We get a lot of requests for taller z axes on our machines. While we can do some things to get you a taller z, there are several things to consider before going this route.
The z-axis is typically the weak link in any gantry style machine with a moving z, as this is the only cantilevered axis (supported on only one end) in the system. For a cantilevered beam, stiffness is a function of the inverse of the axis length cubed, so even a slightly longer z can make the axis significantly less stiff, which can lead to deflections in harder materials and increased vibration while cutting. For materials like foam and balsa, this is less of a concern, but if your main cutting will be in wood or aluminum, extra height may causes issues.
A longer z-axis often requires extremely long tooling to fully take advantage of the travel, especially if there are steep concave portions in your design where a router body cannot fit. These tools can be very expensive and can suffer from vibration issues.
In most instances, the desire for a longer z is because the final workpiece is taller than the standard travel we offer, but there are alternatives to a longer z travel:
- Layering The first strategy we suggest is to cut your part in layers, with CNC'd indexing holes to align the layers. This requires far less z travel, and also removes risk by turning a long machining program into more manageable segments. It can also allow you to add undercuts or other features typically not available in standard 3-axis machining if the layers are segmented properly.
- Lowered bed or raised uprights. In some cases, while the workpiece itself is taller than the standard travel, the actual height delta of contours in the piece are less than the z travel of the machine. In this case, rather than extending the z travel, more room can just be provided for the workpiece. We have several options we can offer in this case, including brackets that allow the cross pieces of the table to mount underneath the x rails (adding ~3" of space), or spacers that add additional height at the gantry risers.
All of this being said, if you have parts that require a larger z travel, we're happy to discuss the best way to accomplish this on your machine. Just drop us a line
and an applications engineer can walk you through various options.