Finally, an update to the blog. The first months of the school year are very busy and sometimes hectic, so there isn't much time for model engineering.
So after the hornblocks (see previous post), the axle boxes were the next things to make. These are the so-called split-type boxes
A simple, standard design of the axle box. Coiled springs will be used to suspend the locomotive. These are easier to adjust and set once the loco is finished and has a full boiler and fire, standing on the rails.
A hefty and expensive bar of bronze was sawed in disks of 16 mm
he round stock material is then milled into a square shape. Although a lot of material is reduced to chips, this method is still more cost-effective than importing castings from the UK.
The side slots were milled to depth and with.
The opening is cut away, and constant measurements ensure that the gap is precisely in the middle of the block.
The bottom piece is milled from the brass bar, achieving a very close fit (0.01 mm) in the axle box.
In the milling machine, the holes were drilled for the keeping pins. Two 3 mm steel pins hold the bottom part in the axle box.
A test fitting in the hornblocks. This is a sliding fit (0.05mm). If this is too tight, the motion of the loco will lock up, when the loco drives over an uneven track or points. Each axle is sprung independently and can move up/down 3 mm.
Clamped between to bars, the middle of the block can be located with an edge-finder and a centre hole is drilled.
With this center hole, the axle box can be set up in the 4-jaw chuck
Using the dial indicator and the ground center, the axle box is clamped and precisely positioned, ready for boring. A wobbler could also be used, but I don't have one. This method works nicely.
After drilling a pilot hole, the axle hole is turned to dimension. An H7 fit (16.00 - 16.02 mm) was used.
In the bottom part of the axle box, holes are drilled and tapped for the spring hanger pins.
A small oil cavity is milled on top...
... and one on the bottom. A small piece of felt will be inserted into these holes. This will keep dirt out of the top oil hole and ensure the bottom part keeps the axle lubricated during the run.
