I have a cheap electric scroll saw, one of those Scheppach for ~ 100 EUR. While they are not the best build quality, some people on youtube apparently are happy enough with it and manage to get the results they desire.
The manual says it can cut not too hard wood up to 25mm thickness. I mainly bought it as I thought finer cuts (vs. electric jigsaw or hand-held circular saw) would translate to more precision, for things like "simple" finger joints, or cutting pars for smaller wooden cases such as for DIY loudspeaker enclosures and what have you.
So I tried to cut my usual material, pine or spruce, 18mm thick. A piece of 20x20 cm², I cut off a 3cm "strip", drew a line across with ruler + pencil before.
I was unable to get anywhere near a straight cut. More of a irregularly modulated sine curve with weak amplitude, but not weak enough... The blade seems reasonably tensioned and I don't think the machine warrants more tension, but still, the blade bends (torsion) rather easily, making the process rather wobbly. Also when I saw I was leaving the drawn line, the only thing that seemed to help to get back onto it was not just trying to correct the angle, but also actually moving the workpiece's cutting line out of the virtual vertical line between the two mounting pins of the blade, i.e. actively bending the blade, which is obviously curving the cut in the sideways dimension, and probably not good for the machine & blade.
I have watched a couple videos of people demoing that cheap saw, but I was not able to replicate their results.
What am I probably doing wrong?