< Steam Chest Cover 1 >
The photo shows castings of steam chest front covesr that have brackets of Gresley conjugated valve gear.
I started from dividing front bush. Before cutting the bush with a fine metal saw, holes for screws are opened.
Two bolting faces are grinded by oil stone, then they are tentatively assembled. Note a top hole for oil pot is already opened but it is enough shallow not to interfere with the next operation.
Both centers are marked by center drill. Front hole is on the parting line, and back hole is at the center of the flange.
I employed proper steel pipe for chucking. First, the casting is aligned in the lathe with bith centers. Care must be taken not to push the tailstock hard, else an elastic distortion makes the center lining wrong.
A steel pipe is chucked and the casting is secured by 6 bolts from the pipe. In advance, tip of each bolt is filed round so as not to damage the casting. The 6 bolts have to be tightened equally. You can check it by a dial gauge sweeping along the tail stock center's cylinder.
Hole of the front bush is drilled and reamed.
Reversing and again lining the casting with the both centers, opposite bottom flange is finished.
Large hole for gland (24mm) is opened. I used 13mm drill, 12mm and 22mm boring tools.
Two screwed holes for oil pots are finished, then the front covers are completed.
Steam chest back covers are also turned with a steel pipe. The casting is designed that the side windows will automatically open when I bore the large hole.
The photo shows cutting the front hole. The purpose is removing useless metal for the next operation.
Small recesses in both sides are milled. Note a large angle plate beside the vise aligns the cover's flange.
Milling vertical slit of the cover. The precise setup is done as follows. 1) scribe cross on flange and angle plate, 2)flange and angle plate are aligned and bolted together, 3) angle plate is bolted onto the stage truly parallel to Y-axis, 4) chuck the casting with vise, 5) vise is bolted onto the stage.
Inner groove for valve cross head is cut with T-slot cutter. Such kind of tool with wide blade and thin neck easily chatters. It is worth rotating the tool by hand at the deep end of the groove.
Opening the oil pot holes, the steam chest back cover is finished.
To tell the truth, I was ready for slotting the groove with a handmade slotter. But I thought the groove is too long to finish parallel with a slotter. So I changed the way to cut the groove with T-slot cutter. The photo shows the useless slotter. 10mm wide blade is formed by 2 of 5mm square carbide tips silver-soldered into 10mm groove of the shank.