I have a fool proof method, it has to be for this fool to use it. I cut the end of the axle just slightly longer that needed for the wheel. I then punch an axle size hole in a small square of 1/64" plywood and slip it over the axle. Place the proper size washer in place and solder. Remove the plywood and you automatically have 1/64 clearance for the wheel to rotate freely. If the washer is soldered properly and the axle not too long it will appear to be a small hub cap. Never lost a wheel yet and I started with ignition free flight in the 30's.