Just takes a couple swipes and a few seconds, as long as you keep the same angle and keep it sharp. You wouldn't think just cutting cardboard would dull a razor blade quickly, but it does.
Phil
Have to agree with this, I use a lot of razor blades to install carpets and I'll sharpen them.
God bless Texas----------------------- Old 300 I will remain what i am until the day I die- A HUNTER......Sitting Bull Its not how you pick the booger.. but where you put it !! Roger V Hunter