Hi Guys,
The next job is the axle boxes. These are machined from cast iron.
This lump of cast came with the loco. Its enough for all four boxes.
The design above calls for solid axle boxes. The trouble with this is that once the wheels are glued onto the axles the boxes can only be removed by first removing the wheels. The design is solid as these are easier to machine. Because I am modifying the Hackworth motion I need to redesign the boxes on the rear axle so I decided it would be easier to make them into split boxes.
First job was to square and size the block of cast ready for machining. I have a CNC mill so used this as there would be a large amount of handle turning on the manual mill. The CNC system acts as a power drive in all directions in manual mode.
All four faces were cleaned up, squared and sized. I took it down to 45mm by about 26mm.
I marked one of the larger faces that will stay against the fixed jaw on the vice. This face will also be the outer face on the completed axle boxes.
First move is to mill the channels on the sides so they fit the horn blocks. I milled along the middle of the first side and took several cuts to go 4mm deep. Once this was done I left the depth alone and using the other two axis's widened the channel until it was 18.5mm wide and the lip on the front against the fixed jaw was 3mm wide.
This needs to be the same on both front lips so the boxes sit level in the horns and all stick out the same distance from the frames. I then turned the block over in the vice keeping the same face against the fixed jaw. I repeated the previous operations to machine the channel on this side to match the first side. The only difference was when the depth neared 4mm I measured the land between the channels until it matched the openings on the horn blocks. This was 36.5mm.
With both sides identical it was time to cut them up. Had I been using solid axle boxes this would have been three cuts but because I am making split boxes each box needs to be cut in half. To allow for a little more cleaning up of the cuts I had to make them slightly shorter.
One at a time I sliced of 20mm lengths in my bandsaw. I have adjusted the blade so it gives an almost 90 degree cut. It is within a half degree so good enough. As I sliced them I labelled the sections so the cuts match each other. They will now stay in these pairs throughout machining for accuracy.
Along one edge of the face that was against the fixed jaw I have scribed a line along the length of the bar to give a common edge for all the boxes. This will be the front edge of every box and will be the common edge for many measurements from now on.
Here are all four boxes ready for drilling which will be the first job next time.
I had planned to install needle roller bearings in the axle boxes but they were a bit too wide to fit comfortably in the boxes and like solid boxes could not easily be removed from the axles if necessary. They would also have increased the size of the axle from 17mm to 20mm diameter. In the boxes for the rear axle I need to add four M5 tapped holes to the inside faces so this would have been virtually impossible with the 26mm diameter of the bearings. This is an easy compromise as a steel axle running in a cast iron box should wear very well.
Cheers
Julian