An iron sheet, approximately 7*14*5mm (this is for one Slot.it chassis, increase the 7mm width to 14mm or 21mm for treating two or three chassis at a time ), with a nice flat surface which is where your chassis will be clamped to. Most blacksmiths can provide it at very little cost.

The principle is very simple: keep the chassis as straight as possible, heat it up, and cool it down slowly, in water, which is very important as it:

floats the chassis, helping the parts that are not clamped to stay the way they should without
bending under their own weight.

A glass (Pyrex) pan, large enough to hold the iron sheet and approximately 6/7cm high,Neodymium magnets – 6, 7 pieces each chassis.

acts as a thermostat, thus preventing the chassis to be burnt as it will get no hotter than 100° Chas a thermal inertia which slows down the cooling process