12.5-inch telescope

My 12.5-inch f/6.3 Newtonian, completed in 2006

They should take me away for putting such a large scope on top of a Meade LXD-75 mount! It rocks 'n rolls (in the motion sense); photography is unthinkable. Optimized for planets but delivers the deep-space objects too; views of both have been great. The optical tube assembly (OTA) structure itself is rock-solid. Someday I might adapt it to a Dobsonian mount, but I like the goto and tracking. My first DIY scope - many lessons learned and modifications planned.

Features

- Split truss. Great for getting through doorways - the bulky upper unit is light in weight, the heavy lower unit is small, not hard to carry. Three wingnuts put them together. Holds collimation from setup to setup.

- Box pier built to hold the tall scope as low as possible, and permits views without collision to the meridian near the zenith . (Mounting surface is 3/4-inch oak, drilled with an adjustable-radius bit in a drill press to conform to the mount. The box of 1/2-inch plywood plus a 2x4 is a bit heavy but very sturdy. Holes give access to the mount clamp, and to the battery packs hiding inside.)

- Extended counterweight shaft with only 20 lbs balances the 40 lb scope. (Total supported weight is the same as Meade's SN-10 setup, but the bending moments are greater.)

Components

- Primary mirror made locally by the shop now known as Optic Wave Labs: http://www.opticwavelabs.com/

- Protostar secondary mirror and arch vane http://fpi-protostar.com/crvmnts.htm

- Wyoroc focuser http://www.wyorocktelescopeworks.com/ (Their website is not smooth, tight, and polished, but the focuser sure is.)

- University Optics 9-point true flotation cell (discontinued after only a brief availability) http://www.universityoptics.com/

- Stellarvue right-angle finder (on the far side, bought in-person from Vic) http://www.stellarvue.com/f50.html

- Silenx 12VDC fans from Fry's are silent and vibration-free on full voltage. Two blow across the mirror face, one onto the back.

- Construction concepts from R.F. Royce: http://www.rfroyce.com/10f6tel/ (Many liberties taken, especially going from square to hexagonal cross-section; doesn't use the rotating head design, to save weight.)

Some Details

All the wood boxes are 3/16 inch (approx) birch plywood, all with 6 sides plus a hexagonal web (or rib) panel on each end. Exceptions are the two that adjoin in the middle, with bolts and wingnuts - of 1/2-inch plywood. To build, after tacking each together with masking tape, I took one piece off at a time, spread slow-setting epoxy on the joints, and taped it back on. (It needed a little care to keep the web panels from slipping in or out. Next time: dado joints.) Spar urethane finish - didn't get into fiberglass-resin.

The top box has much of the wood cut out and covered with posterboard to save weight. It could have been longer for better stray-light blocking, but is helped some by the black cardboard hanging down.

The plastic tabs on top hold my apodizing mask in place. Next time I will inset the top web so the six side panels overhang up to do this job.

Here's a closer view of the mounting. The saddle bar connects not to the wood box, but to the aluminum crossbars. These are bolted to the box. The upper bar's bolts are lag screws through to the 1/2 inch plywood web on top of the lower-central box; the lower bar's bolts go through an extra 1/2 inch plywood layer inside the main panel.See one of the wingnuts, through the round hole, that connect the upper and lower truss assemblies.

The extra-long saddle clamping knob is a piece of metric-thread bolt, then a steel tube that fit tight by hammering on, then an oak knob epoxied on.

This is the mirror box, with cell and mirror, when just barely assembled. Later, the truss poles were connected directly to the three cell mounting bolts, where they stick out of the box. This one box is non-structural, just protective.Two fans were later attached to one of the side panels to blow across the mirror face. A backside fan on the panel from which this hole was cut can be wired up too, and velcroed in place. (Many modifications planned to improve fan effectiveness.)

Google Sites

Report abuse