Straightening saws (or going with the hip)

So, everybody is sharpening and straightening saws nowadays.

First, my favourite american in Hawaii gave us a lesson on how to make things flat:

http://mypeculiarnature.blogspot.nl/2015/05/japanese-saw-tuneup-straighten-out.html

Then, another american appeared who has a few very sexy whale blades and is turning everything into planks

http://granitemountainwoodcraft.com/2015/06/02/just-cant-stop-sawing/

I've been busy cleaning the trees so some sun can reach the house and I haven't had much time for tools. However, today was feeling ill so decided to take it easy and work a bit with the computer.

That's the representation of a not so straight saw. The blue is bent to one side and the red to the other. Green is level.

I took inspiration from this saw:

 What I'm trying to illustrate is the displacement field of the saw. If you wish, how far it has moved form its ideal flat straight state.

Now, some saws will have one "oil puddle"

This are the ones you need to work in a circular manner (isn't it Jason?)  so you expand the ripples around till you get something "flatter"

And eventually much flat

Note that in the different drawing the colour scale is not the same, the amplitude of the waves gets smaller as you have more ripples. (Sorry for that, I was lazy today too so didn't want to code that, perhaps I update it later.)

Now, when I was looking at the saw today I was mentally superimposing this colour map on the surface of the saw, a bit like Jason's pictures but with LSD colours. 

Yeah, I know, reality is not as circular and nice as computer models. But that's the fun of it, isn't it?

So you hammer, change the colours, turn up and down the saw, and keep in your mind updating the colours as you hammer. Check with the saw that the image you have in your mind corresponds to reality by looking at how straight the saw is.

All this is a bit like trying to teach how to play violin by writing, so don't blame us because our explanations are poor. 

After 10 minutes or so the saw was 90% straight.

I sanded the surface and then more hammering. (I had to fix a shitty stanley pein and ball hammer in the meantime.) Then I stopped. 

"Know when to stop" says Mark. 

I upload the picture of the straight saw once the battery of the camera is full. 

Done. Camera is full and I had my tea and bread with cheese. 

Now, there are just a few spots on the saw. 

 And this is how it looks from one side

 And the other.

There's still a kink on one side near the handle but I don't think I will be spending files on this saws, so it doesn't matter. 

Just for the sake of coolness, a before and after picture:

Ok, and since I had more time think about the problem, what follows is the evolution of the "saw" when you invert each of the 3 kinks it has. (Some kinks are pointing in one direction and some in others, and what I do with the code is simply to invert the sign of it). To make it more "realistic" I superimposed a wave as in the first image, that is a saw that has both kinks and it's bowed. 

You start with this:

 then you hit the leftmost

 then the red one down (note how the wave of the saw has changed direction by pressing the kink)

 and finally the middle kink

As you see, it's not so easy. Thanks god you don't need to compute the eigenvalue decomposition of the problem, but simply hammer it straight. 

Continuing with the analogy of the violin, you know where to hammer to produce a sound, and you just do it. It's only a saw. You are only You.