Photos?

I'm not sure what you mean... you have some photos?

How tight a curve??

HI foalma, 

How tight a curve are you trying to wrap these coaches around and what length passenger cars are these bogies under? 

If the wheels are all in gauge and the flanges are in a line parallel with the bogie sideframe, then unless you are running very tight radii (probably well under 15"), then I think your problems may be elsewhere, like couplers binding in their pockets or the swing of the bogies under the coach being restricted by under-car mouldings etc.

A HO scale six-wheel bogie by itself would probably go below 6" radius before lack of sideways flexibility in the middle axle would cause flange-binding and derailment problems. Look for what is pushing your coach sideways on the curve. I doubt that it is the centre axle. 

Another test is to simply remove the centre axle from each bogie and to see if your passenger cars still derail. I'm betting that they might still derail and your problem might not be the centre axles.

The trucks don't swing enough

The trucks don't swing enough to use these cars on less than 24 inch radius.  Underframe details and coupler boxes-draft gear arrangements limit the truck swing.  The track also needs to be in good line and level, as these cars will find any issues.  Fine-tuning the track and the cars is required.  Sometimes the trucks are not level and square.  Loosening up the screws that hold the trucks together, making adjustments and putting it back together can help.  The metal tabs that conduct power into the car can also be misaligned.

You could take out the middle axle, but I doubt that will help the situation. 

Use an axle reamer

Axle reamer - a little tough due to metal sideframes

That is possible, but these sideframes are metal, so the axle reamer (which works great on plastic trucks) might be much use here.  I suppose you could replace the wheelsets with somthing like - if i recall - 36" Proto2k wheelsets, which have plastic axles.  Those might be easier to adjust and roll better in the metal sideframes.

Walthers Passenger truck tuneup

Check out this post,

http://model-railroad-hobbyist.com/node/25167

Almost all my past problems with Walther's HW tracking properly were solved.

John Lockwood

Obstructions under the car

If you are going to run Walthers 6 axle heavyweight passenger cars on tight radiuses you will need to do a little trimming on the trucks and the center sill. The bottom (top when car is upside down) flange on the center sill can notched back to the verticle section. This notch only needs to be as long as the wheel is wide. The Walthers trucks usually curve in on the ends. The curved section can be filed back so they can turn a bit further before hitting the center sill.