Short Tube 80 Piggyback mount for a 10" SCT

I made this piggyback mount for $25.  I bought the rings from Orion Telescopes and all the hardware from Home Depot and Orchard Supply.  See below for more details.

Materials:

A) a pair 116 mm ID rings from Orion Telescopes (Stk# 07372).

B) 3/4" square aluminum tubing, long enough to span the mounting screws in front and back of your SCT (of course, larger sizes than 3/4" can be used, depending on your needs)

C) Two 8-32x1" socket head cap screws (this must be longer if you use larger tube than 3/4").

D) Two #8 flat washers

E) Two 1/4-20 x 1-1/2" Nylon screws.  Note: the top of the rings are already tapped with 1/4-20 for piggybacking a camera.

F) Four 8-32 x 1" nylon thumb screw knurled head

G) Two 1/4-20 x 1/2" socket head cap screws

H) Two 1/4" split lock washers

Tools:

• Drill
• Drill bits
• #8 tap and appropriate drill bit. 
• Cutting oil
• punch and hammer
• hack saw
• 9/64 and 3/32 hex wrenches

Instructions

1. Drill and tapped two #8 holes in each ring.  See photo for location.
2. Select the 2 mounting holes you want to use on OTA.  Determine how long the tube has to be by laying it between the two mounting screws in front and rear of  the OTA.  Allow some extra distance (1/4") between the mounting holes and the ends of the tube.  Cut to desired length.
3. Determine the location of the mounting holes on the tubing and drill a hole all the way through the tubing that's large enough for  #8-32 socket head cap screws (C) to go through.
4. Determine the location of the ST80 on your SCT OTA and where you want the rings to grab it.  Mark the locations where you want the rings' mounting holes to be.
5. Drill two 1/4" holes all the way through the tubing.
6. On the bottom side of the tubing, make the holes large enough for the head of the screw to go through.

7. Attach the rings to the tubing using 1/4-20 x 1/2 socket head screws and 1/4" split washers.  Check that the ring clamps are on the same side. 
8. Insert all six nylon screws.
9. Attach the assembly to the OTA with 8-32 x 1" socket head screws and #8 flat washers.
10. Install your ST80 and enjoy.

Nat Chotinun

August 2, 2002