Collapsing Pen Cup/Caddy

Introduction

Here is a collapsing pen cup/caddy that I made to help my wife carry her fountain pens back and forth commuting to university. There are versions to hold 4, 5 or 6 pens (the first two are about the same overall size).

Making Choices

Select one of the penholder_*x.stl files that you would like to print. The four and five pen versions are almost the same size, whereas the six pen version makes a little more of a difference. Going from four to five adds 1.3mm to the main outer diameter, while going from four to six adds just over 8mm to the diameter.

All versions work with the same top and bottom shaft and retaining clip. For the main clip choose the one that matches the number of pens in the base you picked.

• 1 penholder_*x.stl
• 1 shaft_top.stl
• 1 shaft_bottom.stl
• 1 retaining_clip.stl
• 1 clip_*x.stl (that matces the penholder_*x.stl)

Printing

Once you have chosen your parts, slice your models and print.

Be sure your printer can handle print-in-place models with 0.4mm interior gaps. I have a basic tolerance test model you can use to test things so you can get your printer and slicer dialed in before making mistakes and wasting any of your time.

All the .stl files are designed to print well without supports other than shaft_top.stl. Be sure to enable supports on that unless you have your printer dialed in very well on overhangs, as the tabs at the bottom might deform and the cause issues.

It might be handy to print all of the support models other than penholder_*x.stl together. Or you might want to group up the shaft top and bottom along with the retaining clip and just slice the clip_*x.stl files separately to make for easier printing of different versions.

Settings

For my Neptune 4 plus, I printed everything at 0.3mm layer height, but this should work well at your preferred values.

my settings:

• supports on for shaft_top.stl
• supports off for others
• layer height: 0.3mm
• nozzle: 0.4mm nozzle
• build plate adhesion: none
• infill pattern: gyroid
• infill percentage: 10%

Post-Printing/Assembly

After printing, do your normal print cleanup, but be sure to clean the bottom long edges on the top and bottom shafts. I find a deburring tool is excellent for this.

Test-fit the top shaft into a main grip section. If it slides on fairly easily and goes all the way up to the handle you are probably good to go. If you get a slight resistance you can slide the grip piece up and down until it starts to smooth out. Then rotate it 1/8th of a turn and repeat for each side to get it the most symmetrical. 

If you can't get the grip piece onto the top shaft, try trimming/sanding the long edges on the shaft a bit at a time until it does go on. (Hopefully you're not far enough off to need to tune your slicer's horizontal expansion settings and re-print)

Once the top shaft is working, slide the grip piece onto it then set aside for the moment. Press the bottom shaft gently down into the center hole on the base/main piece. If the fit is too tight smooth off the shaft until it goes in with at most a moderate amount of force so that you could back it out if needed. Push it all the way down, then secure it underneath with the retaining clip.

After the bottom shaft is in place and secured, turn everything right side up and insert the top shaft into the bottom shaft. It should slide up and down a few centimeters but you want to be sure the tabs hold when at full extension for carrying.

Then you should be ready to test closing it up.

Padding

For better gripping, you might try printing the grip section with a flexible filament such as TPU.

In general, though, the intention is for the arms of the grips to be padded with felt cut to match. Standard craft-store felt is about 1.6mm thick, so that was used in the model to get clearance for common pen sizes.

The simplest way is probably to cut strips of felt that are as long as one arm from the start of its main curve at the center, forward and just around the outer curled end, but a bit taller than the arms (unless you're fairly good at measuring and cutting felt). Then I put some simple glue-stick glue on the back of the felt and smooth it into place, making sure that either the top or the bottom edge of the felt lines up with the corresponding edge of the grip arm. After gluing felt on both sides, sliding in a pen can hold it in place until the glue sets. 

Once the glue is dry, use a sharp blade and cutting by pushing it into the felt on the inside and just above the plastic of the arm trim it to the proper height.

Using a simple water based glue will make replacing the felt easier. 

Closing

Closing the container is a simple up, over, and latch operation.

1. collapse the top handle down into the bottom shaft.
2. hold the base in one hand and gently lift the outer piece (the one with the hinge and the lid attached) until the top is at least even with the top of the handle.
3. gently lift and turn the lid over until it closes on the top. You want the slot in the lid to line up with the top of the handle.
4. once the lid is down over the top of the handle, rotate the center part of the lid 90 degrees to lock it into place.

It now should be ready to be carried, put in a school bag, etc. The center handle locks in and keeps the lid closed, avoiding putting any stress on the hinge to do so.

Updates

• Updated my model to keep the same spacing but different grip sizing so that different pens/pencils can be accommodated for four and five pen versions.

Future

• Need to tweak the grips for smaller six holder.
• I'm using a development version of FreeCAD, but as soon as 1.0 is released I'll upload the FreeCAD source. They are expecting that to happen in August, so could be any time now.