This section begins with a short film show you how to check backgauge repeatability. Something you may not think about doing often, but should. This issue alone could be the basis of many gauging issues. The idea being shown is this; you set your backgauge at home or a known position, set a dial indicator to show +/- error.
The first check is for repeatability, does it come to the same location each time?
There are times when side gauging will become necessary to produce parts. This type of gauging can be very accurate and consistent once it is established into the setup.
Figure 1 shows an example of where side gauging could be of great value in forming; a part with a bend 15° off perpendicular is a good example.There are several different ways that you can side gauge a part. The first method is one in which a table is mounted in some manner to the die body or to the bed of the press brake, figure 2.
Generally, the gauge itself is mounted to a table which is then C-clamped to the die, then mounted into the press brake. These may be “Homemade” similar to figure 2 or “factory made” like the side gauge pictured in figure 3.The second method of side gauging is to use the side of the die as your straight edge, figure 4, but it has a problem that is unique to this bend …. the inside radius of the previous bend.
The problem is that the radius can ride up on the die, causing wide variations in the first perpendicular bend dimension and angle, especially if you are using precision ground press brake tooling, you can gauge off the edges of the tooling itself.
Here are a couple of very simple ways to setup side gauging so it works correctly. Either add a piece of material with a thickness equal to or greater than the inside setback (ISSB) a spacer can be attached to the die by means of “super glue” or double sided tape, etc., figure 4. Or use the second die with the same clearance plus a material thickness and gauging off the outside of the part.
By the addition of this spacer or the open space, the first flange will lie flat against the die and, therefore square to the bend line. One last note about gauging from the second bend. Look closely at any piece of material that has been formed, the thicker the better for the sake of this explanation. Notice that there may be a convex blowout on one edge of the bend and a concave area on the other edge; it is sometimes possible to have two concave or convex edges on a part.
This concave or convex condition occurs regardless of the material thickness or bend radius and does increase in direct proportion to an increased thickness. Gauging off a convex blowout could cause angular and dimensional inconsistencies and should be a consideration when you are working out a forming order, and if present, it should be compensated for.
There will be other times when your workpiece is difficult to gauge and the standard ways no longer work, due either to an extra tight edge-to-feature tolerance or a workpiece without any straight edges. These two problems have a common solution, “pin gauge”.
Pin gauges are usually no more than just a piece of sheet metal attached to the backgauge, with a small pin or half-shear.
If you gauged from the front of the hole or feature, the workpiece will clear the pin with ease, assuming that the pin is not too tall.
As a general rule, the height of the pin should not exceed that of the feature size less the diameter of the pin; figure 6 shows the relationship of the pin height to hole diameter, which can be mathematically expressed as:
Gauging from a negative position
When you gauge from a notch or holes that are located at zero (the bend line) or less, as presented in figure 7, it is like gauging off the wrong side of the feature.
The easiest way to get negative gauging to work is to retract the backgauge enough to allow clearance for the workpiece to clear.
The retracting of the backgauge in many cases may be unnecessary as many press brakes have stops that are designed to flip out of the way. Placing the stops close to the tangent of the radius and leg is correct, enough for a solid “bite” without taking so much that binding occurs.
Backgauge without bind
In this location, the stop will flip up and out of the way effortlessly. It also allows for a firm gauging surface. Why not use the retract function? Because when it is used unnecessarily, it can waste time and a lot of it over a run of any size. But when the retract is needed, by all means, use it.
After reviewing this material you should now be able to:
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