The photo above is of the (somewhat) unique power hacksaw, that I built last winter. It isn't much to look at, and it certainly has some minor flaws. But overall it works quite nicely. The pulley system reduces the motor RPM, to allow approximately 70 strokes per minute. Much of the saw is built using scrap metal found at a local steel recycle yard. Other items like the pillow block bearings, were scavenged from machinery found at the same place. Only the pulleys, belts and hacksaw blades were purchased new.
The thing that makes this design a little different from others I've researched, is the guide arm for the blade carrier or slide; which is made using two lengths, of one inch square tube placed in parallel. This provides a simple but very rigid track for the slide to move back and forth in.
The slide itself, is composed of two pieces of 1" x 1" x 1/8" angle steel, placed back-to-back so as to form a 'T'. The blade is held by two pieces of 1/8" thick flat bar, that were sandwiched between the angle steel forming the 'T'. No need for precise pivot points, or engine rods, etc.. It cuts very accurately!
The photo is an 'action shot', of the saw slicing through 1 1/2" x 3" x 3/16" rectangular tube.