For me, most of the the time, cheap is the way to go, and God bless those Chinese. I was looking at a 4 1/2 inch DeWalt grinder and they wanted $90 for it! Well I can buy 3, 4 1/2 inch Chicago grinders from Harbor Freight for the same money, each with a 1 year replacement warrantee. Now its a sure bet that I will be getting it replaced, but for me that is not a problem since they are only 3 miles away. I am currently on my 3rd Chicago grinder now. On the other hand, I would have to ship off the DeWalt if it had a problem.
I also shop auctions and garage sales when the opportunity arises. I
recently just laid to rest my 7" Black and Decker grinder. She
fought the good fight for 2 years until her spindle burned up, but I
only paid $15 for her in the first place. With her death I had to
get a replacement and I had no time to shop around so I forked out
$180 for a top of the line 4HP DeWalt 9 inch grinder. And yes she is
a wonderful tool but she dam well better live longer that I do.
Finally on the other end of the spectrum you can buy too cheap. When I saw that www.Homier.com had 4 1/2" grinders for $6 each, I knew I was looking at a short life tool so I ordered 3. Little did I know how short their life would be. I attached a grinding disk and proceeded to smooth out shallow scratches in some sheeting. Not one of these grinders made it more than 90 seconds!
So my theory is buy what suites your purposes and hopefully that purpose is not just to brag and build bird houses.
Cutting aluminum is easy. (1) You can use normal wood working tools with standard carbide blades. I rigged a light onto an old skill saw so I could work at night. Hearing and eye protection are a must. I don't expect the saws to last too long because the aluminum shavings can't be very good on the motors so I picked up cheapest circular saws and table saw I could find from garage sales. I purchased some new tools too including a router and a circular saw but these are the cheapest available products from Harbor Freight. In hind site its worked out well since I purchased the replacement warrantee too. It makes dropping the saw much less financially painful. All of the blades I use are standard wood working carbide tipped blades, but I do use the blades with narrow kerfs if I have a choice, because the aluminum is not going to close up as it is cut.
I use WD-40 to lubricate my blades and bits, others have recommended "Stick Wax". You can buy it in gallon cans from Home Depot along with a squirt bottles and keep it near saws and drill press. There is a very noticeable difference when using a bit of lubricant especially when cutting bar stock or multiple sheets. Using lubricate of any kind will make cleaning the aluminum prior to welding essential
I don't care to spend the extra money, but you can also buy "non-ferrous Metal Saw Blades" which have more teeth and a 0 or even negative angle for the teeth. This should reduce the amount of kick back, and if I had less than 10 fingers I might feel differently about spending the extra $50 dollars. Kick back will happen, especially with a dull blade, with no lubricant, cutting a small piece on a table saw. Keep your hands clear by using clamps, and push sticks and always wear eye protection. A full face shield is best. Also don't stand directly behind the blade on the table saw. Even my relatively light weight 2 hp table saw can send a small piece of aluminum flying 15 feet across the shop fast enough to puncher a paint can. ...what a mess that was.
(2) If the curve is mild such as a 2 foot radius, then the skill saw can be used to make the cut. Be sure the blade depth is adjusted so that it only protrudes a quarter inch or so through the sheet, and make the kerf wider by making a second pass on the outside of the curve or by lifting the blade out of the cut and dropping it through again tangent to the line.
The utility of a good
table saw is obvious. My preference is for the old school cast
iron tables with belt drive. I got my current table for $50
bucks at a garage sale, and upgraded to a 220 volt, 4 HP motor that
will rip a 2x4 like it's butter. Just remember that the bigger
the motor the more violent the kick back.
(4) Here is a good way to loose a finger if you don't pay attention, but you can cut beautifully round cycles on a table saw. Draw the circle out and make several rough cuts to remove most of the material. Then drill a small hole in the center as well as a piece of scrap. Put a nail through the hole in the scrap and clamp that to the table. Then set your rough cut circle on the nail.
(5)Adjust the distance to the blade so that only an 1/8 inch will be removed from the highest spot. Make consecutive passes to slowly work the edge down.
(3) The router bits are straight bits and carbide, but you will need to use bits with a 3/8 inch wide cut. The smaller bits will get hot and soon clog up their blades with aluminum shavings and stop cutting. The router is great for cutting tight curves and corners. A 1/2 hole is first drilled near the corner so the router bit does not have to plunge through the material.
(4) (5) A router can sometimes also get into hard to reach places. The grinder can not reach into corners, but the router with a straight bit can be used to cut out the excess weld. Support the router as best as you can. In the photo I clamped in a piece of angle so the router could have a level base.
High speed routers can not be used free hand. They must be supported. Even when there is a good support the bit can bight in and the bounce off the edge with enough force to yank the router out of your hands. I had this happen on day while cutting a hole. The router just continued to run and bounce off one side and the other. I started to reach in and try and grab the handle and then better judgment took over and I went for the plug in the wall. It managed to start spinning in circles and winding up it's own power cord and before I could pull the plug and then it bounced up and cut the power cord on it's own.
(6) If you have the extra money and appreciation for you fingers, then I highly suggest investing in a variable speed router. I forked out around $120 for a Bosch, variable speed router. The slower speed along with some WD-40 makes all the difference in the world. As usual, I do not recommend this, but I can free hand this tool as long as I can brace my hand against the work piece. You can also find sanding drum sets with 1/4 inch shanks that will fit the tool, and work well at the slowest speed.
Before I purchased the real thing I also had some success slowing down my non-variable speed router by running the power to it through an off-the-shelf dimmer switch that I normally use for controlling the temperature on a hot wire foam cutter. I was told that this would not work and that it would surly start a fire. Not being one to listen to warnings, I tried it and found neither to be true, however it could only reduce the top speed by about half. Your mileage my vary .
(7) A power planer is not the tool you will use the most when working with aluminum. I have one and it stays in its box most of the time. If we were not building a house last year I would not have even purchased this, but I do own a $120, DeWalt power planer. With that said it is a good tool for straightening out an edge, adding a bevel or even cutting a weld flush. All of which can be done with a skill saw or router and a straight edge. So unless you are going to justify it with some cabinet making, I'd put it on the bottom of the shopping list.
The Arbortech Mini Carver is an attachment for a 4 inch angle
grinder that is commonly used for wood carving, however it can be
fitted with a 2 inch carbide tooth blade that will turn in into a
safe tool for grooving joints between plates or removing or trimming
inside welds. It is much faster and than a grinding wheel and
reaches within a inch of an inside corner. It is also
recommended for back chipping the a weld from the opposite side of
the plate in order to remove contaminations left by the first pass.
I got mine from www.baileysonline.com, but they are not cheep. In fact it is the most expensive tool I have in the collection. The attachment, angle grinder, 2 carbide blades and a spare drive belt goes for $242. The alternative is putting a 3 inch carbide blade directly on the angle grinder, which is then appropriately called a meat axe.