Posts Made By: Sam Greenlaw

Here's a modern one-ton turret type. Imagine this cast iron mill without the upper drilling head, the work table, and the cranks associated with the work table.

Positioning would be done with the column axis (near the top of the main vertical section for RA) and the angular rotator (at the front-end of the top part of the stand for DEC.)

Want heavy ? Got it ! .... ;^)

http://www.litebox-telescopes.com/

Typical well-done low height Dobson.

Same for Ed Taychert, above.

The local probate court would have a name and number for the estate's executor. If the tailpiece looked valuable, it might have been stored. Engraving in 19th century style would have given it priority for appraisal and protection.

Lawyers don't publish results until the filing with the court.

One problem that comes up: PLOP measurements give exact positioning for your individual mirror. A custom 9-point or 18-point mirror cell will beat a generic.

DIY is a doable option. I've done three. Not a major-league craftsman....

Drill or drill press, access to aluminum, a hack saw, nuts and bolts. You'll see examples of cells up to 16" for portables on the web.

Looks first-rate.

Better quality than DIY stuff.

Gotta love it !

I've avoided woodwork perfection. The first project is a 10" prototyping scope. It's a truss-and-string system that uses simple materials and correction-oriented subsystems.

This 10" is a precursor to a major 16" scope project. Got the 16" mirror already, so the 10" is a learning project. Eventually I want a back-packable 10"... ;^)

Seems to me there are five critical Dobsonian subsystems:

-- Base
-- Mirror cell
-- Truss-and-string or tube (with shielding and baffles)
-- Secondary and spider
-- Focuser

Telkit for the 16" costs $1400 USD, which is nothing if not expensive.

I'm budgeting $700 with $400 in the secondary mirror and spyder. The trick to pull off is getting an equatorial rocker (15+ degrees rotation) in under the budget cap.

So far it looks to me that crafting the mirror cell (according to PLOP), the tube system, and a threaded-tube focuser are doable for non-expert hobbyists. Each subsystem can be built to perform as well as over-the-counter alternatives.

If you don't want to do wood work, aluminum is doable. Minimal sanding.... ;^)

For example, a single-ring aluminum upper frame is a major convenience, if you go do-it-yourself. Everything attaches without wood's design issues.

Good luck. Like model airplanes, building the thing is a big part of the fun.

Mercotac makes a line of rotating connectors.

http://www.mercotac.com/html/products.html

These connectors take rubber boots for protection from moisture.

Up to 8 connectors. 4 and 30 amp limits.

Amps, not milliamps.... ;^)

Curing time:

Depends on silicon product. The directions on the tube or package will give the recommended curing times. A warm room helps.

Failover safety-loop:

A little piece of strong thread or fishing line is worth considering.

Silicon-glued to back of the secondary mirror. Tied off to the spider. If the secondary mirror gets loose somehow, the safety-loop saves both mirrors from a nasty early morning.

Cost = 2-cents.

>>> (quoted) >>>
The smallest move .... A reasonable smallest controlable move (one that can be achieved most of the time) is probably somewhere around 1/2 mm on the edge of an 8" knob, and that comes down to less than 1/1000 of a full turn ....

... Small helical is over half a dozen times more precise, because one full turn makes for les than 3mm travel ...
>>>>> (end quote) >>>>

YES abut the helical. But.... The 3mm per turn assumes 10 threads per 30mm.

Getting super fine 20 threads per inch (==> 25.4mm/20) yields 1.27mm per turn. My first experiment used a drain plug with 5 tpi and it worked beautifully with a 6" wheel using a guitar pick.

The guitar pick is a wonder. It's design is sooooo simple.

Super fine threads for a helical, an 8" wheel and a guitar pick. Perfect ???

The helical's focuser tube can be big, at least 2" or so for 1.25" EPs. Cut the adapters to solve the rough focusing issue.

Fine focus adjusts for expansion/contraction of the telescope tube (or trusses.)