Thingiverse has a number of great tripods but I couldn't find a good ball head, so I created this.
It'll handle up to a small DSLR with a short lens.

It has 3/4" tripod threads top and bottom, and I've included printable adapters for the more common 1/4 threads. If you are using a large camera on this, I would strongly recommend investing in metal thread adapters, for better durability.

I've designed it to take a small o-ring, 6mm inner diameter, 1.8mm thickness, to improve the grip on the ball. It works fine without the o-ring, but it feels better with it. I have also included a flat bottomed o-ring which you would be able to print in flexible filament.

I've included 2 ways of making the ball, one which prints in two parts and screws together with a single M3 x 20mm screw, and one which prints without the screw. I strongly recommend using the one with the screw if you area using anything other than a small camera.

The cross-section and exploded view show how to put it together.

This will print entirely without supports, in the orientations shown in the attached image. It has overhangs up to about 60 degrees and one bridge section of about 6mm, so it is not a very challenging print. I recommend printing it with a fine layer height to maximize the quality of the threads and the smoothness of the ball, I used 0.1mm. Use a nozzle diameter of 0.4mm or smaller, the horizontal thread in the main housing will not work with a large nozzle. I used 60 percent infill.

The builds in the photos are a mix of Paramount Matte Black PLA, Verbatim Silver PLA and Proto-Pasta Blue HTPLA.

Update 9/29/2018:
Just updated a few of the files:
"Ball for M3 screw" - extended depth of thread to ensure it accommodates 20mm M3 screw.
"quarter inch base adapter" - extended base 1.5mm to add strength
"quarter inch top adapter" - shortened 1/4" thread by 1mm because it was longer than some camera threads.
"Ball with stalk - M3 screw not required" - reduced depth of 3/8" thread to match that of the M3 stalk, and used a taper to remove the need to bridge inside.

Update 9/30/2018:
I've added an optional printable threaded washer, which you can use as a stand off between a metal adapter and your camera, to protect the base of your camera. This is not needed if you are not using a metal thread adapter.

Print Settings

Rafts:

Doesn't Matter

Supports:

No

Resolution:

<0.15mm layer height recomended

Infill:

50% recommended

Filament:
Doesn't matter Rigid

Notes:

This will print entirely without supports, in the orientations shown in the attached image. It has overhangs up to about 60 degrees and one bridge section of about 6mm, so it is not a very challenging print. I recommend printing it with a fine layer height to maximize the quality of the threads and the smoothness of the ball, I used 0.1mm. Use a nozzle diameter of 0.4mm or smaller, the horizontal thread in the main housing will not work with a large nozzle. I used 60 percent infill.

(Update 9/30/2018:
I made a cool discovery. If you print the housing in wood filled PLA and the ball in PETG, it gives a nice smooth action to the ball. I used Hatchbox Wood PLA for the housing, Amazon Basics Clear PETG for the ball, and Paramount Matte Black PLA for the other parts. PLA printed at 0.1mm layer height, and PETG at 0.15mm. This is shown in one of the photos.) Category: Camera