Our first iteration of table improvement involved replacing the plastic with 4″ thick metal slats. The difficulty was to design and build a slat filled table that was large enough to cut 5′ x 12′ sheets that was fabricated from our most common 4′ x 10′ sheets. We decided to punch slat holders that held slats in the X direction with a slight curve to minimize “jiggling” during cutting. The table seemed to be an improvement, but the slats wiggled considerably during cutting and the holders were quickly cut to shreds (as expected, just not that fast).

Our second iteration involved fabrication of several 2′ x 4′ grid structures. We sheared and punched the slats from 16ga or 14ga drops, interlaced them, and put a small weld in the corner of each intersection. We then simply laid the bricks on top of the existing heavy duty grates that the previous two table sat on. We essentially replace our plastic bricks with metal ones at a considerable cost savings.

The new table has exceeded all of our expectations. The estimated cost of the bricks is minimal due to the fact that all the slats are cut from scrap and they last so much longer than our previous versions. In fact, our first set of bricks lasted long enough to fill the entire waterjet with sand before needing to be replaced (and only a few of the more heavily used ones needed to be replaced). The fact that all of the slats are welded at every join allows the bricks to remain rigid even if parts of them get cut all the way through. The only downside to the new table is that we have to tab small parts to prevent them from falling through the table.

The reasoning behind this rule has to do with the geometry and limits of the tooling that is actually performing the bending. To keep pressing tonnage within reasonable limits, the general rule for bending is to select a die with an opening 6-8 times larger than the thickness of the material (the latter for thicker plate or higher tensile materials). Since half of the bend happens on each side of the bend line, having the edges of holes at least 3x the material thickness away from the bend line will ensure that the hole is properly supported during bending.

There are several options for when a hole absolutely has to be closer to the bend line. One option is to machine the hole or slot after bending, or use special (and expensive) tooling that can handle higher tonnage and supports the entire bending region. For more information on this type of tooling click here.

Another issue to consider that falls along the same principle is the minimum flange length that can be bent with the needed die width.