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Movable Bed CNC machine 10

After testing the movement of the X-axis successfully, my next task was to fabricate the other axes, namely the Y and Z axes. The Y-axis was not much of a problem as it followed very much the same design as the X-axis and was already in place during the previous test.

The Z-axis posed a problem. It was slightly shorter. This meant that I had to cut a lead screw to the correct length and then machine a straight shaft of 1/4″ diameter at the end to take in an end bearing assembly . I could pay a machinist to machine ┬áthis, but ever innovative and eager to try DIY, I managed to modify my bench grinder and used this to grind it to the correct size.

The parallel rods would also need to be cut. Again, I used the bench grinder with a cutting wheel to do it, because these were hardened steel and could not be cut off with an ordinary hacksaw.

There were a few misalignment that were corrected a few times during the course of the fabrication. I found a set of thrust bearings which should be able to take the load of the spindle assembly later. I found that during the up travel of the lead screw, the whole bearing assembly was jacked up from the bearing holder (it was just a hole drilled in the plywood). I added a bearing retainer piece to hold the bearing in place.

Then, I found that because the holes for the parallel rods were not drilled exactly as per measurement, (or maybe the measurements were not correct in the first place) the latter tended to lift or was making the sliding movement too tight. I had no choice but to manually file the holes for the parallel rods slightly bigger to make allowances for the misalignment. To take up the slack, I used a few pieces of cardboard to fill up the clearances.

The Z-axis lead screw nut also needed to be aligned properly. The holder for the nut was epoxied in place.

At the time of writing, the test seemed to be going alright, with all the axes working as they should.

But later, just by adding a piece of plywood that was going to hold the spindle,  the Z-axis gave problems.

Because of the extra weight the Z-axis motor could not turn the lead screw especially in the upward direction against gravity.

Initially, I thought it was the motor flexible coupling slipping due to too great a torque to turn the lead screw versus the weight of the tool assembly. It was logical to assume that because, I did modify the flexible coupling slightly by drilling a bigger hole on the lead screw side to take in the 1/4″ diameter shaft, and naturally the manual grinding might not be as perfect as a machinist’s job.

First, I did all I could to remove any mechanical misalignment that would cause the moving parts to seize. With that done, and still experiencing the seizures, I decided to epoxy the coupling in place at the lead screw shaft side.

But this still did not solve my problem.

Then, I modified the coupling on the motor side. I cut a slot across the shaft end and installed a sliver of hacksaw blade strip across the coupling to act as a key.

But still this did not solve my problem.

Finally, it dawned on me that the Z-axis motor was not slipping at the coupling, but was actually stalling, or missing steps. So it was back to the configuration of the software. After reducing the velocity and acceleration, I finally managed to make the Z-axis work. But the speed was extremely low.

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