PTFE Buffer

This is small PTFE buffer that allows a small amount of back-and-forth filament movement before the it needs to be pushed through the whole tube length.  It can be placed just before the printer's filament entry point on the PTFE tube to a drybox so that retracts and restores don't have to push and pull the filament all the way back to the drybox. It is a parametric design that can be adjusted to fit a wide variety of different PTFE tube sizes and connectors with different clearances.

Printing

There are two uploaded 3mf files for the two different connector types it currently supports. The naming of the files is in the form “PTFE Buffer v<version> <PTFE OD>-<PTFE ID>-<Buffer OD>-<Travel Distance>-<Clearance>-<Output End>.3mf”. 

It should print fine using default “standard” printer settings with 0.2mm layers and 0.4mm line width, but you should use at least 3 shells for strength. If using OrcaSlicer similar slicers, make sure "Detect thin walls" is enabled or the internal supports will be missing, and using "Scarf joint seam" will probably help ensure less seam artifacts that could interfere with the sliding mechanism. Print it standing upright input-side-down (arrow on the side pointing up) without supports. My Flashforge Adventurer3 has excellent bed-adhesion so I don't need a brim or raft, but the bed attachment area is a bit small so if you have bed-adhesion problems I would use them. The tolerances are pretty tight so you will need your printer output geometry well tuned.

Usage

Choose the model that best suits your needs. The “M6Male” version is designed to replace an M6 PTFE coupler and screw into the same hole on your printer. The “Bowden” version is for an interference-fit with a short length of 4mm OD PTFE tube.

The design is a print-in-place mechanism with internal supports that need to be snapped after printing. To snap the supports gently twist the input and output parts back and forth till it snaps. Then push them tightly together and twist back and forth to rub off any remaining fragments of the supports before shaking out the loose bits.

Insert the PTFE tube into input (in the direction of the arrow on the side), and push it all the way in until it can go no further with the buffer fully contracted, or nearly 25mm deep. It needs to be inserted this deep to ensure the buffer slides mostly on the outside of the PTFE tube and not itself.

For the M6Male version, screw the output end into the M6 hole. For the "Bowden" version, push a short length of 4mm OD PTFE tube in and connect it to your printer.

Customizing

If you have special requirements you can generate your own models. Modifying and exporting this model doesn't require you to sign up for any accounts or download any software.  Just follow these instructions below!

Parameters

Currently there are 6 parameters that are adjustable, but let me know if you need anything else to be adjustable and I can update it! Some combinations of values may be invalid and will result in a malformed mount. Play with the values till you get what you want.

• PTFE OD - The outside diameter of the PTFE tube.

• PTFE ID - The inside diameter of the PTFE tube.

• Buffer OD - The outside diameter of the buffer. 10mm is probably the minimum for 4mm OD PTFE tube, but larger values will give you a thicker/stronger buffer.

• Travel Distance - The max fillament retract/restore distance before it starts to push/pull filament back down the input tube. The default of 10mm is probably sufficient for most retract settings, but it can be adjusted if you want more or less.

• Clearance - The base clearance distance used. Note different gaps have different clearances, but they are all multiples of this setting. A larger setting will give larger gaps and a tighter interference fit for the PTFE tube. The default of 0.1mm works well for me.

• Output End - The output attachement type. Currently only “M6 Male” and “Bowden” are available. Let me know if you want other options. I would also be possible to add options for the Input End if people want it.

Directions

1. Navigate to the OnShape Document.

2. Go to the PTFE Buffer tab and change the parameters as needed. 

3. Right click on the PTFE Buffer part in the bottom left corner and click Export… 

4. Choose STL or 3MF as the format, adjust the other settings as you see fit, and click Export