The Torture Chair
The victim would have been secured to the chair by a bar across the chest, and with ankle and wrist restraints. Some versions of the chair had vices that tightened down across the knee-end of the thigh and across the shins, crushing the legs and forcing them hard against the chair spikes.
It is doubtful that just sitting on the spiked seat would have been that uncomfortable. As with most equipment designed to give pain "less is more". A flogger with three strands causes more pain than a flogger with 30 strands, therefore a seat with this many spikes wouldn't hurt nearly as much as a seat with three or four well placed spikes.
With this piece of equipment the pain came from crushing the body down onto the spikes and from heat. A crucible containing hot coals would be placed under the seat and the heat from it would be conducted throughout the structure.
