daniele capo

In the last post of this series I described a device based on a triangular ‘arch’. Today I want to examine some construction problem I’m likely to encounter if I want to follow that way.

Structure

With the arch principle we use the lateral forces generated by the device to produce the pressure (big enough) needed to print. Here is the picture I used:

Now we want to build a structure able to sustain these forces. If we draw another diagram we see that the problem is, actually, simple. Consider to put the levers device inside a rectangular frame. The two almost vertical forces will exert a pressure from inside to outside, causing the horizontal bars of the frame to bend and pulling (and also bending) the vertical bars.

If we make the horizontal bar stiff enough to avoid bending we can consider only the pulling tension on the vertical bars, and basically they can be subtle compared with the horizontal ones.

Stress

Now we can try to classify the parts of the press:

• Horizontal bars are punched by the ‘arch’ and bend
• Vertical bars are subjected to tension
• The pressure device (the ‘arch’) is subjected to compression and bending

From wich we can imagine the way we must build the structure:

• Horizontal bars will be stiff enough to be considered almost perfectly rigid
• Vertical bars are subjected to tension, and can be made relatively thin. They need to substain the weight of the top horizontal bar.
• The pressure device (the ‘arch’) need to be thick to substain compression.

Looking carefully a the ‘arch’ we see that its weakness is in the middle joint that will be subjected to tension. Also, we can say that the main weakness is exactly in the ‘arch’, being compressed and, at the same time, composed by movable parts.

Reversing?

So, what if we could reverse the whole press? I mean if we can trasform the ‘push’ method in a ‘pull’ method?

Follow me to the next post!