Some time ago I was faced with this problem.
The solution I derived came in the following form.
1. Utilising cut up cereal boxes I found one whose sides were aproximately 1mm thick.
2. I carefully cut 1mm sized sand paper strips.
3. Then using ELMERS ALL PURPOSE GLUE glued it to the bottom edge of the cardboard.
4. Utilise a toolthpick or a needle to apply the glue.
5. Make sure that you utilize the bottom straight edge of the cardboard you cut as the tool.
6. Once the 1mm sandpaper strip backing is coted with the glue use both your thumb and index finger to align the strip evenly to the bottom straight edge of the cardboard.
7. Tap the surface thus making it flat and allow to dry.
You will find that the sandpaper will wear out quite fast don't worry thier easily replaceable just pull the worn out strip off. So cut sufficient replacement strips of what you think you might need.
WORKS LIKE A CHARM!
ho henry
Welcome aboard, Henry and thanks for the tip.
Frederic
Thanks Always glad to share,. Happy to be aboard. I've come accross some fantastic ideas at this forum.
henry