A cute little trick that I have used when I didn't have access to a shear is to get two pcs. of bar-stock, like .250" x 2.000" or .375" x 2.500", size is not that all important, just as long as they are longer than your pc. of sheetmetal and that they are at least .250" to 1.000" thick. (cold-roll bar stock is better because it has a nice sharp edges on it).
If the length of the sheetmetal part is important you can scribe you a line on it where you want the final cut to be, this helps to setup the sheetmetal part to be cut. Then cut your sheetmetal with a grinder, bandsaw or a nibbler as straight as you can but about 1/32" to 1/8" or so, longer than needed. Then sandwitch your sheetmetal between the two bar-stock pcs. and c-clamp all 3 pcs. together at the ends of your sheetmetal so that your sheetmetal just sticks out from between the edges of the bar-stock about 1/32" or 1/16", or clamp so that the edge of the bar-stock is right on your scribed line. Clamp on the back side of the bar-stock so you have access to the trimming edged and the c-clamps are not in your way. The two pcs. of bar stock must be exactly on top of one another with no offset or step between them. Then use a small hand grinder like one of those 3" right angle die grinder with a FINE grit dics and grind your sheetmetal down to the edge of the bar-stock. The bar-stock also acts like a heatsink and you will not get any warpage. Sometimes I put some 'layout blueing' on the edges of the bar stock and that lets me know when to stop the grinding. You don't want to grind the bar-stock, just grind the sheetmetal down to the bar-stock all the down the length of your sheetmetal.
Then remove the c-clamps and dress the edge of your sheetmetal with a hand file just enough to remove the grinding burr.
This is not as hard as maybe I have made it out to sound.
But a person can get good enough at doing this that is is hard to tell the part was not cut on a shear.
Yes, it does involve some time to do this but it does make a nice straight clean edge. I have two pcs. of .500" x 2.000" cold roll bar-stock 36" long just for doing this at home.
I have worked for a sheetmetal company for 30 years and would often have to do this if we had a part that already had forms or bends in it and it would not fit under the shear machine hold-downs.
