Press Brake

Gauging challenges on the press brake

Gauging can make or break a bending operation, especially when working with tight-tolerance or unusually shaped workpieces. Sometimes a part is simply impossible to gauge, even with a 5- or 6-axis backgauge system.

If you’re an experienced operator, you could gauge the part properly using a few gauging tricks, like laser stitching or pin gauging, but those workarounds take time.

Now, however, there is another way. To form awkward or otherwise hard-to-gauge parts, you can turn to something you may well have seen at your children’s high school science and engineering lab: a 3-D printer.

The technical name for the process many printers use is fused filament fabrication, or FFF. You’ll find these 3-D printers making plastic parts everywhere these days. Your children may have come home from school with a printed creation. But those little FFF printers have found a use in the fab shop as well.

Part volume still plays a role; after all, printing a gauge does take a little planning and time. But if you have a small 3-D printer at the ready, printing a backgauge insert doesn’t take that much time. Instead of struggling with a pin gauge or deburring a previously laser-stitched edge, you may well find that just printing a custom backgauge insert can make a lot of sense.

Gauging Basics

You have six different ways to gauge a part on a press brake:

  1. You can gauge the blank edge to the bend line, the simplest and often ideal method, especially when you need to hold tight tolerances.
  2. You can gauge a previously formed bend to a bend line, which works just fine in most cases, though this compounds the errors, which over multiple bends can stack up and force a part out of tolerance.
  3. You can gauge a hole or feature to a bend line using a pin gauge or similar method. This works well if the location of that hole or other feature is critical.
  4. You can gauge a tapered edge to a straight bend line. If you have a 6-axis backgauge, you usually can use a cornering finger that can capture the edge of the part. 
  5. The same applies to a similar situation in which you gauge a tapered bend line (that is, one not perpendicular to the sides) to a straight edge.
  6. Finally, you can gauge an irregular shape or edge to a bend line. Barring some unusual circumstances, this almost always involves gauging an irregular edge to a bend line.

A 3-D-printed backgauge insert may be able to help in nearly all of these types of gauging situations, to one degree or another. In some situations—like when gauging against a straight blank edge—you’ll rarely run into a problem. But as anyone who has worked in metal fabrication knows all too well, oddball jobs tend to show up on the schedule. But if you think differently and use 3-D printing strategically, those oddball jobs might not be quite so oddball after all.

Nuts and Bolts of a Printed Backgauge

Shops can use various creative ways to place a printed insert on top of an existing backgauge finger. Some gauging systems today have bolted holders where the gauge finger would normally be. The holder has a normal gauging surface on it, to use for conventional jobs, but onto that holder can be placed a 3-D-printed plastic insert. This means that the finger can not only do standard gauging, but also tackle those challenging gauging jobs, such as those with an irregular edge. 

Gauging With an Irregular Edge

If the irregular edge is just cosmetic and not a critical dimension, you can sometimes just “make it work” by sliding the part as best you can against the stops. You’ll be inconsistent, but if it’s just about looks, slight changes to the flange dimensions may not matter. 

But an irregular edge can be more than about looks. Sometimes the edge serves a function or needs to hold a specific tolerance to fit into a larger assembly. In this case, just “making it work” really won’t do.

Historically you’ve had three choices. One, you can use a pin to gauge against an existing hole, which of course works only if the workpiece has a hole to begin with, and the hole location is a critical dimension that keeps the formed part within tolerance. If gauging against the hole forces the tolerance error where you don’t want it to go, then you’re out of luck. Pin gauging also takes some time to set up, so building one for a prototype or low-volume job often doesn’t make sense.

Your second option is laser stitching. This involves cutting a straight or tapered edge on the laser (an edge that any 6-axis backgauge can handle) and microtabbing the final contoured edge, which you can break off after bending. This can work well if the irregular edge will be hidden in the final assembly, but if it’s an exposed edge, you may need to deburr it, which, again, isn’t free.

You may have a third option if the part has a straight edge on the opposite side. You can simply flip the part around and gauge off the opposite edge. Safety can be an issue here, though. For most part sizes, and particularly for large panels, it’s always best to keep most of the part weight on the operator side. This prevents you from having to reach in deep behind the tooling to manipulate the part. Moreover, for tight-tolerance work, you may have several additional bends in the middle of the workpiece, and gauging against the far edge might force your bending error to a critical dimension.

All this said, what about printing a gauge insert? In this case, you can try designing and printing a gauge insert that mates perfectly to an irregular edge. After a few tryouts, the printed gauge insert could even be placed inside a job traveler, along with prints and other work instructions.

Tapered Bends and Tapered Flanges

Most modern backgauges with cornering capabilities can handle a tapered edge very well. But then you have those oddball parts, the ones with an unusual taper or formed features, that cause gauging problems.

To visualize the problem, think of your backgauge finger as a mitten, with a thumb in the back and finger section to the side. Sliding the workpiece against the backgauge “thumb” gives you the front-to-back (X) position, and the finger section gives the right-to-left position (the Z direction on many press brakes). 

This works great for tapers, until you have a flange in the way. For instance, a previously bent flange could protrude downward (negative R direction). In this case, the mitten backgauge finger can’t get around that downward flange in the back. The same could be said for a side flange that protrudes from right to left. In both cases, you could print a backgauge insert with a slot or similar “holder” that accounts for those side flanges. 

Odd blank shapes can present their own gauging challenges. Say you have a straight bend that you’re gauging off of a tapered flange, giving you a 135-degree (obtuse) angle between the side and the flange edge. A standard backgauge finger may not be able to grab onto that corner very well. 

The same thing would apply to an acute angle between the side and a flange edge. You could have a flange that’s tapered just 15 degrees, and you might think that any 5- or 6-axis backgauge could handle it. But what if the angle between the side and flange edge is only 55 degrees? The gauge fingers may have a tough time grabbing on to that acute corner. So no matter how simple the tapered flange looks, you still could run into problems.

In both of these cases, 3-D-printed corner gauges could be a solution. If you print a gauge insert that will fit perfectly into a 135-degree-angle corner, you have a solid gauging strategy and a repeatable bending process. You could use standard dowel pins along the tapered edge. After all, no matter how oddly shaped a workpiece is, you still need only three points to gauge something adequately. The whole point of printing a gauge insert in this case is to find two points that the standard backgauge finger can’t find.

Pin Gauge or Not to Pin Gauge?

Say you have a tray with a 1-in. flange all the way around—nothing out of the ordinary, except for one small detail. The designer wants the tray to be able to fold down after it’s attached to a larger cart. One end of the tray has a flange with a wide radius on it and a hole for a clevis so the tray can fold downward. Nothing fancy, but how do you gauge this on the brake?

This part has a hole, so you might turn to the pin gauge. But again, setting up and locating a pin gauge takes time. If you have a small 3-D printer handy, you could print a backgauge insert in such a way as to match the contour of the clevis. You could then insert it into one of the gauge fingers, while using the remaining fingers on the brake as standard stops. 

Imagination’s the Limit

All these printed gauge applications aren’t entirely new. A few early adopters of plastic 3-D printing in metal fabrication have been quietly making gauges like this (and not only backgauges but also go-no gauges as well as fixtures of various types) for some time. But 3-D printing is still very new, so there’s lots of territory to be charted. Your imagination can help chart more territory.

For instance, many complex parts today require multiple bends made with precision, which means bending order matters, not only to force the error away from the noncritical dimension, but also to ensure you have a good gauging surface for every bend in the sequence.

Say you have a part in which the last bend in the sequence forced you to slide the piece against the backgauge not head-on, but upward by 30 degrees. That’s not an ideal gauging situation. Changing the bend sequence usually would be the easiest way to avoid this, but what if the part design didn’t make this possible, or another bend sequence forced the error into a critical dimension?

You could attempt a part redesign, but what if there were another way? What if a gauge could be printed that could hold the part not only in the correct X dimension but also at the proper height, so for the final bend, that odd flange could slide neatly up a 30-degree incline, made possible thanks to a custom-printed backgauge insert?

You might say that, sure, that would be great, but you’ve never seen a gauge finger like that. Would a custom 3-D-printed gauge insert work? It may or it may not. But with 3-D printing capability, you can give it a try.

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