My first attempt in 2011 at a powered hand saw was rather naive
It didn't run very well and it was patently not going to be easy to work with.

I used a motor and some gears that I had salvaged from an old printer.

In the end I got to this stage before I abandoned the project.
The crankshaft was just too clunky.

Then, about six years later, I saw this gif on the internet.
It's called a Scotch Yoke and I really liked the idea that the crankshaft was in the middle of the conrod, so that made it more compact than the previous failed attempt.

Seeing a gif work is one thing, so I had to make a physical model to see whether the action was smooth enough to warrant further consideration.
So I made this model out of plastic.

I used my flex shaft motor to power the thing while holding it by hand and it worked surprisingly easy.
I figured the basic drive concept would be able to move a saw frame up and down without too much clatter.

My first attempt at creating the same in actual metal.
At the time I had no milling machine, which would have made everything sooo much easier.
So it was basically a matter of using five or six millimeter brass stock and then solder and fabricate a scotch yoke.

Just having a single 6 mm square column to which the saw frame would be attached to, proved to be unstable.
So my next attempt was to make some nylon sliders and a rectangular bar to which the top and bottom saw frames were soldered to.

There was too much resistance and it still wobbled.
Also my crank was mounted on top of the backing plate and when it ran, it would wobble and touch the backing plate.

So then I cut out the backing plate and mounted the crank flush with the back plate.
I also made a more substantial bearing housing, so there was no more wobble.
In the end, I change back to having the crank mounted above the backing plate, because cutting a hole in the backing plate was labor intensive.

I had no means to power the saw, so I mounted a old 12V drill motor onto the crank shaft, just to see what kind if movement would be generated by the up and down motion of the saw frame.

Then I went back to a single column with harder brass slides to stop the side to side wobble.
But the saw frame was simply to heavy for such small contact area.
If the brass slides were tightened so that there was no side movement, then the up and down motion became to difficult for the motor to move, and if they were loosened, then the side ways motion became unusable.

A different design. This time with a round guide bar sliding in nylon with 4 bearings that acted a guides to stop the sideways motion of the saw frame.
It worked after a fashion, but it was to complicated to build. Too many components had to be adjusted just so for it to run smoothly.

And then came the Eureka moment.
I changed the essential scotch yoke design, and made it into a H shape. Same drive method, but with the arms on the outside.
This proved to be successful, and the sideways motion was gone.

The first H frame was bolted together and the new saw frame I had made was also bolted to the H frame.

I had a shaded pole electric motor and I decided that if I could make a machine that needed only this motor, that would solve the drive problem and also have a power unit that was common to buy and very cheap.
$30 at the time of writing.   I would have to be very careful with the pulley sizes.

Tensioning this saw frame was also a mission. I made a special tensioning tool, which I luckily discarded soon after.

This was also one of my blade support options I made to guide the blade.
It did not work very well.

The strip across the table was supposed to stop the piece being cut from moving up with the blade.
It was OK, but fell short when the material that was being cut was of different thicknesses.

I redesigned the blade support and made it more adjustable, which worked a lot better.

This was also a design I messed around with, trying to get that killer saw frame nailed down.
Alas, it was the frame that had to be killed instead.

Then I redesigned the H yoke and I was able to solder the stainless steel very accurately on some ceramic board and a silver solder I mixed up specifically for this project.

And then, one day, I got tired of messing around with a design that had too many dead ends, and because I had a bit more experience in the direction of where not to go, I started over with a new machine.    I designed a new saw frame.

And I redesigned the whole body of the machine.
You can see the old machine lying in the background.

I made the H guides out of nylon and perspex instead of brass. I still did not have access to a milling machine, so these took quite some time to get everything running even semi smoothly.

The motor was still sticking out too far.
Later I brought that inwards.

I made a hardened steel blade guide and this one worked very well---finally.

Here I am moving the motor inwards to the center of the machine.
Also playing around with a led light with a goose neck to shine on the work piece.

I ordered various sizes of sewing machine fan belts, so I could play around with different pulley sizes.  The trick was to have the saw going up and down at a medium speed and the same time having enough power to push the blade through metal that is up to 3 mm thick.  Also, the shaded pole motor does not have an internal fan, so an outside fan was mandatory.     Without a fan the motor would burn out.

This was my blade tensioning method, which works the same as any commercial hacksaw available today.

I made several designs to hold the work pieces down    This one was too weak

So was this one.

As was this one.

This one worked, but was so clumsy that I was embarrassed to look at it.

This was my final design and this one is easy to adjust and works well.
Simple is always best.

I made the 'foot' removable, just so that I can change the shape more easily, later down the line.

I closed the back of the machine up so that the fan and pulley was not exposed.

The front was also closed up.

The I added a on/off switch and also a switch for the light on the top of the machine.
I tried to find a two speed shaded pole motor online but I was not successful. I know they exist, and one of the switches would be changed to hi/low speed for such a motor.

I made a stl file for the body and had it printed just to see how strong it would be.
The technology is not quite mature enough for this purpose, at the time of writing ( 2017)
The black little box is the transformer for the led light.

The following are just boutique pics.

The top all nicely finished off.

The bottom with the catch tray to catch the gold or silver dust.

I also made a safety grill for the motor in the front of the machine under the catch tray.
I also added a magnifying glass which is an essential components for a dumb boomer like me.  The eyes ain't what they used to be.

All the components that make up the machine.
I have used this machine with saw blades from No 0/8 through to No 1 and they all work well, although good quality blades last a lot longer than chinese cheap ones.

The back of the machine.
The clear plastic circle is so that one can turn the machine by hand, similar to what a sewing machine has.
This makes changing blades a lot easier.
The two brass tubes on the right side at the top of the machine are there so store new saw blades.
I have use this machine for about 500 hours of cutting time, and although it has, like any machine, a small learning curve, overall it works very well.