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What is a gantry cutting machine?
February 11, 2013
Definition of “Gantry”
A gantry is defined as “any of various spanning frameworks, as a bridge-like portion of certain cranes.” In other words, it is a structure that bridges over an area. Like gantry cranes, the word is often used to refer to a structure that moves on wheels, often riding on a set of parallel rails.
Why use a gantry?
Most machines designed for cutting flat steel plate use a gantry design because it is an easy way to move cutting torches in an X-Y coordinate system. The rail system that the gantry rides on forms one axis, usually the X-axis. The gantry bridge itself forms the other axis, usually the Y-axis. By motorizing each axis and coordinating the motion of the two axes simultaneously, you can move a torch in any pattern necessary to cut shapes out of steel plate. Thus, a gantry design lends itself to CNC shape cutting, which primarily uses an X-Y coordinate system for programming parts.
A gantry cutting machine will ride on some sort of rail system in the X-axis, either floor mounted, pedestal mounted, or sometimes integrated onto the side of a table. The rails are designed to provide accurate motion for the machine, and are strong enough to support the weight of the entire machine and all of the equipment mounted to it. Depending on the size of the machine, these rails can be as simple as a small strip of metal, or as complex as a recirculating ball bearing linear rail system, or as large as a railroad train rail.
A gantry cutting machine will also have some sort of guiding system in the Y-axis too, which is mounted to the bridge structure itself. The Y-axis guiding system will usually be smaller than the X-axis rails, because they only have to carry the weight of a small carriage and cutting tool, not the entire gantry. Gantry machines may have one tool carriage or many tool carriages. Some times the tool carriages will each have their own drive motor that moves them in the Y-axis, and some times there will be only one motor that drives the Y-axis, and all of the tool carriages will be connected together by a steel band, tie rod, wire rope, or similar mechanical device.
Gantries can come in a wide variety of sizes. There are some machines available with a 2 foot by 2 foot cutting area. There are other systems that can span nearly 100 feet wide, with rail systems just as long.
Non-gantry machine types
Years ago, flame cutting machines started out primarily as “cantilever” machines, using photo-optical tracers to follow line templates. A cantilever machine will have 2 rails spaced some distance apart, but the beam is extended beyond the rails on one side, with a moving torch-tube that carries the cutting tools. Some cantilever style models still exist. However, as CNCs and machines evolved, the cantilever style machine has largely disappeared in favor of the gantry style machine.
Another design that has been used often for waterjet machines is the “flying bridge”. A flying bridge looks like a gantry with one of the side trucks left off. In fact it is a cantilever machine with the two rails set very close together, often mounted to a single steel tube. This arrangement requires that one rail support the weight from above while the other counteract the torque from the weight of the Y-axis beam. The high loading put on the rails of a flying bridge usually means they are precision linear rails with recirculating ball bearings. Some companies have built flying bridge machines for thermal cutting, but they are not as popular as gantries.