3D Printed Precision Bit Adapter

I use this little power screwdriver for a lot of things. I use it for small screws on switch-plates and places where a drill is either too heavy to be precise or too powerful to work on delicate parts. It's great for tight spaces but in a lot of cases it has all the power I need to drive a larger screw.

I also use these precision screwdrivers a lot. Home Depot sells one for standard screws and one for Torx. Lowes started selling one a few years ago that is just like Home Depot's Husky screwdriver, but the neck is a little longer and that comes in handy from time to time. All of these have bit storage in the handle, and the bits stay in the shaft with a little ball bearing. I like the storage of method and cap of the Husky ones just a little better.

Unfortunately, while a few tool manufacturers have come along with precision power screwdrivers, I still don't like the quality of them, so I decided to look for something better.

I bought a larger set of precision bits with a ratcheting handle because it was cheap and I wanted the extension piece. I figured I could use it in my drill and tighten the chuck down on it, but the drill is too bulky for precision work. I wanted something that would work with my power screwdriver. The other problem was that these bits are all 4mm but the reversible ones seem to be 3.5mm so they are not interchangeable. I wanted something that would work for both kinds of bits.

I found this part on Thingiverse that was almost exactly what I was looking for. The author included 3 different versions with different dimensions. One of his models worked pretty well with the 4mm adapters I had and another would turn my 3.5mm bits, but wasn't long enough to hold them very well. I have been using Cura with my Printrbot and I was able to stretch the model on the Z axis by an extra 25%. This worked and allowed me to use my longer bits without them falling out every time I let go, but I thought I could make it better so I decided to make my own adapter.

I really liked the simple bit adapter I found on Thingiverse, but I had a few ideas to make it better for my purposes. I have a few driver extension pieces that lock in place with a loaded ball bearing collar. I wanted to add a depression to lock this adapter into one of those extensions.

I took all of my dimensions and drew up a quick design on graph paper, then I began building it in Tinkercad. Once it was in Tinkercad, I made a few prints before I got it right and there were a number of revisions. When you are making hexagons in Tinkercad, there is no way that I found to lock the X and Y to resize both together, so instead I had to decide what I wanted the short diagonal to be, then plugged that number into this website and calculate the edge length. From there, I doubled the edge length to get the long diagonal for the other dimension. When I resized the hexagon to these dimensions, it was very close to a perfect hexagon.

After trying a number of times to have 2 stacked hexagonal holes in the middle of the adapter, one 3.5mm with another 4mm hole closer to the end, I found a custom shape generator that someone had made on Tinkercad. It was a "hexagonal wedge" that I would call a tapered hexagonal prism. I took out the 2 holes and replaced them with this tapered hole so I could fit both the 3.5mm or the 4mm driver bits. After laying all the pieces on top of each other I aligned them on the X and Y axises so that the holes, hollows and separate polygons were centered around the same point.

The part came out great and I am very happy with the result. This is my first custom part that I designed for my 3d printers and I am very proud of the result. You can download the adapter here or from the attachment on this page.