OK guys, i need help with this before i lose it. I need to know how long i need to cut a piece of 12mm square bar with a 180degree bend at one end and both legs at 85mm long ?
100mmBend radius?
Bob
Thats how I do it.Oversize, bend, then cut to suit.
What I would like to know is how to work it out for future reference ?
Thanks very much for that Argoshield, that makes perfect sense to me.It is a bit difficult to know how to pitch the explanation. Please do say if it is too simple or too complicated.
When you bend a bar, the inside of the bend compresses (gets shorter) and the outside of the bend extends (gets longer). At some point between the inside and outside of the bend, there will be a place where the length does not change. That is called the neutral axis. For a regular shape (square, circle, rectangle), the neutral axis is halfway through the material (i.e. on its centreline). For a non-regular shape (e.g. a T- section), the neutral axis is more difficult to calculate.
One easy way to calculate your length is to draw it out full size a piece of stiff paper. Draw a vertical line 85mm long, then another one square to it (ie. horizontal, at 90 degrees). From where they intersect (the corner), measure 106mm and put a mark on the line. Why 106mm? You have told us that the inside of the bend needs to have 100mm radius. So the middle of the bar (the neutral axis) is 6mm more than this.
Jab the point of your compasses into the 106mm mark and set the drawing end to the corner (so you are drawing an arc of 106mm radius). Draw a semi circle and where it crosses the horizontal line draw another vertical line 85mm long.
Cut out the paper along the lines. Stand it edgeways on the bench with one end coinciding with the corner. Roll it over the bench and mark where the other end touches. Measure that distance (it should be 85 + 106*pi + 85 = 503mm).
What is described above is only a reduction to two dimensions of the method shown here:
Remember, bending is not an exact science. It is a lot easier to trim oversize material than it is to extend short material.