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.
