moving gantry cnc machine z-axis housing ball bearings running on aluminium strip and guided by linear bearings

moving gantry cnc machine z-axis housing ball bearings running on aluminium strip and guided by linear bearings

In the previous post, I had managed to cut the gantry bottom plate reasonably square and accurately. That was a great help in the alignment of the two gantry sides. Using the same exact measurement as the distance between the gantry sides at the bottom plate, I cut an aluminium strip and screwed it onto the top of the gantry beam where the ball bearings of the z-axis housing were to rest. The two gantry side plates were forced to touch the ends of the aluminium strip and were made reasonably vertical. (The mdf boards of the gantry side plates had bent somewhat and had to be bent back in place)

horizontal check on moving gantry y-axis round rod

horizontal check on moving gantry y-axis round rod

vertical check on moving gantry cnc machine z-axis housing

vertical check on moving gantry cnc machine z-axis housing

When the whole assembly was considered reasonably square, the pieces were clamped in place and epoxy resin was applied to fill up the gaps. After the first application had hardened, the whole assembly was re-arranged so that more epoxy resin could be poured into the gaps from another position – those which previously had not been accessible. In this way, the jointing of the horizontal gantry beam was done.

horizontal check on moving gantry cnc y-axis ball bearing track

horizontal check on moving gantry cnc y-axis ball bearing track

Next, I needed to arrange such that the z-axis holder could be supported by ball bearings running on the horizontal gantry beam. According to my design, the z-axis holder which would be weighed down by two stepper motors would be supported by the ball bearings when running in the y direction.

horizontal y direction check on moving gantry base board

horizontal y direction check on moving gantry base board

In order for the cnc machine to work properly, I needed to fabricate the z-axis holder so that I could drill the holes needed for the ball bearing shafts, let the ball bearings rest on the horizontal cross beam and then adjust the sliding linear bearings accordingly. So, I drilled the holes for the ball bearings, linear bearings and the motor housing as per the design.

horizontal x direction check on moving gantry base board

horizontal x direction check on moving gantry base board

horizontal check on moving gantry base aft board frame

horizontal check on moving gantry base aft board frame

Unfortunately, the location of the holes were not drill correctly as planned. Somehow the centers had shifted, so I had to do some corrections to the centering of the holes. The sides of the z-axis housing were not vertical.

After the corrections, the z-axis housing seemed accurate enough.

bearing spacer cut from phenolic board

bearing spacer cut from phenolic board

During the installation of the ball bearings, I also needed to fabricate some spacer washers so that the bearings could be tightened on the inner races while keeping the outer races free. This was when my existing movable bed cnc machine became useful. Previously, I had already fabricated four pieces of the spacer washers and had installed them at the movable gantries. I just used the same design and run it again through the movable bed cnc machine and hi presto, I had made them all ready for use.

horizontal check on z-axis housing top. It was found to be slightly sloping and needed to be adjusted.

horizontal check on z-axis housing top. It was found to be slightly sloping and needed to be adjusted.

horizontal check on z-axis housing top. It was found to be slightly sloping and needed to be adjusted.

horizontal check on z-axis housing top. It was found to be slightly sloping and needed to be adjusted.

To confirm that the moving gantry cnc machine was made reasonably accurate, I did some checking using a spirit level. The x and y axes were found reasonably level, but the z-axis top seemed to be slanting slightly. I planned to unscrew this, adjust the level and then glue it in place so that the stepper motor placed on top would be completely vertical.