copper bending. my pennys worth.i bend by eye also,but remember the basics.the measuring etc is farely time consuming so not practical
pullin 90's- put a line on the pipe at a distance from the end of the pipe equal to that between the fixed point and the back of the finnished bend.u need to b sure that the line on the pipe is square with the back of the former.and pull away mad.
An offset
The first bend can be pulled at any angle.
The pipe is then pushed further along the benders and turned around to make the first bend look upwards away from the former.
A ruler and a straight edge are used to measure the distance of the offset that you want.
When marking this out, make sure that the straight edge is running parallel with the piece of pipe looking upwards away from the former.
Once the correct measurement is got the bend can be pulled around until it is at the same angle as the first bend and can be seen to run parallel.
Check this then using the straight edge.
Passover-hop over
There is a lot of ways of forming a passover.
The easiest I think is to pull a bend first, the angle of this depends upon the size of the obstruction.
The bend cannot be too sharp because it will be very awkward pulling the offset bends.
A straight edge is positioned over the bend centrally to a distance equal to the passover wanted.
The pipe is marked with two lined which will be at the back of the finished offsets.
Put the pipe in the benders, and when the first mark is in line with the back of the former, the first set is pulled.
Once this bend is done, the pipe is simply reversed in the benders, and the second mark lined up in the former and pulled to complete the passover.
not easy to explain, not sure if u follow.
the formula s are used for heat bends. there s something about findind the center of the radius of the bend.then u find the amount of pipe length to heat by the formula -pie x radius x 2 divided by 4
not certain .if u don t have a perticular radius for the bend u would just go 4 times the nominal diameter of the pipe.
not too sure of special measurements.there are other formula s though i think.