You guys better stick to electronics and leave this sort of thing to a first year engineering student, an apprentice carpenter or Bob Vila on a slow day. What in the world is this guy doing cutting wood with a hack saw? Has he found some wood cutting blade somewhere? These are for metal. The chips he is making sure look like an abused hacksaw to me. A decent back saw would have this done in half the time.
The first year engineering student might notice that this is a version of a perpetual motion machine. Somehow, we will get more force out of that recoil mechanism than we put in and that will make everything faster. Ain\'t gonna work that way.
The inventor should run a race with a regular hand saw and your editor should learn more about woodworking.

ok, why use a fine tooth metal cutting blade to cut wood? you still have to load the spring, why not just use a wood saw, in any case, you will expend energy to load the spring, what is the return of energy?

This actually a brilliant idea. A lot of the energy in sawing is used bringing the saw to a stop in order to reverse direction, and of course that energy is usually wasted. In this invention that energy is stored and then released to help the stroke reverse direction. I suspect this might actually work.

I won't bother repeating the issues with using a hack saw to cut wood. It's pretty clear that this person doesn't do a lot of hand sawing. Any energy that could even conceivably be saved through these springs (which still need to be compressed, wasting energy) is wasted by creating a shorter cutting stroke that becomes less efficient when compressing the springs.
"Using a hand saw is nobody's idea of a good time"; It is to me. I use hand tools almost exclusively in my projects.

Run a test simultaneously to compare with & without. He is using the energy wasted on the back-stroke to impel the saw forward, conserving that energy. Great idea. Five years from now all handsaws will have a similar device.

I think this may be a working advantage. If you ever ran across a trampoline you would probably feel the same effect, the bounce back propels you to the next step, much like the stroke would be propelled back into the opposite direction. Perhaps a physicist could calculate the momentum and change thereof.
I think this guy should set up a test fixture, one with a set downward pressure and set force for the forward and return stroke using the full stroke for a standard and his modified saw. I have just such a device already set up if he would like to use it. I am in San Diego California. You can go to this site to see the description and there is a link to the circuit schematic. http://members.cox.net/paulvild/RecipricatingTestCircuit.shtml
Also, he may want to use a metalic substance as a test subject. This is so that the woodworkers wont get distracted by the selection of the blade.

Well D\'UH! Of course it cuts faster, as the bumpers allow the user to use the entire blade without slowing down at the ends to avoid hitting the frame.
Anyone that has ever used a saw knows that you use primarily the center section of the blade to avoid hitting the handle or the saw sliding out of the cut. These shock absorber/limiters allow use of the entire blade. Twice the cutting length = twice the speed. Not rocket science.

40 seconds versus 61 seconds. The faster saw wins the race.
Doesn\'t matter what kind of saw he was using. Rebound from the springs allows the blade to travel faster across the piece, reducing the time it takes to finish the cut.
This is an excellent innovation. If you have to use hand saws, this is the way.

LOVE IT! Three thousand years of saw technology leaps forward in the year 2010.

Hope he makes millions, as he makes the rest of us more efficienct, without having to changes sawing arms in the middle of a long cutting task.

Three Cheers!
Doc R

amazingly simple!!!! wow!