Gantry uprights join the gantry’s X rails to the Y rails and are a weak point in many CNC router designs. They should be stiff to resist the lateral forces from X-axis moves. But some machines use relatively thin stamped metal, MDF or even HDPE.
The Pilot Pro gantry side-plates are cut from ½” thick 6061 aluminum bar-stock. If you order the Pilot Pro parts kit from PDJ, these will come face-milled perfectly flat to assure precise alignment.
The gantry side-plates bolt to the Y-axis linear slides. Then the X-axis rails are bolted to the side plates.
The X-axis rails are constructed from the same 15 Series 80/20 extrusions and linear slides as the Y-axis rails. The recirculating ball slides are not quite as massive as the Y-axis units, but still quite beefy since they need to support the Z-axis assembly with the spindle.
PDJ shipped the Z-axis partly pre-assembled. I guess they were trying to save me the work of writing another blog post. The Z-axis is designed to hold up to a 3hp spindle. It is constructed mostly from ½” aluminum plate with all the critical alignment surfaces face-milled. The linear rails and bearings are a bit smaller than the X and Y axis slides since these only need to carry the mass of the spindle. A ball screw assembly with pre-loaded axial bearings is used to drive the slides along the Z-axis. The Z-axis assembly bolts directly to the X-axis slides.
At this point, we take some time to square everything up and align all the linear slides. Once we are sure that everything is aligned and sliding smoothly, we go back through the whole assembly, removing one bolt at a time and re-assembling each with a drop of thread-locking compound. This will prevent loosening over time due to vibration.
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