[Arctictanker]

Anyone have suggestions on fabricating hard bag pannier supports out of flat aluminum stock?  I am thinking of using 3/4in stock and I am not sure of the alloy as of now.  This is going to be my winter project.  Do I use a regular drill and bits for holes? How do I bend it? Painting? Thanks in advance for the advice/assistance.

[High On Octane]

How exactly do you plan to fabricate these brackets?  Aluminum flat stock is very flimsy and in thinking it will not hold it's shape very well.  I personally would use steel flat stock, will depending on how you plan on using it anyways.

[sven trials]

Not to disagree with HOO, but aluminium stock is "stiffer" than steel and is a great material for framework. It can be an easy material to fab with. Drilling/milling and cutting are done at higher speeds and cutting lube is cleaner than oil.  Grinding is fast also.  Depending on the alloy, welding goes good and heat treating is not always needed.  Bending is another issue. Since aluminium is not ductile, you get one shot at bending typically. it does not like to be bent multiple times.
3/4 flat bar seems overkill, which is fine.  easier to fix mistakes that way.

[Arctictanker]

The brackets will be used to mount 30mm ammo cans as hard panniers.  I like how clean the ones Kingrock made turned out.  The cans weigh about 22 lbs each.  After adding some lighting and the brackets I am thinking they will be about 25 lbs empty.
http://www.enfieldmotorcycles.com/forum/index.php/topic,10837.0.html

[Arizoni]

Just for the record, 6061 T6 wrought aluminum bars have the following mechanical properties .  6061 T6 is an aircraft quality aluminum alloy, far stronger than many aluminum alloys.

Tensile strength = 45 ksi** (This is the point where stress will break the part)
Yield strength = 40 ksi (This is the point where the bent part will stay bent)
Modulus of Elasticity in tension = 10 X 10^6 psi (This is the materials resistance to bending used to calculate deflections of structures).

Aluminum is subject to failure from high and low cycle fatigue.

Low Carbon Cold Rolled Steel (AISI 1018)***  wrought bars have the following mechanical properties:

Tensile Strength = 64 ksi
Yield Strength = 54 ksi
Modulus of Elasticity in tension = 29 X 10^6 psi

From this one can see that the steel is 42 percent stronger, and 290 percent less likely to deflect a given distance under load.

Steel also has very good resistance to fatigue failures.

The bottom line IMO is the only material to use to support loads in an environment where vibration is common is to use steel for the project.

** "ksi" stands for 1000 times the value in pounds per square inch .  29 ksi = 29,000 pounds per square inch (crossectional area of beam).  64 ksi = 64,000 pounds per square inch (crossectional area of beam).

*** 1018 is one of the weakest of the common steels.  A chrome-molly steel will have strengths ranging from 98 to 234 ksi Tensile strength depending on its heat treatment.

[Arctictanker]

So from the sounds of things as a first time project and fabricating...steel would be the most forgiving and better option.  Can I get away with a propane torch, a bench vice and a drill press?  Recommendations on flat stock steel?

[Arizoni]

Without seeing exactly what you intend to build I can't say what is needed. 
Based on what I've seen others do I would say some 3/32" X 3/4" (2.38mm x 19mm) or some 1/8" X 3/4" (3.18mm X 19mm) Cold Rolled steel bars would be more than adequate.

Bending the 1/8 inch thick material can be done with a bench vise and a hammer.  You can bend it without heating it but the vise needs to be pretty healthy to withstand the forces.

Joining the pieces can be done either with steel pop rivets (not aluminum pop rivets), nuts and bolts or just bolts if you want to try drilling and tapping the threads on one of the pieces.  You would need to buy the correct size tap drill, a tap of the right size and a small bottle of thread cutting oil to create the threads.

The propane torch would only be useful for soldering pieces together and for the loads that a carrier will undergo, I would not suggest soldering.  It creates a very weak bond.
Given enough time a propane could heat a small area up to a brazing temperature for a brass filler but if brazing is desired an oxyacetylene torch is the best way to go.

Unless your familiar with welding, I do not recommend trying to use one of the cheap Harbor Freight electric welders.  Welding is an art in itself and the novice can make a really nice looking weld bead without any penetration into the steel.
If that happens it will break the first time it gets a load put on it.
There is also the expense of the equipment to protect the welder from the ultra-violet radiation given off by the arc.  Just a half second of that light can blind a person.

[High On Octane]

+1 to what Arizoni said

But I'll add a couple of notes.  It is very very difficult to braze with a propane torch.  I tried fixing a fuel leak in my tank with MAPP gas and brass brazing rods, I couldn't even get the rod to melt when I held the flame directly on it.

As for the HF welder, I personally haven't used one, but I have heard from 2 different friends that theirs do a good job for welding up simple jobs.

Scottie J