Make a scroll saw! (using only upcycled/free materials)

Step 4: Parallelogram arms

Okay, now time to start cutting wood!

This is very important!! The goal here is to make a parallelogram where the the center of the bolts and the center of your blade pivot pins forms the corners. 

In other words:
1) The two oak "arms" are the top and bottom of the parallelogram.
2) The blade and the post are both sides of the parallelogram.
3) The distance between the center of the bolts MUST BE EXACTLY the same distance between the blade pivot pins.
4) Likewise, the distance between the center of each arm's bolt and it's corresponding blade pivot pin, MUST BE EXACTLY the same!

If any side of the parallelogram does not match the opposite side, then the blade will not stay parallel to the post as it goes up and down.  Instead it of sawing straight up and down, it will also tilt back and forth and be impossible to saw with.

Both of my blade mounts go up through the bottom of their arm, and the handle is on the top of the top arm.  Also, the arms extend slightly past the opposite side of the post.  You'll see why in the next step.

For the mounting bolts, I went bolt->washer->arm->washer->nylon washer->washer->post->washer->lock nut. 

(The nylon washers originally came with a set of toilet mounting bolts.  I just through them in there to try and make things quieter.  Don't know if it was necessary, but hey, whatever.)