First, FreddyZ took up Martin Rigatoni's challenge to make a miniature ratcheting screwdriver. Now I've decided to take up FreddyZ on his (probably unintended) challenge to make a miniature reversible ratcheting screwdriver. We all know where this leads…

This design has a little knob on the back that when pushed in, drives in the CW direction and ratchets in the CCW direction. Pull the knob out and the drive and ratchet directions are reversed. And the end of the driver unscrews to reveal storage for up to 6 additional bits.

It is designed for double-ended, 4mm shank bits up to 32mm long (or single-ended bits up to 25mm long). With a total of 7 double-ended bits, that gives you a total of 14 tips to choose from. Oh, and with no bit, it can be used as a 4mm nut driver, hence, the 15-in-1!

The secret to the reversing mechanism is a sliding ratchet piece with two sets of flexing fingers (one angled CW, the other CCW) that engage nubs on the the inside of the handle. When the ratchet piece is slid towards the tip, the CW angled fingers engage when driving CW but ratchet when going CCW. Sliding the ratchet piece towards the butt-end engages the CCW set of fingers, reversing the action.

Printing
I printed this in PLA, but PETG or ASA should work as well. All parts print in the orientations provided and without supports. Print one of each part using 0.2mm layer thickness. (I've provided two screw cap files - one with the key ring hole and one without – just print one.) The shaft piece prints on end, so you will probably print it with a brim to keep it from tipping over. This is a tight-tolerence mechanism, so all your parts need to be very clean. Use a file or sandpaper to remove any nits, strings etc.. Also test assemble all of the various mating surfaces individually before assembly as disassembly is rather difficult.

Assembly
1. The ratchet piece consists of upper and lower flexing fingers, with the upper fingers printing right on top of the lower fingers, with a one layer gap between them. Push on the end of each of the six fingers to break it free from the adjoining finger. Make sure each finger flexes freely without hanging up on anything. (Remove any lumps or bumps that cause problems with a razor blade or X-acto knife.)

2. Insert the shaft into the front cap so that the smooth side of the cap rests against the socket-end flange.

3. Insert the push rod into the end of the shaft, orienting it so that the little hole in the end of the push rod can be seen through the oval slot in the side of the shaft.

4. The ratchet piece has a small hole in one corner aligned with the fingers that go towards the butt-end of the driver. (See last photo.) Slide the ratchet over the shaft so that the small hole aligns with the oval slot in the shaft.

5. Take a 7mm long piece of 1.75mm filament (the ends should be cut square and with just a slight chamfer) and insert it through the hole in the ratchet and into the hole in the end of the push rod. Push it firmly into place and make sure that when you push and pull on the end of the push rod, the ratchet slides up and down along the shaft. Make sure the end of the piece of filament doesn't stick out and interfere with the neighboring flexing finger. When you are satisfied it's all working properly, place a tiny drop of superglue on the end of the piece of filament to keep it from working itself out.

6. Place the body over the shaft and into the notches in the front cap. You may need to rotate the shaft slightly so that the ratchet fingers land between the nubs on the inside of the handle.

7. Slide the collar over the tail end of the shaft and press in place firmly. It should be a pretty tight fit, and the top of the collar should be flush with the end of the shaft. Note: if the collar is not a tight fit, or too tight, try reprinting it scaled up or down by 0.5% - 1.0%.

8. Now, you are ready to load your bits in the handle storage and screw on the end cap.

Bits
Single-ended, 4mm shank bits are pretty easy to find (just search for mini driver bits). Double-ended ones are a bit (sorry) harder to find. I lifted mine from a multi-bit driver I got from a hardware store now out of business. In know Victorinox also makes double-ended bits for their Cybertool pocket knife. If you know of a good source for double-ended bits, please let me know and I'll post that here.

UPDATE: I've added another version of the body for single-end bits up to 30mm long (which are much more common). Just print one body piece, depending on which bits you have. I've also added the file Driver.STEP for anyone wanting to hack on the model.