Bolt-Action Mechanical Pen with Knurled Grip (Parker G2 Refill Compatible)

I decided to model a mostly 3d printable mechanical pen. There are several other designs out there, but mine uses heat set inserts for durability. It is mostly printable without supports, with the exception of the clip, which will end up with a better surface finish if you support the curve at least part way up the side (from 6-8 on the clock if looking down the clip.)

Print Settings:

Nozzle Size: 0.4mm
Layer Height 0.15mm
Perimeters: 3
Infill Density: 30%
Infill Type: Cubic
Scarf Joint Placement: everywhere
Scarf Joint on Inner Perimeters: yes

Hardware Required

1x M2 Brass Heat Set Insert
1x M2x8mm Socket Head Cap Screw
1x M3 Brass Heat Set Insert
1x M3x10mm Socket Head Cap Screw
1x Compression Spring (the thicker the wire, the stronger the action)
1x Parker G2 Compatible Ink Refill

A quick note on Parker G2 Refill Cartridges. There are a lot of them out there, and if you want to nerd out have a look at Reddit. 

I did use some Permatex high strength thread locker on the bolts just so that I didn't need to over-tighten them.

Colors

Any STL marked with [a] is intended to be in the accent color.
I used variable height painting to easily color pen_front STL on the grip.

Materials

I experimented a lot with materials on this model. My favorite was using glass fiber reinforced PLA, because it left a very nice texture on the body of the pen.

Heat Set Insert Insertion

I modeled a small jig to help hold the parts when installing the heatset inserts, and to keep the pen_action_mechanism STL from deforming when putting in the M2 insert (it's delicate work). 

Assembly Instructions

1. Put the heat set insets in the pen_action_mechanism (M2) and pen_rear (M3).

2. With a toothpick, put a very small amount of CA glue on the inside of the nub, and slide the M2 bolt through. 

3. Drop the pen_action_mechanism into pen_rear, and with a clean toothpick, rotate the threaded hole so that it's visible through the J-slot. 

4. Brush a small amount of thread locker on to the tip of the M2 bolt/nub combo, and screw it in to the threaded hole in the J-slot.

5. Put a small amount of thread locker on to the tip of the M3 bolt. Sandwich the pen_rear, clip, and pen_rear_cap, together, and hold it together with the M3 bolt.

6. Slide the spring around the roller ball, and insert it in to the pen front. It should slide freely through the hole in the front of the pen.

7. Screw the assembled pen_rear into the pen_front. If the action is sticky, work it a bit. (or use a stronger spring.)