I usually solder a washer on inside of wheel rather than use a wheel collar, so just solder one on outside also. Cut axle off flush and you have a neat setup. Use one of those aluminum wheel collars, that do not work well, slide it on axle for a guide to keep the washer square with axle, solder will not stick to aluminum. Also use a thick paper shim (file folder material) between the washer and wheel for spacing.