QUOTE: Actually, it rips ON THE GRAIN (the cross grain); but the grain isn't always heat set staight so when it is ripped it appears to be ascew.
When this happens, I usually lose a little bit by serging along the ripped edge. This will prevent the threads fronm getting tangled in the wash. If you desire to have the fabric on the true grain (if ypu want stripes straight, etc) you can pull it on the bias (opposite corners) and continue to do so until the ripped edge is straight. I bet that is as clear as Louisiana mud.
When cutting borders and bindings on the straight grain (following the selvege) I rip but allow a little extra that I can trim off to remove the threads. Then I know my pieces will be straight.
ME: imagine that your fabric is on an assembly line and the selvedges are hooked onto rails on either side of a belt. the belt, with the rails, is traveling through a something (oven? steamer?) that will heat set and size the fabric. imagine that one rail is moving a teeeny bit faster than the other. the lengthwise grain is not affected at all because it's not being pulled side to side. the cross weave, however, is affected greatly. it's being pulled, not off-grain, but unevenly. at a different rate of speed so that one edge is being set before the other. if you could see the weave under a magnifying glass, you would see that the cross-threads are no longer at right angles to each other. once they are heat set they are that way forever. forever. when the fabric is torn, ripped. whatever, it is being ripped on grain, but the grain is no longer straight. it's been heat set at the wrong angle. it has little or nothing to do with the quality of the fabric. it has to do with the quality of manufacture. unless the rails are moving very evenly, you can't get straight grain. straight grain means straight across. when you rip fabric, it will rip on grain, but not straight across. no amount of tugging, steaming, ironing, etc., will permanently re-set the fabrics. so if you cut, even though it's not on straight cross grain, whatever shape you cut, it will stay that shape due to the heat setting, which is why some people prefer cutting. it's very reliable.
to test your ripped fabric, lay your fabric on the floor. fold the way it is when you buy it. make sure the folded part has no wrinkles, and the edges are smack up against each other. if you look at the two ends, you will almost always see that one half of each end is longer than the other half. you have paid for the longer length, but can only use the shorter. if you are a 'washer', the problem is compounded, because the stiffening agent, which has helped keep the fabric even this even, has now dissolved. there is nothing to prevent the fabric from scewing even more.
waah? can anyone understand this? i almost don't myself.
when all of our fabrics were made in this country, this was a very unusual occurrence even in cheap fabrics. cheap meaning thin, poor thread quality or a loose weave. our fabric isn't made here anymore, and the quality has suffered. there are exceptions, but not many. if anyone has been lucky enough to rip and still have true cross grain, they are very lucky indeed.