I've always wanted to make a powered hacksaw, not because of any particular need for one, but after seeing a homemade one at a Model Train exposition 20 years ago, I figured that I could do that. The one that I saw had an old windshield motor as the power source.
Fast forward 7 years and I was lucky to become the proud owner of several portable ventilators (used in respiratory therapy) that were destined for a dumpster at a hospital that I worked at. This was before E Waste recycling depots became wide spread around the country. I took them, after obtaining permission to do so, not knowing exactly what they contained, but to me they were too good to be sent to the landfill.
The compact motor/gearbox from one of them would become the power source for the hacksaw. A big bonus was that the motor runs on 12 volts, so it would be easy to power it almost anywhere.
Step 1: Parts I Used- A pine board 10 inches wide by 3 feet long.
- The geared motor (you can see the information about it on the nameplate).
- Assorted length S.S. bolts and regular steel nuts and washers (I used S.S. because I had some and figured they would wear better). Also some 1/4 inch hole bearings and some large plastic spacers that I had to cut to length.
- An industrial drawer slide from a 19" rack cabinet - the slide is approximately 17 inches long.
- A large 1/4 inch thick angle bracket and some mounting bolts for it.
- A piece of 4 inch long by 2 inch wide channel steel (I think it came from a desk).
- A 12 inch long by 1 inch wide piece of steel with pre-drilled holes; this attaches the motor drive arm to the saw.
- An old hacksaw I picked up at a yard sale.
- An aluminum vice that I picked up from somewhere that has two holes for screwing it down.
The frame that the motor was attached to in the ventilator is aluminum and has two mounting holes with threaded inserts for #8 machine screws on the bottom. I marked these holes on the piece of pine and drilled the two holes. Then, using appropriate screws with washers and lock washers, I fastened the motor from the bottom to the board.
I then fastened the angle bracket to the board using bolts.
The saw needed two 1/4 inch holes for mounting it to the motor and guide rail; this took a bit of experimenting and figuring out on my part.
The connector arm was then fastened to the motor and the saw. Where it connects to the saw is where the two 1/4 inch bearings where used. The arm from the motor has a similar sized bearing in it.
The channel bracket was then attached to the angle bracket. The industrial drawer slide was then attached to the channel / angle bracket setup. The other end of the industrial drawer slide was then attached to the saw. The vice was then lined up with the saw blade and screwed down in place.
Step 3: TestingI powered the saw with one of my ham radio power supplies (13.5 volts at 12 amps), and hooked up a digital meter to measure the current draw. The current draw when sawing is less than one amp.
I test saw various items pieces: plywood, wood dowel, 1/4 inch bolt and old epoxy-filled dinner knife handle.
The saw runs a little faster than a person would saw, but doesn't get tired. Because of this relatively slow rate, the blade or the bolt or knife handle didn't really heat up. I checked the temperature of the blade and item being sawn with my non-contact digital thermometer and the temperature was only two degrees above my basement temperature of 17 degrees C.
Pictured is the knife handle being sawn and the result. When I need to cut larger pieces of steel, I would do it outside and use cutting oil. It took me several years to get around to building this, but I'm happy with the result.
Step 4: What's Next? The Start/Stop Auto-Shut-Off ControlI've added the start/stop switch and a circuit for automatic shut off when the cut is finished. The first picture is a ladder diagram of the circuit I made to add start/stop and auto-shut-off control to the powered hacksaw.
I mounted a micro switch on a piece of aluminum attached to the vice. I used the normally open contacts from it to stop the saw via the relay. When the saw drops after the cut is finished (the saw frame drops down), the lever from the micro switch is activated.
The start/stop buttons start and stop the saw: pressing the start button turns on the relay, and power to the relay is maintained by a set of contacts from it. A second set of contacts supplies power to the hacksaw motor.
When the limit switch is activated, it cuts power to the relay and stops the saw. The saw can also be stopped at any time by pressing the stop button.
Materials I used
The items listed are what I had on hand:
- Square D Industrial start/stop switch
- Micro switch
- 4 pole 12 volt D.C. relay and socket
- Assorted colours hookup wire
- Spiral wire wrap
- Piece of aluminum
- Tye-wraps
- Cable straps
- Screws
The last picture is the ladder diagram and my hook up diagram.
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