Zero-Play Tapping Arm (PTFE Rail Guide)

Zero-Play Tapping Arm

A remix of Muffelkraft's Improved Tapping Arm with a guide that actually holds the tap holder square. No wobble, no supports.

I liked the Improved Tapping Arm, but my 12 mm tap holder rattled around in it. The original bore is 12.6 mm, so there was about half a millimeter of play, and the horizontal PTFE tubes only touched the holder from two sides. Push the handle sideways and the tap leaned. Not what you want from a tapping guide.

So I rebuilt the head. The holder now rides on four vertical PTFE tubes (the same 4 mm Bowden tube you already have in a drawer) set into pockets around the bore. The two in the arm form a V that sets where the holder sits. The two in the clamp cap push it into the V. The holder never touches plastic, only PTFE, so it slides and turns smoothly.

The cap doesn't close flush. You leave a small gap and snug the four screws with the holder in place until the wobble is gone. The PTFE has just enough give to make that easy, and if the tubes bed in over time, a little more on the screws takes up the slack.

What else changed

• The column bolts down square. It sits flat on the floor of the base socket, with a little side clearance, and two flat head wood screws pull it down from underneath. The floor sets the angle, not a tight press fit.

• Carry handle kept. The cutout in the column stays. Its lower end is flattened slightly so it prints as a short bridge instead of a drooping arch.

• Small chamfers on the clamp faces, so a blob or a bit of elephant foot can't hold the cap open.

What you print

- Arm
- Clamp cap
- Base

The 3mf has all three on one plate, set up for a Prusa CORE One L (HF 0.4) at 0.25 mm in PLA. About 4 h 20 min and 120 g. STLs and a STEP of the assembly are included too.

Hardware

- 4 × PTFE tube, 4 mm OD, cut to about 33 mm
- 4 × M3 heat-set inserts (I used 4.6 mm OD × 4.5 mm long)
- 4 × M3 × 16 button head screws for the cap, but you can sub socket, etc.
- 2 × #6 × 3/4" flat head wood screws for the base
- Optional: a 2 mm rod or a length of filament inside each tube to stiffen it (a q-tip shaft works well)
- Dry PTFE lube (optional)

Assembly

1. Melt the four inserts into the arm. Keep a 4 mm rod or drill bit in each tube pocket while you do it so the pocket can't bulge.

2. Cut the tubes to about 33 mm and push them in. There's a small hole under each pocket if you ever need to push one back out.

3. Put the tap holder in, fit the cap, and snug the four screws evenly until the holder slides and turns with no wobble. Don't crank them.

4. Screw the column to the base from underneath. Snug only. Those screws cut their own threads along the layer lines and will strip if you lean on them.

5. A light chamfer on the end of your tap holder helps it slide past the tube tops.

Will it fit my tap holder?

It's built for a 12 mm shaft (mine measures 12.05). The clamp gap soaks up some variation in your holder and your tubes. If yours is a different size, the STEP is in the files.

Printing

Print it the way the 3mf has it: the arm upside down, standing on the top of the head, the cap upright, and the base flat. No supports. That orientation prints the tube pockets as round, vertical holes, which is what matters here.

4 perimeters, 25% gyroid. Use a 5 mm brim on the arm and the cap, because the arm is tall and narrow at the bed. Clean any brim out of the bore opening afterward.

Credits

Remix of Improved Tapping arm by Muffelkraft, which is itself a remix of Tapping Arm by David Holecko. Same license as Muffelkraft's version: CC BY-NC-SA.