Intro: How to Build a Metal Arm
With a clear vision how it could look like, but not had to look like, i just started the building process, using my right arm as a model. I used no blue prints or other patterns, it was more a trial an error process, where i made some building steps and decided after finishing them, if the result was good enough, considering function and design. If i wasn´t satisfied with the result, i putted it aside and tryed something different, even though it meant i had worked half a day in vain. This also means, that i have no drawings or accurate dimensions of the metal arm, each individual part is simply adapted to my own body dimensions, while attemting to get out a nice optics.
My general intention was to build an arm out of full metal, while maintaining the mobility of all joints as much as possible. Maintaining the mobility is the biggest challenge, if you try to rebuild the human limbs out of stiff materials like metal. To work around this problem and to achive a good result, i used some silver colored leather for some critical parts.
As i have no machines for working with metal, i mostly used some pliers, files and hammers. All together, this metal arm consists out of about 1200-1300 separate parts. Putting all these parts together, took me about 8 weeks, working mostly in the evening hours.
With most parts of the result i´m satisfied, if you think the same, support me in the instructables design contest and vote for me! Thanks ;)
# Note: Safety first! Working with metal plates means, working with sharp edges and sharp tools. Therefore it is always very important to wear gloves! I prefer using the thinnest cut-resistant gloves i can find, with thick gloves, i loose the fine feeling in my fingers.
# Note: As pictures sometimes tell a lot more than words, most instructions for assembling the metal arm can be found in the pictures. In the introducing text passages of the following steps, i only mention the essential basics.
# Note: The red light-effects in some pictures are realized with red led´s, coin cells and magnets which can be fixed easily to nearly every position of this metal arm. Further informatiion about these "throwies" can be found here:
Some impressions of the building process and the finished metal arm are summed up in the following video:
Step 1: Tools & Materials
For construction parts:
- Tin coated steel sheets (thickness: 0.2 mm)
- Perforated steel band (12 x 0,8 mm; diameter of boring: 4.5 mm)
- Silver colored leather
- Rivets 6/6 mm
- Eyelets 4 x 3.8 mm
- Bolts M3x10
- Press fasteners 10mm
- Metal glue, also useable for leather and other stuff
- Elastic band
- Metal shears
- Bind rail for bending (mask the jaws with tape, to avoid scratching the metal surface)
- Bind rail for punching holes (for rivets/eyelets)
- Bind rail for fixing eyelets
- Files for burring sharp edges
+ gloves for your safety!
Step 2: The Hand / Glove
The hand is the most difficult part of this instructable.
It has to be worked with a lot of small pieces of different materials and at some parts it has to be worked with one hand. As i wanted to fit the glove perfectly to my hand, i used my right hand directly as model. That meant, sometimes i only had my left hand to put everything together.
Thus, it is necessary to plan some building processes in before, especially those where you can only use one hand. So put all tools and materials you will need for these steps to a place you can reach with your left hand and also prepare all materials regarding size and quantity as accurate as possible before you start.
Another option is to make a model of your hand/arm and to put everything together on the basis of this model. I decided for using my real hand/arm.
Step 3: The Forearm
While building the forearm, it is important to focus on two areas.
On the one hand, you have to assure that the end of the forearm (elbow), fits to the piece of the upper arm. Therefore it is necessary to build at least the basic skeletal structure of the upper arm to make sure, that size, diameter and length of the forearm fit to the upper arm.
On the other hand the area at the wrist must be made very accurate. As is did not want to connect the glove with the rest of the arm, i decided to put the end of the forearm over the end of the glove to get an overlap.
This means, the diameter of the end of the forearm has to be a little bit wider than the diameter of the wrist part of the glove.
The bigger diameter of the forearm and the overlapping cause the following problem. The glove end must lie below the forearm end but the entire metal arm is putted to the body before putting the glove on. This means, it is not possible to put the glove completly on your hand.
To solve this problem, i constructed an opening mechanism at the end of the forearm. With this, i can put the entire metal arm to my arm, open the mechanism at the forearm to get more space, put the glove on, and close the mechanism.
There are definitely other possibilities to solve this, but near that functional factor, i liked the look of an opening/closing mechanism at the forearm so i decided for that solution.
Step 4: The Upper Arm
The skeletal structure of the upper arm has to be made together with the forearm to ensure everything has the right length and fits together.
At the area of the elbow, where she skin of the upper arm and forearm touches, while bending the elbow, i worked with leather. Using metal makes this area to stiff, what effects the flexibility of this joint substantially.
The same applies to the upper inside, at the area of the armpit. Here i used leather for having more comfort as it is not very comfortable when metal scrubs on the thorax.
Step 5: The Shoulder
The shoulder consists out of three articulated elements which are fixed to the end of the upper arm. Here too, it makes sense to build the parts not directly done. Attach the parts in between to the rest of the arm in order to test, that everything is working and the length and sizes of the pieces fit to the body shape.
Step 6: The Fastening
The metal arm weights about 1.8 kg which is not very much. Nevertheless it is necessary to fix the entire construction somewhere on the body.
Therefore, two loops are attached to the inside of the upper arm. Through these loops, a belt is pulled, which is placed around the chest.
As it is difficult to determine the required length of this fastening in before, it is useful to make it adjustable in its length. The belt is adjustable by nature, the loops can be adjusted in their length, by putting them to different places (see picture). With this, it is possible to make the metal arm fitting perfectly to the body shape.