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Movable Bed CNC machine 8

After the linear bearing housing for the movable bed was set, I went about with the next step, which was to assemble all the components of the movable bed x-axis which consisted of the following:

  • Lead screw,
  • Parallel rods,
  • Bearings,
  • Motor,
  • Motor shaft coupling,
  • Bearing support structure,
  • Lead screw nut and its attachment to the movable bed.

The idea was to make every mechanical part for the movable bed move as they should.

movable bed complete with motor, lead screw, linear bearings

Movable bed complete with motor, lead screw, linear bearings

But before that, I needed to confirm whether the movable bed sitting on the x-axis slide bearings was exactly perpendicular to the y-axis. So I had to assemble part of the y-axis by joining its parallel bars with a vertical piece of plywood, drilled exactly to take in four sets of nuts and bolts. With the partly assembled y-axis in place, I temporarily fixed a pencil at the y-axis and moved the y-axis part assembly horizontally, so that it would make a line marking on a piece of paper attached to the movable bed. Then while maintaining the pencil at the y-axis at a fixed position, I would move the x-axis movable bed, to mark another line which ideally would be perpendicular to the previously drawn line.

In this way, I could determine whether the lines were exactly perpendicular to each other. The results were considered satisfactory at this time as there was only a slight deviation from the ideal. I am keeping my fingers crossed hoping that the performance of the cnc machine on completion later would be good.

Having tested for perpendicular alignment of the axis, it was time to fix the lead screw nut to the movable bed. As before, because some dimensions were expected to deviate from the ideal, I had to glue in a bracket connecting the bottom of the movable bed to the lead screw nut by epoxy resin. This glue was chosen not only because it would give a strong joint, but also because it was able to fill in any gaps in between the inaccurately-cut mating surfaces.

Next, I had to source for the bolts and nuts, some of which would only work for a particular size (metric or imperial or US) and type of threads. The lengths and diameters were also different for different attachment location applications. This was not a problem as I knew where to buy these.

So with the motor attached with long bolts through the spacers, motor shaft attached to the lead screw via the flexible coupling, lead screw attached with ball bearings at each end, and with the lead screw nut in between attached to a bracket, the latter was glued in place to the center of the movable bed at the bottom. Whew, that took a bit of adjusting.

cnc x-axis movable bed and partly completed y-axis

Cnc x-axis movable bed and partly completed y-axis

Basically, finding the position to fit the bracket was a challenge and it involved putting all the components in place and then gluing it so that it would work perfectly when the glue had set.

When the glue had set, I tried to turn to lead screw so that the movable bed would move linearly. That was when I realized that the movable bed was too long! It almost covered everything below. There was no space to put my fingers in to turn the lead screw. Luckily, I had made a groove at one of the the motor coupling spacers to allow for loosening and tightening of the coupling bolt using an allen key. I was able to insert my finger onto the coupling and turn it and so turned the lead screw which was attached to it.

Back to the design drawing board! After examining it, I decided that I could cut about 30 mm away from each end of the movable bed and still maintain the function. I did not want to cut too much away as I wanted to leave some space for attaching work piece holders later.

So there was another round of dismantling and modification to cut away some pieces, increasing some clearances, drilling starter holes for screws, countersinking holes, grinding off edges of guide bars and other minor touching ups.

At this time, I still needed to add in bearing covers to prevent the bearings from falling off, but essentially, the x-axis mechanical part could be considered completed.

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