We need to cut the profile pipe at 90 degrees. Work begins with the correct marking of the place of this cut. We marked all 4 sides in a circle, but at the end it often turns out that the lines do not coincide by several millimeters, as in the photo above. This happens often with beginners, and not only.
If you cut it off with a grinder according to such a marking, then the end of the pipe will be uneven and uneven gaps will be obtained during welding. Profile pipes for their household needs are often taken with a thickness of 1.5 - 2 mm; gaps at such small thicknesses will not be easy to weld, and especially with little experience. I'll show you how to make such markup perfectly accurately.
We mark the first line in a square. Now we flip the pipe away from us. We put a small line on an unmarked shelf, it should be like a continuation of the first line.
We hold the pencil on this line and gently move the square ruler to the core of the pencil. Also, most squares will not be exactly 90 degrees. So that it doesn't bother us, just turn the square with a ruler to the other side. In this position we draw the second line
We do the third line according to the same rules that I described above. Do not forget to turn the square's ruler to the other side for each new line. Even if there is a deviation of 1 degree on the square, then after marking all the sides, it will still take 4 degrees away, ideally.
That's all, we made a marking of all 4 sides of the profile pipe. The last feature almost coincided with the first. The deviations were less than a millimeter. When marking in a circle, this is an excellent result, now you can safely cut with a grinder.
Video with all the details of such markup-watch HERE