Julian Roberts wrote:I have to make a pair of joggled B switches with full height blades as in the straightcut blades pictures earlier on this thread. I can file the blades to a minimum sensible thickness of about 0.2mm. 3/8" blades scale out at 0.125mm.
Hi Julian,
You should be able to file them thinner than that at the top of the tip -- 3/8" scales to 5 thou.
The diagram you posted shows only the rail top view, or more specifically the horizontal section at the gauging line, which is 9/16" below the rail top to allow for the 1/2" corner radius on the rail. The blade tip is left much thicker below that.
Here is the view on the model rail tip (for vertical rail - if you are using inclined rail the dimensions remain the same):
The top corner radius is 1/2", so filing the rail to 3/8" thickness would initially require 75% of that radius at full height. After fitting the blade against the stock rail and fettling the rounded end, you will more likely end up with something along the green line, at 2" back from the tip.
Here's the green line in a photo:
Model rail section often has an incorrect top corner profile, so it's difficult to get prototype accuracy in 4mm/ft scale. In practice you clamp the blade to the stock rail, and then attack it with fine files and abrasive paper until you can run your finger along it without leaving any trace of blood.
cheers,
Martin.