Hemispherical "Bowling Ball" Mount

Hemispherical Mount Design

This project started more out of curiosity than to build an actual functioning hemispherical telescope mount. I found several on-line references to "bowling ball" telescope mounts and decided to test the idea. This design has several advantages:
  1. Used bowling balls are very inexpensive (actually you can get them for free from a local bowling hall if they are sufficiently damaged)
  2. This is a very simple design that is quick, easy, and inexpensive to build
  3. The hemisphere is a single rotational element that replaces two traditional bearings, so it's a mechanically simpler design
  4. This mount uses Dobsonian bearings, so it's simple but very sturdy
I obtained two used bowling balls (free of charge) from a local bowling hall, but they were very damaged. All of the bowling ball surface damage was scratches, pits, and holes rather than raised damage. Since the damage was in the form of depressions, it does not affect the ball from sliding over a smooth surface, such as Teflon.

Hemispherical Dobsonian Bearings

The Dobsonian bearings consist of three Teflon rings that just slide over wood disks attached to small wedges (below left photo). The below right photo shows the bowling ball seated on the Teflon bearings. The bowling ball sits very securely inside the three Teflon rings and there is a very smooth motion, typical of Dobsonian bearings. Since the bowling ball surface damage is scratches and depressions, it does not affect the bearing performance; the Teflon just slides over the depressions without causing problems.


Hemispherical Mount Prototype

The below photos show a prototype hemisphere mount with my C90. I drilled a 16 mm hole through the bowling ball, inserted a M16 threaded rod, and a small piece of scrap plywood connects the M16 rod to the C90 spotting scope mount.  Because the M16 threaded rod is 1 meter long, it adds enough weight to counterbalance the C90, so a counterweight isn't necessary. I used a large steel table leg to support the mount, this is just for prototyping the system and requires replacement with something more solid. I'm using the C90 prototype mount to better understand how this type of mount functions and dimension components prior to scale up; I like using scale models because this helps me to visualize and work out construction problems prior to building a full sized model. 


Project Status

This project started mainly out of curiosity, however I have developed several interesting ideas for incorporation into this mount. I plan to build a hemisphere mount capable of supporting my 10" Newtonian, but this project is currently on hold until I complete several other telescope building projects.