Ptfe Sculpting Guides For Tight Filament Constraint

Improve flexible filament printability by better constraining their path with sculpted PTFE tips.
These guides make PTFE tips that closely conform to Bondtech drive gears. Very little space is left for filament escape.

Sculpting Guides are Provided for the following extruders with either E3D V6 or Slice Mosquito hot ends...

Bunny Science
- BNBSX MK3S Short Ears Extruder
- BNB Short Ears MK3
- Bunny and Bear Geared MK3 Extruder

Original Prusa Stock Extruders
- MK3S (R4 and R5)
- MK3 (R3)


PTFE tubing is typically cut flat across and internal chamfered. This adequately constrains rigid filaments, but leaves openings through which flexible filaments readily escape. Sometimes, a chisel shaped end is used to bring PTFE tubing into closer approximation, but that too leaves gaps that can be reduced.

This PTFE Shaping jig produces a dual sided curve to extend coverage all the way up to Bondtech axle height. This improves flexible filament handling - allowing success even when idler door tension is high.

BNBSX Printing TPU after sculpting PTFE
https://www.youtube.com/watch?v=BhZYdRv45sY

4 cm diameter cylinder in TPU is being printed at 0.2 mm layer height, 4 perimeters, 150% speed on front control dial, PrusaSlicer perimeter speed 100 mm/sec, and volumetric max 2.0 mm3/sec. This is NOT 150 mm/sec. Speed is limited by volumetric max.


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Usage

Obtain PTFE 4.0 mm OD, length should be length of sculpting guide. This is intentionally longer than final PTFE length.

Trim one end as perfectly a 90 degree cut as possible. You can do so by clamping PTFE in sculpting guide and using end of guide to direct your blade. We will use the 90 degree cut end as the bottom of the PTFE tube.

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E3D hot ends - Need outer chamfer at bottom end. Chamfering is more accurate if your 90 degree cut is flat and perpendicular.

Create 60 degree outer chamfer using PTFE Chamfer Tool 60 Degree and #11 hobby knife blade. Insert blade fully into blade slot and hold steadily in position. Use light touch as you rotate PTFE in chamfering tool like sharpening a pencil. Best results are made with light pressure taking thin slices. Recheck the PTFE tip as you progress. Chamfer only until you NEARLY reaches inner passage of PTFE, but don't chamfer too far.

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Slice Mosquito hot end - Leave bottom end flat cut at 90 degrees. Do not outer chamfer PTFE if for Mosquito.

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Place PTFE into sculpting guide. Bottom end of PTFE end should be at end of PTFE trough. Inspection holes let you verify tip is fully seated. Clamp PTFE in position with M3 bolts and nuts through sculpting guide halves.

Note the pairs of sculpting holes. Pair creating the longest PTFE tube is for E3D. The hold pair closest to bottom end of PTFE is for the shorter Mosquito.

Insert PTFE support plug into one of the sculpting holes. The support plug keeps PTFE from buckling while you sculpt the tubing. Flat portion of PTFE support goes against PTFE tubing.

Use FRESH, long, thin #11 hobby knife to gradually trim away a rounded bite from PTFE tubing. Shallow, progressive shaves from each direction yields best results. Trim until a round bite is removed from PTFE tubing that matches contour of sculpting hole.

Alternatively, super nice bits can be made using an 8 mm OD stainless steel tube that has been internally chamfered and sharpened. Chuck in a drill and spin at medium speed to create very neat bits. Best is to orient spin direction so PTFE is driven into sculpting guide for each cut. That means cutting from opposite side when making 2nd bite. Don't forget to move the PTFE support plug between cuts.

Remove PTFE support plug and move it to the other sculpting hole. Now that one sculpted cut has already been made in the PTFE, place the ROUND portion of support plug against the sculpted PTFE bite.

Sculpt the other side of the your PTFE tubing. Properly done, you will produce two rounded bites, each shaped to fit a Bondech drive gear.

Unclamp PTFE from sculpting guide.

Cut PTFE through thin section just above center of bites.

Clean up loose stranding and slightly internally chamfer with a hobby knife.

Install PTFE in hot end with bits oriented towards Bondtech gears.

Bunnies adjusted sculpting guide to create correct length for E3D and Mosquito hot ends, but your printer may be slightly different.

Check that height of PTFE tips is about level with idler door Bondtech axle. If PTFE is too long, further trimming or chamfer bottom end to make correct length.

Additional picts and explanation are at https://forum.prusaprinters.org/forum/original-prusa-i3-mk3s-mk3-user-mods-octoprint-enclosures-nozzles-.../ptfe-sculpting-for-tight-fit-on-bnbsx/#post-159682

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Changes

Added versions of PTFE sculpting guides for additional extruders...
BNB Short Ears MK3
Prusa MK3S (stock)
Prusak MK3 (stock)

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