The movable gantry cnc machine would be driven by timing belts because I did not have lead screws that were long enough to cover the lengths of travel of the x and y axes. Compared to the movable bed cnc machine that I had made, this machine was designed for bigger work pieces and therefore the spindle need to cover a larger area and the footprint was naturally larger.

The x-axis would be driven by 2 stepper motors working in sync at opposite ends of the gantry. While the weight of the gantry assembly, motors, z-axis, and spindle would be supported by horizontal ball bearings, the lateral forces would be taken up by the linear bearings running on round parallel rods.

In order to drive the x axis movements, the motors were fitted with gt2 gear timing pulleys which would engage with the 9 mm wide gt2 timing belts. The belts would loop over the timing pulleys at the motors, and then make 90 degree turns so that the ends of the pulley could be stretched taut along the direction of travel.

One end of each timing belt would be clamped tight in place while the other end would be connected to a tensioner so that the former would remain taut at all times.

The body of the tensioners were made out of short lengths of steel cable ties bent into position and reinforced with square nuts. Short lengths of threaded bolts were inserted at the center to act as the adjusting mechanism for tensioning the belt. In our case, the heads of the bolts had to be filed thinner in order to enlarge the space needed to accommodate the timing belts.

The round rods that secured the timing belts were made from steel nails of about 4″ lengths because their shanks were about 5 mm in diameter. These were fitted into the holes of the steel cable ties, cut to the required lengths and then expanded on one side in order to prevent them from coming out.

The timing belts were looped over the round rods of the tensioner, and then clamped in place at their ends by rings made from soft copper tubes.

The timing belts were then looped over and engaged with the timing pulleys attached to the motors, looped over the idler ball bearings, attached to both ends of the x-axis travel frame, and then stretched taut by the tensioner.

It was then time for testing. The gantry was moved by hand to check the results. At first, the belts tend to drift away from the straight moving paths due to some misalignment, but after a few attempts at alignment of the idler ball bearing shafts, the defects were corrected.

The video below showed the progress of the x-axis belt drive fabrication and installation.