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This is a little question that I have been wondering when I need to cut sand paper with scissors.

Sand paper can be used to sharpen knives etc. when applied parallel with the blade surface. Also it can be used to dull sharp edges when applied nonparallel with the blade surface.

My assumption is that it should dull the scissors since paper is being cut using the sharp edge and nonparallel with the abrasive material. But I still have doubts about the validity of the assumption.

How is it?

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  • $\begingroup$ Hi M.L., and welcome to Physics Stack Exchange! I've removed a number of comments that were attempting to answer the question and/or responses to them. Commenters, please keep in mind that comments should be used for suggesting improvements and requesting clarification on the question, not for answering. $\endgroup$
    – David Z
    Jul 22, 2020 at 23:51

3 Answers 3

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Sand paper removes material. When used properly, that removal of material can make a blade sharper. However, when cutting the sandpaper, there is no attempt to structure the removal of the material. It will simply dull the scissors. It will remove material in a relatively haphazard manner, taking off the sharp edge.

If you have any questions of this, ask someone who sews for their nice fabric scissors, and let them know you're going to go cut some paper with them. Find out how quickly they respond in an effort to avoid dulling their scissors. Perhaps its not the most scientific approach, but it is a well documented one, and very evidence based! And that's just normal paper!

Sorry Marvin.  It says right here: Using her fabric scissors for cutting paper IS grounds for divorce.

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    $\begingroup$ Note that it's the angle of the blade that causes the sharpening or dulling. Scissors tend to be perpendicular to the object you're cutting, whereas a knife on a whetstone is at an angle (ideally 15° I believe). If you hold a knife perpendicular to a whetstone it will also dull. I'm genuinely interested what would happen if you hold your scissors at an angle as well. My suspicion is that it may in fact sharpen the blades (assuming sandpaper is appropriate material to sharpen scissor blades, which the question presupposes) $\endgroup$
    – Flater
    Jul 22, 2020 at 14:28
  • $\begingroup$ @Flater Excelent points! As to sharpening with sandpaper, it should indeed do so. However, for a good cutting edge, one also wants a smooth edge. Most sandpapers are too coarse of grit to form a smooth edge. However, the 6000 grit automotive sandpaper I have in my garage would probably do nicely. One would probably want to glue it to a hard back to ensure that angle is maintained. $\endgroup$
    – Cort Ammon
    Jul 22, 2020 at 16:23
  • $\begingroup$ This will also become clear if you use a razor or exacto knife to cut sandpaper or skateboard grip tape (which is essentially sandpaper with adhesive on the back). The grit aggressively dull the blade in no time $\endgroup$
    – Kevin
    Jul 22, 2020 at 18:00
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    $\begingroup$ Be very cautious when attempting the recommended experiment. You may find, through personal experience, that their extremely sharp fabric scissors make an excellent dagger, and that they are unafraid of using it. :) $\endgroup$ Jul 22, 2020 at 18:40
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Duller

Scissors are sharpened by honing the narrow "chisel" edges, not the broad flat edges where the two blades sandwich together. Here's an image of someone sharpening tiny scissors with an even tinier file:

sharpening scissors

So, cutting sandpaper will abrade the point between the chisel edge and flat edge.

*You can use the sandpaper to re-sharpen the scissors afterwards, if it makes you feel better!

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The answer given by Duller is halfway correct.When the blade is very blunt , the point of contact is flattened or shapeless. When you cut sandpaper , it being abrasive itself it abrades the blunt edge at the cutting point , this making the scissors sharper than before. The finer the sandpaper the better the sharpening. However this is not meant for light or sharp scissors. It is only meant for scissors which have started bending the cutting material.

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