< Expansion Link Brackets >
The photo shows parts for 'inside slide bar support' which also hold the expansion link brackets. The actual component is a complicated single casting. So as to cast easier, I divided it into two of castings and three of laser-cut plates.
I started with the center dome casting. After cutting front and back face parallel, the casting is reversed and chucked in machine vise. And then both bolting faces (side faces) are milled to a width between the main frames.
Bolting face for the inside slide bar was cut. The face is at the ceiling of the dome and tilt at 7.5 degree. Note the angle plate is tilt at the degree and hold the casting.
When opening holes for wheel spring hanger pins, a problem occurred. Due to 'chill' of the casting, surface hardness is ununiform around the hole. As a result, the drill tip slipped and the hole is opened in oval shape. And the position was far deviated from the punch mark. It is serious problem because I will use a lot of cast irons with thin profile.
I obtained a tiny electric furnace in an auction. Furnace size is 175x120mm. Heater power is 700W. It is useful in many ways but my purpose is just annealing cast irons so as to remove 'chill'. Chilled iron can be annealed by heating over 900 centigrade and cooling slowly. Heating is easily done with propane gas torch, but cooling slowly is difficult. Electric furnace can 'cool' the job in a desired speed.
Immediately the above casting was annealed. The job was heated to 950 C in an hour, and cooled down to room temperature for one night. I tried to true up the oval hole by boring with an oversize endmill. The casting surface was a little hard but I could smoothly open a clean hole. When assembly, I will reduce the hole diameter with a bush.
The photo shows before and after annealing. The right hand castings are after annealing. Casting surface is deeply oxidized by long time heating. If you wish to avoid oxidization, you must have a professional vacuum furnace.
The next is front plate casting. Back side bolting face and both side edges are milled. Both ends of the casting are shinning after cutting. It is a sign of 'chill'! Unfortunately the casting is too long to anneal by the tiny furnace.
Holes for bolts were opened. To prevent distortion of the hole by chill, I clamped a mild steel bar onto the casting and drilled through. It means the steel bar is employed as a guide hole for drilling.
The expansion link brackets are machined. Front, back, side and bottom faces are milled. Expansion link hole and weighshaft hole are drilled and reamed. All of operations are controlled by X-Y coordinates of the milling stage. There was no sign of chill.
'Inside slide bar support' was assembled between the main frames. And a back side plate for the expansion link bracket was mounted onto the frames with cross shape castings. The distance between front and back plate was determined by the expansion link brackets.
The pair of link brackets was aligned with two round bars through each pair of holes. The bars are maintained in a desired height with suitable packing on the frame. And then front and back bolting area are clamped firmly.
It needs 40 bolts to secure the brackets. The inside 20 are screwed into the brackets without nuts, while the outside 20 are through the hole and secured with nuts. The photo shows drilling the bracket through the front plate.
I divided the weighshaft hole with 0.3mm metal saw. Before that, two screw holes beside the main hole are opened. When assembly, 0.3mm brass sheet is used to pack the 0.3mm thickness shortage.
Expansion link brackets were assembled. The whole job becomes more and more heavy!
In this month, I joined Shigiya miniature railway meet. My William kept on running over six miles in two days. Famous Kozo Hiraoka also joined the meet. He took pictures of William and sent them to me. I introduced two of them in Photo Gallery.