In this project I tried to make an electric screwdriver, in which I feel I did a pretty good job. The device is powerful, strong and is truly handy when assembling some project or when taking apart some old gadget. I however would like to make a note that this is by no means cheaper than the commercial alternative. This in total costed me almost 1000 rupees which translates to around 15USD. Although it might sound less to some of you in west but keep in mind that I could have bought the commercial one for around 800 rupees.
However I do not discourage you to make one of these. This one will make it to my favourite tools.
All the best.
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Step 1: Motor and Attachment
Motor is the heart of this project and hence its better you chose a powerful geared DC motor. The one I had was rated for 250 RPM at 12V. This is a reasonable speed for tightening the screws. This turned out to be a perfect choice.
Make sure your motor has some arrangement to transfer the torque. There must be some hole through the shaft were in you can insert a screw as a pin and lock the motor and the coupler rigidly.
The attachment shown in the picture is the one form a Bosch 500W drill kit.
Step 2: Measure Your Tools
I had a motor lying around which is why I decided to make this project. So, as a first step you would like to get introduced to your motor and the clamp and the possible attachments to the shaft of the motor. My motor had a shaft diameter of 6mm. So further I had a look at my tool holding attachment. I simply took it from my Bosch Drill Kit. It was a bit impractical to tighten or loosen the screws with a drill machine and it was not a sad compromise to use the tools to make a new fancy project.
The attachment had a hexagonal attachment and the distance between to opposite vertices was around 7.2 mm and distance between two parallel sides was 6.32mm. This however meant that the tool holding attachment could be hammered into a 6mm hole if the material was soft enough. I used solid wood as ply would not have performed will under torsional conditions.
I finally drilled 6mm hole through a 20mmX20mm square wood rod roughly 30mm in length. I failed twice but on the third run, satisfied with the drill quality, I hammered my drill tip holding attachment into the hole. It was a tight fit and then I drilled a hole to lock a screw with the hole in the shaft of the motor.
Step 3: The Body
I chose to use simple old ply wood to make the physical body of the screwdriver. I wanted it to look like a gun or a hand drill. I finally narrowed my design to one in the above pictures. I also have the dimensions of my project. The most difficult part is drilling the holes . In order to fix the structure, at some point you will have to make perpendicular joints and this means that the screw will have to be put in the small width.
The ply I used was only 6mm thick. This means that I had to drill holes 2.5 mm in diameter on cross section of the ply. The most disappointing moment is when things decide to not to go your way and ply decides to split. Please be incredibly careful when trying to drill on such small piece. Use a holding device like a clamp or a bench vice as I did. Your fingers are precious and be careful when using power tools.
When cutting the ply in shape, I used a jig saw which eased the work a lot and went through the wood like a hot knife through butter. Using a hacksaw would certainly be not so easy but is definitely possible.
Step 4: Powering the Motor
As stupid was, I initially used a fancy motor driver. LM329 to be precise. This IC uses BJT in its final switching stage. This means that there was a 0.7V on both i.e. the high side and low side transistor. This means that there was around a watt of wasted power inside the IC. The IC would easily heat up but the motor worked.
Sometime later I realized that using relays would be much much better and hence I got two of those 12V relays and connected them as shown in above circuit diagram. This meant that there was almost no power loss in the switching side and more power for the motor. The design was flawless and works perfectly. With this, the problem of reverse polarity was also eliminated. Revering the polarity of the supply would now only reverse the direction of rotation and there would be no magic smoke would the BJT would have certainly produced.
As a power source I decide to go with a sealed lead acid battery. The battery was rated for 1.3 Ah. Trust me, this is a lot of time to screw and unscrew. If you try to screw or unscrew for this long you will be screwed for sure.
Please note that handling a lead acid battery is a great responsibility. Any short can potentially lead to fire or you may burn yourself with wires. Also charging and discharging the batteries requires some knowledge.
If all done right, a powerful screwdriver is ready to help you do your beautiful projects.
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