Why are the blades on guillotines shaped the way they are? In most images I have seen the blade is slanted to some degree but I am certain I have seen variations such as the bottom of the blade resembling a half-circle (this is as close as I could find to an image of the type of blade I am describing, not great I know!!). Anyway, what is the reason for having the blade shaped anyway other than straight across? As far as I can see in my mind the blade will still make contact with the same degree of force, the only difference being that the part of neck the blade first makes contact with is different.
Slicing cuts better than chopping. For instance take a knife and press down on a pepper. If you press hard enough the skin will break and the knife will go through. But with a lot less effort if you slice (i.e. pull back on the knife while excerting some downward pressure) it will go right through.
I’m not sure of the mechanics of this though I would imagine that it has to do with their being less internal structure to prevent a surface from pushed sideways than there is downwards. For instance, if you had a bin full of metal balls, you can slide the balls on the top around pretty easy, but you can’t press them down nearly as easily. The same even as you go deeper, anything which helps to make the balls move sideways, or even allows them to go up, out of your way is going to be more successful than just pressing down and hoping it slides off to the side.
cute. 
One example is The Halifax Gibbet, an English device that pre-dates the French use by many years.
http://www.ff.iij4u.or.jp/~yeelen/system/howto/halifax_l.jpg
Gillette has announced the new *Fusion[sup]TM[/sup] * five-bladed guillotine. The first blade pulls the hairs back, the second pulls the skin taut, then tyhe next three slice through the skin, muscle, and vertebrae before anything has a chance to spring back. It cuts through so quickly and cleanly that you’re in the basket and still conscious before you’ve had a chance to realize you’re dead. And there’s no stubble.
Schick is jealous. Their ive-bladed guilotine is nowhere near ready, so they’re gearing up for a six-bladed system. Right now they’re trying to salvage with sales of their beheading creme.
I’ve never seen a picture of a guillotine looking like that (with a round blade).
I also wonder why you added ducks on the picture…
…picture…(picture)…((picture))
Seriously, to elaborate on Sage Rat’s response most materials fail much more easily in shear modes. Shear is a combination of compression and tension acting together. In the case of the guillotine the downward motion obviously imparts a great deal of compression to the victim’s neck. But with an added angle to the blade there is a component of tension as the blade is effectivley drawn across the flesh laterally.
You see this type of arrangement in a number of applications. Paper knives, sheet metal shears (no pun intended) and even scissors are using this advantage. In the case of a steel punch where the idea is no movement whatsoever as the hole is punched you will often find the bottom of the punch concave to provide a modicum of tension in the area being forced out.
Materials are cool things to break.
Just to clarify, I didn’t make that picture, it’s just the closest thing I could find to what I was looking for on Google images!! :smack:
Thanks for the replies, I understand now why the slant is a better design for the blade. I guess the inventors of the Halifax Gibbet went for the brute force approach as the Google images results tend to show a large weight with the blade at the bottom, perhaps they spent too long arguing over how many times the severed heads would be able to blink after the chop.
So you still end up dead but no guillotine burn, eh?