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Figure 9 is a table of coefficient (H/R) for arc edge bent down model. For example, assume the forming angle is 45 degrees, with radius 0.8 in. at the first pass. From Figure 9, when the forming angle a is 45, the coefficient (H/R) is 0.136. The elevation of the entrance guide H is:
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The elevation of the entrance guide H, then, should be set to 0.109 in.
Keep It Flat
By ensuring your entrance guide is set to the correct elevation, you can reduce the stress and strain on formed parts and reduce the longitudinal elongation differential in the cross section. The correct elevation of the entrance guide will form metal flat out of the first pass. The straight metal can easily self-thread, getting into the second pass without any assistance.
The entrance guide isn't a direct forming tool, but as the starting point of the forming process, it is a very important accessory. A good start will make the whole forming process run more smoothly.
