain cocks, to be removed from the frame as a single unit.

The drain‑cock bodies are turned from brass. Copper washers were initially considered, but they conflicted with the available height and were therefore omitted. Teflon tape is sufficient to provide the required sealing.

By first mounting the drain cocks in their respective holes and then determining the hole locations according to their position in the frame, they can all be screwed into blind (dead‑end) holes in the cylinder block. This ensures that their installed height is identical.

Marking them is therefore necessary. I used the following identification: RF (right front), RR (right rear), LF (left front), and LR (left rear). Of course, any other clear marking system would work equally well.

The body is drilled and reamed to 3 H7. A parallel bore is sufficient, and I have successfully used this design on other locomotives. I experienced problems with conical drain cocks: the drain spindle tends to work loose and leak, or the spindle seizes. This parallel version, when made to close tolerances, is steam‑tight and will remain easy to operate over the years, without suffering from these issues.

The spindles are turned from stainless steel. A small rectangular journal is milled on the end; this engages with the operating lever, which has a matching square hole.

The cross‑drilling is carried out in a spare body. By positioning the square section at 45 degrees, the operating lever will align correctly in its working position.

On the cylinder block, a spindle with the cross‑drilled hole is visible. Also shown is a 2 mm brass blank, which will be machined into the operating lever.

Using a small hand press and a square die, the pre‑drilled hole is punched to a square profile.

The punch was first ground square using a tool grinder. It was then finished in the lathe with a diamond cutting blade to form a small cutting edge at the top, where the guide pin is located.

Achieving an exact size is always difficult, so I make the punch first (from a standard punch nipple or silver steel) and use it to punch a test hole. I then measure the size of the hole produced. This measured dimension is used as the target size for machining the square on the stainless‑steel spindle.

The final operation is CNC milling the outer contour to shape.

The spindle is a light press fit in the lever. Care must be taken, as this design uses left‑hand and right‑hand levers. When pressing the lever onto the spindle, this must be taken into account so that all drain cocks open and close with the same movement of the operating mechanism.

Next, the correct length of the main operating rod is determined.

The operating rods were CNC‑milled from 1.5 mm stainless‑steel plate.

The rods are secured for CNC milling by screwing them to a jig; M2.5 screws are sufficient to hold them in place. To avoid distortion, only light cuts are taken at each machining step.

The complete assembly is mounted on the cylinder blocks. The extension on the central operating rod serves as an end stop for the open position of the drain cocks.

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