How to reassemble edge trimmers?

I have several pairs of lawn edge trimmers. I have sharpened them and re assembled them but they never seem to cut properly. I mentioned this to a local "repairman" who gave me a wink and said there is a knack to re assembling them so that they cut properly does anyone know what it is. It is not a case of just putting them back together and tightening the bolt, the edges never seem to be close enough together.I have tried the gentle persuasion of a hammer to flatten the blades but still no use.