<p>In retrospect, I don't know how I missed it, but here are the details for anyone else wondering:</p>
<ol>
<li><p>Pulling the feeding arm extends the spring. When the arm is pulled all the way back, it's locked.</p>
</li>
<li><p>At this point, rotating the sharpener crank (without a pencil) will release the lock, and cause the arm to spring back all the way in.</p>
</li>
<li><p>But instead we keep the arm locked, and secure a pencil inside. When we rotate the crank, the arm (which now 'carries' the pencil with it) doesn't spring all the way in because the pencil end hits the blade - which is laid out diagonally (thus creating the desired cone shape when rotating). The spring power is used to push the pencil towards the diagonal blade while it's rotating.</p>
</li>
<li><p>A secondary goal of the arm is to keep longer pencils leveled to create a symmetric sharpening.</p>
</li>
</ol>
<p>(Thanks @wolff &amp; @Janus!).</p>

CC BY-SA 4.0
2021-06-01T23:06:39.197Z
Have you tried out what happens if you keep turning the handle? If you did, you could observe that the entire structure in question is to **keep pulling the pencil inwards** as the sharpening process progresses.
Levente
CC BY-SA 4.0
2021-06-01T13:44:00.747Z
2021-06-01T19:06:23.787Z
2021-06-01T19:06:23.787Z
OmerB
<p>Pretty minor - but it puzzles me. All desk pencil sharpeners I've encountered have a spring triggered &quot;feeding arm&quot; (see image where the arm is extended).</p>
<p><a href="https://i.sstatic.net/a0L3K.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/a0L3K.jpg" alt="Extended pencil sharpener" /></a></p>
<p>What's its purpose? I can sharpen a pencil without extending it, and after extending, why do I need the spring mechanism? It never triggers while there's a pencil inside.</p>

CC BY-SA 4.0
2021-05-29T22:09:16.417Z
Keeping the pencil straight obviously, but I didn't even know such a thing existed :)))
Lucian
<pencils><tool-usage>
Desk Pencil Sharpener - what's the purpose of the feeding arm?
OmerB
# Desk Pencil Sharpener - what's the purpose of the feeding arm?

(Asked by: username_0 on 2021-05-29)

Pretty minor - but it puzzles me. All desk pencil sharpeners I've encountered have a spring triggered "feeding arm" (see image where the arm is extended).

[![Extended pencil sharpener](https://i.sstatic.net/a0L3K.jpg)](https://i.sstatic.net/a0L3K.jpg)

What's its purpose? I can sharpen a pencil without extending it, and after extending, why do I need the spring mechanism? It never triggers while there's a pencil inside.

**Tags:** pencils, tool-usage

> **Comments:**
> **username_1**: Keeping the pencil straight obviously, but I didn't even know such a thing existed :)))  

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## 1 answers

### Answer by username_0 on 2021-06-01. Score: 3 | Accepted answer

In retrospect, I don't know how I missed it, but here are the details for anyone else wondering:

1. Pulling the feeding arm extends the spring. When the arm is pulled all the way back, it's locked.
2. At this point, rotating the sharpener crank (without a pencil) will release the lock, and cause the arm to spring back all the way in.
3. But instead we keep the arm locked, and secure a pencil inside. When we rotate the crank, the arm (which now 'carries' the pencil with it) doesn't spring all the way in because the pencil end hits the blade - which is laid out diagonally (thus creating the desired cone shape when rotating). The spring power is used to push the pencil towards the diagonal blade while it's rotating.
4. A secondary goal of the arm is to keep longer pencils leveled to create a symmetric sharpening.

(Thanks @wolff & @Janus!).

> **Comments:**
> **username_2**: Have you tried out what happens if you keep turning the handle? If you did, you could observe that the entire structure in question is to **keep pulling the pencil inwards** as the sharpening process progresses.  

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