Telescope Reviews: Re: Rebuild/Upgrade of my old 10" f4.66 newtonian

Making an 10-inch Obsession style is a lot of trouble, but there is another way to make a smaller truss-tube Dob, namely join the tubing with brackets made from aluminum angle. You can then attach the combined poles and brackets to the mirror box and the upper cage. No welding required for anything since you can use a sheet of plywood as the "tailgate" for the primary mirror. Way easier than cutting, drilling, tapping, fitting and welding tubular steel as I have done for my 15-inch that is under way.

As for learning to weld, you will want a 230-volt MIG welder if you plan to weld aluminum, or a AC/DC stick welder. You cannot stick weld aluminum with an AC-only SMAW or stick welder as they're called in the trade. If you have access to a TIG welder, that is the best method to weld aluminum, especially thin aluminum. When molten aluminum does not glow, it turns into a shiny but still very hot liquid that is at least 1,300 degrees Fahrenheit. You must clean the metal thoroughly to weld aluminum, especially with the MIG and TIG process. There is no flux to bind to impurities and you must weld in a draft free area to prevent wind from blowing away the shielding gas. The arc is very intense and the noise is very loud compared to welding steel, and before trying to learn aluminum, practice on mild steel scrap first if you never did any welding.

Be careful while welding, the potential for electric shock, explosions, fire and burns are a constant hazard. Keep a fire extinguisher handy, and a first aid kit isn't a bad idea too. Safety glasses are a must when cutting or grinding, I can tell you all about what it's like getting metal taken out of your eye. It's not fun. The fumes can also be very harmful, even deadly if inhaled, so do this in an area with good ventilation free of flammables. And do not cut into anything or weld anything that ever held anything flammable, it could explode and a number of welders have died this way. I'm not trying to scare you off from welding, but be careful. It's a good thing to know how to do, because you can repair a lot of things around your house, or even your vehicles.

Last of all, build or get a metal table to do your welding and cutting on. You need a set of tools for welding that includes sqaures, a tape measure, files, hammers, clamps and a good visor and pair of gloves. Old woolen or cotton clothes and closed, leather shoes are a must. Do not tuck your pants into your shoes or boots, slag can slide right down to your feet and you will never forget the sensation of your feet on fire. Starching your clothes helps deflect slag and sparks. The arc is a hazard to the eyes of nearby people or animals, so you want to prevent them from getting their eyes scorched when you're welding. Keeping an extra visor handy is a good thing in case someone else has to be near you. And if someone is near you, warn them before starting a weld so they can look away.

Taras

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15-inch F/4.5 Dob under construction
10-inch F/4.5 Discovery Dob
6-inch F/8 Homebuilt Dob
4 1/4-inch F/4 Homebuilt reflector
A whole bunch of eyepieces, filters and other accessories....
One curious cat

Edited by Achernar (08/22/09 07:18 PM)

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