East Riding Astronomers

TS20 Upgrades and Modifications

The Club has a range of equipment to help with our hobby. First amongst all of these is our 20″ Dobsonian Mounted Newtonian Telescope – the TS20

Built almost 25 years ago, refurbished in the 2020s, the TS20 has undergone some recent minor improvements.

2023: New bearing and Azimuth setting circle

The azimuth bearing of the scope is made up of three large rubber roller bearings.  In 2023 we removed the central locating bolt and replaced it with a 20mm bearing.  

We also installed a 600+mm diameter paper printed setting circle.

The bearing and setting circle were an improvement, but further improvement is possible.

We also added at this time a digital inclinometer and bracket to allow us to accurately set the altitude of the scope.  Accuracy was aided by having an adjustable levelling table for the scope to sit on.

December 2025: New Azimuth bearing.

December 2025: A 18″ Lazy Susan Bearing was fitted.  This replaced the three large rubber roller bearings (1) with a slimmer ball-type bearing.

The aluminium Lazy Susan bearing is attached to the lower base with 6 x 25mm stainless screws.  The bearing attachment to the upper base is by means of 4 x 6mm stainless. There are 6 mounting holes, but 2 of these are unsupported (see photos).  The bearing has been tapped (3) so the bolts are firmly fixed in place (4), allowing easier fitting of the upper box assembly.  The fixing is finished by four butterfly nuts (5).

1. Original azimuth bearings
2. 18″ Lazy Susan bearing
3. Tapped bolt holes
4. Bolts firmly fixed
5. Finally fixed

February 2026: New Azimuth Setting Circle.

January 2026 we had a new setting circle printed, and fitted in February.

The setting circle rotates around three bearing points 120 degrees apart and made up of 8mm plastic bolts.  The heads of the bolts keep the setting circle “doughnut” in place.

The bearing reading is taken against a sighting line. By lining up both lines you can achieve greater accuracy.

Azimuth Circle
Azimuth sight line

Proposals for 2025/26.

  1. Replace the central bearing and three roller bearings with a lazy-Susan bearing. DONE.
  2. Replace the DIY azimuth circle with a professionally printed aluminium and rubber composite circle. Done, fitted in February 26.
  3. Replace the full-contact (480mm) altitude bearing strips with either shorter strips or Teflon blocks.
    • There are issues with this as the TS20 Alt bearing is NOT angled. See photos 1 to 5.
  4. Seek permission (from the Village Hall site managers) for a permanent, level, weatherproof base for the TS20 to replace the levelling table.
  5. Improve the wheelbarrow handles by replacing the slide-in sockets with bolt on connectors.
  6. 6. Make modifications to the TS20 to improve it’s “portability”. (see below)

1. Typical rocker bearing
2. TS20 rocker bearing
3. Typical mirror box bearing
4. TS20 mirror box bearing
5. Typical angled bearing

Upgrade Proposals Costs etc.

  1. A lazy-Susan bearing around £30
  2. Professionally printed aluminum and rubber composite setting circle approx. £36
  3. Reduce size of bearing contact surfaces £0.00
  4. Permanent, level, weatherproof base for the TS20 to replace the levelling table. £10.00
  5. Replacing the slide-in sockets with bolt on connectors. £20.00

6. “Portability” Improvements

  • Replace certain fastenings with bolts that can be used without tools.
  • Use rod end bearings for struts.
  • Move the altitude bearings to increase the centre of gravity so that the balance weight can be removed or significantly lighten.