There is no one type of metal cutting tool that will be best for all types of cuts. To me if I could only have one , my first pick would be a portaband type saw. I have found that there are many times that a 4 1/2 grinder with a cutting blade is the only thing to use , particularly in tight spots. Just an FYI they do make a guard with a slid shoe for cutting blades for a 4 1/2 grinder. I have one I use on a grinder set up with a carbide tiped blade for cutting alum. skegs off of outboard motors when I need to weld on a new one. It would work with an abrasive cut of blade too but does reduce the depth of cut you can get from a 4 1/2 in grinder. Even a sawzall has its place and there are times when it is the tool of choice. I do a lot of work in a saw mill and I try to not use a torch or plasma unless I have to, because of fire danger. I have to carry a vast assortment of cutting tools to use in different situations . I have found I need them all from a hand held dry cut saw to a sawzall in order to do what needs to be done.
For about a year I was stubborn and did not want to buy a new horizontal cut off saw. ( I had an old cheap one That I purchased about 25 years ago ) Mainly because of cost. A good one can be anywhere from $2500 to $5000. About 2 months ago I took a gamble on the harbor freight heavy duty band saw . With a 25% off coupon and a sale I walked out with it for a little over $600. I did not expect a lot ( since I all ready had a version of their cheaper horz. band saw ) I will have to say I have beed very impressed with the new saw. Once I got it all squared up it now will cut an 6x10 tube square within 1/32 of an inch all day long. The only thing It needs is a good finer tooth blade put on it . I am very pleased with it now.
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