Giant Pencil Case That Actually Writes - Working 3-Jaw Chuck

Intro

A pencil case shaped like a giant pencil is not a new idea. Making one that actually writes is the part I wanted to solve.

The nose is a working three-jaw chuck. Push an ordinary pencil in point first, turn the wooden cone about three quarters of a turn, and three jaws close on it the way a drill chuck closes on a bit. It grips 6.6 mm to 9.2 mm, which covers hex pencils, round pencils, golf pencils and most colouring pencils. Then you are writing with a 313 mm pencil.

Ten full-length pencils fit inside the barrel. A new unsharpened pencil is 190 mm and the clear bore is 204 mm, so nothing has to be cut down to fit. Under the eraser there is a second compartment, about 40 cm³, which takes a sharpener and a couple of spares.

Nine printed parts. No screws, no magnets, no glue, no bearings. Every joint is a thread, a taper or a snap fit. Nothing needs supports and nothing needs a multi-material setup, because every colour is simply a different part.

Assembled it is 313 mm long and 40 mm across the flats, and it comes to roughly 155 cm³ of plastic. Print time depends entirely on your profile, so I have not quoted one: the barrel is the long pole and everything else is quick.

Parts List

Files

Both STL and 3MF are provided for every part. The 3MF files carry the licence and credit in their metadata, so use those if your slicer takes them.

• 01-eraser

• 02-ferrule

• 03-barrel

• 04-carrier

• 04-jaw (print three)

• 05-nut

• 06-tip

• 07-cap

• 08-band

• LICENSE.txt

Filaments

• PLA or PETG for the barrel, ferrule, eraser, eraser cap, chuck nut and tip. Any brand.

• PETG or PCTG for the carrier and the three jaws. This one is not optional, see the print instructions.

• TPU 95A for the compression band. It is one flat ring, about half a gram.

Colour is up to you.

Printed Parts

Special Print Instructions

• The jaws and the carrier have to be PETG or PCTG. The jaws are the only part that flexes, and PLA ones snap. I know because mine did.

• Drop the files on the plate as they arrive and do not rotate them. Each one is already sitting in the orientation that makes it print without supports. The jaws especially: they lie flat on their side so the bending load runs along the extrusions instead of across the layer lines, and that is the difference between a jaw that works and a jaw that breaks.

• 0.4 mm nozzle. I print the barrel and the nut at 0.25 mm layers and the rest finer; nothing in the design needs a particular layer height.

• 15% gyroid infill, two perimeters. The barrel is a 195 mm tube, so if you want it stiffer put the extra into perimeters rather than infill.

• Brim on the barrel, the nut and the jaws.

• It is designed to print without supports except the barrel, and every exported file is measured for down-facing area steeper than 45 degrees against a set budget before it ships. I put a little organic support under the barrel's front spigot, where the nut screws on, just to catch that overhang cleanly. Everywhere else genuinely needs none.

Non-Printed Parts

None. Bring one ordinary pencil if you want it to write.

Assembly

Intro

About five minutes, no tools, no glue. The threads are all two-start with an 8 mm lead, so everything does up in roughly three quarters of a turn and nothing needs winding.

Instructions

1. Press the three jaws into the carrier's three sockets, anchor end first. They are a press fit. If one is tight, ease the bottom edge with a knife rather than forcing it.

2. Drop the carrier into the front of the barrel, pilot first, until its shoulder lands flat on the barrel's face.

3. Slide the TPU band over the barrel's front spigot.

4. Screw the wood cone on over the open jaws. Three quarters of a turn takes it from fully open to fully closed.

5. Push the black tip onto the nose of the wood cone. It snaps on. sometimes needs light force.

6. Screw the ferrule onto the back of the barrel.

7. Press the eraser into the ferrule. Six dogs key it so the twist carries through, and a bead snaps it home.

8. Screw the eraser cap on. That is the lid of the second compartment.

To write with it, push a pencil in through the nose until it stops, then turn the wood cone clockwise until it grips. To load pencils for storage, take the eraser off the back and drop them in.

How the chuck works

The cosmetic taper is the compression nut. The tan cone that makes it look like a sharpened pencil is the same part that squeezes the jaws, so there is no separate mechanism and nothing extra to print.

Each jaw is an anchor, a thin flexure strip and a wedge with a 15 degree back face. The nut's internal cone rides on that back face and drives all three wedges inward together. Slacken the nut and the flexures spring the jaws open again.

It is three separate jaws rather than one split collet for a printing reason. A split collet grips by bending, and it has to print standing up, which puts every squeeze straight onto the layer bonds. That version broke. Three jaws printed flat solve it, and they are easier to reprint if you ever do break one.

Conclusion

The parts carry a 3D3D mark cut into them. It is part of the geometry rather than a surface decoration, and I would appreciate it being left alone.

Licence: CC BY-NC-ND 4.0. Print it, use it, give one away, post photos of it. Please do not sell prints of it and please do not publish a modified version.

Commercial use is available and the answer is usually yes. Print-for-sale, classroom sets, school fundraisers, market stalls: email [email protected] and ask. I would much rather license it to you than find it on a marketplace.

If you print one, please post a Make. I want to see it.