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    What Are Trim Allowances?

     When quoting jobs for rolling we often have to specify how much trim allowance or grips are required to ensure no flat spots after rolling. What does that mean? A very simple example of that can be demonstrated by trying to wrap a paper clip around a pen. See that flat spot? That's the grip.

    If you refer to Fig. A you can see as the material is being loaded into the roller everything is laying flat, this applies when we roll plate, pipe, channel, beams. To begin to put form in the material one (or two) of the rolls must move toward the top one and move the material through. As they go back and forth, there will be a section that does not receive any form because of the gap between tangent points of the rollers; refer to Fig. B & Fig. C to see this. To finish the part, the same need for grips arises as shown in Fig. D where the roller tangents can only put so much form into the material.

    On larger diameter barrel rolling we can often roll without needing any because the flat spots are nearly undetectable.