The instructions given to Guidon, the carpenter tasked with making a guillotine, written by Antoine Louis in March 1792, are posted here. My French wood- and metalworking vocabulary is less than great, but I made an attempt at translating it. I put brackets where I couldn't make sense of the text, but please let me know if anything else came out incomprehensible

This machine must be composed of several pieces.

#1 Two parallel upright pieces of oak 10 feet high, joined at the top by a rail and mounted solidly on a joist, with [contre-fiches] at the sides and back. These two upright pieces will be, in the work, one foot apart, and around six inches thick; on the inside of these pieces there will be a square longitudinal groove one inch deep, to receive the [oreillons] of a slicer. At the upper part of each of these upright pieces, under the rail and in their depth [?], will be placed a copper pulley.

#2 The well-made slicer, with the solidity of the best cleavers, made by a skillful edge tool maker, will cut by the convex surface [?]. This cutting blade will be eight inches across and six high. The back of this cutting blade will be thick like that of an axe; under this back there will be openings made by the blacksmith so that it will be possible to attach a weight of 30 pounds or more to the back with iron hoops; if during attempts it is found appropriate to make the mass of this weight heavier, a ring of iron will be added. As the slicer must glide from the top of the grooves of the upright pieces, it's back will be one foot across, plus two square [oreillons] protruding an inch to enter into the grooves.

#3 A cord, sufficiently long and strong, will pass inside the ring and support the slicer under the upper rail; each end of this cord will be connected from inside to outside the corresponding pulley and will be tied on the outside towards the base of each upright piece.

#4 The wooden block on which the patient's [!] neck must be placed, will be eight inches high and four inches thick. Its base will be one foot wide, the distance of the two upright pieces; a detachable peg will go across each upright piece and affix the block by its base on each side. The upper part of this block will only be eight inches wide. A groove will be dug at the top to receive the cutting edge of the convex slicer. Therefore, the internal grooves of the two upright pieces must not extend lower than this groove, so that the block is not cut by the slicer. The upper part of the block will be lightly scalloped to easily hold the neck of the patient.

#5 But to secure the head and so that it can not be raised at the moment of execution, there needs to be an iron crescent, like a horse shoe, around the neck of the patient, up by the nape, level with the base of the cranium, where the hairline ends, and that the sufficiently elongated extremities of this crescent be pierced to be secured by a bolt which traverses the upper part of the block with a thickness of four inches. The patient, laying on his stomach, will have his chest raised by his elbows, and his neck will be placed without discomfort in the indentation of the block. If all is well organized, the executioner placed behind the machine will be able to reunite the two ends of the cord supporting the slicer, et, releasing them at the same time, this instrument falling from above, with its weight and acceleration will separate the head from the trunk in the blink of an eye.

If there are any errors in these details, they will be easy to verify by the least intelligent constructor.

We're, uh, not going to be hauled up for aiding and abetting a very complicated murder, are we?